A multi-range platinum resistance temperature measurement circuit and method

Abstract

The present invention discloses a multi-range platinum resistor temperature measurement circuit and method. The circuit includes a constant current source, a single-pole double-throw switch, a reference circuit, a circuit to be measured, a temperature measurement chip, and a microcontroller. The reference circuit includes a constant resistor and a variable resistor. The resistor to be measured includes a platinum resistor and a variable resistor identical to the reference circuit. By changing the size of the variable resistor, the maximum resistance of the variable resistor is made greater than the resistance of the platinum resistor at the maximum temperature measurement point, and the minimum resistance of the variable resistor is made greater than the resistance of the constant resistor. Through internal calculation of the temperature measurement chip, the input voltage across the constant resistor and the input voltage across the platinum resistor are read respectively. The constant current is used to provide the same current to both, and the resistance of the platinum resistor is calculated, thereby obtaining the temperature value corresponding to the platinum resistor at this time. When dealing with small-range problems, using this temperature measurement method can effectively avoid the problem of a large difference between the platinum resistor and the variable resistor, thereby improving temperature measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the field of temperature measurement, and particularly to a multi-range platinum resistance temperature measurement circuit and a temperature measurement 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 various complex industrial environments. According to the characteristic that the temperature measurement range of the platinum resistance is relatively large, a multi-range temperature measurement circuit is often designed to measure the environment with relatively large temperature changes.

[0003] Currently, a fixed resistor is selected and connected in series with the platinum resistance in the measurement circuit of the multi-range platinum resistance. The specific resistance value of the platinum resistance is calculated by the temperature measurement chip by calculating the voltage ratio of the two. And according to the resistance value algorithm of the platinum resistance by the temperature measurement chip, it is necessary to satisfy that the resistance value of the fixed resistor is greater than the resistance value of the platinum resistance. However, as pointed out above, the resistance value of the platinum resistance shows a non-linear change rule with the change of temperature. For example, taking the commercially available PT100 platinum resistance as an example, when the temperature is close to 100°C, the resistance value of the platinum resistance is about 138 Ω, and when the temperature is close to 500°C, the resistance value of the platinum resistance is about 280Ω. In order to meet the measurement requirements of different ranges, the resistance value of the series-connected fixed resistor is usually selected to be greater than the maximum value of the platinum resistance in the maximum range. However, such a selection will cause the difference between the resistance value of the fixed resistor and the resistance value of the platinum resistance to be too large when dealing with a small range. This difference will amplify the error inside the temperature measurement chip, resulting in a large deviation in the measurement result and a decrease in the accuracy of the temperature measurement circuit. Summary of the Invention

[0004] Aiming at the problem of decreased accuracy in small and medium ranges of multi-range platinum resistance temperature measurement, the present invention proposes a multi-range platinum resistance temperature measurement circuit and a measurement method.

[0005] The multi-range platinum resistance temperature measurement circuit of the present invention includes a constant current source, a single-pole double-throw switch, a reference circuit, a circuit to be measured, and a temperature measurement chip. The fixed end of the single-pole double-throw switch is connected to the constant current source, and the two moving ends of the single-pole double-throw switch are respectively connected to the reference circuit and the circuit to be measured, so that the single-pole double-throw switch controls different circuits to work.

[0006] The reference circuit includes a constant resistor and a variable resistor, the circuit to be measured includes a platinum resistor to be measured and a variable resistor shared with the reference circuit, the constant resistor and the platinum resistor have a common end and are connected in series to the variable resistor, the other ends of the constant resistor and the platinum resistor are respectively connected to the two moving ends of the single-pole double-throw switch, the maximum resistance of the variable resistor is greater than the resistance of the platinum resistor at the maximum temperature measurement point, and the minimum resistance of the variable resistor is greater than the resistance of the constant resistor.

