Intelligent temperature transmitter and measurement method

Abstract

The present invention relates to an intelligent temperature transmitter and a measuring method, comprising: a constant current source generating circuit, which outputs a constant current excitation to a sensor through a signal and excitation switching circuit to supply power to the sensor; a signal and excitation switching circuit, which determines the operation mode according to a mode switching instruction sent by a single-chip microcomputer; a differential voltage analog signal is obtained according to a sensing signal output by the sensor; an analog-to-digital conversion circuit, which performs analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal; a single-chip microcomputer, which obtains first temperature, resistance and / or voltage data according to the differential voltage digital signal; and a transmitter output circuit, which is used to convert the first temperature, resistance and / or voltage data into a standard signal. The present invention supports various thermocouple sensors, differential voltage signals, 2-wire, 3-wire and 4-wire thermal resistance sensors or resistors, and also supports sensor fault self-diagnosis, post-fault reduced efficiency operation and fault indication functions.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial instruments and meters, and more specifically, to an intelligent temperature transmitter and a measuring method. Background Art

[0002] Transmitters are instruments that convert the output signal of a sensor into a standardized output signal that can be transmitted. They are mainly used for industrial process measurement and control. Among them, temperature transmitters are one of the most commonly used transmitters, with a wide range of use occasions and market demands.

[0003] Existing temperature transmitters have the following problems: ① It is difficult to achieve input compatibility with all sensors, especially the 4-wire measurement compatible with thermal resistors. ② It does not have sensor fault diagnosis or has weak fault diagnosis function, and does not support the transmitter to operate at a reduced efficiency when a fault occurs. ③ It does not have a fault indication function, and it is complicated to troubleshoot when a transmitter fails. ④ The power consumption of the whole machine is high, and it is difficult to support the NE43 standard. ⑤ Most of the cold-end compensation of thermocouples uses diode simulation compensation, which has low compensation accuracy and poor stability. ⑥ It does not support online current measurement, and on-site inspection is inconvenient. ⑦ The transmitter has low measurement accuracy, the ambient temperature has a great impact on the accuracy, and the anti-interference performance is poor. Summary of the invention

[0004] The present invention provides an intelligent temperature transmitter and a measuring method to solve the problem of how to measure a sensor efficiently and accurately.

[0005] In order to solve the above problems, according to one aspect of the present invention, a design scheme of an intelligent temperature transmitter is provided, wherein the temperature transmitter comprises: a sensor signal measuring device and a transmission output circuit, wherein the sensor signal measuring device comprises: a constant current source generating circuit, a signal and excitation switching circuit, an analog-to-digital conversion circuit and a single-chip microcomputer; wherein,

[0006] The constant current source generating circuit is connected to the signal and excitation switching circuit, and is used to output a constant current excitation to the sensor through the signal and excitation switching circuit to supply power to the sensor;

[0007] The signal and excitation switching circuit is connected to the sensor, the analog-to-digital conversion circuit and the single-chip microcomputer respectively, and is used to determine the operation mode according to the mode switching instruction sent by the single-chip microcomputer; and is used to obtain the differential voltage analog signal according to the sensing signal output by the sensor;

[0008] The analog-to-digital conversion circuit is connected to the single-chip microcomputer and is used to perform analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal;

[0009] The single chip microcomputer is connected to the transmission output circuit, and is used to send the mode switching instruction to the signal and the excitation switching current; and is used to obtain the first temperature, resistance and / or voltage data according to the differential voltage digital signal;

[0010] The transmission output circuit is used to convert the first temperature, resistance and / or voltage data into a standard signal of a preset type.

[0011] Preferably, the temperature transmitter further comprises:

[0012] An ambient temperature measurement circuit, connected to the single chip microcomputer, for measuring the ambient temperature to obtain a second temperature;

[0013] A single-chip computer, for, when the sensor is a thermocouple, converting the differential voltage digital signal into a first thermoelectric potential according to a preset conversion relationship between the differential voltage digital signal and the thermoelectric potential; converting the second temperature into a second thermoelectric potential according to a preset conversion relationship between the temperature and the thermoelectric potential; determining a third thermoelectric potential after cold-end compensation of the thermocouple according to the sum of the first thermoelectric potential and the second thermoelectric potential; converting the third thermoelectric potential into a temperature according to a preset conversion relationship between the thermoelectric potential and the temperature, so as to obtain and output a corrected first temperature; or

[0014] When the sensor is a thermocouple, the differential voltage digital signal is converted into a first thermoelectric potential according to a preset conversion relationship between the differential voltage digital signal and the thermoelectric potential, and the first thermoelectric potential is converted into temperature according to a relationship between the first thermoelectric potential and temperature to obtain a corrected first temperature and output it.

[0015] Preferably, the signal and excitation switching circuit comprises: a dual-way four-channel analog multiplexer, a first terminal, a second terminal, a third terminal and a fourth terminal for connecting to a sensor, a first control pin and a second control pin for performing channel switching, an excitation current sinking terminal, an excitation current sinking terminal, a differential positive output terminal for outputting the differential voltage analog signal, a differential negative output terminal, a pull-up resistor and a pull-down resistor;

[0016] The pull-up resistor is respectively connected to the differential positive output terminal and the power supply terminal of the signal and excitation switching circuit, and the pull-down resistor is respectively connected to the differential negative output terminal and the ground terminal of the signal and excitation switching circuit.

[0017] Preferably, the signal and excitation switching circuit is further used for:

[0018] The high-low level differential signal and excitation output by the single-chip microcomputer through the IO port are switched to different terminals to realize the switching of the operation mode of the signal and excitation switching circuit, including: controlling the channel control end of the dual-way four-channel analog multiplexer to switch the output signals on the first terminal, the second terminal, the third terminal and the fourth terminal to the differential negative output end of the differential voltage analog signal, and controlling the channel control end of the dual-way four-channel analog multiplexer to switch the current injection end to the first terminal, the second terminal, the third terminal and the fourth terminal.

[0019] Preferably, wherein

[0020] When the signal and excitation switching circuit is in the first operation mode, the first control pin is at a low level, the second control pin is at a low level, the current sink is connected to the third terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the third terminal;

[0021] When the signal and excitation switching circuit is in the second operation mode, the first control pin is at a high level, the second control pin is at a low level, the current sink is connected to the first terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the fourth terminal;

[0022] When the signal and excitation switching circuit is in the third operation mode, the first control pin is at a low level, the second control pin is at a high level, the current sink is connected to the second terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the third terminal;

[0023] When the signal and excitation switching circuit is in the fourth operating mode, the first control pin is adjusted to a high level, the second control pin is adjusted to a high level, the current injection end is connected to the second terminal, the current absorption end is connected to the third terminal, the differential positive output end is connected to the second terminal; and the differential negative output end is connected to the fourth terminal.

[0024] Preferably, the single chip microcomputer is also used for:

[0025] When the type of the sensor is a thermocouple or a differential voltage, the positive electrode of the thermocouple or the differential voltage is connected to the second terminal, the negative electrode of the thermocouple is connected to the third terminal, and the signal and excitation switching circuit is controlled to be in a first operating mode through the control instruction to perform signal measurement;

[0026] When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, a pair of cables of the 4-wire thermal resistor or the 4-wire resistor with the same polarity are connected to the first terminal and the second terminal, and another pair of cables of the same polarity are connected to the third terminal and the fourth terminal, and the signal and excitation switching circuit is controlled to be in the second operation mode through the control instruction to perform signal measurement;

[0027] When the type of the sensor is a 2-wire thermal resistor or a 2-wire resistor, two cables of the 2-wire thermal resistor or the 2-wire resistor are connected to the first terminal and the second terminal respectively, and the signal and excitation switching circuit is controlled to be in a third operation mode through the control instruction to perform signal measurement;

[0028] When the sensor type is a 3-wire thermistor or a 3-wire resistor, two cables of the same polarity of the 3-wire thermistor or the 3-wire resistor are respectively connected to the second terminal and the third terminal, and another cable of a single polarity is intercepted to the fourth terminal, and the signal and excitation switching circuit is controlled by the control instruction to repeatedly switch between the fourth operating mode and the third operating mode to perform signal measurement.

[0029] Preferably, the single chip microcomputer is also used for:

[0030] According to the differential voltage digital signal, according to the preset judgment rules, the fault type and fault cause of the temperature transmitter are determined; wherein the fault type includes: serious fault and minor fault;

[0031] Wherein, when the type of the sensor is a thermocouple or a differential voltage and is in the first operating mode, the actual voltage value is determined according to the differential voltage digital signal, and when the actual voltage value is greater than a preset voltage upper limit threshold or less than a preset voltage lower limit threshold, the fault type is determined to be a serious fault;

[0032] When the type of the sensor is a 2-wire thermal resistor or a 2-wire resistor and is in a third operation mode, a first resistance is determined according to the differential voltage digital signal, and when the first preset resistance is greater than a first preset resistance upper limit threshold or less than a first preset resistance lower limit threshold, the fault type is determined to be a serious fault;

[0033] When the type of the sensor is a 3-wire thermal resistor or a 3-wire resistor, and is in the fourth operation mode, the second resistance is determined according to the differential digital signal, and when the second resistance is greater than a second preset resistance upper threshold or less than a second preset resistance lower threshold, the operation mode is switched to a third operation mode, and the third resistance is determined according to the differential digital signal in the third operation mode, and when the third resistance is less than or equal to the third preset resistance upper threshold and greater than or equal to the third preset resistance lower threshold, the fault type is determined to be a first minor fault; when the third resistance is greater than the third preset resistance upper threshold or less than the third preset resistance lower threshold, the fault type is determined to be a serious fault;

[0034] When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, and is in the second operating mode, the fourth resistor is determined according to the differential digital signal, and when the fourth resistor is greater than the fourth preset resistance upper limit threshold or less than the fourth preset resistance lower limit threshold, the operating mode is switched to the fourth operating mode, and the fifth resistor is determined according to the differential digital signal in the fourth operating mode, and when the fifth resistor is less than or equal to the fifth preset resistance upper limit threshold and greater than or equal to the fifth preset resistance lower limit threshold, the fault type is determined to be a second minor fault; when the fifth resistor is greater than the fifth preset resistance upper limit threshold or less than the fifth preset resistance lower limit threshold, the operating mode is switched to the third operating mode, and the sixth resistor is determined according to the differential digital signal in the third operating mode, and when the sixth resistor is less than or equal to the sixth preset resistance upper limit threshold and greater than or equal to the sixth preset resistance lower limit threshold, the fault type is determined to be a third minor fault; when the sixth resistor is greater than the sixth preset resistance upper limit threshold or less than the sixth preset resistance lower limit threshold, the fault type is determined to be a serious fault.

