Temperature acquisition circuit and temperature detection system

Abstract

The utility model discloses a temperature acquisition circuit and a temperature detection system, and relates to the field of temperature detection, when a four-wire system is used for temperature acquisition, current flows in from a first end of a temperature detector and flows out from a fourth end of the temperature detector, because the input impedance of a differential operational amplifier circuit is relatively large, and no current flows through a second end and a third end, the temperature is acquired. Therefore, the temperature acquisition is not influenced by the wire resistance; when a three-wire system is used for temperature acquisition, current flows in from the second end and the third end of the temperature detector and flows out from the fourth end, and at the moment, the influence of line resistance can be eliminated through data processing. Switching of a two-wire system, a three-wire system and a four-wire system is realized by adjusting output of different constant current sources, influence of wire resistance on acquisition results can be effectively avoided under the conditions of the three-wire system and the four-wire system, acquisition precision when the three-wire system and the four-wire system are adopted is ensured, internal resistance and electric leakage introduced by an analog switch and a mechanical switch are avoided, and acquisition accuracy is improved. And the precision of the temperature acquisition result is further improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to temperature detection field, especially a kind of temperature acquisition circuit and temperature detection system. BACKGROUND

[0002] Temperature detector is resistance element, and resistance changes with temperature.Due to high precision, good linearity, it is widely used in temperature measurement application.Commonly used are RTD (Resistance Temperature Detector, resistance temperature detector), NTC temperature sensor (Negative Temperature Coefficient Sensor) and other temperature detectors.When temperature detector is applied in industrial field, circuit board can be set to connect with sensor in temperature detector to carry out temperature acquisition, to facilitate use, sensor distance is used for temperature acquisition board card generally has far distance, and this long-distance wire also correspondingly introduces greater resistance.Want to obtain higher measurement precision, can eliminate wire error by four-wire system, but four-wire system also correspondingly brings the increase of wiring cost.Considering various engineering wiring, temperature detection product generally needs to simultaneously integrate two-wire system, three-wire system and four-wire system to meet various application requirements.

[0003] In the process of realizing the utility model, the inventor finds that at least the following problems exist in the prior art:

[0004] Most of prior art adopts analog switch or mechanical switch to carry out two-wire system, three-wire system and four-wire system switching, but analog switch and mechanical switch can introduce internal resistance and leakage, which has influence on the precision of final temperature acquisition result. UTILITY MODEL CONTENTS

[0005] The utility model aims at providing a kind of temperature acquisition circuit and temperature detection system, the output of different constant current source is adjusted to realize two-wire system, three-wire system and four-wire system switching, can effectively avoid the influence of line resistance on acquisition result in the case of three-wire system and four-wire system, ensure the acquisition precision when using three-wire system and four-wire system, simultaneously also avoid the internal resistance and leakage introduced by analog switch and mechanical switch, further improve the precision of temperature acquisition result.

[0006] To solve the above technical problems, the utility model provides a kind of temperature acquisition circuit, comprising:

[0007] First constant current source, the output end of the first constant current source is connected with the first end of temperature detector, for when using four-wire system to carry out temperature acquisition, output first preset current to the first end of the temperature detector;

[0008] a second constant current source, an output end of the second constant current source being connected with a second end of the temperature detector, for outputting a second preset current to the second end of the temperature detector when temperature collection is performed in a three-wire mode or in a two-wire mode;

[0009] a third constant current source, an output end of the third constant current source being connected with a third end of the temperature detector, for outputting a third preset current to the third end of the temperature detector when temperature collection is performed in the three-wire mode; and a fourth end of the temperature detector being grounded;

[0010] a differential operational amplifier circuit, a first input end of the differential operational amplifier circuit being connected with the second end of the temperature detector, and a second input end of the differential operational amplifier circuit being connected with the third end of the temperature detector, for detecting a voltage between the second end of the temperature detector and the third end of the temperature detector, so as to determine a temperature detection result of the temperature detector based on the voltage.

[0011] Optionally, the first constant current source, the second constant current source, the third constant current source and the differential operational amplifier circuit are built-in circuits of an ADC chip.

[0012] Optionally, the ADC chip further comprises a first reference voltage input pin and a second reference voltage input pin, and the temperature collection circuit further comprises:

[0013] a reference resistor, a first end of the reference resistor being connected with the fourth end of the temperature detector and the first reference voltage input pin of the ADC chip respectively;

[0014] and / or,

[0015] a margin resistor, a first end of the margin resistor being connected with a second end of the reference resistor and the second reference voltage input pin of the ADC chip respectively, and a second end of the margin resistor being grounded.

[0016] Optionally, the temperature collection circuit further comprises:

[0017] a first common mode filter circuit, a first end of the first common mode filter circuit being connected with the first end of the reference resistor and the fourth end of the temperature detector respectively, a second end of the first common mode filter circuit being connected with the first reference voltage input pin of the ADC chip, and a third end of the first common mode filter circuit being grounded;

[0018] and / or,

[0019] a second common mode filter circuit, a first end of the second common mode filter circuit being connected with the second end of the reference resistor and the first end of the margin resistor respectively, a second end of the second common mode filter circuit being connected with the second reference voltage input pin of the ADC chip, and a third end of the second common mode filter circuit being grounded.

[0020] Optionally, further comprising:

[0021] a first filter capacitor, a first end of the first filter capacitor is connected with the second end of the first common mode filter circuit and the first reference voltage input pin of the ADC chip respectively, and a second end of the first filter capacitor is connected with the second end of the second common mode filter circuit and the second reference voltage input pin of the ADC chip respectively.

[0022] Optionally, further comprising:

[0023] an RFI filter module, an input end of the RFI filter module is connected with the second end of the temperature detector and the third end of the temperature detector respectively, for filtering out electromagnetic interference;

[0024] and / or,

[0025] an EMC filter module, an input end of the EMC filter module is connected with the second end of the temperature detector and the third end of the temperature detector respectively, for filtering out electrostatic interference.

