A platinum resistance temperature measurement circuit and method

Abstract

The present invention discloses a platinum resistance temperature measurement circuit and method. The circuit has the function of eliminating parasitic thermoelectric potential. The circuit includes an analog-to-digital conversion chip, a first single-pole double-throw switch, a second single-pole double-throw switch, a reference circuit, a circuit to be measured, and a microcontroller. The circuit to be measured includes a platinum resistor, a first voltage follower, and a second voltage follower. One end of the first voltage follower and the second voltage follower are respectively connected to the two ends of the platinum resistor, and the other ends of the first voltage follower and the second voltage follower are respectively connected to the two input ends of the analog-to-digital conversion chip. The reference circuit includes a reference resistor, which is connected in series with the platinum resistor, and the two ends of the reference resistor are respectively connected to the two reference input ends of the analog-to-digital conversion chip. Through this temperature measurement circuit and method, the influence of parasitic thermoelectric potential on the platinum resistor temperature measurement circuit can be effectively eliminated, thereby improving the accuracy of temperature measurement.

Description

Technical Field

[0001] The present invention relates to the field of temperature measurement, and particularly to a platinum resistance temperature measurement circuit and method. Background Art

[0002] Temperature is one of the basic physical quantities in the International System of Units. Temperature detection is widely used in the fields of industrial automation and scientific research. Thermal resistance temperature measurement is based on the characteristic that the resistance value of a metal conductor increases with the increase of temperature. Most thermal resistances are made of pure metal materials. Currently, the widely used temperature measurement element is platinum. Due to the stable characteristics of platinum, it will not cause physical or chemical changes due to high or low temperatures, and has a large measurement range, reaching -250°C to 850°C, high temperature measurement accuracy, high indication reproducibility, etc. The characteristic curve between the platinum resistance and the ambient temperature is a non-linear relationship. When the measured temperature is -250°C < t < 0°C, R t = R0[1 + At + Bt 2 + Ct 3 (t - 100)]; when the measured temperature is 0°C ≤ t ≤ 850°C, R t = R0[1 + At + Bt 2 ; where A = 3.9083×10 -3 ; B = -5.775×10 -7 ; C = 4.183×10 -12 ; According to this relationship, the temperature value corresponding to the resistance value of the platinum resistance can be obtained from the resistance value of the platinum resistance. Therefore, the circuit using platinum resistance for temperature measurement is widely used in the industrial production field, especially in the field of precision temperature measurement.

[0003] In precision temperature measurement systems, metal conductors of different materials are often used to meet measurement requirements, depending on the measurement environment. In platinum resistance temperature measurement circuits, connecting metals of different materials inevitably creates a junction. Due to the contact between metal conductors of different materials and the different electron densities of the different metals, free electrons migrate from the metal with higher density to the metal with lower density. When equilibrium is reached, a certain potential difference, known as the contact potential, is formed between the metals of different materials. In actual temperature measurement, the connection point at the two ends of the platinum resistor is subjected to an uneven temperature field, resulting in different temperatures at the two ends of the platinum resistor. The high-temperature end with higher free electron density diffuses toward the low-temperature end with lower free electron density. When a new equilibrium is reached, a certain potential difference, known as the thermoelectric potential, is formed at the high and low temperature ends. The contact potential and the thermoelectric potential constitute the parasitic thermoelectric potential in the temperature measurement circuit. It is precisely because of the influence of the parasitic thermoelectric potential that the measured resistance of the platinum resistor in the temperature measurement circuit often deviates from the actual resistance value, thus affecting the accuracy of the temperature measurement circuit. Therefore, it is necessary to propose a temperature measurement circuit to eliminate the influence of parasitic thermoelectric potential on the temperature measurement circuit and improve the accuracy of the platinum resistance temperature measurement circuit. Summary of the Invention

[0004] In response to the problem that parasitic thermoelectric potential in a platinum resistor temperature measurement circuit affects the temperature measurement accuracy, the present invention proposes a platinum resistor temperature measurement circuit and method for eliminating the parasitic thermoelectric potential in the temperature measurement circuit, thereby improving the temperature measurement accuracy.