[0035] Preferably, the single chip microcomputer is also used for:

[0036] According to the fault type and the preset control rules, a control instruction is sent to the fault indication device, so that the fault indicator light gives an alarm according to the control instruction and indicates the fault level at the same time;

[0037] When the fault type is a first minor fault, a second minor fault or a third minor fault, a reduced efficiency operation mode is determined according to the fault type and a preset reduced efficiency operation rule, and the signal and excitation switching circuit is controlled to operate according to the reduced efficiency operation mode; and when the operating time of the temperature transmitter in the fault state reaches a preset time threshold, the operating mode is adjusted to the operating mode before the fault according to the sensor type, and the fault type and fault cause of the temperature transmitter are determined again according to the preset judgment rule;

[0038] Wherein, the degraded operation rule includes: when the fault type is a first minor fault, determining the degraded operation mode to operate in accordance with the third operation mode;

[0039] When the fault type is the second minor fault, the reduced efficiency operation mode is determined to be operated according to the normal measurement operation mode of the 3-wire thermal resistor or the 3-wire resistor;

[0040] When the fault type is a third minor fault, the degraded operation mode is determined to be operation according to the third operation mode.

[0041] According to another aspect of the present invention, a sensor signal measuring device is provided, the sensor signal measuring device comprising: a constant current source generating circuit, a signal and excitation switching circuit, an analog-to-digital conversion circuit and a single-chip microcomputer; wherein,

[0042] The constant current source generating circuit is connected to the signal and excitation switching circuit, and is used to output a constant current excitation to the sensor through the signal and excitation switching circuit to supply power to the sensor;

[0043] The signal and excitation switching circuit is connected to the sensor, the analog-to-digital conversion circuit and the single-chip microcomputer respectively, and is used to determine the operation mode according to the mode switching instruction sent by the single-chip microcomputer; and is used to obtain the differential voltage analog signal according to the sensing signal output by the sensor;

[0044] The analog-to-digital conversion circuit is connected to the single-chip microcomputer and is used to perform analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal;

[0045] The single chip microcomputer is connected to the transmission output circuit, and is used to send the mode switching instruction to the signal and the excitation switching current; and is used to obtain the first temperature, resistance and / or voltage data according to the differential voltage digital signal.

[0046] According to another aspect of the present invention, a measurement method based on the above-mentioned intelligent temperature transmitter is provided, the method comprising:

[0047] The single chip microcomputer sends a mode switching instruction to the signal and excitation switching circuit, so that the signal and excitation switching circuit determines the operation mode according to the mode switching instruction;

[0048] The constant current source generating circuit outputs a constant current excitation to the sensor to supply power to the sensor;

[0049] The signal and excitation switching circuit obtains a differential voltage analog signal according to the sensing signal output by the sensor;

[0050] The analog-to-digital conversion circuit performs analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal;

[0051] The single chip microcomputer obtains first temperature, resistance and / or voltage data according to the differential voltage digital signal;

[0052] The transmission output circuit converts the first temperature, resistance and / or voltage data into a standard signal of a preset type.

[0053] The present invention provides an intelligent temperature transmitter and a measuring method. The temperature transmitter includes: a constant current source generating circuit, a signal and excitation switching circuit, an analog-to-digital conversion circuit, a single-chip microcomputer and a transmission output circuit. The intelligent temperature transmitter of the present invention can accurately measure the induction signals of different types of sensors and convert them into 4-20mA current signal output; for the measurement of thermal resistors or resistors, it supports the compatibility of three wiring methods: 2-wire, 3-wire and 4-wire, especially the support of the 4-wire system of thermal resistors, which improves the accuracy of temperature measurement and broadens the use scenarios of the transmitter. At the same time, it supports sensor fault self-diagnosis, post-fault reduced efficiency operation and fault indication functions, which is convenient to operate and use. The present invention also provides a sensor signal measuring device, which can accurately measure the induction signals of different types of sensors, supports the compatibility of three wiring methods: 2-wire, 3-wire and 4-wire, especially the support of the 4-wire system of thermal resistors, improves the accuracy of temperature measurement and broadens the use scenarios of the transmitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0055] Figure 1 is a structural schematic diagram of an intelligent temperature transmitter 100 according to an embodiment of the present invention;

[0056] Figure 2 An exemplary diagram of an intelligent temperature transmitter according to an embodiment of the present invention;

[0057] Figure 3 A schematic diagram of a constant current source generating circuit according to an embodiment of the present invention;

[0058] Figure 4 A schematic diagram of a signal and excitation switching circuit according to an embodiment of the present invention;

[0059] Figure 5 is a schematic diagram of an analog-to-digital conversion circuit according to an embodiment of the present invention;

[0060] Figure 6 is a schematic diagram of a single chip computer according to an embodiment of the present invention;

[0061] Figure 7 A schematic diagram of a transmission output circuit according to an embodiment of the present invention;

[0062] Figure 8 is a circuit diagram of a communication interface according to an embodiment of the present invention;

[0063] Fig. 9 is a schematic diagram of a protection circuit according to an embodiment of the present invention;

[0064] Fig.10 is a schematic structural diagram of a sensor signal measuring device 1000 according to an embodiment of the present invention;

[0065] Fig.11 FIG. 11 is a flow chart of a measurement method 1100 of an intelligent temperature transmitter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0066] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0067] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0068] Figure 1 FIG. 1 is a schematic diagram of the structure of an intelligent temperature transmitter 100 according to an embodiment of the present invention. Figure 1 As shown, the intelligent temperature transmitter 100 provided in the embodiment of the present invention includes: a sensor signal measuring device 101 and a transmission output circuit 102, wherein the sensor signal measuring device 101 includes: a constant current source generating circuit 1011, a signal and excitation switching circuit 1012, an analog-to-digital conversion circuit 1013 and a single-chip microcomputer 1014.

[0069] Preferably, the constant current source generating circuit 1011 is connected to the signal and excitation switching circuit, and is used to output a constant current excitation to the sensor through the signal and excitation switching circuit to supply power to the sensor.

[0070] Combination Figure 2As shown, in the embodiment of the present invention, the temperature transmitter includes: a single chip computer, a constant current source generating circuit for measuring thermal resistors, a signal and excitation switching circuit for realizing multi-sensor compatibility, an analog-to-digital conversion circuit for performing analog-to-digital conversion of sensor signals, and a transmission output circuit for realizing transmission output. Among them, the sensors include: Pt100 thermal resistor, Pt500 thermal resistor, Cu100 thermal resistor, Cu50 thermal resistor, pure resistance signal, platinum-rhodium 10-platinum thermocouple (S type), platinum-rhodium 13-platinum thermocouple (R type), nickel-chromium-nickel silicon thermocouple (K type), nickel-chromium silicon-nickel silicon thermocouple (N type), nickel-chromium-constantan thermocouple (E type), iron-constantan thermocouple (J type), copper-constantan thermocouple (T type), platinum-rhodium 30-platinum-rhodium 6 (B type), differential voltage signal, and can provide non-standard adjustment and calibration for special types of thermal resistors or thermocouples.

[0071] In the embodiment of the present invention, a constant current source generating circuit is used to drive the sensor measurement, and the constant current source generates a current output constant current excitation to the sensor to power the sensor. In order to ensure the accuracy of the thermal resistance measurement, the current stability of the constant current source is very important. In the embodiment of the present invention, the constant current source is used as follows: Figure 3 The constant current source generating circuit shown in the figure is implemented by the LMV321 low-power amplifier. The amplifier has very low power consumption and only needs a current of less than 110uA under normal working conditions. It is particularly suitable for 2-wire transmitters with limited power consumption. The reference input of the constant current source generating circuit uses the 3.0V reference voltage output by the reference reference circuit to obtain the voltage division through R7 and R9. The signal obtained by the voltage division of the two resistors is a 0.6V voltage signal. The signal is connected to the positive input terminal of LMV321 after filtering by capacitor C2 as the given signal of the constant current source generating circuit. The output of LMV321 is used as the output terminal of the constant current source to drive the measured thermal resistor. Since the amplifier is powered by 3.3V and the amplifier is rail-to-rail output, this means that the maximum voltage output swing amplitude of the constant current source can reach 3.3V. The current returned by the thermal resistor passes through the reference resistor R6 to form a feedback voltage. After filtering by capacitor C21, the feedback voltage is returned and connected to the negative input terminal of LMV321 to form a closed-loop feedback control of the constant current source. In the above circuit, the voltage divider resistors R7 and R9 are key components for generating a given voltage, and the feedback resistor R6 is a sampling reference resistor for deep negative feedback. The time stability and temperature stability of these three resistors determine the stability of the constant current source. Therefore, the three resistors used in this solution are metal film resistors or thin film resistors with a temperature drift of less than or equal to ±25PPM / ℃.