[0026] Optionally, the RFI filter module comprises:

[0027] a third common mode filter circuit, a first end of the third common mode filter circuit is connected with the output end of the second constant current source and the second end of the temperature detector respectively, a second end of the third common mode filter circuit is connected with the first input end of the differential operational amplifier circuit, and a third end of the third common mode filter circuit is grounded;

[0028] and / or,

[0029] a fourth common mode filter circuit, a first end of the fourth common mode filter circuit is connected with the output end of the third constant current source and the third end of the temperature detector respectively, a second end of the fourth common mode filter circuit is connected with the second input end of the differential operational amplifier circuit, and a third end of the fourth common mode filter circuit is grounded.

[0030] Optionally, the RFI filter module further comprises:

[0031] a second filter capacitor, a first end of the second filter capacitor is connected with the second end of the third common mode filter circuit and the first input end of the differential operational amplifier circuit respectively, and a second end of the second filter capacitor is connected with the second end of the fourth common mode filter circuit and the second input end of the differential operational amplifier circuit respectively.

[0032] Optionally, the EMC filter module comprises:

[0033] a first TVS tube, a first end of the first TVS tube is connected with a second end of the temperature detector, and a second end of the first TVS tube is grounded;

[0034] a second TVS tube, a first end of the second TVS tube is connected with a third end of the temperature detector, and a second end of the second TVS tube is grounded;

[0035] a first diode, an anode of the first diode is grounded;

[0036] a second diode, an anode of the second diode is connected with a cathode of the first diode and the second end of the temperature detector respectively, and a cathode of the second diode is connected with a preset power supply;

[0037] a third diode, an anode of the third diode is grounded;

[0038] a fourth diode, an anode of the fourth diode is connected with a cathode of the third diode and the third end of the temperature detector respectively, and a cathode of the fourth diode is connected with the preset power supply.

[0039] To solve the above technical problems, the utility model also provides a temperature detection system, including temperature detector, pin terminal and as preceding described temperature acquisition circuit, temperature detector is connected with temperature acquisition circuit through pin terminal.

[0040] Compared with the prior art, the technical scheme provided by the utility model has at least the following beneficial effects:

[0041] The utility model provides a temperature acquisition circuit, including first constant current source, second constant current source, third constant current source and difference operational amplifier circuit, when adopting four -wire system to carry out temperature acquisition, first constant current source output current, current flows in from the first end of temperature detector at this moment, and current flows out from the fourth end of temperature detector, at this moment, because the input impedance of difference operational amplifier circuit is relatively big, the second end and the third end of temperature detector will not have current flow, therefore, difference operational amplifier circuit will not be affected by line resistance when carrying out voltage acquisition, when adopting three -wire system to carry out temperature acquisition, second constant current source and third constant current source output current, current flows in from the second end and the third end of temperature detector respectively at this moment, and all flows out from the fourth end of temperature detector, at this moment, can pass through control second constant current source and third constant current source and eliminate line resistance influence to carry out data processing, the output of different constant current source is adjusted to realize the switching of two -wire system, three -wire system and four -wire system, can effectively avoid the influence of line resistance on the acquisition result in the case of three -wire system and four -wire system, ensure the acquisition precision when adopting three -wire system and four -wire system, also avoid the internal resistance and leakage of analog switch and mechanical switch, further improve the precision of temperature acquisition result.

[0042] The utility model also provides a temperature detection system, has same beneficial effect with above-mentioned temperature collection circuit. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical scheme in the utility model embodiment, the following will briefly introduce the drawing needed to be used in prior art and embodiment, obviously, the drawing in the following description only is some embodiments of the utility model, for ordinary skilled person in the art, under the premise of not paying creative labor, can also obtain other drawings according to these drawings.

[0044] Figure 1 The utility model provides a temperature collection circuit's structural schematic diagram;

[0045] Figure 2 The utility model provides another temperature collection circuit's structural schematic diagram. DETAILED DESCRIPTION

[0046] The core of the utility model provides a temperature collection circuit and temperature detection system, and the output of different constant current source is adjusted to realize the switching of two-wire system, three-wire system and four-wire system, can effectively avoid the influence of line resistance on the collection result in the case of three-wire system and four-wire system, ensures the collection accuracy when using three-wire system and four-wire system, also avoids the internal resistance and leakage introduced by analog switch and mechanical switch, further improves the accuracy of temperature collection result.

[0047] To make the purpose, technical scheme and advantage of the utility model embodiment clearer, the following will combine the drawing in the utility model embodiment, and the technical scheme in the utility model embodiment is clearly and completely described, obviously, the described embodiment is a part of the embodiment of the utility model, not all the embodiment.Based on the embodiment in the utility model, all other embodiments obtained by ordinary skilled person in the art without making creative labor belong to the protection scope of the utility model.

[0048] Please refer to Figure 1 , Figure 1 The utility model provides a temperature collection circuit's structural schematic diagram;Please refer to Figure 2 , Figure 2 Another temperature collection circuit's structural schematic diagram provided by the utility model, wherein TGND indicates working ground, and GND indicates ground.In order to solve the above technical problem, the utility model provides a temperature collection circuit, comprising:

[0049] The first constant current source I1 is connected with the first end of the temperature detector, and is used for outputting the first preset current to the first end of the temperature detector when collecting temperature by four-wire system;

[0050] a second constant current source I2, an output end of which is connected with the second end of the temperature detector, for outputting a second preset current to the second end of the temperature detector when temperature collection is performed in the three-wire mode or in the two-wire mode;

[0051] a third constant current source I3, an output end of which is connected with the third end of the temperature detector, for outputting a third preset current to the third end of the temperature detector when temperature collection is performed in the three-wire mode; and a fourth end of the temperature detector is grounded;

[0052] a differential operational amplifier circuit U0, a first input end of which is connected with the second end of the temperature detector, and a second input end of which is connected with the third end of the temperature detector, for detecting a voltage between the second end of the temperature detector and the third end of the temperature detector, so as to determine a temperature detection result of the temperature detector based on the voltage.

