Current signal output automatic calibration circuit and temperature transmitter

Abstract

The utility model discloses a current signal output automatic calibration circuit and a temperature transmitter, and aims to solve the problems that the precision of an existing current type transmitter is difficult to guarantee and an existing high-precision current signal output circuit needs multi-point manual calibration. The device comprises a signal input interface, an MCU module, a DAC module, a resistor R1, a signal output interface, a voltage / current detection module, an ADC module and a voltage reference source. The input end of the MCU module is connected with the signal input interface, and the output end of the MCU module is connected with the input end of the DAC module; the output end of the DAC module is connected to the signal output interface through a resistor R1; the non-inverting input end of the voltage / current detection module is connected with the positive electrode of the resistor R1, the inverting input end is connected with the negative electrode of the resistor R1, and the output end is connected with the first input end of the ADC module; the output current precision does not need to be manually adjusted, and the production efficiency is improved while the output precision is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of temperature transmitters, in particular to a current signal output automatic calibration circuit and a temperature transmitter. BACKGROUND

[0002] With the increasing requirements of energy saving and emission reduction, in order to achieve the goal of carbon peak and carbon neutral, the accurate measurement and control of environmental temperature are paid more and more attention. Temperature sensors and transmitters, as the source of temperature control systems, play a key role in accurate temperature control and are widely used in air conditioners and fresh air systems. Especially in some high-precision laboratories, libraries and museums, the requirements for temperature and humidity are very high.

[0003] Current transmitters are widely used in various control systems due to their strong anti-interference ability and long-distance transmission. In the existing building control system, the output error precision of the temperature transmitter reaches 0.5FS, which is already high precision. The current temperature transmitter needs to convert the collected temperature signal into a corresponding current signal output through an analog circuit. The analog conversion circuit itself has conversion error, and the precision is difficult to guarantee.

[0004] The current signal output circuit generally uses a transistor constant current source or a special DAC chip to realize. In order to ensure the output precision and linearity, the circuit needs to be calibrated at least 2 points or more points manually. For high-precision current temperature transmitters, the output circuit linearity of each device is calibrated at multiple points manually before leaving the factory. The production process is complex, and the production efficiency is not high. SUMMARY

[0005] The present application provides a current signal output automatic calibration circuit and a temperature transmitter, which aims to solve the problem that the precision of the existing current transmitter is difficult to guarantee and the existing high-precision current signal output circuit needs to be calibrated at multiple points manually.

[0006] In a first aspect, a current signal output automatic calibration circuit includes a signal input interface, an MCU module, a DAC module, a resistor R1, a voltage / current detection module, an ADC module, and a signal output interface.

[0007] The signal input interface, the MCU module, the DAC module, the resistor R1, and the signal output interface are connected in series. The input end of the MCU module is divided into a target signal input end and a feedback signal input end, and the target signal input end is connected to the signal input interface.

[0008] The voltage / current detection module is used for detecting the voltage difference between the two ends of the resistor R1; the output end of the current detection module is connected to the input end of the ADC module, and the output end of the ADC module is connected to the feedback signal input end of the MCU module; the MCU module compares the feedback signal with the target signal to determine whether the output value is within the error accuracy range, and automatically compensates and calibrates if the error exceeds the error range, so as to ensure that the output value is within the error range.

[0009] In the above scheme, optionally, the automatic calibration circuit further comprises a voltage reference source connected to the ADC module, used to ensure the accuracy of the acquisition level.

[0010] In the above scheme, further optionally, the voltage reference source is selected according to the output range of the voltage / current detection module, and the output voltage of the voltage reference source is greater than the output range of the voltage / current detection module.

[0011] In the above scheme, optionally, the signal input interface, the MCU module, the MCU module and the DAC module, and the ADC module and the MCU module are connected through a digital interface I2C or SPI.

[0012] In the above scheme, optionally, the resolution of the ADC module is selected according to the actual range of the input signal.

[0013] In the above scheme, optionally, the resistor R1 adopts a resistor with an accuracy of ≤0.1%, a resistance of ≤10Ω, and a temperature drift of <±10ppm / ℃.