[0005] A platinum resistance temperature measurement circuit and method of the present invention has the function of eliminating parasitic thermoelectric potential, and is characterized in that: the circuit includes an analog-to-digital conversion chip, a first single-pole double-throw switch, a second single-pole double-throw switch, a reference circuit, and a circuit to be measured;

[0006] The analog-to-digital conversion chip is provided with two high-precision constant current source output ports, two input ports, and two reference input ports. The two high-precision constant current source ports can output two stable high-precision currents.

[0007] The common end of the first single-pole double-throw switch is connected to the circuit to be tested, one selection end thereof is connected to a port output by the high-precision constant current source, and the other selection end is grounded;

[0008] The common end of the second single-pole double-throw switch is connected to the reference circuit, one selection end thereof is connected to the other output port of the high-precision constant current source, and the other selection end is grounded;

[0009] The circuit to be tested includes a platinum resistor, a first voltage follower, and a second voltage follower, one end of the first voltage follower and one end of the second voltage follower are respectively connected to two ends of the platinum resistor, and the other ends of the first voltage follower and the second voltage follower are respectively connected to two input ends of the analog-to-digital conversion chip;

[0010] The reference circuit includes a reference resistor, which is connected in series with the platinum resistor. Both ends of the reference resistor are respectively connected to two reference input ends of the analog-to-digital conversion chip.

[0011] Preferably, a relay is provided between the platinum resistor and the reference resistor, and the relay is used to switch circuits and control different circuits to be connected. The common end of the relay is connected to the reference resistor, and the two selection ends are connected to the platinum resistor.

[0012] Preferably, when the platinum resistor is a four-wire platinum resistor, only one of the two selection terminals of the relay is used to put the current circuit in a conductive state; when the platinum resistor is a three-wire platinum resistor, both selection terminals of the relay are used.

[0013] Preferably, the circuit to be tested further includes a filter circuit, and the filter circuit is arranged between the first voltage follower, the second voltage follower and the two input terminals of the analog-to-digital conversion chip.

[0014] Preferably, the reference circuit further includes a filter circuit, and the filter circuit is arranged between the reference resistor and two reference input terminals of the analog-to-digital conversion chip.

[0015] Preferably, the filtering circuit adopts a first-order RC low-pass filtering circuit.

[0016] Preferably, a microcontroller is further included, which is connected to the analog-to-digital conversion chip and is used to control the entire temperature measurement circuit.

[0017] A method for a platinum resistance temperature measurement circuit, characterized in that:

[0018] S1: When the analog-to-digital conversion chip does not output current, the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, and the offset voltage of the second voltage follower;

[0019] S2: Swap the positive and negative input terminals of the analog-to-digital conversion chip, and read the voltage output by the analog-to-digital conversion chip, including the first voltage follower offset voltage, the parasitic thermoelectric potential across the platinum resistor, and the second voltage follower offset voltage.

[0020] S3: When one end of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the constant current source output end, and the second single-pole double-throw switch selects the ground end. The voltage read from the analog-to-digital conversion chip includes the first voltage follower offset voltage, the parasitic thermoelectric potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, and the second voltage follower offset voltage.

[0021] S4: When the other end of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the ground end and the second single-pole double-throw switch selects the constant current source output end. The voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, and the offset voltage of the second voltage follower.

[0022] The parasitic thermoelectric potential across the platinum resistor is obtained through steps S1 and S2 , and the voltage across the platinum resistor is obtained through steps S3 and S4 .

