CN219348003U

CN219348003U - Three-wire PT100 temperature measurement circuit

Info

Publication number: CN219348003U
Application number: CN202223404399.9U
Authority: CN
Inventors: 程霖
Original assignee: Shanghai Yiheng Electronic Technology Co ltd
Current assignee: Shanghai Yiheng Electronic Technology Co ltd
Priority date: 2022-12-19
Filing date: 2022-12-19
Publication date: 2023-07-14
Anticipated expiration: 2032-12-19

Abstract

The utility model provides a three-wire PT100 temperature measurement circuit, which comprises a first capacitor C1, a second capacitor C2, a third capacitor C3, a first inductor L1 and a second inductor L2, wherein the first capacitor C3 is a measurement channel A; a B measuring channel formed by the fourth capacitor C4, the fifth capacitor C5, the sixth capacitor C6, the third inductor L3 and the fourth inductor L4 is used for measuring the voltage of the two ends of the PT100 resistor and the lead resistor, so that the total resistance of the PT100 resistor and the lead resistor is calculated; measuring the voltage at two ends of the wire resistor by adopting the measuring channel A, so as to calculate the wire resistor; the final calculated resistance of PT100 is the total resistance minus the wire resistance. By adopting the three-wire PT100 measuring circuit, an ADC with no independent reference voltage input or reference voltage input and input current larger than 0.1uA can be used, so that a low-cost circuit for measuring PT100 can be realized, an ADC chip for weighing at home at present can be used, the design cost is greatly reduced, zero self calibration can be realized with lower cost, and the cost is further reduced.

Description

Three-wire PT100 temperature measurement circuit

Technical Field

The utility model belongs to the technical field of temperature measurement, and particularly relates to a three-wire PT100 temperature measurement circuit.

Background

The PT100 platinum resistance sensor is widely used in the above temperature measurement field, and because the PT100 platinum resistance sensor is very sensitive to temperature changes and has small resistance change when corresponding to temperature changes, the PT100 platinum resistance sensor needs to be used in combination with a high-precision and high-sensitivity measurement circuit.

The prior PT100 high-precision measuring circuit adopts two main technical schemes, wherein the first scheme is to adopt a constant current source to supply power to the PT100 and then measure the voltages at two ends of the PT 100; the second scheme is to supply power to the series circuit of the PT100 and the reference resistor by using a constant voltage source or a constant current source, then take the voltage at two ends of the reference resistor as the reference voltage of the ADC, and finally use the ADC to measure the voltage at two ends of the PT 100.

For example, the technical scheme provided by chinese patent application No. 2021100676584 includes a PT100 temperature acquisition circuit and an AD conversion module, where the PT100 platinum thermal resistor sensor adopts a three-wire connection method, uses a bridge circuit to measure a sampling signal, performs differential amplification processing on the sampling signal through an op amp, converts a voltage value from an analog quantity to a TTL digital signal through the AD conversion module, and the voltage adopted by the PT100 temperature acquisition circuit and the voltage adopted by an interface of the AD conversion module are the same voltage source.

The two schemes are insufficient, and when the two schemes realize zero self-calibration, an additional set of circuit is needed, and the cost is high.

The first scheme has the defects that the precision of the constant current source and the voltage measurement is required to be higher, the process is difficult to realize, and the design and manufacturing cost is higher.

The disadvantage of scheme two is that the requirement for the ADC is high, the ADC is required to have an independent reference voltage input, and the input current of the reference voltage input cannot be too large (the input current is at least less than 0.1 uA), so that a low cost ADC cannot be used.

Therefore, it is necessary to design a novel PT100 temperature measuring circuit, which overcomes the shortcomings of the prior art.

Disclosure of Invention

The utility model aims to design an ADC which can use no independent reference voltage input or reference voltage input and has input current larger than 0.1uA, so as to realize a low-cost circuit for measuring PT100, further use the ADC chip which is currently used for weighing in China, greatly reduce the design cost, realize zero self-calibration with lower cost and further reduce the cost.

In order to solve the defects in the prior art, the utility model provides a three-wire PT100 high-precision measuring circuit, which has the following technical scheme:

the three-wire PT100 temperature measurement circuit comprises a PT100 platinum thermal resistance sensor, and further comprises a first capacitor C1, a second capacitor C2, a third capacitor C3, a first inductor L1, an A measurement channel formed by the second inductor L2, an INNA pin and an INPA pin of a first chip U1, wherein the first capacitor C1 is connected with the second capacitor C2 in series and then connected with the third capacitor in parallel, the INNA pin of the first chip U1 is respectively connected with the first inductor L1, the first capacitor C1 and the third capacitor C3, and the other section of the first inductor L1 is connected with a second load resistor RL2; the INPA pin of the first chip U1 is respectively connected with a second capacitor C2, a third capacitor C3 and a second inductor L2, and the other end of the second inductor L2 is connected with a third load resistor RL3;