[0053] It can be understood that in different application scenarios, the application requirements for temperature detection will also be different. If a higher measurement precision of the temperature detection result is desired, a four-wire mode of wiring is needed at this time. If a certain measurement precision is desired while reducing the cost, a three-wire mode of wiring can be used. If the cost is to be reduced as much as possible and the requirement for measurement precision is not very high, a two-wire mode of wiring can be used. Therefore, considering various engineering wiring, the temperature detection product generally needs to integrate two-wire, three-wire and four-wire modes to meet various application requirements. In order to facilitate the switching of the three wiring modes, a 4PIN terminal is generally provided to connect the temperature detector and the temperature collection circuit. The first end of the temperature detector is connected with the output end of the first constant current source I1 in the temperature collection circuit through PIN 1 of the terminal. The second end of the temperature detector is connected with the output end of the second constant current source I2 and the first input end of the differential operational amplifier circuit U0 in the temperature collection circuit through PIN 2 of the terminal, respectively. The third end of the temperature detector is connected with the output end of the third constant current source I3 and the second input end of the differential operational amplifier circuit U0 in the temperature collection circuit through PIN 3 of the terminal, respectively. The fourth end of the temperature detector is connected with the ground end in the temperature collection circuit through PIN 4 of the terminal. The various PINs of the terminal and the temperature collection circuit are always connected. When different wiring modes need to be switched, only the connection between the PIN of the terminal and the temperature detector needs to be adjusted.

[0054] It is not difficult to understand that when the temperature probe adopts the four-wire wiring mode, the first end, the second end, the third end and the fourth end of the temperature probe are all connected with the 4 PIN pins of the terminal through the wires, at this time, when the difference operational amplifier circuit U0 detects the voltage between the second end of the temperature probe and the third end of the temperature probe, it will be affected by the internal resistance of the connecting wire itself, in order to avoid this internal resistance influence, when the temperature probe adopts four-wire system, only the first constant current source I1 will output current in the temperature acquisition circuit, at the same time, since the fourth end of the temperature probe is grounded, the current output by the first constant current source I1 will flow from the first end of the temperature probe, directly flow out from the fourth end of the temperature probe, and will not flow through the second end or the third end of the temperature probe to the difference operational amplifier circuit U0, there is no current on the connecting wire between the temperature probe and the difference operational amplifier circuit U0, so there will be no voltage, therefore the voltage detected by the difference operational amplifier circuit U0 is the voltage between the second end and the third end of the temperature probe, without voltage error caused by the internal resistance of the wire. When the temperature probe adopts the three-wire wiring mode, only the second end, the third end and the fourth end of the temperature probe are connected with the 3 PIN pins of the terminal through the wires, at this time, in order to avoid the voltage error caused by the internal resistance of the wire as much as possible, the second constant current source I2 and the third constant current source I3 will be used to output current respectively, the output current of the second constant current source I2 flows from the second end of the temperature probe and flows out from the fourth end of the temperature probe, at this time, the voltage error caused by the connecting wire between the second end of the temperature probe and the output end of the second constant current source I2 exists in the voltage detected by the difference operational amplifier circuit U0; the output current of the third constant current source I3 flows from the third end of the temperature probe and flows out from the fourth end of the temperature probe, at this time, the voltage error caused by the connecting wire between the third end of the temperature probe and the output end of the third constant current source I3 exists in the voltage detected by the difference operational amplifier circuit U0. In this case, the output current size of the second constant current source I2 and the third constant current source I3 can be replaced, and secondary acquisition can be performed, there will still be voltage error in the secondary acquisition, but the error voltage caused by the wire resistance can be eliminated by replacing the output current in the two acquisition processes. When the temperature probe adopts the two-wire wiring mode, only the second end and the third end of the temperature probe are connected with the 2 PIN pins of the terminal through the wires, at this time, the influence of the wire resistance on the detection result of the difference operational amplifier circuit U0 cannot be avoided, therefore it is rarely used in scenes requiring high precision control.

[0055] It can be understood that the differential operational amplifier circuit U0 detects the voltage between the second end and the third end of the temperature detector, which is the voltage generated across the temperature detector when current flows through it. The current value output by the constant current source and the current value output by the constant current source can be used to calculate the current resistance of the temperature detector. The temperature detector itself is a thermistor, and its resistance changes with temperature. Therefore, after determining the current resistance of the temperature detector, the temperature detected by the temperature detector can be determined according to the characteristics of the corresponding thermistor. The specific type and implementation of the temperature detector are not particularly limited herein.

[0056] It should be noted that by switching different constant current sources for current output, the detection error of the differential operational amplifier circuit U0 under different wiring modes can be avoided as much as possible, thereby realizing the application switching of four-wire, three-wire and two-wire, ensuring the detection accuracy in four-wire and three-wire applications, and realizing an anti-interference temperature acquisition circuit compatible with two, three and four-wire temperature detectors. The specific types of the first constant current source I1, the second constant current source I2, the third constant current source I3 and the differential operational amplifier circuit U0 are not particularly limited herein. The size of the preset current output by each constant current source can be switched according to the actual application scenario, and is not limited to a certain value. The current size may also be switched during temperature acquisition, which is not particularly limited herein.

[0057] Further, the temperature acquisition circuit provided by the present application can be used with high-precision resistance temperature detectors to realize a temperature measurement system. The output switching of the constant current source can realize the switching of the acquisition mode under different wiring conditions of two-wire, three-wire and four-wire, thereby solving the problem of compatibility of two-wire, three-wire and four-wire temperature detectors by means of analog switches and mechanical switches, avoiding the influence of the internal resistance and leakage introduced by analog switches and mechanical switches on the detection accuracy, and realizing very high-precision, high-resolution multifunctional measurement through a simple structure. It can be compatible with various common temperature detectors such as PT100, PT1000 and NTC. It has high flexibility and wide application range.