[0072] Preferably, the signal and excitation switching circuit 1012 is respectively connected to the sensor, the analog-to-digital conversion circuit and the single-chip microcomputer, and is used to determine the operating mode according to the mode switching instruction sent by the single-chip microcomputer; and is used to obtain the differential voltage analog signal according to the sensing signal output by the sensor.

[0073] Preferably, the signal and excitation switching circuit 1012 comprises: a dual-way four-channel analog multiplexer, a first terminal, a second terminal, a third terminal and a fourth terminal for connecting to a sensor, a first control pin and a second control pin for performing channel switching, an excitation current sinking terminal, an excitation current sinking terminal, a differential positive output terminal for outputting the differential voltage analog signal, a differential negative output terminal, a pull-up resistor and a pull-down resistor;

[0074] The pull-up resistor is respectively connected to the differential positive output terminal and the power supply terminal of the signal and excitation switching circuit, and the pull-down resistor is respectively connected to the differential negative output terminal and the ground terminal of the signal and excitation switching circuit.

[0075] Preferably, the signal and excitation switching circuit 1012 is further used for:

[0076] The high-low level differential signal and excitation output by the single-chip microcomputer through the IO port are switched to different terminals to realize the switching of the operation mode of the signal and excitation switching circuit, including: controlling the channel control end of the dual-way four-channel analog multiplexer to switch the output signals on the first terminal, the second terminal, the third terminal and the fourth terminal to the differential negative output end of the differential voltage analog signal, and controlling the channel control end of the dual-way four-channel analog multiplexer to switch the current injection end to the first terminal, the second terminal, the third terminal and the fourth terminal.

[0077] Preferably, wherein

[0078] When the signal and excitation switching circuit is in the first operation mode, the first control pin is at a low level, the second control pin is at a low level, the current sink is connected to the third terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the third terminal;

[0079] When the signal and excitation switching circuit is in the second operation mode, the first control pin is at a high level, the second control pin is at a low level, the current sink is connected to the first terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the fourth terminal;

[0080] When the signal and excitation switching circuit is in the third operation mode, the first control pin is at a low level, the second control pin is at a high level, the current sink is connected to the second terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the third terminal;

[0081] When the signal and excitation switching circuit is in the fourth operating mode, the first control pin is adjusted to a high level, the second control pin is adjusted to a high level, the current injection end is connected to the second terminal, the current absorption end is connected to the third terminal, the differential positive output end is connected to the second terminal; and the differential negative output end is connected to the fourth terminal.

[0082] In the embodiment of the present invention, through the switching circuit of excitation and signal, the 2-wire, 3-wire and 4-wire measurement of thermal resistor can be realized while being compatible with thermocouple measurement. The circuit can switch the operation mode freely according to the sensor type under the control of the single-chip computer program. Figure 4 As shown, the core of the circuit is the dual-channel four-channel analog multiplexer RS2252 (similar model is CD4052). This chip realizes the measurement of different sensors by switching the excitation source and the measurement terminal connection. Among them, P1, P2, P3 and P4 are the first terminal, second terminal, third terminal and fourth terminal of the externally connected sensor; CS_A and CS_B are the first control pin and the second control pin of RS2252; the signal and the excitation can be switched to different terminals by outputting high and low levels through the IO port of the microcontroller. AN and AP are the two differential voltage signal output terminals of the switched sensor, AN is the differential negative output terminal, AP is the differential positive output terminal, and the output signal will be sent to the digital-to-analog conversion circuit for data acquisition and processing. By controlling the channel control terminal of the analog multiplexer RS2252, the signals on P1, P2, P3 and P4 can be switched to the differential negative output terminal AN, and the differential positive output terminal AP is always fixed on the P2 terminal. I+ and I- are the excitation current sources for the sensor without switching. I+ is the excitation current sink terminal, and I- is the sensor excitation current sink terminal. The excitation current is generated by the constant current source generating circuit. By controlling the channel control terminal of the analog multiplexer RS2252, the constant current excitation current sink terminal I+ can be switched to P1, P2, P3 and P4, and the constant current excitation current sink terminal is always fixed on the P3 terminal. The channel control terminal of the analog multiplexer RS2252 switches the constant current excitation current terminal I+ and the differential negative output terminal AN to the corresponding terminals according to the control instructions of the microcontroller to change the operation mode of the excitation and signal switching circuit to achieve the measurement of different types of sensors. Among them, the corresponding relationship between the CS_A signal, CS_B signal, the current sink terminal I+ connection terminal and the differential negative output terminal AN connection terminal in different operation modes is shown in Table 1.

[0083] Table 1 Correspondence table under different operation modes

[0084]

[0085] In an embodiment of the present invention, a pull-up resistor is set on the signal path of the sensor of the switching circuit of the signal and the excitation, that is, on the differential positive signal line of the digital analog conversion input signal path, and a pull-down resistor is set on the differential negative signal line (a pull-up resistor R19 is set on AP, and a pull-down resistor R3 is set on AN). In order to avoid the interference of the resistor on the normal measured effective signal, the resistance values ​​of the two resistors are set as large as possible. The pull-up and pull-down resistors of this design are both 10 megohms, and a larger resistor can also be selected. By adding pull-up and pull-down resistors, the default state of the digital-to-analog converter can be set to full-scale or over-range input when the signal path is short-circuited, thereby producing a larger conversion result. The switching circuit of the signal and the excitation can provide a physical implementation basis for realizing fault inspection and reduced efficiency operation after a minor fault, and is an indispensable part of the fault diagnosis function. In the process of fault diagnosis, it is necessary to continuously switch the wiring mode of the thermal resistor to analyze the type of fault; when a fault is found, it is also necessary to rely on switching the signal and excitation channels to realize the reduced efficiency operation of the transmitter.

[0086] Preferably, the analog-to-digital conversion circuit 1013 is connected to the single-chip microcomputer and is used to perform analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal.

[0087] In an embodiment of the present invention, the differential voltage analog signal is converted into a digital signal by an analog-to-digital conversion circuit to obtain a differential voltage digital signal. Figure 5 As shown, the digital-to-analog conversion circuit of the embodiment of the present invention is implemented by the CS1237 (similar to CMS1237) high-precision, low-power analog-to-digital conversion chip produced by Xinhai Semiconductor. The chip not only supports 24-bit digital-to-analog conversion without missing codes, but also has a built-in differential amplifier with optional PGA amplification factors of 1, 2, 64, and 128, which avoids the need to build an external signal amplification circuit separately while achieving high-precision signal measurement. The specific implementation process is: the weak signal transmitted by the external sensor first passes through the low-pass filter network composed of R4 and R5 and C8, C9 and C10 and directly enters the differential voltage signal input terminals AINP and AINN of CS1237 to convert analog signals to digital signals. The converted digital signal is transmitted to the single-chip microcomputer through DOUT and SCLK of CS1237 for calculation and processing.

[0088] Preferably, the single chip microcomputer 1014 is connected to the transmission output circuit, and is used to send the mode switching instruction to the signal and the excitation switching current; and is used to obtain the first temperature, resistance and / or voltage data according to the differential voltage digital signal.

[0089] Preferably, the single chip microcomputer is also used for:

[0090] When the type of the sensor is a thermocouple or a differential voltage, the positive electrode of the thermocouple or the differential voltage is connected to the second terminal, the negative electrode of the thermocouple is connected to the third terminal, and the signal and excitation switching circuit is controlled to be in a first operating mode through the control instruction to perform signal measurement;

[0091] When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, a pair of cables of the 4-wire thermal resistor or the 4-wire resistor with the same polarity are connected to the first terminal and the second terminal, and another pair of cables of the same polarity are connected to the third terminal and the fourth terminal, and the signal and excitation switching circuit is controlled to be in the second operation mode through the control instruction to perform signal measurement;

[0092] When the type of the sensor is a 2-wire thermal resistor or a 2-wire resistor, two cables of the 2-wire thermal resistor or the 2-wire resistor are connected to the first terminal and the second terminal respectively, and the signal and excitation switching circuit is controlled to be in a third operation mode through the control instruction to perform signal measurement;

[0093] When the sensor type is a 3-wire thermistor or a 3-wire resistor, two cables of the same polarity of the 3-wire thermistor or the 3-wire resistor are respectively connected to the second terminal and the third terminal, and another cable of a single polarity is intercepted to the fourth terminal, and the signal and excitation switching circuit is controlled by the control instruction to repeatedly switch between the fourth operating mode and the third operating mode to perform signal measurement.