[0023] Preferably, when the platinum resistor is a three-wire platinum resistor: after completing steps S1 to S4, the parasitic thermoelectric potential at both ends of the platinum resistor is obtained, and steps S5 and S6 are also required:

[0024] S5: One port of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the constant current source end, the second single-pole double-throw switch selects the ground end, the reference resistor is connected to the low end of the platinum resistor voltage, and the voltage read from the analog-to-digital conversion chip includes the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the lead voltage at both ends of the platinum resistor.

[0025] S6: The output current of the other port of the analog-to-digital conversion chip, the ground terminal of the first single-pole double-throw switch, the constant current source terminal of the second single-pole double-throw switch, the reference resistor is connected to the low end of the platinum resistor voltage, and the voltage read from the analog-to-digital conversion chip includes the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the lead voltage at both ends of the platinum resistor.

[0026] The lead voltage at one end of the three-wire platinum resistor is obtained through S1 to S6, and finally the voltage at both ends of the three-wire platinum resistor is obtained.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention controls whether a constant current source within an analog-to-digital conversion chip outputs current and uses a first single-pole double-throw switch and a second single-pole double-throw switch to control the direction of the current to read the measurement result of the analog-to-digital conversion chip. A functional relationship is established between the voltage across a platinum resistor and the reading of the analog-to-digital conversion chip to calculate the parasitic thermoelectric potential that affects the accuracy of the temperature measurement circuit, and then obtain the true resistance value of the platinum resistor. The resistance value of the platinum resistor measured by the present invention is more accurate, thereby improving the accuracy of the temperature measurement circuit.

[0029] 2. The platinum resistor of the present invention can adopt a four-wire platinum resistor or a three-wire platinum resistor, which can eliminate the influence of the lead voltage at both ends of the platinum resistor on the resistance value of the platinum resistor and improve the accuracy of the temperature measurement circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1: Four-wire platinum resistance temperature measurement circuit block diagram;

[0031] Figure 2 : Three-wire platinum resistance temperature measurement circuit block diagram;

[0032] Figure 3 : Schematic diagram of the four-wire platinum resistance temperature measurement circuit;

[0033] Figure 4 : Schematic diagram of the three-wire platinum resistance temperature measurement circuit;

[0034] Figure 1: Analog-to-digital converter chip; 2: First single-pole dual-throw switch (SPDT); 3: Platinum resistor; 4: First voltage follower; 5: Second voltage follower; 6: Relay; 7: Reference resistor; 8: Second SPDT switch; 9: Microcontroller DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to the specific embodiments shown in the accompanying drawings, but these embodiments do not limit the present invention. Structural, methodological, or functional changes made by ordinary technicians in this field based on these embodiments are all included in the scope of protection of the present invention.

[0036] like Figure 1 and Figure 2 A platinum resistance temperature measurement circuit shown in the figure includes an analog-to-digital conversion chip 1, a first single-pole double-throw switch 2, a second single-pole double-throw switch 8, a reference circuit, and a circuit to be measured;

[0037] The analog-to-digital conversion chip 1 is provided with two high-precision constant current source output ports, two input ports, and two reference input ports. The two high-precision constant current source ports can output two stable high-precision currents.

[0038] The circuit to be tested includes a platinum resistor 3, a first voltage follower 4, and a second voltage follower 5. One end of the first voltage follower 4 and the second voltage follower 5 are respectively connected to the two ends of the platinum resistor 3, and the other ends of the first voltage follower 4 and the second voltage follower 5 are respectively connected to the two input ends of the analog-to-digital conversion chip; the function of the first voltage follower 4 and the second voltage follower 5 is impedance matching, and the input and output impedance matching is achieved by utilizing the characteristics of high input impedance and low output impedance of the voltage follower.

[0039] There is a preferred solution, in which a filtering circuit is provided between the first voltage follower 4, the second voltage follower 5 and the analog-to-digital conversion chip 1 to process the analog signal in the circuit so that signals of a certain frequency pass smoothly while signals of another frequency are sharply attenuated; a more preferred solution is that the filtering circuit adopts a first-order RC low-pass filtering circuit.