[0058] The utility model provides a kind of temperature acquisition circuit, including first constant current source I1, second constant current source I2, third constant current source I3 and difference operational amplifier circuit U0, when four-wire system is used to carry out temperature acquisition, first constant current source I1 output current, current flows into from the first end of temperature detector at this time, and flows out from the fourth end of temperature detector, at this time, because the input impedance of difference operational amplifier circuit U0 is relatively large, the second end and third end of temperature detector will not have current flow, so difference operational amplifier circuit U0 will not be affected by line resistance when carrying out voltage acquisition;When three-wire system is used to carry out temperature acquisition, second constant current source I2 and third constant current source I3 output current, current flows into from the second end and third end of temperature detector at this time respectively, and all flows out from the fourth end of temperature detector, at this time, line resistance influence can be eliminated by controlling second constant current source I2 and third constant current source I3 to carry out data processing.The output of different constant current sources is adjusted to realize the switching of two-wire system, three-wire system and four-wire system, and the influence of line resistance on acquisition result can be effectively avoided in the case of three-wire system and four-wire system, so as to ensure the acquisition accuracy when three-wire system and four-wire system are used, and the internal resistance and leakage introduced by analog switch and mechanical switch are also avoided, and the accuracy of temperature acquisition result is further improved.

[0059] On the basis of the above embodiment:

[0060] As an optional embodiment, the first constant current source I1, the second constant current source I2, the third constant current source I3 and the difference operational amplifier circuit U0 are all built-in circuits of an ADC chip.

[0061] It is not difficult to understand that, in order to further reduce the size of the entire temperature acquisition circuit and reduce the cost, the first constant current source I1, the second constant current source I2, the third constant current source I3 and the difference operational amplifier circuit U0 can be directly realized by using an ADC chip. The ADC chip integrates the functions of the first constant current source I1, the second constant current source I2, the third constant current source I3 and the difference operational amplifier circuit U0, as shown in Figure 2 The analog signal pins AIN0, AIN1 and AIN4 of the ADC chip support constant current output, so AIN0 can be used as the output terminal of the first constant current source I1, AIN1 can be used as the output terminal of the second constant current source I2, and AIN4 can be used as the output terminal of the third constant current source I3. The analog signal pins AIN2 and AIN3 of the ADC chip support voltage signal detection, so AIN2 can be used as the first input terminal of the difference operational amplifier circuit U0, and AIN3 can be used as the first input terminal of the difference operational amplifier circuit U0. The ADC chip can control AIN0, AIN1 and AIN4 to output constant current, and at the same time receive the detected voltage signal through AIN2 and AIN3.

[0062] As a specific embodiment, taking an RTD temperature detector as an example, as shown in Figure 2As shown, the temperature acquisition circuit includes an EMC (Electro Magnetic Compatibility) filter module, an RFI (Radio Frequency Interference) filter module, a high-resolution ADC chip, a high-precision reference resistor R1, and a margin resistor R2. The ADC chip needs to be selected to have high resolution, multi-channel differential input, and an internal constant current source to realize the functions of the first constant current source I1, the second constant current source I2, the third constant current source I3, and the differential operational amplifier circuit U0. The temperature sensor is connected to the temperature acquisition circuit through a 4PIN terminal, and the four output lines of the temperature sensor are denoted as RW1, RW2, RW3, and RW4. To achieve two-, three-, and four-wire compatibility, seven pins of the ADC chip are used, wherein AIN0, AIN1, and AIN4 are constant current source output pins, AIN2 and AIN3 are differential input pins, and REFIN+ and REFIN- are reference voltage input pins. REFIN+ and REFIN- collect the voltage across the reference resistor R1. At the same time, the current output by the constant current source flows through the RTD and the reference resistor R1, and the voltage generated across the reference resistor R1 is proportional to the voltage across the RTD, so the detection error caused by the jitter and fluctuation of the constant current source output current and any other changes can be eliminated by collecting the voltage across the reference resistor R1. Next, the acquisition logic of the temperature acquisition circuit is described in detail. The following acquisition logic is also applicable to NTC and other temperature sensors and temperature detectors implemented by using other thermistors.

[0063] When the temperature sensor adopts four-wire system, the four wires of the RTD are connected to the temperature acquisition circuit through a 4PIN terminal. At this time, AIN0 is used as a constant current source output pin, and AIN1 and AIN4 are used to close the constant current source output. AIN2 and AIN3 are configured as differential input channels to collect the voltage. Since the input impedance of the differential operational amplifier circuit U0 is infinite, the leakage is theoretically only pA or fA level, so the flow direction of the constant current source is AIN0→RW1→RTD→RW4→reference resistor R1→margin resistor R2→ground. AIN2 and AIN3 collect the voltage across the RTD by differential sampling, and the ADC has an operational amplifier inside. The input impedance of the operational amplifier is very high, generally in the order of MΩ to GΩ, so RW2 and RW3 will not have current flowing into the ADC, and the voltage is collected into the ADC through RW2 and RW3 without loss. Since no current flows through, the line resistance of RW2 and RW3 has no effect on the voltage across the RTD, and the collection value of the differential operational amplifier circuit U0 is the constant current output by AIN0, that is, the resistance value of the RTD.

[0064] When the temperature sensor adopts three-wire system, the three wires RW2, RW3 and RW4 of the RTD are connected to the temperature collection circuit through the 4PIN terminal. The three-wire system uses current chopping, that is, AIN1 and AIN4 are used as constant current source output pins, the constant currents output by AIN1 and AIN4 are configured as IOUT0 and IOUT1 respectively, and AIN0 is closed. At this time, the constant current source flow direction output by AIN1 is AIN1 (IOUT0)→RW2→RTD→RW4→reference resistance R1→margin resistance R2→ground, the constant current source flow direction output by AIN4 is AIN4 (IOUT1)→RW3→RW4→reference resistance R1→margin resistance R2→ground, and the RTD voltage collected by the differential amplifier circuit U0 at this time is RTD resistance*IOUT0+RW2 line resistance*IOUT0-RW3 line resistance*IOUT1, and the voltage across the reference resistance R1 is (IOUT0+IOUT1)*reference resistance R1.

[0065] Then the output currents of AIN1 and AIN4 are exchanged by software configuration, that is, the output current of AIN1 is configured as IOUT0, and the output current of AIN4 is configured as IOUT1, and secondary collection is performed, at this time the RTD voltage collected by the differential amplifier circuit U0 is RTD resistance*IOUT1+RW2 line resistance*IOUT1-RW3 line resistance*IOUT0, and the voltage across the reference resistance R1 is (IOUT0+IOUT1)*reference resistance R1.