[0014] In a second aspect, a temperature transmitter comprises a temperature sensor, characterized in that it further comprises the current signal output automatic calibration circuit described above, the signal input interface of the automatic calibration circuit is connected to the signal output interface of the temperature sensor, and the signal output interface of the automatic calibration circuit serves as the output end of the temperature transmitter.

[0015] Compared with the prior art, the present application has at least the following beneficial effects:

[0016] The present application is based on further analysis and research on the problems of the prior art, and it is realized that the current output precision of the existing high-precision current signal output circuit needs to be manually adjusted, the production process is complex, and the production efficiency is affected. Although the output precision of the temperature sensor probe part of the existing high-precision current temperature transmitter can reach 0.1FS, due to the discreteness of the current conversion analog circuit components, conversion errors are common, and it is difficult to achieve an accuracy of 0.1FS. By connecting a high-precision resistor R1 in series through the current signal output circuit, the two ends of R1 are connected to a high-precision current detection chip. When there is an output current, a voltage difference is generated across R1. The high-precision voltage / current detection module detects the voltage difference across R1 and outputs the proportional transformed voltage difference to the ADC module. The ADC module sends the received voltage value to the MCU unit in digital form. The MCU compares the input value of the ADC with the input value of the sensor to determine whether the output value is within the error precision range (e.g. 0.1FS). If the output value is out of tolerance, the DAC module output is automatically compensated and calibrated to ensure that the output value is within the error range, thereby realizing a high-precision current signal output automatic calibration circuit. The circuit realizes a current temperature transmitter with an error precision of 0.1FS.

[0017] The present application also uses digital error adjustment, software configuration, and automatic adjustment of current signal output error precision. The present application does not require manual adjustment of output current precision, and improves production efficiency while ensuring output precision. The present application improves the output error precision of the current temperature transmitter to 0.1FS. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A current signal output automatic calibration circuit schematic diagram is provided for an embodiment of the present application.

[0019] Figure 2 A signal input interface and MCU module connection schematic diagram is provided for an embodiment of the present application.

[0020] Figure 3 A MCU module and DAC module connection schematic diagram is provided for an embodiment of the present application.

[0021] Figure 4 A DAC module connected to the signal output interface through resistor R1 is provided for an embodiment of the present application.

[0022] Figure 5 A DAC module, resistor R1, signal output interface, and current detection chip connection relationship schematic diagram is provided for an embodiment of the present application.

[0023] Figure 6A connection relationship schematic diagram of a current detection chip, an ADC module and a voltage reference source provided by an embodiment of the present application is provided.

[0024] Figure 7 A connection relationship schematic diagram of an ADC module, an MCU and a signal input interface provided by an embodiment of the present application is provided.

[0025] Figure 8 A current signal output automatic calibration circuit schematic diagram provided by an embodiment of the present application is provided. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0027] In the description of the present application: unless otherwise specified, the meaning of "multiple" is two or more. The terms "first", "second", "third" and the like in the present application are intended to distinguish the objects referred to, and do not have special meanings in the technical connotation aspect (for example, it should not be understood as emphasizing importance or order, etc.). The expressions "include", "contain", "have" and the like also mean "not limited to" (some units, components, materials, steps, etc.).

[0028] With the increasing requirements of energy saving and emission reduction, in order to achieve the goal of carbon peak and carbon neutral, the accurate measurement and control of environmental temperature are paid more and more attention. Temperature sensors and transmitters, as the source of temperature control system, play a key role in accurate temperature control and are widely used in air conditioning and fresh air systems. Especially in some high-precision laboratories, libraries and museums, the requirements for temperature and humidity are very high.

[0029] Current transmitters are widely used in various control systems due to their strong anti-interference ability and long-distance transmission.

[0030] The first purpose of the present application is to provide a current signal output automatic calibration circuit, which is software configurable, does not require manual calibration of output current value, and the output error precision can reach 0.1FS. The second purpose of the present application is to provide a current type temperature transmitter.

[0031] In one embodiment, reference Figure 1 , a current signal output automatic calibration circuit is provided, which includes a signal input interface, an MCU module, a DAC module, a resistor R1, a voltage / current detection module, an ADC module and a signal output interface.