[0040] The common end of the first single-pole double-throw switch 2 is connected to a platinum resistor, one of its selection ends is connected to an output port of a high-precision constant current source of the analog-to-digital conversion chip 1 , and the other selection end is grounded.

[0041] The reference circuit includes a reference resistor 7, which is connected in series with the platinum resistor 3. The two ends of the reference resistor 7 are respectively connected to the two reference input ends of the analog-to-digital conversion chip 1 to provide a reference voltage signal for the analog-to-digital conversion chip 1.

[0042] There is a preferred embodiment, in which a relay 6 is further provided between the reference resistor 7 and the platinum resistor 3, the common end of the relay 6 is connected to the reference resistor 7, and the two selection ends are connected to the platinum resistor 3, and the relay is used to switch the circuit and control different circuits to be connected; when the platinum resistor is a four-wire platinum resistor, the selection end of the relay 6 is connected to the current low end of the platinum resistor 3; when the platinum resistor 3 is a three-wire platinum resistor, the relay 6 can be connected to the current low end of the platinum resistor, and can also be connected to the voltage low end of the platinum resistor.

[0043] In a preferred embodiment, a filter circuit is provided between the reference resistor 7 and the analog-to-digital conversion chip 1 to process the analog signal in the circuit so that signals of a certain frequency pass smoothly while signals of another frequency are sharply attenuated. In a more preferred embodiment, the filter circuit adopts a first-order RC low-pass filter circuit.

[0044] The common end of the second single-pole double-throw switch 8 is connected to the reference resistor 7, one of its selection ends is connected to the output port of the high-precision constant current source of the analog-to-digital conversion chip 1, and the other selection end is grounded;

[0045] In a preferred embodiment, the temperature measurement circuit further includes a microcontroller 9 , which is connected to the analog-to-digital conversion chip 1 and is used to control the entire circuit.

[0046] There is a specific example, such as Figure 3 and Figure 4 As shown, the analog-to-digital conversion chip 1 uses the TI ADS1248. This chip has four differential inputs, two differential reference inputs, and two internal precision constant current source outputs. Both precision current sources can output stable currents of 0.5mA, 1mA, and 2mA, with 24-bit measurement accuracy. It communicates with the microprocessor 9 via a serial peripheral interface, and the digital and analog circuits are powered in isolation. The microcontroller 9 uses the ST Microcontroller STM32F103RCT6 chip, which has 256KB of Flash, 48KB of RAM, and 51 general-purpose I / O ports.

[0047] The first and second single-pole double-throw switches 2 and 8 are TI's TS5A3154DCUR. Relay 6 is specifically model TX2-L2-5V. Both control terminals of the relay are driven by NPN transistors S8050. The first and second voltage followers 4 and 5 both use OPA188. Reference resistor 7 is an RJ711 150Ω precision metal foil resistor with a temperature coefficient of 0.05ppm. Platinum resistor 3 is a PT100.

[0048] like Figure 3 As shown, the platinum resistor is a four-wire platinum resistor, the common end of the first single-pole double-throw switch is connected to the current high end of the platinum resistor R3 (the voltage high end, low end and current high end, low end mentioned in the text are relative to the output current of the high-precision constant current source output port IEXC1), the first single-pole double-throw switch has two selection ends, one of which is connected to the high-precision constant current source output port IEXC1 of the analog-to-digital conversion chip ADS1248, and the other selection end is connected to the ground; the input end of the first voltage follower is connected to the voltage high end of the platinum resistor R3, the input end of the second voltage follower is connected to the voltage low end of the platinum resistor R3, and the output end of the first voltage follower and the second voltage follower are connected. The filter circuit connects the positive and negative input terminals of the analog-to-digital converter chip ADS1248. The low-current and low-voltage terminals of platinum resistor R3 are connected to the two selector terminals of the relay, respectively. The common terminal of the relay is connected to the high-current terminal of reference resistor R12. The low-current terminal of reference resistor R12 is connected to the common terminal of a second single-pole double-throw switch. One of the two selector terminals of the second single-pole double-throw switch is connected to the other output terminal IEXC2 of the high-precision constant current source of the analog-to-digital converter chip, and the other is connected to ground. The high-voltage and low-voltage terminals of reference resistor R12 are connected to the positive and negative reference input terminals of the analog-to-digital converter chip ADS1248 through the filter circuit. The analog-to-digital converter chip ADS1248 is connected to the microcontroller STM32F103RCT6 via a digital bus.