[0066] The voltages collected twice are averaged, the collected RTD voltage is [(IOUT0+IOUT1)*RTD resistance+(IOUT0+IOUT1)*RW2 line resistance-(IOUT0+IOUT1)*RW3 line resistance], and the reference voltage is (IOUT0+IOUT1)*reference resistance R1. If the line resistances of RW2 and RW3 are matched, this scheme can also achieve the accuracy of four-wire system. Therefore, when designing the temperature collection circuit, the first wire between the second end of the temperature detector and the first input end of the differential amplifier circuit U0 and the second wire between the third end of the temperature detector and the second input end of the differential amplifier circuit U0 can be set to two wires of the same type, the same length and other parameters, so that the line resistance influence can be eliminated by twice collection in the three-wire system, and the detection accuracy is improved.

[0067] When the temperature sensor adopts two-wire system, the two lines RW2 and RW3 of the RTD are connected to the temperature acquisition circuit through the 4PIN terminal. At this time, in order to ensure that the current exists in the conduction loop, it is necessary to further short RW3 and RW4 at the terminal. At this time, AIN1 is used as the constant current source output pin, and AIN0 and AIN4 are used to close the constant current source output. The constant current source flow direction output by AIN1 is AIN1→RW2→RTD→RW3→reference resistance R1→margin resistance R2→ground. The RTD voltage collected by the differential operational amplifier circuit U0 is the output current of the constant current source*(RTD resistance+line resistance of RW2+line resistance of RW3). Two-wire system inevitably introduces line resistance interference, so it is rarely used in scenarios that require high-precision control.

[0068] Specifically, considering that the ADC chip has the functions of switching, collecting and outputting a constant current source at the same time, the ADC chip can be directly used to realize the first constant current source I1, the second constant current source I2, the third constant current source I3 and the differential operational amplifier circuit U0, which is simple and effective, easy to implement, can further reduce the size and cost of the entire temperature acquisition circuit, and can achieve the functions of two-wire system, three-wire system and four-wire system of the temperature detector with fewer devices on the basis of ensuring high-precision detection results. When the temperature acquisition circuit is integrated on a circuit board, the flexibility of PCB (Printed Circuit Board) layout can be improved.

[0069] As an optional embodiment, the ADC chip further comprises a first reference voltage input pin and a second reference voltage input pin, and the temperature acquisition circuit further comprises:

[0070] a reference resistance R1, a first end of which is connected to the fourth end of the temperature detector and the first reference voltage input pin REFIN+ of the ADC chip respectively;

[0071] and / or,

[0072] a margin resistance R2, a first end of which is connected to the second end of the reference resistance R1 and the second reference voltage input pin REFIN- of the ADC chip respectively, and a second end of which is grounded.

[0073] It can be understood that, in order to further improve the accuracy and reliability of the detection result, a reference resistor R1 can also be added in series between the fourth end of the temperature detector and the ground. Regardless of the wiring mode, the current output by the constant current source will eventually pass through the reference resistor R1 to the ground, so the voltage across the reference resistor R1 is always linearly related to the voltage collected by the differential operational amplifier circuit U0. At the same time, the voltage across the reference resistor R1 can effectively reflect the current output by the constant current source. The reference resistor R1 itself has a certain resistance value. When the voltage across the reference resistor R1 fluctuates during a certain collection process, it indicates that the current output by the constant current source may not remain constant and there is an abnormal change. At this time, according to the fluctuation of the voltage across the reference resistor R1, the abnormal change of the current output by the constant current source can be deduced, so as to determine the error of the detection result of the differential operational amplifier circuit U0 caused by the abnormal change of the current output by the constant current source. Therefore, by collecting the voltage across the reference resistor R1, the error caused by the abnormal change of the current output by the constant current source in the detection result of the differential operational amplifier circuit U0 can be effectively eliminated, thereby eliminating this error and further improving the accuracy of the final detection result.

[0074] Further, when the ADC chip is directly used to realize the first constant current source I1, the second constant current source I2, the third constant current source I3 and the differential operational amplifier circuit U0, considering that the ADC chip is internally provided with a reference voltage buffer, a bias voltage is required when using the reference voltage buffer, therefore, a margin resistor R2 is further added in the temperature collection circuit to provide a bias voltage for the ADC chip, so that the ADC chip can be normally applied.

[0075] It should be noted that the specific type and implementation of the reference resistor R1 and the margin resistor R2 are not particularly limited in this application. The reference resistor R1 is preferably a high-precision low-temperature-drift foil resistor, which can effectively improve the detection accuracy and reduce data fluctuations. The resistance value of the reference resistor R1 can be designed according to the actual situation of the temperature detector (RTD), and the resistance value must be greater than the resistance value of the RTD, i.e. the temperature detector itself. By selecting appropriate reference resistor R1 and ADC chip, the final detection accuracy of the entire temperature collection circuit can reach within 1mk (millikelvin).

[0076] Specifically, the reference resistor R1 can be further added in the temperature collection circuit to eliminate the detection error caused by the abnormal change of the current output by the constant current source and improve the accuracy of the final detection result. In order to ensure the normal application of the ADC chip, the margin resistor R2 can also be further provided in the temperature collection circuit, and a bias voltage required for the operation of the ADC chip can be provided by forming a voltage dividing circuit with the reference resistor R1.

[0077] As an optional embodiment, it further comprises:

[0078] The first common mode filter circuit has a first end connected to a first end of the reference resistor R1 and a fourth end of the temperature detector respectively, a second end connected to a first reference voltage input pin of the ADC chip, and a third end grounded.

[0079] and / or,

[0080] The second common mode filter circuit has a first end connected to a second end of the reference resistor R1 and a first end of the margin resistor R2 respectively, a second end connected to a second reference voltage input pin of the ADC chip, and a third end grounded.