[0007] The two ends of the constant resistor are respectively connected to the two ports of the first input end of the temperature measuring chip, the two ends of the platinum resistor are respectively connected to the two ports of the second input end of the temperature measuring chip, and the two ends of the variable resistor are also respectively connected to the two ports of the reference end of the temperature measuring chip.

[0008] Preferably, the variable resistor is a precision resistor network, including a plurality of precision resistors connected in series, and each precision resistor is controlled by a single-pole single-throw switch to control whether to be connected to the circuit, thereby achieving variable resistance of the precision resistor network.

[0009] Preferably, a second multi-way selection switch is provided between the constant resistor or the platinum resistor and the precision resistor network, for controlling whether the constant resistor or the platinum resistor is connected to the precision resistor network, and the second multi-way selection switch has at least three selection terminals, one of which is connected to the constant resistor, and two of which are connected to the platinum resistor.

[0010] Preferably, when the platinum resistor is a four-wire system, only one of the two selection ends connected to the platinum resistor is used; when the platinum resistor is a three-wire system, both selection ends connected to the platinum resistor are used simultaneously.

[0011] Preferably, a first multi-way selection switch is provided between the precision resistor network and the temperature measuring chip, and the first multi-way selection switch is used to match the resistor network formed by the precision resistors currently connected to the circuit, and output the voltage of the resistor network to the reference end of the temperature measuring chip.

[0012] Preferably, the variable resistor is a potentiometer with continuously adjustable resistance.

[0013] Preferably, the constant resistor and the variable resistor are low temperature coefficient resistors, and the temperature coefficient thereof is at least less than 5 PPM / °C.

[0014] Preferably, a microcontroller is further included, which is connected to the temperature measurement chip and is used to control the entire temperature measurement circuit.

[0015] A temperature measurement method matching a multi-range platinum resistance temperature measurement circuit, characterized by:

[0016] S1: After selecting the temperature measurement range, calculate the platinum resistor resistance R corresponding to the highest temperature in the range, and control the resistance of the variable resistor so that the resistance of the variable resistor connected to the circuit is greater than or equal to R;

[0017] S2: Control the single-pole double-throw switch to select the reference circuit, and at the same time close the selection end of the second multi-way selection switch connected to the constant resistor, and read the temperature measurement chip reading D0;

[0018] S3: Control the single-pole double-throw switch to select the circuit to be tested, and at the same time close one of the two selection terminals of the second multi-way selection switch connected to the platinum resistor, and read the temperature measurement chip reading D1;

[0019] S4: When the platinum resistance is a four-wire system, calculate the platinum resistance R PT Calculate according to the following formula:

[0020]

[0021] Preferably, when the platinum resistor is a three-wire platinum resistor, after steps S1 to S3, step S4 is performed: obtaining the calculated platinum resistor R PT The calculation formula is:

[0022]

[0023] S5: Control the single-pole double-throw switch to select the circuit to be tested, and at the same time close the other of the two selection terminals connected to the platinum resistor in the second multi-way selection switch, read the temperature measurement chip reading D2, and calculate the platinum resistor lead resistance R according to the same current in step S3 and step S5. L Calculate according to the following formula:

[0024] The calculation formula of platinum resistance is obtained by subtracting formula (2) from formula (3):

[0025]

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention adopts a variable resistor connected in series with a platinum resistor and a constant resistor to design a multi-range temperature measurement circuit, so that the maximum resistance of the variable resistor is greater than the resistance of the platinum resistor at the maximum temperature measurement point, and the minimum resistance of the variable resistor is greater than the resistance of the constant resistor; when processing a small range, the size of the variable resistor can be adjusted to avoid the problem of excessive difference in resistance between the variable resistor and the platinum resistor, reduce the influence of the internal calculation error of the temperature measurement chip on the temperature measurement circuit, and effectively improve the accuracy of the temperature measurement circuit.