the measuring circuit further comprises a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, a third inductor L3 and a B measuring channel formed by the fourth inductor L4, an INNB pin and an INPB pin of the first chip U1, wherein the fourth capacitor C4 is connected with the fifth capacitor C5 in series and then connected with the sixth capacitor C6 in parallel, the INNB pin of the first chip U1 is respectively connected with the third inductor L3, the fourth capacitor C4 and the sixth capacitor C6, and the other end of the third inductor L3 is connected with the second load resistor RL2; the INPB pin of the first chip U1 is respectively connected with a fifth capacitor C5, a sixth capacitor C6 and a fourth inductor L4, and the other end of the fourth inductor L4 is connected with a first load resistor RL1;

measuring the voltage of both ends of the PT100 resistor and the lead resistor by adopting a measuring channel B, so as to calculate the total resistance of the PT100 resistor and the lead resistor; measuring the voltage at two ends of the wire resistor by adopting the measuring channel A, so as to calculate the wire resistor; the final calculated resistance of PT100 is the total resistance minus the wire resistance.

Further, the model of the first chip U1 is HX717.

Further, the circuit further comprises a first triode Q1, a first diode D2 and an eighth capacitor C8, wherein the model of the first triode Q1 is SI2302, the S electrode of the first triode Q1 is connected with the first diode D2 and the eighth capacitor C8 and grounded, the D electrode of the first triode Q1 is connected with the other ends of the first resistor R1 and the first diode D2, the G electrode of the first triode Q1 is connected with a fifth input signal, and the other ends of the first resistor R1 and the eighth capacitor C8 are connected with a second load resistor RL2.

By adopting the three-wire system PT100 temperature measuring circuit, an ADC with no independent reference voltage input or reference voltage input and input current larger than 0.1uA can be used, so that a low-cost circuit for measuring PT100 can be realized, an ADC chip which is currently used for weighing in China can be further used, the design cost is greatly reduced, zero self-calibration can be realized with lower cost, and the cost is further reduced.

Drawings

Fig. 1: three-wire PT100 temperature measurement circuit diagram of the present utility model.

Detailed Description

Reference will now be made in detail to the present preferred embodiments of the utility model, examples of which are illustrated in the accompanying drawings, and although the utility model will be described in connection with the preferred embodiments, it should be understood by those skilled in the art that the embodiments are not limiting the utility model to these embodiments, but on the contrary, the utility model is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the utility model as defined by the appended claims.

Referring to fig. 1, in the high-precision measurement circuit diagram of the three-wire PT100 of the present utility model, the PT100 is a platinum thermal resistor sensor, one end of the PT100 is connected to a first load resistor RL1, the other end is connected to a second load resistor RL2 and a third load resistor RL3, the first load resistor RL1, the second load resistor RL2 and the third load resistor RL3 together form a circuit resistor of a measurement circuit, the third resistor R3 and the fourth resistor R4 determine a power output of the first chip U1, the power output of the first chip U1 is used as a reference voltage input, a preferred voltage value is 3.3V, preferably, the model of the first chip U1 is HX717, the power output is used for supplying power to the PT100 after passing through a second resistor R2, the current returns after passing through the PT100 and is connected to the ground after passing through the third resistor R3 and the first transistor Q1, the first transistor Q1 is a MOS transistor, preferably, the model of the first transistor Q2301 is SI2, the first transistor Q1 is connected to the first transistor Q1 and the other end is connected to a capacitor D8, and the other end of the first transistor Q1 is connected to a capacitor D8.

Compared with the scheme II in the prior art, the utility model uses the total voltage at two ends of the PT100 series reference resistor as the reference voltage of the ADC, solves the problem that the low-cost ADC has no independent reference voltage input or the input current of the reference voltage is larger, and simultaneously can realize zero self-calibration by only one MOS triode due to the specificity of the circuit, thereby greatly reducing the overall cost compared with the original scheme.

In fig. 1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first inductor L1, and a second inductor L2 together with an INNA pin and an inp a pin of a first chip U1 form an a measurement channel, where the first capacitor C1 is connected in series with the second capacitor C2 and then connected in parallel with the third capacitor, the INNA pin of the first chip U1 is connected to the first inductor L1, the first capacitor C1, and the third capacitor C3, respectively, and another section of the first inductor L1 is connected to a second load resistor RL2; the INPA pin of the first chip U1 is respectively connected with a second capacitor C2, a third capacitor C3 and a second inductor L2, and the other end of the second inductor L2 is connected with a third load resistor RL3.