[0094] In an embodiment of the present invention, the single-chip microcomputer can send corresponding mode switching instructions to the signal and excitation switching circuit according to the type of sensor to achieve switching between different operating modes. Specifically, when the type of the sensor is a thermocouple or a differential voltage, the positive pole of the thermocouple or the differential voltage is connected to P2, and the negative pole of the thermocouple is connected to P3, and the signal and excitation switching circuit is controlled to be in the first operating mode through the control instruction to perform signal measurement; when the type of the sensor is a 4-wire thermistor or a 4-wire resistor, a pair of same-polarity cables of the 4-wire thermistor or the 4-wire resistor are connected to P1 and P2, and another pair of same-polarity cables are connected to P3 and P4, and the signal and excitation switching circuit is controlled to be in the second operating mode through the control instruction to perform signal measurement; when the sensor is a 4-wire thermistor or a 4-wire resistor, a pair of same-polarity cables of the 4-wire thermistor or the 4-wire resistor are connected to P1 and P2, and another pair of same-polarity cables are connected to P3 and P4, and the signal and excitation switching circuit is controlled to be in the second operating mode through the control instruction to perform signal measurement; When the type of the sensor is a 2-wire thermistor or a 2-wire resistor, the two cables of the 2-wire thermistor or the 2-wire resistor are connected to P1 and P2 respectively, and the signal and excitation switching circuit is controlled to be in the third operating mode through the control instruction to perform signal measurement; when the type of the sensor is a 3-wire thermistor or a 3-wire resistor, the two cables of the 3-wire thermistor or the 3-wire resistor with the same polarity are connected to P2 and P3 respectively, and another cable with a single polarity is connected to P4, and the signal and excitation switching circuit is controlled to repeatedly switch between the fourth operating mode and the third operating mode through the control instruction to perform signal measurement.

[0095] Based on the above mode switching, the process of measuring different wiring methods of different sensors can be realized as follows:

[0096] (1) Thermocouple or differential voltage measurement: Fixed in Mode 1.

[0097] Thermocouple or differential voltage wiring is as follows: the positive pole of the thermocouple is connected to the P2 terminal and the negative pole is connected to the P3 terminal.

[0098] The specific signal and excitation paths are as follows: P2 is for signal measurement, which is directly connected to the AP signal without switching. P3 is the negative terminal of the signal measurement, which is connected to the AN signal through the X0 to X terminal of RS2252. The excitation current flows into the Y port of RS2252 after switching, flows out of the Y0 port, and returns through resistor R22. The excitation current provides a stable negative terminal measurement reference for the thermocouple at terminal P3. All types of thermocouples are measured by this circuit, and the conversion between the measurement signal and temperature is realized by the thermocouple coefficients stored in the microcontroller. If the differential analog voltage is measured, there is no need to convert the voltage to the temperature, and the voltage signal is directly output.

[0099] (2) 4-wire RTD or resistance measurement: Fixed in Mode 2.

[0100] The wiring method of a 4-wire thermal resistor or resistor is as follows: a pair of cables of the thermal resistor with the same polarity are connected to the P1 and P2 terminals, and another pair of cables with the same polarity are connected to P3 and P4.

[0101] The specific signal and excitation paths are as follows: P2 is the positive end of the signal measurement, which is directly connected to the AP signal without switching. P4 is the negative end of the signal measurement, which is connected to the AN signal through X1 of RS2252. The excitation current I+ is connected to the P1 terminal after switching from Y to Y1, and returns from the P3 terminal through the thermal resistor and directly returns to I- without switching. The 4-wire measurement provides the highest measurement accuracy. The above circuit realizes the complete separation of the measurement circuit and the excitation circuit. The measurement of the thermal resistor is not affected by the wire resistance. After obtaining the resistance value of the thermal resistor, the measurement of the 4-wire thermal resistor can be completed by performing calculations through the single-chip microcomputer. If the pure resistance is measured, there is no need to convert the voltage to the temperature, and the resistance signal is directly output.

[0102] (3) 2-wire RTD or resistance measurement: Fixed in Mode 3.

[0103] The wiring method of a 2-wire thermal resistor or resistor is as follows: the two cables of the thermal resistor are connected to the P1 and P2 terminals.

[0104] The specific signal and excitation paths are as follows: P2 is the positive terminal of the signal measurement, which is directly connected to the AP signal without switching. P3 is the negative terminal of the signal measurement, which is connected to the AN signal through the X2 to X terminal of RS2252. The excitation current I+ is connected to the P2 terminal after switching from Y to Y2, and returns from the P3 terminal through the thermal resistor to I- without switching. The 2-wire test of the thermal resistor will be affected by the wire resistance, and it is not suitable to measure the thermal resistor with too long wire. However, it has only two connections to ensure the reliability of the measurement. After obtaining the resistance value of the thermal resistor, the measurement of the 2-wire thermal resistor can be completed by performing calculations through the microcontroller. If the pure resistance is measured, there is no need to convert the voltage to the temperature, and the resistance signal is directly output.

[0105] (4) Measurement of 3-wire RTD or resistor: Switch back and forth between Mode 4 and Mode 3.

[0106] The wiring method of a 3-wire thermal resistor or resistor is as follows: two wires of the thermal resistor with the same polarity are connected to terminals P2 and P3 respectively. Another wire with a single polarity is connected to P4.

[0107] The 3-wire measurement is divided into two steps. For the convenience of description, we assume that the resistance of the measured thermal resistor is RT and the resistance of the wire is RL. Step 1: Control RS2252 to switch to mode 4, and measure the impedance of the thermal resistor plus one wire, that is, RT+RL. The specific signal and excitation paths are as follows: P2 is the positive end of the signal measurement, which is directly connected to the AP signal without switching. P4 is the negative end of the signal measurement, which is connected to the AN signal through X3 of RS2252. The excitation current I+ is connected to the P2 terminal after switching from Y to Y3, and returns from the P3 terminal through the thermal resistor without switching directly to I-. In this way, the P2 terminal has both the excitation current and the signal measurement function, so the impedance of the wire connected to it will be calculated. However, there is only a measurement signal on the P4 terminal, no excitation current, so there is no influence of the wire impedance. Therefore, at this time, the data obtained by the measurement of AN and AP is the impedance of the thermal resistor plus one wire.

[0108] Step 2: Control RS2252 to switch to mode 3, and measure the impedance of the thermal resistor plus two wires, that is, RT+2*RL. The specific signal and excitation path at this time are the same as those of the 2-wire thermal resistor measurement.

[0109] When calculating a 3-wire thermal resistor, subtract the 2-wire data (RT+2*RL) from twice the data measured in step 1 (RT+RL), which can offset all wire impedances, thereby avoiding the influence of wire impedance on the thermal resistor. The specific calculation formula is as follows, assuming that the measured resistance is RM: then RM=2*(RT+RL)-(RT+2*RL)=RL; thus the measured resistance RM is the resistance of the thermal resistor, and the error of the wire impedance is offset. When the transmitter is working, execute steps 1 and 2 in a loop, and after obtaining the resistance of the thermal resistor that offsets the cable resistance, the measurement of the 3-wire thermal resistor can be completed by performing calculations through the microcontroller. If the pure resistance is measured, there is no need to convert the voltage to the temperature, and the resistance signal is directly output.

[0110] When the sensor is a thermal resistor, the single chip microcomputer can convert the acquired differential voltage digital signal into resistance according to the conversion relationship between the standard differential voltage digital signal and resistance, and then convert the resistance to temperature according to the relationship between resistance and temperature to obtain the first temperature and output it.

[0111] When the sensor is used to measure resistance, the single chip microcomputer can also convert the acquired differential voltage digital signal into resistance data and directly output it according to the conversion relationship between the standard differential voltage digital signal and resistance.

[0112] When the sensor is a thermocouple, the single-chip microcomputer can convert the acquired differential voltage digital signal into a first thermoelectric potential according to the conversion relationship between the standard differential voltage digital signal and the thermoelectric potential. At the same time, the second temperature is obtained by measuring the ambient temperature, and the second temperature is converted into a second thermoelectric potential according to the conversion relationship between the standard temperature and the thermoelectric potential. The first thermoelectric potential is added to the second thermoelectric potential to obtain the third thermoelectric potential after the cold end compensation of the thermocouple. Then, according to the relationship between the third thermoelectric potential and the temperature, the conversion of the thermoelectric potential to the temperature is performed to obtain the corrected first temperature and output it. At the same time, the cold end compensation function of the thermocouple can also be turned off according to the usage scenario, and the conversion of the thermoelectric potential to the temperature is directly performed according to the relationship between the first thermoelectric potential and the temperature to obtain the uncorrected first temperature and output it.

[0113] When the sensor is used to measure differential voltage, the single chip microcomputer can also convert the acquired differential voltage digital signal into real differential analog voltage data and directly output it according to the conversion relationship between the standard differential voltage digital signal and the real differential analog voltage.