[0028] 2. The multi-range platinum resistance temperature measurement circuit of the present invention uses a three-wire or four-wire platinum resistor to eliminate the influence of lead resistance on the accuracy of the temperature measurement circuit, thereby improving the accuracy of the temperature measurement circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Block diagram of temperature measurement circuit of four-wire platinum resistance;

[0030] Figure 2 Block diagram of temperature measurement circuit of three-wire platinum resistance;

[0031] Figure 3 Schematic diagram of the principle of four-wire platinum resistance;

[0032] Figure 4 Schematic diagram of the principle of three-wire platinum resistance;

[0033] Figure 1: Constant current source; 2: Single-pole dual trough (SPDT) switch; 3: Constant resistor; 4: Platinum resistor; 5: Second multiplexer; 6: First single-pole single-throw (SPST) switch; 7: Second single-pole single-throw switch; 8: Variable resistor; 9: First multiplexer; 10: Temperature measurement chip; 11: Microcontroller. DETAILED DESCRIPTION

[0034] 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.

[0035] like Figure 1 and Figure 2 A multi-range platinum resistance temperature measurement circuit is shown, which includes a constant current source 1, a single-pole double-throw switch 2, a reference circuit, a circuit to be measured, a temperature measurement chip 10 and a microcontroller 11;

[0036] The constant current source 1 provides a constant and identical current signal to the reference circuit and the circuit to be measured through the single-pole double-throw switch 2. The temperature measuring chip 10 has two input terminals and one reference input terminal, and is connected to the microcontroller 11, which controls the entire temperature measuring circuit.

[0037] The fixed end of the single-pole double-throw switch 2 is connected to the constant current source 1, and the two moving ends of the single-pole double-throw switch 2 are respectively connected to the reference circuit and the circuit to be tested, so that the single-pole double-throw switch 2 controls different circuits to work;

[0038] The reference circuit includes a constant resistor 3 and a variable resistor 8. The circuit to be tested includes a platinum resistor 4 to be tested and a variable resistor 8 shared with the reference circuit. The constant resistor 3 and the platinum resistor 4 have a common terminal and are connected in series with the variable resistor 8 via a second multiplexer switch 5. The second multiplexer switch 5 has at least three selection terminals, one of which is connected to the constant resistor 3 and the other two are connected to the platinum resistor 4. The second multiplexer switch 5 is controlled to determine whether the constant resistor 3 is connected in series with the variable resistor 8 or the platinum resistor 4 is connected in series with the variable resistor 8.

[0039] The variable resistor 8 can be a precision resistor network, which is composed of several precision resistors connected in series, and each precision resistor except the last one is controlled by a single-pole single-throw switch to control whether to be connected to the circuit, thereby realizing the variable resistance of the precision resistor network; the variable resistor 8 can also be a potentiometer with continuously adjustable resistance; by changing the size of the variable resistor 8, the maximum resistance of the variable resistor 8 is greater than the resistance of the platinum resistor 4 at the maximum temperature measurement point, and the minimum resistance of the variable resistor 8 is greater than the resistance of the constant resistor 3.

[0040] In a specific embodiment, a precision resistor network is composed of three precision resistors connected in series. Except for the last precision resistor, the remaining two precision resistors are connected in parallel with a first single-pole single-throw switch 6 and a second single-pole single-throw switch 7, respectively. By controlling whether the first single-pole single-throw switch 6 and the second single-pole single-throw switch 7 are connected to the circuit, the resistance value of the precision resistor network can be made variable.

[0041] The other ends of the constant resistor 3 and the platinum resistor 4 are respectively connected to the two moving ends of the single-pole double-throw switch 2; the two ends of the constant resistor 3 are respectively connected to the two ports of the first input end of the temperature measuring chip 10, the two ends of the platinum resistor 4 are respectively connected to the two ports of the second input end of the temperature measuring chip 10, and the two ends of the variable resistor 8 are also respectively connected to the two ports of the reference end of the temperature measuring chip 10.