[0049] When the high-precision constant current source output port IEXC1 of the analog-to-digital conversion chip ADS1248 outputs current, the selection end of the first single-pole double-throw switch is connected to the high-precision constant current source output port IEXC1, the selection end of the second single-pole double-throw switch is connected to the ground, and the relay selection is connected to the current low end "2" of the platinum resistor R3. At this time, current flows through the current high end "4" of the platinum resistor R3, the platinum resistor R3, and the current low end "2" of the platinum resistor R3; while no current flows through the voltage high end "3" of the platinum resistor R3 and the voltage low end "1" of the platinum resistor R3, and only the voltage signal is transmitted to the analog-to-digital conversion chip. The voltage output by the analog-to-digital conversion chip includes the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the voltage at both ends of the platinum resistor;

[0050] When the high-precision constant current source of the analog-to-digital conversion chip ADS1248 outputs current at another port IEXC2, the selection end of the second single-pole double-throw switch is connected to the high-precision constant current source output port IEXC2, the selection end of the first single-pole double-throw switch is connected to the ground, and the relay selection is connected to the current low end "2" of the platinum resistor R3. Similarly, current flows through the two current ends of the platinum resistor R3, while no current flows through the two voltage ends of the platinum resistor R3. At this time, the voltage output by the analog-to-digital conversion chip includes the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the voltage at both ends of the platinum resistor.

[0051] like Figure 4 As shown, the platinum resistor is a three-wire platinum resistor, the common end of the first single-pole double-throw switch 2 is connected to the high-end "3" of the platinum resistor R2, and the first single-pole double-throw switch 2 has two selection ends, one of which is connected to the high-precision constant current source output port IEXC1 of the analog-to-digital conversion chip ADS1248, and the other selection end is connected to the ground; the input end of the first voltage follower is connected to the high-end "3" of the platinum resistor R2, and the input end of the second voltage follower is connected to the low-end voltage end "1" of the platinum resistor R2. The output ends of the first voltage follower and the second voltage follower are respectively connected to the positive and negative input ends of the analog-to-digital conversion chip ADS1248 through a filtering circuit. The low-current terminal "2" and low-voltage terminal "1" of platinum resistor R2 are connected to the two selector terminals of the relay, respectively. The common terminal of the relay is connected to the high-current terminal "4" of reference resistor R11. The low-current terminal "2" of reference resistor R11 is connected to the common terminal of a second single-pole double-throw switch. One of the two selector terminals of the second single-pole double-throw switch is connected to the other output terminal IEXC2 of the high-precision constant current source of the analog-to-digital converter chip, and the other is connected to ground. The high-voltage terminal "3" and low-voltage terminal "1" of reference resistor R11 are connected to the positive and negative reference input terminals of the analog-to-digital converter chip ADS1248 through a filter circuit. The analog-to-digital converter chip ADS1248 is connected to the microcontroller STM32F103RCT6 via a digital bus.

[0052] When the high-precision constant current source output port IEXC1 of the analog-to-digital conversion chip ADS1248 outputs current, the first single-pole double-throw switch is connected to the high-precision constant current source output port IEXC1, the second single-pole double-throw switch is connected to the ground, and the relay is connected to the current low end "2" of the platinum resistor R2. At this time, current flows through the high end "3" of the platinum resistor R2 and the current low end "2" of the platinum resistor R2. At the same time, the high end "3" of the platinum resistor R2 and the voltage low end "1" of the platinum resistor R2 provide a voltage signal for the analog-to-digital conversion chip. The voltage output by the analog-to-digital conversion chip includes the high-end lead voltage of the platinum resistor, the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the voltage at both ends of the platinum resistor.