[0114] Preferably, the single chip microcomputer is also used for:

[0115] According to the differential voltage digital signal, according to the preset judgment rules, the fault type and fault cause of the temperature transmitter are determined; wherein the fault type includes: serious fault and minor fault;

[0116] Wherein, when the type of the sensor is a thermocouple or a differential voltage and is in the first operating mode, the actual voltage value is determined according to the differential voltage digital signal, and when the actual voltage value is greater than a preset voltage upper limit threshold or less than a preset voltage lower limit threshold, the fault type is determined to be a serious fault;

[0117] When the type of the sensor is a 2-wire thermal resistor or a 2-wire resistor and is in a third operation mode, a first resistance is determined according to the differential voltage digital signal, and when the first preset resistance is greater than a first preset resistance upper limit threshold or less than a first preset resistance lower limit threshold, the fault type is determined to be a serious fault;

[0118] When the type of the sensor is a 3-wire thermal resistor or a 3-wire resistor, and is in the fourth operation mode, the second resistance is determined according to the differential digital signal, and when the second resistance is greater than a second preset resistance upper threshold or less than a second preset resistance lower threshold, the operation mode is switched to a third operation mode, and the third resistance is determined according to the differential digital signal in the third operation mode, and when the third resistance is less than or equal to the third preset resistance upper threshold and greater than or equal to the third preset resistance lower threshold, the fault type is determined to be a first minor fault; when the third resistance is greater than the third preset resistance upper threshold or less than the third preset resistance lower threshold, the fault type is determined to be a serious fault;

[0119] When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, and is in the second operating mode, the fourth resistor is determined according to the differential digital signal, and when the fourth resistor is greater than the fourth preset resistance upper limit threshold or less than the fourth preset resistance lower limit threshold, the operating mode is switched to the fourth operating mode, and the fifth resistor is determined according to the differential digital signal in the fourth operating mode, and when the fifth resistor is less than or equal to the fifth preset resistance upper limit threshold and greater than or equal to the fifth preset resistance lower limit threshold, the fault type is determined to be a second minor fault; when the fifth resistor is greater than the fifth preset resistance upper limit threshold or less than the fifth preset resistance lower limit threshold, the operating mode is switched to the third operating mode, and the sixth resistor is determined according to the differential digital signal in the third operating mode, and when the sixth resistor is less than or equal to the sixth preset resistance upper limit threshold and greater than or equal to the sixth preset resistance lower limit threshold, the fault type is determined to be a third minor fault; when the sixth resistor is greater than the sixth preset resistance upper limit threshold or less than the sixth preset resistance lower limit threshold, the fault type is determined to be a serious fault.

[0120] Preferably, the single chip microcomputer is also used for:

[0121] According to the fault type and the preset control rules, a control instruction is sent to the fault indication device, so that the fault indicator light gives an alarm according to the control instruction and indicates the fault level at the same time;

[0122] When the fault type is a first minor fault, a second minor fault or a third minor fault, a reduced efficiency operation mode is determined according to the fault type and a preset reduced efficiency operation rule, and the signal and excitation switching circuit is controlled to operate according to the reduced efficiency operation mode; and when the operating time of the temperature transmitter in the fault state reaches a preset time threshold, the operating mode is adjusted to the operating mode before the fault according to the sensor type, and the fault type and fault cause of the temperature transmitter are determined again according to the preset judgment rule;

[0123] Wherein, the degraded operation rule includes: when the fault type is a first minor fault, determining the degraded operation mode to operate in accordance with the third operation mode;

[0124] When the fault type is the second minor fault, the reduced efficiency operation mode is determined to be operated according to the normal measurement operation mode of the 3-wire thermal resistor or the 3-wire resistor;

[0125] When the fault type is a third minor fault, the degraded operation mode is determined to be operation according to the third operation mode.

[0126] Whether it is the initial deployment stage of the transmitter or in the control system operation and maintenance stage, the fault diagnosis function of the transmitter can help construction or operation and maintenance personnel quickly locate the fault problem. In response to the demand, the present invention designs a green fault indicator light on the temperature transmitter, and the user can determine the sensor fault according to the prompt given by the indicator light. If the user wants to see more detailed information, he can also use the supporting configuration software to directly read the sensor's fault information through the communication interface of the transmitter. In addition, when a minor fault occurs in the sensor connected to the transmitter, if the transmitter can adjust its own operating state, it will undoubtedly further increase the reliability and stability of the system. In response to the demand, the present invention also implements a reduced efficiency operation mechanism when the transmitter fails. It can ensure that the system can still guarantee the sensor output signal even in the event of a minor fault.

[0127] The present invention divides the fault of the sensor into two levels, namely, serious fault and minor fault. No matter which fault state the sensor is in, the fault indication device is operated to inform the user that a fault has occurred, and inform the user whether it is a serious fault or a minor fault. The fault indication device can be a fault indicator light. The following is the definition of these two faults. A serious fault refers to a fault that affects the basic work of the sensor, that is, the temperature measurement function is completely lost. At this time, the transmitter outputs not a measurement signal but an alarm current, and can output a current of ≤3.6mA or ≥22mA according to the user's setting. In the serious fault mode, the fault indicator light controlled by the single-chip microcomputer will flash quickly. A minor fault refers to a fault that does not cause the complete loss of its measurement function, and the sensor will be switched to a worse measurement mode to complete the measurement. At this time, the transmitter still outputs a measurement signal, but its output accuracy is worse than that of the normal working state. In the minor fault mode, the fault indicator light controlled by the single-chip microcomputer is always on and off. If the sensor is working normally, the transmitter will operate in the state set by the user. At this time, the transmitter outputs a measurement signal with the accuracy expected by the user, and the fault indicator light controlled by the single-chip microcomputer is always on, indicating that the working state is normal.

[0128] In order to realize the fault diagnosis of the transmitter and the reduced efficiency operation of the minor fault, the hardware and software of the transmitter need to cooperate with each other. In the hardware, the pull-up resistor and the pull-down resistor are designed in the signal and excitation switching circuit. In the software, the upper and lower limits for determining the fault are set according to the working temperature range of different types of thermal resistors and thermocouples.

[0129] Specifically, when the sensor type is a thermocouple or a differential voltage and is in the first operating mode, the actual voltage value is determined based on the differential voltage digital signal, and when the actual voltage value is greater than a preset voltage upper limit threshold or less than a preset voltage lower limit threshold, the fault type is determined to be a severe fault.

[0130] When the sensor type is a 2-wire thermistor or a 2-wire resistor and is in the third operating mode, the first resistance is determined according to the differential voltage digital signal, and when the first preset resistance is greater than a first preset resistance upper limit threshold or less than a first preset resistance lower limit threshold, the fault type is determined to be a serious fault.

[0131] When the sensor is a 3-wire thermistor or a 3-wire resistor and is in the fourth operating mode, the second resistance is determined according to the differential digital signal, and when the second resistance is greater than the second preset resistance upper limit threshold or less than the second preset resistance lower limit threshold, the operating mode is switched to the third operating mode, and the third resistance is determined according to the differential digital signal in the third operating mode, and when the third resistance is less than or equal to the third preset resistance upper limit threshold and greater than or equal to the third preset resistance lower limit threshold, the fault type is determined to be a first minor fault; when the third resistance is greater than the third preset resistance upper limit threshold or less than the third preset resistance lower limit threshold, the fault type is determined to be a serious fault.

[0132] When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, and is in the second operating mode, the fourth resistor is determined according to the differential digital signal, and when the fourth resistor is greater than the fourth preset resistance upper limit threshold or less than the fourth preset resistance lower limit threshold, the operating mode is switched to the fourth operating mode, and the fifth resistor is determined according to the differential digital signal in the fourth operating mode, and when the fifth resistor is less than or equal to the fifth preset resistance upper limit threshold and greater than or equal to the fifth preset resistance lower limit threshold, the fault type is determined to be a second minor fault; when the fifth resistor is greater than the fifth preset resistance upper limit threshold or less than the fifth preset resistance lower limit threshold, the operating mode is switched to the third operating mode, and the sixth resistor is determined according to the differential digital signal in the third operating mode, and when the sixth resistor is less than or equal to the sixth preset resistance upper limit threshold and greater than or equal to the sixth preset resistance lower limit threshold, the fault type is determined to be a third minor fault; when the sixth resistor is greater than the sixth preset resistance upper limit threshold or less than the sixth preset resistance lower limit threshold, the fault type is determined to be a serious fault.

[0133] In the embodiment of the present invention, fault diagnosis can be performed in the manner of Table 1. Assume that: the actual test thermal resistor resistance is RM, the lower limit alarm resistance of the thermal resistor is RL, and the upper limit alarm resistance is RH; the actual test thermocouple voltage is VM, the lower limit alarm voltage of the thermocouple is VL, and the upper limit alarm voltage is VH.

[0134] Table 1 Fault type identification table

[0135]

[0136] In an embodiment of the present invention, when the transmitter finds that there is a problem in working in the configured mode, it will automatically switch to other modes for further inspection. If the mode configured by the user works normally, it works normally according to the configured mode. If a fault occurs, on the one hand, the single chip will send a control instruction to the fault indicator light according to the preset control rule according to the fault type, so that the fault indicator light will warn according to the control instruction and indicate the fault level; and send detailed fault information through the communication interface. On the other hand, the single chip will determine the reduced efficiency operation mode and control the signal and excitation switching circuit to operate in the reduced efficiency operation mode; at the same time, when it is in a fault state, whether it is a serious fault or a minor fault. It will try to restore the normal operation mode in a loop. Once the normal mode runs successfully, it runs in the normal mode, and again determines the fault type and cause of the temperature transmitter according to the preset judgment rule. If the normal mode fails to run, it returns to the original fault state. Specifically, when the operating time of the temperature transmitter in the fault state reaches the preset time threshold, it is adjusted to the operating mode before the fault according to the sensor type, and the fault type and cause of the temperature transmitter are determined again according to the preset judgment rule.

[0137] Among them, the reduced efficiency operation rules include: when the fault type is a first minor fault, determining the reduced efficiency operation mode to operate according to the third operation mode; when the fault type is a second minor fault, determining the reduced efficiency operation mode to operate according to the normal measurement operation mode of a 3-wire thermal resistor or a 3-wire resistor; when the fault type is a third minor fault, determining the reduced efficiency operation mode to operate according to the third operation mode.