The method comprises the steps that a measurement channel B is formed by a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, a third inductor L3, a fourth inductor L4, an INNB pin and an INPB pin of a first chip U1, wherein the fourth capacitor C4 is connected with the fifth capacitor C5 in series and then connected with the sixth capacitor C6 in parallel, the INNB pin of the first chip U1 is respectively connected with the third inductor L3, the fourth capacitor C4 and the sixth capacitor C6, and the other end of the third inductor L3 is connected with a second load resistor RL2; the INPB pin of the first chip U1 is respectively connected with a fifth capacitor C5, a sixth capacitor C6 and a fourth inductor L4, and the other end of the fourth inductor L4 is connected with a first load resistor RL1.

The measuring circuit adopts the B measuring channel of the first chip U1 to measure the voltage of the two ends of the PT100 resistor and the lead resistor, so as to calculate the total resistance of the PT100 resistor and the lead resistor; measuring the voltage at two ends of the wire resistor by using an A measuring channel of the first chip U1, thereby calculating the wire resistor; finally, the resistance=total resistance-wire resistance of the PT100 is calculated, so that a high-precision temperature measurement value is obtained, the wire resistance of the PT100 can be compensated, and the measurement precision is improved.

The first chip U1 is kept on in normal measurement and is disconnected in zero self-calibration, when the first chip U1 is disconnected, the current of PT100 is 0, the reference voltage input of the ADC is unchanged, the input signals of all the ADCs are 3.3V, the sampling value of the ADC at the moment is taken as the zero point, the zero point self-calibration of the system can be realized, the drift of the zero point of the ADC and the drift of the loop contact potential are compensated, the measurement precision is improved, and the requirement of the zero point self-calibration is met in the range of the signal input common mode allowed by the ADC.

For the sake of brevity, the connection between the seventh capacitor C7, the ninth capacitor C9, the tenth capacitor C10 and the remaining pins of the first chip U1 in fig. 1 of the present utility model is common knowledge of those skilled in the art, wherein the resistance and capacitance of each electronic component can be adjusted according to the purpose of circuit measurement, which is not limited in the present utility model.

As an improvement of the technical scheme of the utility model, if the PT100 of the two-wire system needs to be measured, a measuring circuit related to the a measuring channel of the first chip U1 can be omitted; if zero self-calibration is not needed, the first triode Q1 can be omitted, and the first resistor R1 is directly connected to the ground; if PT1000 is required to be measured, the utility model can replace the first resistor R1 and the second resistor R2 with reference resistors with resistance values of 30kΩ for measurement, and can realize the purpose of high-precision measurement.

By adopting the three-wire PT100 measuring circuit, an ADC with no independent reference voltage input or reference voltage input and input current larger than 0.1uA can be used, so that a low-cost circuit for measuring PT100 can be realized, an ADC chip for weighing at home at present can be used, the design cost is greatly reduced, zero self calibration can be realized with lower cost, and the cost is further reduced.

Claims

1. The three-wire PT100 temperature measurement circuit comprises a PT100 platinum thermal resistance sensor and is characterized by further comprising a first capacitor C1, a second capacitor C2, a third capacitor C3, a first inductor L1, an A measurement channel formed by the second inductor L2, an INNA pin and an INPA pin of a first chip U1, wherein the first capacitor C1 is connected in series with the second capacitor C2 and then connected in parallel with the third capacitor, the INNA pin of the first chip U1 is respectively connected with the first inductor L1, the first capacitor C1 and the third capacitor C3, and the other section of the first inductor L1 is connected with a second load resistor RL2; the INPA pin of the first chip U1 is respectively connected with a second capacitor C2, a third capacitor C3 and a second inductor L2, and the other end of the second inductor L2 is connected with a third load resistor RL3;

the B measuring channel is used for measuring the voltage of the two ends of the PT100 resistor and the lead resistor, so that the total resistance of the PT100 resistor and the lead resistor is calculated; the A measuring channel is used for measuring the voltages at two ends of the wire resistor so as to calculate the wire resistor; the resistance of PT100 is the total resistance minus the wire resistance.

2. The three wire PT100 temperature measuring circuit of claim 1, wherein the first die U1 is model HX717.

3. The three-wire PT100 temperature measuring circuit of claim 1, further comprising a first transistor Q1, a first diode D2 and an eighth capacitor C8, wherein the model of the first transistor Q1 is SI2302, the S-pole of the first transistor Q1 is connected to the first diode D2 and the eighth capacitor C8 and grounded, the D-pole of the first transistor Q1 is connected to the other ends of the first resistor R1 and the first diode D2, the G-pole of the first transistor Q1 is connected to a fifth input signal, and the other ends of the first resistor R1 and the eighth capacitor C8 are connected to a second load resistor RL2.