[0053] When the high-precision constant current source of the analog-to-digital conversion chip ADS1248 outputs current at another port IEXC2, the second single-pole double-throw switch is connected to the high-precision constant current source output port IEXC2, the first single-pole double-throw switch is connected to the ground, and the relay is connected to the current low end "2" of the platinum resistor R2. At this time, the voltage output by the analog-to-digital conversion chip includes the high-end lead voltage of the platinum resistor, the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the voltage at both ends of the platinum resistor;

[0054] When the high-precision constant current source output port IEXC1 of the analog-to-digital conversion chip ADS1248 outputs current, the first single-pole double-throw switch is connected to the high-precision constant current source output port IEXC1, the second single-pole double-throw switch is connected to the ground, and the relay is connected to the low voltage end "1" of the platinum resistor R2. At this time, current flows through the high-end "3" of the platinum resistor R2 and the low voltage end "1" of the platinum resistor R2, and a voltage signal is provided to the analog-to-digital conversion chip. The voltage output by the analog-to-digital conversion chip includes the high-end lead voltage of the platinum resistor, the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the offset voltage of the second voltage follower, the voltage at both ends of the platinum resistor, and the low-end lead voltage of the platinum resistor;

[0055] When the high-precision constant current source of the analog-to-digital conversion chip ADS1248 outputs current at another port IEXC2, the second single-pole double-throw switch is connected to the high-precision constant current source output port IEXC2, the first single-pole double-throw switch is connected to the ground, and the relay is connected to the low-end "1" of the platinum resistor R2 voltage. At this time, the voltage output by the analog-to-digital conversion chip includes the high-end lead voltage of the platinum resistor, the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the offset voltage of the second voltage follower, the voltage at both ends of the platinum resistor, and the low-end lead voltage of the platinum resistor;

[0056] like Figure 3 As shown, when the platinum resistance is a four-wire system, the method of the platinum resistance temperature measurement circuit is:

[0057] S1: When the high-precision constant current source output terminal IEXC1 built into the analog-to-digital conversion chip does not output current, the measurement result of the analog-to-digital conversion chip is D0.

[0058] D0=V offset2 +V EMF -V offset1 (1)

[0059] Where: V offset1 is the offset voltage of the first voltage follower, V EMF is the parasitic thermoelectric potential of the platinum resistor, V offset2 is the offset voltage of the second voltage follower;

[0060] S2: Swap the positive and negative input terminals of the analog-to-digital conversion chip. The measurement result of the analog-to-digital conversion chip is D′0, D′0=V offset1 +V EMF -V offset2 , (2)

[0061] From formula (1) and formula (2), we can get: V EMF =(D0+D′0) / 2 (3)

[0062] S3: When the high-precision constant current source output terminal IEXC1 built into the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the constant current source IEXC1 output terminal, the second single-pole double-throw switch selects the ground terminal, and the relay is connected to the low end of the platinum resistor current. At this time, the measurement result of the analog-to-digital conversion chip is D1.

[0063] D1=V offset2 +V PT +V EMF -V offset1 ; (4)

[0064] S4: When the high-precision constant current source output terminal IEXC2 built into the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the ground terminal, the second single-pole double-throw switch selects the high-precision constant current source IEXC2 output terminal, and the relay is connected to the low end of the platinum resistor current. At this time, the measurement result of the analog-to-digital conversion chip is D′1.