[0032] The signal output interface, the signal input interface, the MCU module, the DAC module, the resistor R1, and the signal output interface are connected in series; the input end of the MCU module is divided into a target signal input end and a feedback signal input end, and the target signal input end of the signal output interface is connected to the signal output interface signal input interface;

[0033] The signal output interface voltage / current detection module is used for detecting the voltage difference between the two ends of the resistor R1; the output end of the current detection module is connected to the input end of the signal output interface ADC module, and the output end of the ADC module is connected to the feedback signal input end of the signal output interface MCU module; the MCU module compares the feedback signal with the target signal to determine whether the output value is within the error accuracy range, and automatically compensates and calibrates if the error exceeds the error range, so as to ensure that the output value is within the error range.

[0034] Reference Figure 1 In the embodiment, the sensor input signal is transmitted to the MCU in the form of a digital quantity, the MCU transmits the acquired value to the digital-to-analog conversion DAC chip in the form of a digital quantity, and the DAC outputs a corresponding 4-20 mA current signal. The current signal output circuit is connected in series with a high-precision resistor R1, the two ends of R1 are connected to a high-precision current detection chip, when there is an output current, a voltage difference is generated between the two ends of R1, the voltage / current detection module detects the voltage difference between the two ends of R1, and outputs the voltage difference value to the ADC module after proportional conversion, the ADC module transmits the received voltage value to the MCU unit in the form of a digital quantity, the MCU compares the input value of the ADC with the input value of the sensor to determine whether the output value is within the error accuracy range (such as 0.1 FS), and if the error exceeds the error range, the output of the DAC module is automatically compensated and calibrated to ensure that the output value is within the error range.

[0035] In one embodiment, the signal input interface, the MCU module, the MCU module, the DAC module, and the ADC module are connected through a digital interface I2C or SPI.

[0036] Reference Figure 2 The external high-precision temperature sensor transmits the detected temperature value to the MCU module through a digital interface (I2C or SPI, I2C is used in the embodiment). Because digital transmission is adopted between the MCU, there is no conversion error in the middle, which well guarantees the accuracy of the high-precision value.

[0037] Reference Figure 3 The MCU module receives the temperature value (with an accuracy error of 0.1 FS) sent by the high-precision sensor through a digital interface (I2C or SPI, I2C is used in the embodiment), and transmits the acquired temperature value to the DAC module without distortion.

[0038] Reference Figure 4The DAC module receives the measurement value input by the MCU module through a digital interface (I2C or SPI, I2C is used in the present example) and converts the measurement value into a corresponding analog current signal output.

[0039] In one embodiment, the resistance R1 is a high-precision, small-resistance, low-temperature-drift resistance.

[0040] In the present embodiment, the resistance R1 is a resistance with a precision of ≤0.1%, a resistance of ≤10Ω, and a temperature drift of <±10ppm / ℃.

[0041] Reference Figure 5 The shunt resistance R1 is connected in series at the output end, and a voltage difference V1 is formed at both ends of the resistance when the output current passes through R1. Assuming that the output current is Io, then V1=Io*R1. The R1+ of R1 is connected to the same direction input end of the voltage / current detection module, and the R1- is connected to the reverse input end of the voltage / current detection module, and the voltage / current detection module receives the value of V1. To ensure high-precision detection, the resistance R1 needs to be high-precision, small-resistance, and low-temperature-drift, and R1 is configured as 2R*0.01%. When Io is 4mA, V1=4mA*2R=8mV, which is a very weak voltage. To facilitate the detection of the back-end ADC, after V1 passes through IC1, the voltage value is amplified to V1*, and the amplification factor is selected to be 50V / V, so that V1*=50*V1. When the output current is 4-20mA, the corresponding V1 is 8-40mV, and the corresponding V1* is 0.4-2V.

[0042] In one embodiment, the automatic calibration circuit further comprises a voltage reference source connected to the signal output interface ADC module, for ensuring the accuracy of the collected level.

[0043] In one embodiment, the voltage reference source is selected according to the output range of the voltage / current detection module, and the output voltage of the voltage reference source is greater than the output range of the voltage / current detection module.

[0044] In one embodiment, the resolution of the ADC module is selected according to the actual range of the input signal.