[0081] It is not difficult to understand that, considering that the ADC chip needs to collect the voltage across the reference resistor R1 to improve the accuracy of the final temperature detection result, in order to ensure the accuracy and reliability of the voltage across the reference resistor R1 collected by the ADC chip, an RFI filter module connected to both ends of the reference resistor R1 can also be added in the temperature collection circuit. The RFI filter module specifically includes a first common mode filter circuit arranged between the first end of the reference resistor R1 and the first reference voltage input pin of the ADC chip, and a second common mode filter circuit arranged between the second end of the reference resistor R1 and the second reference voltage input pin of the ADC chip. By arranging the two common mode filter circuits, common mode interference in the circuit is suppressed, thereby improving the accuracy and reliability of the voltage across the reference resistor R1 collected by the ADC chip. The specific types and implementation methods of the first common mode filter circuit and the second common mode filter circuit are not particularly limited in this application. As shown in FIG. 1, the first common mode filter circuit is implemented by an RC circuit composed of a resistor R21 and a capacitor C21, and the second common mode filter circuit is implemented by an RC circuit composed of a resistor R22 and a capacitor C22. The RC circuit can suppress abnormal fluctuations in the circuit, making the collected values fluctuate less. Figure 2

[0082] Specifically, by adding the RFI filter module composed of the first common mode filter circuit and the second common mode filter circuit in the circuit for collecting the voltage across the reference resistor R1 by the ADC chip, common mode interference in the circuit can be effectively suppressed, avoiding the influence of interference signals on the collected voltage across the reference resistor R1, and ensuring the accuracy and reliability of the collected voltage across the reference resistor R1.

[0083] As an optional embodiment, it further includes:

[0084] The first filter capacitor C1 has a first end connected to the second end of the first common mode filter circuit and the first reference voltage input pin of the ADC chip respectively, and a second end connected to the second end of the second common mode filter circuit and the second reference voltage input pin of the ADC chip respectively.

[0085] ​It can be understood that, on the basis of setting the first common mode filter circuit and the second common mode filter circuit, a first filter capacitor C1 can be further set to further constitute a differential mode filter structure with the first common mode filter circuit and the second common mode filter circuit. The first filter capacitor C1 can further realize differential mode filtering on the basis of common mode filtering, and avoid the influence of differential noise and other differential mode interference on the voltage across the reference resistor R1 collected by the ADC chip. The specific type and implementation of the first filter capacitor C1 are not particularly limited herein.

[0086] Specifically, by setting the first filter capacitor C1 to cooperate with the first common mode filter circuit and the second common mode filter circuit to constitute a differential mode filter, the internal structure of the RFI filter module is further improved, the differential mode interference in the circuit is effectively suppressed, the influence of interference signals on the voltage across the reference resistor R1 collected is avoided, and the accuracy and reliability of the collection result of the voltage across the reference resistor R1 are ensured.

[0087] As an optional embodiment, further comprising:

[0088] The RFI filter module is connected to the second end of the temperature detector and the third end of the temperature detector, respectively, and is used to filter electromagnetic interference;

[0089] and / or,

[0090] The EMC filter module is connected to the second end of the temperature detector and the third end of the temperature detector, respectively, and is used to filter electrostatic interference.

[0091] It is not difficult to understand that the differential operational amplifier circuit U0 will be affected by various types of interference signals during voltage collection, resulting in errors in the final detection result. Therefore, RFI filter modules and / or EMC filter modules can be further set in the circuit to filter interference signals during collection. The RFI filter module can filter common mode interference and / or differential mode interference, and the EMC filter module can suppress electromagnetic interference and reduce the influence of external electromagnetic interference on the temperature collection circuit, so that the temperature collection circuit can meet the electromagnetic compatibility standard. By setting the RFI filter module and the EMC filter module, the poor anti-interference performance of the temperature collection board in the industrial environment can be effectively solved. The specific type and implementation of the RFI filter module and the EMC filter module are not particularly limited herein.

[0092] Specifically, by increasing the RFI filter module and / or the EMC filter module in the detection loop of the differential operational amplifier circuit U0 to filter signals, the influence of various interference signals on the detection result of the differential operational amplifier circuit U0 can be effectively avoided, and the accuracy and reliability of the final temperature detection can be improved.

[0093] As an optional embodiment, the RFI filtering module comprises:

[0094] a third common-mode filtering circuit, a first end of which is connected to an output end of the second constant current source I2 and a second end of the temperature detector respectively, a second end of which is connected to a first input end of the differential operational amplifier circuit U0, and a third end of which is grounded;

[0095] and / or,

[0096] a fourth common-mode filtering circuit, a first end of which is connected to an output end of the third constant current source I3 and a third end of the temperature detector respectively, a second end of which is connected to a second input end of the differential operational amplifier circuit U0, and a third end of which is grounded.

[0097] It can be understood that the RFI filtering module can comprise the third common-mode filtering circuit arranged at the first input end of the differential operational amplifier circuit U0 and the fourth common-mode filtering circuit arranged at the second input end of the differential operational amplifier circuit U0, and the two common-mode filtering circuits are arranged to suppress common-mode interference in the circuit, thereby improving the accuracy and reliability of the voltage between the second end and the third end of the temperature detector collected by the differential operational amplifier circuit U0. The specific types and implementation manners of the third common-mode filtering circuit and the fourth common-mode filtering circuit are not particularly limited in the present application. As shown in Figure 2 the third common-mode filtering circuit is implemented by an RC circuit composed of a resistor R12 and a capacitor C12, and the fourth common-mode filtering circuit is implemented by an RC circuit composed of a resistor R11 and a capacitor C11. The RC circuit can suppress abnormal fluctuations in the circuit, and the collected value fluctuates less.

[0098] Specifically, by increasing the RFI filtering module composed of the third common-mode filtering circuit and the fourth common-mode filtering circuit in the circuit for collecting the voltage between the second end and the third end of the temperature detector by the differential operational amplifier circuit U0, the common-mode interference in the circuit can be effectively suppressed, the influence of the interference signal on the collected voltage between the second end and the third end of the temperature detector can be avoided, the accuracy and reliability of the collected voltage between the second end and the third end of the temperature detector can be ensured, and the accuracy of the final temperature collection result can be improved.

[0099] As an optional embodiment, the RFI filtering module further comprises:

[0100] a second filtering capacitor C2, a first end of which is connected to the second end of the third common-mode filtering circuit and the first input end of the differential operational amplifier circuit U0 respectively, and a second end of which is connected to the second end of the fourth common-mode filtering circuit and the second input end of the differential operational amplifier circuit U0 respectively.