[0065] D′1=V offset1 +V PT +V EMF -V offset2 , (5)

[0066] From equations (3), (4) and (5), the voltage VPT across the four-wire platinum resistor can be obtained as:

[0067] V PT =(D1+D′1-D0-D′0) / 2 (6)

[0068] like Figure 4 As shown, when the platinum resistor is a three-wire platinum resistor: after completing steps S1 to S4, D1 and D′1 are obtained, and D1 = V offset2 +V PT +V L +V EMF -V offset1 (7)

[0069] D′1=V offset1 +V PT +V L +V EMF -V offset2 (8)

[0070] In formula (7) and formula (8), V L is the high-side lead voltage;

[0071] Steps S5 and S6 are also required:

[0072] S5: When the high-precision constant current source output terminal IEXC1 built into the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the high-precision constant current source output terminal IEXC1, the second single-pole double-throw switch selects the ground terminal, and the relay is connected to the low end of the platinum resistor voltage. At this time, the result measured by the analog-to-digital conversion chip is D2;

[0073] D2=V offset2 +V PT +2V L +V EMF -V offset1 (9)

[0074] S6: When the high-precision constant current source output terminal IEXC2 built into the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the ground terminal, the second single-pole double-throw switch selects the high-precision constant current source output terminal IEXC2, and the selection terminal of the relay is connected to the low end of the platinum resistor voltage. At this time, the measurement result of the analog-to-digital conversion chip is D′2.

[0075] D′2=V offset1 +V PT +2V L +V EMF -V offset2 , (10)

[0076] Then, the voltage V across the three-wire platinum resistor can be obtained from equations (3), (7), (8), (9), and (10): PT .

[0077] The present invention controls whether a constant current source inside an analog-to-digital conversion chip outputs current and uses a first single-pole double-throw switch and a second single-pole double-throw switch to control the direction of the current, thereby reading the measurement result of the analog-to-digital conversion chip; establishes a functional relationship between the voltage across a platinum resistor and the reading of the analog-to-digital conversion chip, calculates the parasitic thermoelectric potential that affects the accuracy of the temperature measurement circuit, and then obtains the true resistance value of the platinum resistor. The resistance value of the platinum resistor measured by the present invention is more accurate, thereby improving the accuracy of the temperature measurement circuit.

[0078] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A platinum resistance temperature measurement circuit, which has the function of eliminating parasitic thermoelectric potential, characterized by: The circuit includes an analog-to-digital conversion chip, a first single-pole double-throw switch, a second single-pole double-throw switch, a reference circuit, and a circuit to be tested; The analog-to-digital conversion chip is provided with two high-precision constant current source output ports, two input ports, and two reference input ports. The two high-precision constant current source ports can output two stable high-precision currents. The common end of the first single-pole double-throw switch is connected to the circuit to be tested, one selection end thereof is connected to a port output by the high-precision constant current source, and the other selection end is grounded; The common end of the second single-pole double-throw switch is connected to the reference circuit, one of the selected ends is connected to the other output port of the high-precision constant current source, and the other selected end is grounded; The circuit to be tested includes a platinum resistor, a first voltage follower, and a second voltage follower, one end of the first voltage follower and one end of the second voltage follower are respectively connected to two ends of the platinum resistor, and the other ends of the first voltage follower and the second voltage follower are respectively connected to two input ends of the analog-to-digital conversion chip; The reference circuit includes a reference resistor, the reference resistor is connected in series with the platinum resistor, and both ends of the reference resistor are respectively connected to the two reference input ends of the analog-to-digital conversion chip; The platinum resistance temperature measurement circuit also includes a microcontroller connected to the analog-to-digital conversion chip, which is used to control the entire temperature measurement circuit using the following strategy: S1: When the analog-to-digital conversion chip does not output current, the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, and the offset voltage of the second voltage follower; S2: swapping the positive and negative input terminals of the analog-to-digital conversion chip, and reading the voltage output by the analog-to-digital conversion chip, including the first voltage follower offset voltage, the parasitic thermoelectric potential across the platinum resistor, and the second voltage follower offset voltage; S3: When one end of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the constant current source output end, and the second single-pole double-throw switch selects the ground end, and the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, and the offset voltage of the second voltage follower; S4: When the other end of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the ground end, the second single-pole double-throw switch selects the constant current source output end, and the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermoelectric potential across the platinum resistor, the voltage across the platinum resistor, and the offset voltage of the second voltage follower; Obtain the parasitic thermoelectric potential across the platinum resistor through steps S1 and S2, and then obtain the voltage across the platinum resistor through steps S3 and S4; A relay is further provided between the platinum resistor and the reference resistor, and the relay is used to switch circuits and control different circuits to be connected. The common end of the relay is connected to the reference resistor, and the two selection ends are connected to the platinum resistor; When the platinum resistor is a four-wire platinum resistor, only one of the two selection terminals of the relay is used to keep the current circuit in a connected state; when the platinum resistor is a three-wire platinum resistor, both selection terminals of the relay are used; The circuit to be tested further includes a filter circuit, which is arranged between the first voltage follower, the second voltage follower and two input terminals of the analog-to-digital conversion chip.