[0138] As shown in Table 1, when a minor fault 1 occurs, the measurement mode of the 3-wire thermal resistor or 3-wire resistor is automatically switched to the measurement mode according to the 2-wire thermal resistor or 2-wire resistor, and the measurement signal is output normally. When a minor fault 2 occurs, the measurement mode of the 4-wire thermal resistor or 4-wire resistor is automatically switched to the measurement mode according to the 3-wire thermal resistor or 3-wire resistor, and the measurement signal is output normally. When a minor fault 3 occurs, the measurement mode of the 4-wire thermal resistor or 4-wire resistor is automatically switched to the measurement mode according to the 2-wire thermal resistor or 2-wire resistor, and the measurement signal is output normally.

[0139] It should be noted that minor faults also require troubleshooting during initial installation or regular maintenance on site to improve the reliability and measurement accuracy of the transmitter. The identification of the above faults and the output of the alarm light can improve the convenience of the user's use of the transmitter and enhance the reliability of the transmitter. For construction and operation and maintenance, it is of great value.

[0140] The microcontroller circuit is the core of digital signal processing, such as Figure 6As shown, STM8L151G4U6 is used to implement it. The microcontroller has low power consumption and small package, and is very suitable for use in temperature transmitters with limited power consumption and size. In addition, the microcontroller also has a 12-bit DAC peripheral, which is very useful for subsequent current output transmission, which can greatly simplify the design of the V / I output circuit and improve the accuracy and response time of the current output. The power supply of the microcontroller is not the 3.3V power supply output by the LDO, but the 3.0V reference voltage output by the reference. This is because considering that the reference used by the DAC is the power supply voltage of the microcontroller, this circuit design can maximize the accuracy and stability of the current output. The power supply of the microcontroller is filtered by C18 and then connected to the VCC pin of the microcontroller through the C19 decoupling capacitor. In addition, in order to ensure the reliable reset of the microcontroller, the reset circuit of the microcontroller is built using R11 and C16.

[0141] The single-chip microcomputer of the present invention plays a control role on the one hand, which is used to switch the excitation and signal paths, control the state of the indicator light, and output analog voltage signals to control the 4-20mA current output; on the other hand, it performs data collection work, which is used to collect the output data of the analog-to-digital converter and the data of the ambient temperature measurement. Secondly, the collected signals are processed to realize the nonlinear calibration of the transmitter signal, the calculation and correction of the temperature value, the monitoring of the system status, and the switching of the working state according to the configuration of the communication. In addition, the monitoring, analysis and judgment of sensor failures are also realized by the logic output of the single-chip microcomputer.

[0142] In an embodiment of the present invention, the fault indicator light adopts a misty emerald green LED, the indicator light adopts 3.3.V power supply, and is connected to the single-chip microcomputer through a current limiting resistor R2. If the transmitter is in a normal working state, the indicator light remains on, informing the user that the transmitter is in a normal working state. If the transmitter is in a serious fault state, the single-chip microcomputer controls the LED light to flash quickly, informing the user that the transmitter is in a fault state. If the transmitter is in a minor fault state, the single-chip microcomputer controls the LED light to be on and off, informing the user that the transmitter is in a reduced efficiency operation state. Although the transmitter can output signals normally, the accuracy of the output signal is poor.

[0143] Preferably, the transmission output circuit 102 is used to convert the first temperature, resistance and / or voltage data into a standard signal of a preset type.

[0144] In the embodiment of the present invention, the transmitter output circuit can collect the signal of the external sensor and calculate the temperature according to the standard of the 2-wire 4-20mA current output transmitter. The temperature information will eventually be mapped to the 4-20mA current output, output the standard signal, and realize the remote transmission of the transmitter signal. Figure 7As shown, in order to realize the V / I conversion circuit of the transmitter current output, the digital-to-analog converter peripheral of the single-chip computer will send the modulated voltage signal through the DAC lead. As shown in the figure above, the DAC signal will map the temperature signal to a standard signal of 4-20mA through the V / I transmitter circuit built by LMV321. The voltage of the DAC will be connected to the positive input of LMV321 as a given voltage through the voltage divider of R10 and R14. The output of LMV321 drives the BCX56 NPN transistor through the R12 resistor to control the output of the loop circuit. The output loop current is sampled by R15 and introduced into the negative output of LMV321 to form a current output with deep negative feedback. The above-mentioned voltage divider resistors R10 and R14 are in a given loop, and the feedback resistor R15 is in the sampling link. The characteristics of these three resistors play a decisive role in the accuracy and stability of the current output. Therefore, the present invention selects a low-temperature drift resistor with a temperature drift less than or equal to ±25PPM / ℃.

[0145] Preferably, the temperature transmitter further comprises:

[0146] An ambient temperature measurement circuit, connected to the single chip microcomputer, for measuring the ambient temperature to obtain a second temperature;

[0147] A single-chip computer, for, when the sensor is a thermocouple, converting the differential voltage digital signal into a first thermoelectric potential according to a preset conversion relationship between the differential voltage digital signal and the thermoelectric potential; converting the second temperature into a second thermoelectric potential according to a preset conversion relationship between the temperature and the thermoelectric potential; determining a third thermoelectric potential after cold-end compensation of the thermocouple according to the sum of the first thermoelectric potential and the second thermoelectric potential; converting the third thermoelectric potential into a temperature according to a preset conversion relationship between the thermoelectric potential and the temperature, so as to obtain and output a corrected first temperature; or

[0148] When the sensor is a thermocouple, the differential voltage digital signal is converted into a first thermoelectric potential according to a preset conversion relationship between the differential voltage digital signal and the thermoelectric potential, and the first thermoelectric potential is converted into temperature according to a relationship between the first thermoelectric potential and temperature to obtain a corrected first temperature and output it.

[0149] In an embodiment of the present invention, digital calculation is used to perform cold-end compensation on the thermocouple. The circuit uses the NST1001 digital temperature chip to measure the ambient temperature. The NST100 chip produced by Nanochip Microelectronics is a high-precision dual-pin digital pulse output temperature sensor chip. The chip measures a temperature range of -50°C to 150°C, with a resolution of up to 0.0625°C, a full temperature range accuracy better than 0.75°C, a short conversion time, and high accuracy. The cold-end compensation of the thermocouple is implemented as follows: ① Obtain the ambient temperature value inside the transmitter through NST1001. ② Calculate the compensated electromotive force of the thermocouple based on the ambient temperature value. ③ Add the compensated temperature electromotive force to the electromotive force obtained by the thermocouple measurement to obtain the compensated temperature electromotive force. ④ Calculate the actual temperature value on the thermocouple based on the compensated electromotive force combined with the thermocouple calculation coefficient inside the single-chip microcomputer.

[0150] Preferably, the sensor signal measuring device further comprises:

[0151] A communication interface, connected to the single-chip microcomputer, for realizing the interaction between the single-chip microcomputer and an external device;

[0152] The power supply and reference circuit comprises a power supply subcircuit and a reference subcircuit; wherein the power supply subcircuit is connected with a constant current source generating circuit, a signal and excitation switching circuit, an analog-to-digital conversion circuit, a single-chip microcomputer, an ambient temperature measuring circuit, a fault indicator light and a transmission output circuit to provide a stable power supply; the reference subcircuit is connected with a constant current source generating circuit, an analog-to-digital conversion circuit and a transmission output circuit to provide a reference voltage signal;

[0153] The protection circuit is connected with the external power supply, the transmission output circuit, and the power supply and reference circuit, and is used to protect the power supply circuit of the intelligent temperature transmitter and provide the function of online current measurement.

[0154] like Figure 2 As shown, the temperature transmitter also includes: a communication interface, a power supply and reference circuit, and a protection circuit (not shown in the figure). The communication interface is connected to the single-chip microcomputer and is used to realize the interaction between the single-chip microcomputer and the external device. The power supply and reference circuit include a power subcircuit and a reference subcircuit; wherein the power subcircuit is connected to the constant current source generating circuit, the signal and excitation switching circuit, the analog-to-digital conversion circuit, the single-chip microcomputer, the ambient temperature measurement circuit, the fault indicator light and the transmission output circuit to provide a stable power supply; the reference subcircuit is connected to the constant current source generating circuit, the analog-to-digital conversion circuit and the transmission output circuit to provide a reference voltage signal. The protection circuit is connected to the external power supply, the transmission output circuit, and the power supply and reference circuit to protect the power supply circuit of the intelligent temperature transmitter and provide the function of online current measurement.

[0155] like Figure 8As shown, in the embodiment of the present invention, the communication interface is implemented using a standard Mini-USB socket. The TX and RX lines of the UART cable of the single-chip microcomputer are directly connected to the D+ and D- data lines of the USB socket, and the calibration and parameter modification of the transmitter can be directly realized through the TTL serial port. The program download and DEBUG debugging cable of the single-chip microcomputer is directly connected to the shielded pin of the USB socket, and the program download and debugging can be realized through an external downloader. In addition, the reset pin of the single-chip microcomputer is also led out to the ID pin of the USB, and the reset and restart of the single-chip microcomputer can be easily realized externally.