[0045] Reference Figure 6 The ADC chip IC2 receives the voltage value V1* input by IC1, and to ensure the accuracy of the collected level, a low-temperature-drift or zero-temperature-drift voltage reference source is connected to IC2. Because the input range of V1* is 0.4V-2V, we select a voltage reference source of 2.5V.

[0046] To ensure 0.1FS high precision, the ADC module needs to select the corresponding resolution according to the actual range. The full range of the transmitter is 0℃-100℃, so the 0.1FS precision error needs to be 100℃*0.1%=±0.1℃. The current output range is 4-20mA, and the corresponding precision error is (20mA-4mA)*0.1%=0.016mA. The actual design precision is doubled to 0.008mA. The corresponding ADC recognition precision needs to be at least: 0.008mA*2R*50=0.8mV=0.0008V. The ADC resolution is increased by one bit to 0.00001. Therefore, we select 16bit, and the resolution can be 1 / 2^16, i.e. 0.00001.

[0047] Reference Figure 7 The ADC chip sends the collected voltage value V1* to the MCU module without loss through the digital I2C interface, and the MCU module converts V1* into the corresponding current value Io. The current conversion formula is Io=V1*÷50÷2. Assuming that the actual input temperature value at the input end is Ti, and the full range of 0℃-100℃ corresponds to the 4-20mA output, then the current value per 1℃ is (20-4)÷100=0.16mA, and the ideal output current I=0.16*Ti+4mA. Io-I=ΔI. If ΔI is within ±0.1℃, i.e. ±0.016mA, no compensation is needed. If the error is exceeded, corresponding compensation is performed. If ΔI>0.016mA, the compensation current I*=ΔI-0.016mA; if ΔI<-0.016mA, the compensation current I*=ΔI+0.016mA.

[0048] Because the ADC and the MCU communicate through the I2C interface, they do not participate in the conversion of the signal quantity, and the system has a lower requirement for the MCU. An 8-bit low-cost single-chip microcomputer can meet the requirement.

[0049] In one embodiment, a temperature transmitter is provided, comprising a temperature sensor, and further comprising the above-mentioned current signal output automatic calibration circuit, wherein the signal input interface of the automatic calibration circuit is connected with the signal output interface of the temperature sensor, and the signal output interface of the automatic calibration circuit serves as the output end of the temperature transmitter.

[0050] In summary, the application realizes a high-precision current signal output automatic calibration circuit. The circuit realizes a current-type temperature transmitter with an error precision of 0.1FS.

[0051] The technical features of the above embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered as within the scope of the present application.

Claims

1. A current signal output automatic calibration circuit, characterized by, The current signal output automatic calibration circuit comprises a signal input interface, an MCU module, a DAC module, a resistor R1, a voltage / current detection module, an ADC module and a signal output interface. The signal input interface, the MCU module, the DAC module, the resistor R1 and the signal output interface are connected in series; the input end of the MCU module is divided into a target signal input end and a feedback signal input end, and the target signal input end is connected to the signal input interface. The voltage / current detection module is used for detecting the voltage difference between the two ends of the resistor R1; the output end of the current detection module is connected to the input end of the ADC module, and the output end of the ADC module is connected to the feedback signal input end of the MCU module.

2. The current signal output automatic calibration circuit of claim 1, wherein, The automatic calibration circuit further comprises a voltage reference source connected to the ADC module, which is used for ensuring the accuracy of the acquisition level.

3. The current signal output automatic calibration circuit according to claim 2, wherein The output voltage of the voltage reference source is greater than the output range of the voltage / current detection module.

4. The current signal output automatic calibration circuit according to claim 1, wherein The signal input interface, the MCU module, the DAC module, the ADC module and the MCU module are connected through a digital interface I2C or SPI.

5. The current signal output automatic calibration circuit according to claim 1, wherein The resolution of the ADC module is selected according to the actual range of the input signal.

6. The current signal output automatic calibration circuit according to claim 1, wherein The resistor R1 adopts a resistor with an accuracy of ≤0.1%, a resistance of ≤10Ω and a temperature drift of <±10ppm / ℃.

7. A temperature transmitter comprising a temperature sensor, characterized by The current signal output automatic calibration circuit further comprises a temperature sensor connected to the signal input interface of the automatic calibration circuit, and the signal output interface of the automatic calibration circuit serves as the output end of the temperature transmitter.

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