2. A platinum resistance temperature measurement circuit according to claim 1, characterized in that: The reference circuit further includes a filter circuit, which is arranged between the reference resistor and two reference input terminals of the analog-to-digital conversion chip.

3. A platinum resistance temperature measurement circuit according to claim 1 or 2, characterized in that: The filtering circuit adopts a first-order RC low-pass filtering circuit.

4. A method for measuring temperature of a platinum resistance circuit, characterized in that: The method uses the platinum resistance temperature measurement circuit according to any one of claims 1 to 3, and the method comprises the following steps: S1: When the analog-to-digital conversion chip does not output current, the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, and the offset voltage of the second voltage follower; S2: swapping the positive and negative input terminals of the analog-to-digital conversion chip, and reading the voltage output by the analog-to-digital conversion chip, including the first voltage follower offset voltage, the parasitic thermoelectric potential across the platinum resistor, and the second voltage follower offset voltage; S3: When one end of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the constant current source output end, and the second single-pole double-throw switch selects the ground end, and the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermoelectric potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, and the offset voltage of the second voltage follower; S4: When the other end of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the ground end, the second single-pole double-throw switch selects the constant current source output end, and the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermoelectric potential across the platinum resistor, the voltage across the platinum resistor, and the offset voltage of the second voltage follower; The parasitic thermoelectric potential across the platinum resistor is obtained through steps S1 and S2 , and the voltage across the platinum resistor is obtained through steps S3 and S4 .

5. The method of a platinum resistance temperature measurement circuit according to claim 4, characterized in that: When the platinum resistor is a three-wire platinum resistor: after completing steps S1 to S4, the parasitic thermoelectric potential at both ends of the platinum resistor is obtained, and steps S5 and S6 are required: S5: A port of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the constant current source end, the second single-pole double-throw switch selects the ground end, the reference resistor is connected to the low voltage end of the platinum resistor, and the voltage read from the analog-to-digital conversion chip includes the offset voltage of the first voltage follower, the parasitic thermal potential across the platinum resistor, the voltage across the platinum resistor, the offset voltage of the second voltage follower, and the lead voltage across the platinum resistor; S6: The other port of the analog-to-digital conversion chip outputs current, the first single-pole double-throw switch selects the ground terminal, the second single-pole double-throw switch selects the constant current source terminal, the reference resistor is connected to the low voltage terminal of the platinum resistor, and the voltage of the analog-to-digital conversion chip is read, including the offset voltage of the first voltage follower, the parasitic thermal potential at both ends of the platinum resistor, the voltage at both ends of the platinum resistor, the offset voltage of the second voltage follower, and the lead voltage at both ends of the platinum resistor; The lead voltage at one end of the three-wire platinum resistor is obtained through S1 to S6, and finally the voltage at both ends of the three-wire platinum resistor is obtained.

Images