[0156] In the embodiment of the present invention, a linear voltage regulator is selected as the power supply scheme for the entire transmitter. The reference circuit provides a reference source for the constant current source generating circuit, the analog-to-digital conversion circuit and the current transducer circuit. The power supply circuit is implemented by the linear voltage regulator HT7533, and the static power consumption of the chip is as low as 2.5uA. The maximum input voltage of the voltage regulator is 30V, which can meet the DC24V power supply requirements of the transmitter. A capacitor is set on each input and output side of the voltage regulator to filter out noise. In order to ensure the measurement accuracy, a dedicated series reference source is used to generate the reference source required for the entire system. This scheme uses the reference chip REF3330 to implement the constant current reference. The reference chip can operate under -40-125℃ conditions, and the maximum temperature drift in the full temperature range is less than 30PPM / ℃. The excellent temperature stability and long-term stability of the voltage reference source represent the smaller temperature drift and time drift of the temperature transmitter. All the references of the transmitter, including the constant current source generating circuit, the digital-to-analog conversion circuit and the current output transducer circuit (the power supply of the single-chip microcomputer), are provided by the reference circuit. This not only reduces costs, but also ensures that when the reference source drifts, all circuit drifts in the same direction, further reducing the overall drift of the transmitter and ensuring measurement accuracy and environmental stability.

[0157] like Fig. 9As shown, it is a schematic diagram of the protection circuit, P5 is the positive terminal of the external power supply, and P6 is the negative terminal. The external power supply first passes through the safety high-voltage capacitor C5 to protect against instantaneous glitch voltage. Then it passes through the TVS tube D4 to protect against instantaneous pulses or electrostatic interference. Then it passes through the insurance F1 to prevent the rear-end load failure from causing circuit damage. Then it passes through the inductors L1 and L2 to filter out the EMI inside the circuit. After being protected by the anti-reverse diode D1, it is filtered by C1 and enters the transmitter. The present invention also designs a special test interface for online current measurement of the transmitter without disassembly. The interface is implemented using the Zener voltage regulator D2, and the measurement terminals T+ and T- are led to the outside at both ends of the diode. When measuring the loop current, it is only necessary to contact the ammeter to the measurement terminals T+ and T-. At this time, the voltage regulator is short-circuited, and all currents will flow through the measuring ammeter to achieve online current measurement. In addition, the circuit is equipped with ESD electrostatic surge protection diodes on all touchable and accessible terminals. For detailed information, please refer to the signal and excitation switching circuit and communication interface.

[0158] The temperature transmitter of the present invention has the following advantages: (1) It realizes the input compatibility of multiple sensors, especially supports the 4-wire measurement of thermal resistors, and improves the measurement accuracy and usage scenarios of the sensor. (2) The transmitter has a sound sensor fault diagnosis function. Combined with the fault indicator light of the transmitter, it can greatly improve efficiency and help construction or operation and maintenance personnel quickly locate the fault problem. (3) The transmitter's minor fault reduction operation mechanism enables the transmitter to automatically switch the working mode when a minor fault occurs, ensuring the effective signal output of the transmitter. This improves the reliability of the transmitter. (4) The power consumption current of the whole machine reaches a minimum of 3.5mA, supporting the NE43 standard. In addition to the indicator light, an alarm can also be given on the output current. It is convenient for the configuration system to do fault control. (5) Pure digital thermocouple cold end compensation has high compensation accuracy, good stability, and fast response speed. (6) It supports online current measurement, which is convenient for on-site inspection. (7) The transmitter has high measurement accuracy, little effect of ambient temperature on accuracy, and good anti-interference performance. Experimental tests show that: in terms of anti-electromagnetic interference: for a group pulse of signal or power supply of 2000V, the output signal temperature is +2℃, and it returns to normal after the group pulse is cancelled (PT100 thermal resistor, range setting 0-100℃). In terms of anti-environmental changes: 20 to 80℃ temperature drift +0.05℃ / 10℃; 20 to -40℃ temperature drift -0.1℃ / 10℃ (PT100 thermal resistor, range setting 0-100℃).

[0159] Fig.10 FIG. 1 is a schematic diagram of the structure of a sensor signal measuring device 1000 according to an embodiment of the present invention. Fig.10As shown, the sensor signal measuring device 1000 provided in the embodiment of the present invention includes: a constant current source generating circuit 1001 , a signal and excitation switching circuit 1002 , an analog-to-digital conversion circuit 1003 and a single-chip microcomputer 1004 .

[0160] Preferably, the constant current source generating circuit 1001 is connected to the signal and excitation switching circuit, and is used to output a constant current excitation to the sensor through the signal and excitation switching circuit to supply power to the sensor.

[0161] Preferably, the signal and excitation switching circuit 1002 is respectively connected to the sensor, the analog-to-digital conversion circuit and the single-chip microcomputer, and is used to determine the operating mode according to the mode switching instruction sent by the single-chip microcomputer; and is used to obtain the differential voltage analog signal according to the sensing signal output by the sensor.

[0162] Preferably, the analog-to-digital conversion circuit 1003 is connected to the single-chip microcomputer and is used to perform analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal.

[0163] Preferably, the single chip microcomputer 1004 is connected to the transmission output circuit, and is used to send the mode switching instruction to the signal and the excitation switching current; and is used to obtain the first temperature, resistance and / or differential analog voltage data according to the differential voltage digital signal.

[0164] The sensor signal measuring device 1000 of the embodiment of the present invention corresponds to the sensor signal measuring device 101 in the intelligent temperature transmitter 100 of another embodiment of the present invention, and will not be described in detail herein.

[0165] Fig.11 FIG. 1 is a flow chart of a measurement method 1100 of an intelligent temperature transmitter according to an embodiment of the present invention. Fig.11 As shown, the measurement method 1100 based on the intelligent temperature transmitter provided in the embodiment of the present invention includes:

[0166] Step 1101, the single chip microcomputer sends a mode switching instruction to the signal and excitation switching circuit, so that the signal and excitation switching circuit determines the operation mode according to the mode switching instruction;

[0167] Step 1102, the constant current source generating circuit outputs a constant current excitation to the sensor to supply power to the sensor;

[0168] Step 1103, the signal and excitation switching circuit obtains a differential voltage analog signal according to the sensing signal output by the sensor;

[0169] Step 1104: the analog-to-digital conversion circuit performs analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal;

[0170] Step 1105, the single chip microcomputer obtains first temperature, resistance and / or differential analog voltage data according to the differential voltage digital signal;

[0171] Step 1106: The transmission output circuit converts the first temperature, resistance and / or differential analog voltage data into a standard signal of a preset type.

[0172] The measuring method 1100 of the intelligent temperature transmitter of the embodiment of the present invention corresponds to the intelligent temperature transmitter 100 of another embodiment of the present invention, and will not be described in detail herein.

[0173] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0174] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of the means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0175] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0176] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0177] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0178] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0179] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An intelligent temperature transmitter, characterized in that: The temperature transmitter includes: a sensor signal measuring device and a transmission output circuit, wherein the sensor signal measuring device includes: a constant current source generating circuit, a signal and excitation switching circuit, an analog-to-digital conversion circuit and a single-chip microcomputer; wherein, The constant current source generating circuit is connected to the signal and excitation switching circuit, and is used to output a constant current excitation to the sensor through the signal and excitation switching circuit to supply power to the sensor; The signal and excitation switching circuit is connected to the sensor, the analog-to-digital conversion circuit and the single-chip microcomputer respectively, and is used to determine the operation mode according to the mode switching instruction sent by the single-chip microcomputer; and is used to obtain the differential voltage analog signal according to the sensing signal output by the sensor; The analog-to-digital conversion circuit is connected to the single-chip microcomputer and is used to perform analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal; The single chip microcomputer is connected to the transmission output circuit, and is used to send the mode switching instruction to the signal and the excitation switching current; and is used to obtain the first temperature, resistance and / or voltage data according to the differential voltage digital signal; The transmission output circuit is used to convert the first temperature, resistance and / or voltage data into a standard signal of a preset type; Wherein, the temperature transmitter further includes: An ambient temperature measurement circuit, connected to the single chip microcomputer, for measuring the ambient temperature to obtain a second temperature; The signal and excitation switching circuit includes: a dual-way four-channel analog multiplexer, a first terminal, a second terminal, a third terminal and a fourth terminal for connecting to a sensor, a first control pin and a second control pin for channel switching, an excitation current sink, an excitation current sink, a differential positive output terminal for outputting the differential voltage analog signal, a differential negative output terminal, a pull-up resistor and a pull-down resistor; Wherein, the pull-up resistor is respectively connected to the differential positive output terminal and the power supply terminal of the signal and excitation switching circuit, and the pull-down resistor is respectively connected to the differential negative output terminal and the ground terminal of the signal and excitation switching circuit; Wherein, the signal and excitation switching circuit is also used for: The high and low level differential signals and stimuli output by the receiving single-chip microcomputer through the IO port are switched to different terminals to realize the switching of the operation mode of the signal and stimulus switching circuit, specifically: the channel control end of the dual-way four-channel analog multiplexer is controlled to switch the output signals on the first terminal, the second terminal, the third terminal and the fourth terminal to the differential negative output terminal of the differential voltage analog signal, and the channel control end of the dual-way four-channel analog multiplexer is controlled to switch the current injection end to the first terminal, the second terminal, the third terminal and the fourth terminal.

2. The temperature transmitter according to claim 1, characterized in that: The single chip microcomputer is used for, when the sensor is a thermocouple, converting the differential voltage digital signal into a first thermoelectric potential according to a preset conversion relationship between the differential voltage digital signal and the thermoelectric potential; converting the second temperature into a second thermoelectric potential according to a preset conversion relationship between the temperature and the thermoelectric potential; determining a third thermoelectric potential after the thermocouple cold end is compensated according to the sum of the first thermoelectric potential and the second thermoelectric potential; converting the third thermoelectric potential into a temperature according to a preset conversion relationship between the thermoelectric potential and the temperature, so as to obtain a corrected first temperature; or When the sensor is a thermocouple, the differential voltage digital signal is converted into a first thermoelectric potential according to a preset conversion relationship between the differential voltage digital signal and the thermoelectric potential, and the first thermoelectric potential is converted into temperature according to a relationship between the first thermoelectric potential and temperature to obtain a corrected first temperature.