[0042] In order to reduce the influence of other resistance elements on the temperature measurement circuit, the constant resistor 3 and the variable resistor 8 in the reference circuit use resistors with low temperature coefficients, and their temperature coefficients are at least less than 5 PPM / °C.

[0043] To reduce the influence of the 4-wire resistance of the platinum resistor on the temperature measurement circuit, the platinum resistor 4 adopts a four-wire platinum resistor as shown in Figure 1 or a three-wire platinum resistor as shown in Figure 2 .

[0044] There is a specific example, as shown in Figure 3 and Figure 4 . The constant current source 1 is implemented using an improved version of the Howland current source circuit. Among them, the precision voltage source uses REF5050IDR, OPA551 constitutes a non-inverting summing circuit, and OPA188 constitutes a voltage follower to provide a constant current signal for the reference circuit and the circuit under test. The single-pole double-throw switch 2 uses TS5A3154DCUR of TI Corporation. The first single-pole single-throw switch 6 and the second single-pole single-throw switch 7 use TS5A23166DCUR, and TS5A23166DCUR is internally integrated with two single-pole single-throw switches. The temperature measurement chip 10 uses ADS1247. This chip has two differential inputs and one differential reference input, has a 24-bit measurement accuracy, communicates with the microprocessor through SPI, and the digital and analog parts are isolated from the power supply. The microcontroller uses the STM32F103RCT6 chip of ST Corporation. This chip has 256KB of Flash and 48KB of RAM, and 51 general-purpose I / O ports.

[0045] The platinum resistor 4 uses PT100. The 100 after PT indicates that its resistance value at 0°C is 100Ω. Its resistance value will change with the change of temperature. When the measured ambient temperature is -250°C < t < 0°C, R Pt100 = 100[1 + At + Bt 2 + Ct 3 (t - 100)]. When the measured ambient temperature is 0°C ≤ t ≤ 850°C, R Pt100 = 100(1 + At + Bt2); In the formula, A = 3.9083×10 -3 ; B = -5.775×10 -7 ; C = 4.183×10 -12 . Both the first multiplexer switch and the second multiplexer switch use MUX509, and MUX509 has four selection terminals. Both the constant resistor and the variable resistor use the precision metal foil resistor RJ711 with a low temperature coefficient.

[0046] Because the range of PT100 platinum resistance thermometer on the market is usually -50~100℃; -100~300℃; -100~500℃, according to the PT100 graduation table, the resistance of PT100 is about 138.51Ω at 100℃, about 212.05Ω at 300℃, and about 280.98Ω at 500℃. In order to meet market demand, the variable resistor can be made up of three resistors in series, namely R9 is 50Ω, R10 is 100Ω and R11 is 150Ω. The TS5A23166DCUR integrates two single-pole, single-throw (SPST) switches. One is connected in parallel with resistor R9, and the other is connected in parallel with R10. By controlling whether the two SPST switches are connected to the circuit, the variable resistor's resistance is adjusted, ensuring that its maximum resistance is greater than the platinum resistor's resistance at the maximum temperature measurement point, and its minimum resistance is greater than the constant resistor's resistance. With R11 set to 150Ω, the constant resistor R3 is set to 100Ω.

[0047] A first multiplexer switch MUX509 is connected in series between the variable resistor 8 and the temperature measuring chip 10:

[0048] When the single-pole single-throw switch connected in parallel with the resistor R9 is turned on and the single-pole single-throw switch connected in parallel with the resistor R10 is turned off, the resistor R9 is short-circuited. At this time, the selection terminal 2 of the first multiplexer switch MUX509 is connected to the temperature measurement chip ADS1247, providing the temperature measurement chip ADS1247 with a reference input voltage across the two resistors connected in series, the resistors R10 and R11;

[0049] When the single-pole single-throw switch connected in parallel with the resistor R9 and the single-pole single-throw switch connected in parallel with the resistor R10 are turned on at the same time, the resistors R9 and R10 are short-circuited at the same time. At this time, the selection terminal 3 of the first multiplexer MUX509 is connected to the temperature measurement chip ADS1247, providing the temperature measurement chip ADS1247 with a reference input voltage across R11;