[0101] It is not difficult to understand that, on the basis of setting the third common mode filter circuit and the fourth common mode filter circuit, a second filter capacitor C2 can be further set to further constitute a differential mode filter structure with the third common mode filter circuit and the fourth common mode filter circuit. The second filter capacitor C2 can further realize differential mode filtering on the basis of common mode filtering, thereby avoiding the influence of differential noise and other differential mode interference on the voltage between the second end and the third end of the temperature detector collected by the differential operational amplifier circuit U0. The specific type and implementation of the second filter capacitor C2 are not particularly limited herein.

[0102] Further, a common mode inductor L1 can be further provided in the RFI filter module to suppress common mode interference. As shown in FIG. 4, the RFI filter includes the common mode inductor L1, a common mode RC filter, and a differential mode RC filter. The common mode inductor L1 with high impedance can improve the conducted immunity of the temperature acquisition circuit. Figure 2 The common mode RC filter includes a first common mode filter circuit, a second common mode filter circuit, a third common mode filter circuit, and a fourth common mode filter circuit, and the differential mode RC filter includes a first filter capacitor C1 and a differential mode RC filter structure realized by cooperation of the first common mode filter circuit and the second common mode filter circuit, and a second filter capacitor C2 and a differential mode RC filter structure realized by cooperation of the third common mode filter circuit and the fourth common mode filter circuit.

[0103] Specifically, by setting the second filter capacitor C2 to cooperate with the third common mode filter circuit and the fourth common mode filter circuit to constitute a differential mode filter, the internal structure of the RFI filter module is further improved, the differential mode interference in the circuit is effectively suppressed, the influence of interference signals on the voltage between the second end and the third end of the temperature detector collected is avoided, the accuracy and reliability of the collection result of the voltage between the second end and the third end of the temperature detector are ensured, and the accuracy of the final temperature acquisition result is improved.

[0104] As an optional embodiment, the EMC filter module includes:

[0105] A first TVS tube TVS1 has a first end connected to the second end of the temperature detector and a second end grounded.

[0106] A second TVS tube TVS2 has a first end connected to the third end of the temperature detector and a second end grounded.

[0107] A first diode D1 has an anode grounded.

[0108] A second diode D2 has an anode connected to the cathode of the first diode D1 and the second end of the temperature detector, and a cathode connected to a preset power supply V1.

[0109] A third diode D3 has an anode grounded.

[0110] The fourth diode D4 has an anode connected to the cathode of the third diode D3 and the third end of the temperature detector, and a cathode connected to the preset power supply V1.

[0111] It can be understood that, considering that the second end of the temperature detector and the third end of the temperature detector are both connected to the ADC chip, in order to protect the ADC chip, the EMC filter module includes the first TVS tube TVS1, the first diode D1 and the second diode D2 arranged at the second end of the temperature detector, and the second TVS tube TVS2, the third diode D3 and the fourth diode D4 arranged at the third end of the temperature detector, which respectively perform EMC filtering on the second end of the temperature detector and the third end of the temperature detector. The first TVS tube TVS1 and the second TVS tube TVS2 are low-leakage TVS tubes, which can be used as protective devices to prevent static electricity and surges. The first diode D1, the second diode D2, the third diode D3 and the fourth diode D4 are low-leakage common-cathode diodes. The main purpose of the TVS tube and the common-cathode diode is ESD (Electro-Static discharge) protection and error prevention. Low-leakage parameters need to be selected, otherwise it may cause abnormal rise or fall after power-on and other problems. The specific types and implementation methods of the first TVS tube TVS1, the second TVS tube TVS2, the first diode D1, the second diode D2, the third diode D3 and the fourth diode D4 are not particularly limited in the present application. The first diode D1 and the second diode D2 can also be directly implemented by a double diode, and the third diode D3 and the fourth diode D4 can also be directly implemented by a double diode. The first diode D1 and the second diode D2 clamp the voltage at the first input end of the differential operational amplifier circuit U0 within a safe range by being connected to ground and the preset power supply V1. The third diode D3 and the fourth diode D4 clamp the voltage at the second input end of the differential operational amplifier circuit U0 within a safe range by being connected to ground and the preset power supply V1, thereby protecting the ADC chip. The specific value and implementation method of the preset power supply V1 are not particularly limited in the present application, and the power supply voltage of the ADC chip can be directly connected to realize it. In particular, when the ADC chip is integrated on a circuit board, a power supply layer is arranged in the circuit board. At this time, the cathodes of the second diode D2 and the fourth diode D4 are directly connected to the power supply layer. The connection of the preset power supply can be realized by selecting a wiring connection or a punching method during circuit design according to the specific application, and is not limited to the implementation method given in the present embodiment.

[0112] Further, the temperature acquisition circuit generally adopts working ground in working, in order to further avoid static electricity residue in the circuit, realize ESD protection, the EMC filter module further includes Y capacitor and megaohm resistance arranged between working ground and ground. Y capacitor and megaohm resistance are arranged to quickly discharge abnormal interference and static electricity, and if there is no Y capacitor and megaohm resistance, static electricity residue will occur in ESD test, temperature data is abnormally stopped and even the chip is damaged. Figure 2 As shown in FIG. 3, capacitor C31 and capacitor C32 are arranged as Y capacitor between working ground and ground, and resistance R31 and resistance R32 are arranged as megaohm resistance, and the resistance value of megaohm resistance needs to be megaohm level, to ensure the quick discharge of static electricity.

[0113] Specifically, by arranging the EMC filter module including low leakage TVS tube, low leakage common cathode diode Y capacitor and megaohm resistance, the EMC performance of the temperature acquisition link can be improved without affecting the high precision of the temperature acquisition circuit, the static protection of the temperature acquisition circuit is realized, and the safety and reliability of the temperature acquisition circuit are ensured.

[0114] To solve the above technical problems, the utility model further provides a temperature detection system, including temperature detector, pin terminal and as aforementioned temperature acquisition circuit, temperature detector is connected with temperature acquisition circuit through pin terminal.