3. The temperature transmitter according to claim 1, characterized in that: When the signal and excitation switching circuit is in the first operation mode, the first control pin is at a low level, the second control pin is at a low level, the current sink is connected to the third terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the third terminal; When the signal and excitation switching circuit is in the second operation mode, the first control pin is at a high level, the second control pin is at a low level, the current sink is connected to the first terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the fourth terminal; When the signal and excitation switching circuit is in the third operation mode, the first control pin is at a low level, the second control pin is at a high level, the current sink is connected to the second terminal, the current sink is connected to the third terminal, the differential positive output is connected to the second terminal; and the differential negative output is connected to the third terminal; When the signal and excitation switching circuit is in the fourth operating mode, the first control pin is adjusted to a high level, the second control pin is adjusted to a high level, the current injection end is connected to the second terminal, the current absorption end is connected to the third terminal, the differential positive output end is connected to the second terminal; and the differential negative output end is connected to the fourth terminal.

4. The temperature transmitter according to claim 3, characterized in that: The single chip microcomputer is also used for: When the sensor is a thermocouple or a differential voltage, the positive electrode of the thermocouple or the differential voltage is connected to the second terminal, the negative electrode of the thermocouple is connected to the third terminal, and the signal and excitation switching circuit is controlled to be in a first operating mode through a control instruction to perform signal measurement; When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, a pair of cables of the 4-wire thermal resistor or the 4-wire resistor with the same polarity are connected to the first terminal and the second terminal, and another pair of cables of the same polarity are connected to the third terminal and the fourth terminal, and the signal and excitation switching circuit is controlled to be in the second operation mode through the control instruction to perform signal measurement; When the type of the sensor is a 2-wire thermal resistor or a 2-wire resistor, two cables of the 2-wire thermal resistor or the 2-wire resistor are connected to the first terminal and the second terminal respectively, and the signal and excitation switching circuit is controlled to be in a third operation mode through the control instruction to perform signal measurement; When the sensor type is a 3-wire thermistor or a 3-wire resistor, two cables of the same polarity of the 3-wire thermistor or the 3-wire resistor are respectively connected to the second terminal and the third terminal, and another cable of a single polarity is intercepted to the fourth terminal, and the signal and excitation switching circuit is controlled by the control instruction to repeatedly switch between the fourth operating mode and the third operating mode to perform signal measurement.

5. The temperature transmitter according to claim 1, characterized in that: The single chip microcomputer is also used for: According to the differential voltage digital signal, according to the preset judgment rules, the fault type and fault cause of the temperature transmitter are determined; wherein the fault type includes: serious fault and minor fault; Wherein, when the type of the sensor is a thermocouple or a differential voltage and is in the first operating mode, the actual voltage value is determined according to the differential voltage digital signal, and when the actual voltage value is greater than a preset voltage upper limit threshold or less than a preset voltage lower limit threshold, the fault type is determined to be a serious fault; When the type of the sensor is a 2-wire thermal resistor or a 2-wire resistor and is in a third operation mode, a first resistance is determined according to the differential voltage digital signal, and when the first resistance is greater than a first preset resistance upper limit threshold or less than a first preset resistance lower limit threshold, the fault type is determined to be a serious fault; When the type of the sensor is a 3-wire thermal resistor or a 3-wire resistor, and is in the fourth operation mode, the second resistance is determined according to the differential voltage digital signal, and when the second resistance is greater than a second preset resistance upper limit threshold or less than a second preset resistance lower limit threshold, the operation mode is switched to the third operation mode, and the third resistance is determined according to the differential voltage digital signal in the third operation mode, and when the third resistance is less than or equal to the third preset resistance upper limit threshold and greater than or equal to the third preset resistance lower limit threshold, the fault type is determined to be a first minor fault; when the third resistance is greater than the third preset resistance upper limit threshold or less than the third preset resistance lower limit threshold, the fault type is determined to be a serious fault; When the type of the sensor is a 4-wire thermal resistor or a 4-wire resistor, and is in the second operating mode, a fourth resistor is determined according to the differential voltage digital signal, and when the fourth resistor is greater than a fourth preset resistance upper limit threshold or less than a fourth preset resistance lower limit threshold, the operating mode is switched to the fourth operating mode, and a fifth resistor is determined according to the differential voltage digital signal in the fourth operating mode, and when the fifth resistor is less than or equal to the fifth preset resistance upper limit threshold and greater than or equal to the fifth preset resistance lower limit threshold, the fault type is determined to be a second minor fault; when the fifth resistor is greater than the fifth preset resistance upper limit threshold or less than the fifth preset resistance lower limit threshold, the operating mode is switched to the third operating mode, and a sixth resistor is determined according to the differential voltage digital signal in the third operating mode, and when the sixth resistor is less than or equal to the sixth preset resistance upper limit threshold and greater than or equal to the sixth preset resistance lower limit threshold, the fault type is determined to be a third minor fault; when the sixth resistor is greater than the sixth preset resistance upper limit threshold or less than the sixth preset resistance lower limit threshold, the fault type is determined to be a serious fault.

6. The temperature transmitter according to claim 5, characterized in that: The single chip microcomputer is also used for: According to the fault type and the preset control rules, a control instruction is sent to the fault indication device, so that the fault indicator light gives an alarm according to the control instruction and indicates the fault level at the same time; When the fault type is a first minor fault, a second minor fault or a third minor fault, a reduced efficiency operation mode is determined according to the fault type and a preset reduced efficiency operation rule, and the signal and excitation switching circuit is controlled to operate according to the reduced efficiency operation mode; and when the operating time of the temperature transmitter in the fault state reaches a preset time threshold, the operating mode is adjusted to the operating mode before the fault according to the sensor type, and the fault type and fault cause of the temperature transmitter are determined again according to the preset judgment rule; Wherein, the degraded operation rule includes: when the fault type is a first minor fault, determining the degraded operation mode to operate in accordance with the third operation mode; When the fault type is the second minor fault, the reduced efficiency operation mode is determined to be operated according to the normal measurement operation mode of the 3-wire thermal resistor or the 3-wire resistor; When the fault type is a third minor fault, the degraded operation mode is determined to be operation according to the third operation mode.

7. A sensor signal measuring device, characterized in that: The sensor signal measuring device comprises: a constant current source generating circuit, a signal and excitation switching circuit, an analog-to-digital conversion circuit and a single-chip microcomputer; wherein, The constant current source generating circuit is connected to the signal and excitation switching circuit, and is used to output a constant current excitation to the sensor through the signal and excitation switching circuit to supply power to the sensor; The signal and excitation switching circuit is connected to the sensor, the analog-to-digital conversion circuit and the single-chip microcomputer respectively, and is used to determine the operation mode according to the mode switching instruction sent by the single-chip microcomputer; and is used to obtain the differential voltage analog signal according to the sensing signal output by the sensor; The analog-to-digital conversion circuit is connected to the single-chip microcomputer and is used to perform analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal; The single chip microcomputer is connected to the transmission output circuit, and is used to send the mode switching instruction to the signal and the excitation switching current; and is used to obtain the first temperature, resistance and / or voltage data according to the differential voltage digital signal; The signal and excitation switching circuit includes: a dual-way four-channel analog multiplexer, a first terminal, a second terminal, a third terminal and a fourth terminal for connecting to a sensor, a first control pin and a second control pin for channel switching, an excitation current sink, an excitation current sink, a differential positive output terminal for outputting the differential voltage analog signal, a differential negative output terminal, a pull-up resistor and a pull-down resistor; Wherein, the pull-up resistor is respectively connected to the differential positive output terminal and the power supply terminal of the signal and excitation switching circuit, and the pull-down resistor is respectively connected to the differential negative output terminal and the ground terminal of the signal and excitation switching circuit; Wherein, the signal and excitation switching circuit is also used for: The high and low level differential signals and stimuli output by the receiving single-chip microcomputer through the IO port are switched to different terminals to realize the switching of the operation mode of the signal and stimulus switching circuit, specifically: the channel control end of the dual-way four-channel analog multiplexer is controlled to switch the output signals on the first terminal, the second terminal, the third terminal and the fourth terminal to the differential negative output terminal of the differential voltage analog signal, and the channel control end of the dual-way four-channel analog multiplexer is controlled to switch the current injection end to the first terminal, the second terminal, the third terminal and the fourth terminal.

8. A measurement method based on the intelligent temperature transmitter according to any one of claims 1 to 6, characterized in that: The method comprises: The single chip microcomputer sends a mode switching instruction to the signal and excitation switching circuit, so that the signal and excitation switching circuit determines the operation mode according to the mode switching instruction; The constant current source generating circuit outputs a constant current excitation to the sensor to supply power to the sensor; The signal and excitation switching circuit obtains a differential voltage analog signal according to the sensing signal output by the sensor; The analog-to-digital conversion circuit performs analog-to-digital conversion on the differential voltage analog signal to obtain a differential voltage digital signal; The single chip microcomputer obtains first temperature, resistance and / or voltage data according to the differential voltage digital signal; The transmission output circuit converts the first temperature, resistance and / or voltage data into a standard signal of a preset type.

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