[0050] When the single-pole single-throw switch connected in parallel with the resistor R9 and the single-pole single-throw switch connected in parallel with the resistor R10 are disconnected at the same time, the selection terminal 1 of the first multiplexer MUX509 is connected, and the reference input voltage across the three resistors R9, R10 and R11 connected in series is provided to the temperature measurement chip ADS1247;

[0051] When the single-pole single-throw switch connected in parallel with resistor R9 is disconnected and the single-pole single-throw switch connected in parallel with resistor R10 is connected, the selection terminal 1 of the first multiplexer MUX509 is connected, and the reference input voltage across the two resistors R9 and R11 connected in series is provided to the temperature measurement chip ADS1247.

[0052] The constant resistor R3 and the platinum resistor R2 are connected in series with the variable resistor by controlling the second multiplexer switch MUX509 , so that the constant resistor R3 and the variable resistor are connected in series with each other, and the platinum resistor R2 and the variable resistor are connected in series with each other.

[0053] In order to reduce the influence of lead resistance on the temperature measurement circuit, such as Figure 3 and Figure 4 The two ends of the constant resistor R3 shown in the figure adopt a four-wire system. When the single-pole double-throw switch is connected to the selection terminal 4, the line "2" connected to the constant resistor R3 and the line "4" have current signals passing through them. Among them, the line "2" is the high-end current end of the resistor R3, and the line "4" is the low-end current end of the resistor R3. They are connected in series with the variable resistor through the selection terminal 3 of the second multiplexer MUX509; the line "1" connected to the constant resistor R3 and the line "4" are connected in series with the variable resistor.

[0054] "3" provides the input voltage signal across the constant resistor R3 of the temperature measurement chip ADS1247, where the line "1" connected to the constant resistor R3 is the high-end voltage end of the constant resistor R3, which is connected to port 11 of the temperature measurement chip ADS1247; the line "3" connected to R3 is the low-end voltage end of R3, which is connected to port 12 of the temperature measurement chip ADS1247.

[0055] like Figure 3 As shown, when the platinum resistor adopts a 4-wire system, when the single-pole double-throw switch is connected to the selection terminal 3, current signals pass through the line "2" and the line "4" connected to the platinum resistor R2, where the line "2" is the high-end current end of the platinum resistor R2, and the line "4" is the low-end current end of the platinum resistor R2, which is connected in series with the variable resistor through the selection terminal 2 of the second multiplexer MUX509; the line "1" and the line "3" connected to R2 provide the temperature measuring chip ADS1247 with input voltage signals across the platinum resistor R2, where the line "1" connected to the platinum resistor R2 is the high-end voltage end of the platinum resistor R2, which is connected to port 9 of the temperature measuring chip ADS1247, and the line "3" connected to the platinum resistor R2 is the low-end voltage end of the platinum resistor R2, which is connected to port 10 of the temperature measuring chip ADS1247.

[0056] like Figure 4 As shown, when a platinum resistor uses a three-wire system, when the single-pole double-throw switch is connected to selection terminal 3 and the second multiplexer is connected in series with the variable resistor via selection terminal 2, a current signal flows through line "3" and line "1" connected to platinum resistor R2, forming a series circuit with the variable resistor. Line "3" and line "2" connected to platinum resistor R2 provide a voltage input signal to the temperature measurement chip ADS1247, connected to ports 9 and 10 of the ADS1247, respectively. The voltage provided to the temperature measurement chip ADS1247 is the sum of the voltage of platinum resistor R2 and the voltage of the high-end lead "3" of platinum resistor R2.