[0115] It is not difficult to understand that, in order to facilitate the switching of wiring mode, the temperature detector can be connected with the temperature acquisition circuit through the pin terminal, and the switching of wiring mode can be realized by directly adjusting the line connection between the temperature detector and the pin terminal, without too much adjustment of the temperature acquisition circuit. The specific type and implementation mode of the pin terminal are not particularly limited in the present application, and generally a 4PIN terminal is directly used to realize the pin terminal.

[0116] For the temperature detection system provided by the utility model, please refer to the above-mentioned embodiment of the temperature acquisition circuit, and the utility model will not be repeated here.

[0117] Various embodiments are presented in the specification and claims below. Each embodiment can represent a distinct application of the present application. The applicant expects to be able to amend the claims to expressly recite one or more of the specific embodiments shown herein. The application may, however, also include any other applications shown in the specification or otherwise envisioned by the applicant, which are within the four corners of the claims submitted with the present application. The embodiments described herein are presented by way of example to enable one of ordinary skill in the art to practice the application. The applicant is not to be limited to or by these examples. Other embodiments can include a combination of features from different examples. The scope of the application is limited only by the claims submitted with the present application.

[0118] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to those skilled in the art, and all such modifications are within the scope of the present application as defined by the appended claims. The particular embodiments disclosed above are shown by way of example, and numerous other embodiments will become apparent to those skilled in the art, from the disclosure herein, without departing from the scope of the application. The scope of the application is limited only by the claims submitted with the present application.

Claims

1. A temperature acquisition circuit, characterized in that, include: A first constant current source, the output terminal of which is connected to the first terminal of the temperature detector, is used to output a first preset current to the first terminal of the temperature detector when a four-wire system is used for temperature acquisition. The second constant current source, the output terminal of the second constant current source is connected to the second terminal of the temperature detector, and is used to output a second preset current to the second terminal of the temperature detector when temperature acquisition is performed using a three-wire system or a two-wire system. The third constant current source has its output terminal connected to the third terminal of the temperature detector. When a three-wire system is used for temperature acquisition, it outputs a third preset current to the third terminal of the temperature detector. The fourth terminal of the temperature detector is grounded. A differential operational amplifier circuit is provided, wherein the first input terminal of the differential operational amplifier circuit is connected to the second terminal of the temperature detector, and the second input terminal of the differential operational amplifier circuit is connected to the third terminal of the temperature detector, for detecting the voltage between the second terminal and the third terminal of the temperature detector, so as to determine the temperature detection result of the temperature detector based on the voltage.

2. The temperature acquisition circuit as described in claim 1, characterized in that, The first constant current source, the second constant current source, the third constant current source, and the differential operational amplifier circuit are all built-in circuits of the ADC chip.

3. The temperature acquisition circuit as described in claim 2, characterized in that, The ADC chip further includes a first reference voltage input pin and a second reference voltage input pin, and the temperature acquisition circuit further includes: A reference resistor, the first end of which is connected to the fourth terminal of the temperature detector and the first reference voltage input pin of the ADC chip, respectively; And / or, The margin resistor has its first end connected to the second end of the reference resistor and the second reference voltage input pin of the ADC chip, and its second end is grounded.

4. The temperature acquisition circuit as described in claim 3, characterized in that, Also includes: The first common-mode filter circuit has its first terminal connected to the first terminal of the reference resistor and the fourth terminal of the temperature detector, its second terminal connected to the first reference voltage input pin of the ADC chip, and its third terminal grounded. And / or, The second common-mode filter circuit has its first terminal connected to the second terminal of the reference resistor and the first terminal of the margin resistor, respectively. The second terminal of the second common-mode filter circuit is connected to the second reference voltage input pin of the ADC chip, and the third terminal of the second common-mode filter circuit is grounded.

5. The temperature acquisition circuit as described in claim 4, characterized in that, Also includes: The first filter capacitor has its first end connected to the second end of the first common-mode filter circuit and the first reference voltage input pin of the ADC chip, and its second end connected to the second end of the second common-mode filter circuit and the second reference voltage input pin of the ADC chip.

6. The temperature acquisition circuit as described in any one of claims 1 to 5, characterized in that, Also includes: The RFI filter module has its input terminals connected to the second and third terminals of the temperature detector, respectively, and is used to filter out electromagnetic interference. And / or, The EMC filter module has its input terminals connected to the second and third terminals of the temperature detector, respectively, to filter out electrostatic interference.

7. The temperature acquisition circuit as described in claim 6, characterized in that, The RFI filtering module includes: The third common-mode filter circuit has its first terminal connected to the output terminal of the second constant current source and the second terminal of the temperature detector, its second terminal connected to the first input terminal of the differential operational amplifier circuit, and its third terminal grounded. And / or, The fourth common-mode filter circuit has its first terminal connected to the output terminal of the third constant current source and the third terminal of the temperature detector, its second terminal connected to the second input terminal of the differential operational amplifier circuit, and its third terminal grounded.

8. The temperature acquisition circuit as described in claim 7, characterized in that, The RFI filtering module also includes: The second filter capacitor has its first end connected to the second end of the third common-mode filter circuit and the first input end of the differential operational amplifier circuit, respectively, and its second end connected to the second end of the fourth common-mode filter circuit and the second input end of the differential operational amplifier circuit, respectively.

9. The temperature acquisition circuit as described in claim 6, characterized in that, The EMC filtering module includes: A first TVS diode, the first end of which is connected to the second end of the temperature detector, and the second end of which is grounded; The second TVS diode has its first end connected to the third end of the temperature detector, and its second end grounded. The first diode, with its anode grounded; The anode of the second diode is connected to the cathode of the first diode and the second terminal of the temperature detector, respectively, and the cathode of the second diode is connected to a preset power supply. The third diode, wherein the anode of the third diode is grounded; The fourth diode has its anode connected to the cathode of the third diode and the third terminal of the temperature detector, and its cathode connected to the preset power supply.

10. A temperature detection system, characterized in that, It includes a temperature detector, pin terminals, and a temperature acquisition circuit as described in any one of claims 1 to 9, wherein the temperature detector is connected to the temperature acquisition circuit via the pin terminals.

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