[0057] When a platinum resistor uses a three-wire system, when the single-pole double-throw switch is connected to selector terminal 3 and the second multiplexer is connected in series with the variable resistor via selector terminal 1, current signals flow through line 3 and line 2 connected to platinum resistor R2, forming a series circuit with the variable resistor. Lines 3 and 2 connected to platinum resistor R2 also provide voltage input signals to the temperature measurement chip ADS1247, connecting to ports 9 and 10 of the ADS1247, respectively. The voltage provided to the temperature measurement chip ADS1247 is the sum of the voltage of platinum resistor R2, the voltage of the high-end lead "3" of platinum resistor R2, and the voltage of the low-end lead "2" of platinum resistor R2.

[0058] like Figure 3 As shown, when the platinum resistor R2 is a four-wire platinum resistor, a temperature measurement method of a multi-range platinum resistance temperature measurement circuit is:

[0059] S1: After selecting the temperature measurement range, calculate the platinum resistor resistance R corresponding to the highest temperature in the range, and control the on and off of the single-pole single-throw switch to make the resistance of the variable resistor greater than the resistance of the platinum resistor to be measured;

[0060] S2: Control the single-pole double-throw switch to connect to the reference circuit, and connect the selection terminal 3 of the second multiplexer switch to the variable resistor. At this time, the constant resistor R3 and the variable resistor form a series circuit. Through the internal calculation of the temperature measurement chip, the voltage signal reading D0 across the constant resistor R3 is read.

[0061] S3: Control the single-pole double-throw switch to connect to the circuit to be measured, and connect the selection terminal 2 of the second multiplexer switch to the variable resistor. At this time, the platinum resistor R2 and the variable resistor form a series circuit. Through the internal calculation of the temperature measurement chip, the voltage signal reading D1 across the platinum resistor is read.

[0062] S4: Using the same principle as the current passing through the R3 resistor and the current passing through the platinum resistor R2, the platinum resistor R PT Calculate according to the following formula:

[0063]

[0064] Where: R S is the resistance of the constant resistor R3.

[0065] like Figure 4 As shown in the figure, when the platinum resistor is a three-wire platinum resistor, a temperature measurement method of a multi-range platinum resistor temperature measurement circuit is:

[0066] S1~S2: Same as steps S1~S2 in the four-wire platinum resistance temperature measurement method, read the reading D0 of the temperature measurement chip.

[0067] S3: Same as step S3 in the four-wire platinum resistance temperature measurement method; read the reading D1 of the temperature measurement chip; the reading D1 is the sum of the high-end lead voltage of the platinum resistor R2 and the voltage across the platinum resistor R2;

[0068] S4: Using the principle that the current passing through the constant resistor R3 is the same as the current passing through the platinum resistor R2, we can get:

[0069]

[0070] Where: R L1 The resistance corresponding to the high-end lead voltage of the platinum resistor.

[0071] S5: Control the single-pole single-throw switch to be connected to the circuit to be measured, and connect the selection terminal 1 of the second multi-way switch to the variable resistor. At this time, the platinum resistor R2 and the variable resistor form a series circuit. Through internal calculation of the temperature measuring chip, the D2 read by the temperature measuring chip at this time is the sum of the high-end lead voltage of the platinum resistor, the voltage across the platinum resistor R2, and the low-end lead voltage of the platinum resistor; using the principle that the current passing through the constant resistor R3 is the same as the current passing through the platinum resistor R2, the formula is obtained:

[0072]

[0073] Where: R L2 The resistance corresponding to the low-end lead voltage of the platinum resistor.

[0074] From formula (2) and formula (3), we can get:

[0075] When designing the circuit, in order to minimize the lead error as much as possible, the lead lengths at both ends of the resistor are designed to be the same.

[0076] Then R L1 =R L2 (5)

[0077] The calculation formula of three-wire platinum resistance is obtained from formula (2), (4) and (5):

[0078]

[0079] By controlling whether a single-pole, single-throw switch is connected to the circuit, the resistance of the variable resistor is adjusted, making the maximum resistance of the variable resistor greater than the resistance of the platinum resistor at the maximum temperature measurement point, and the minimum resistance of the variable resistor greater than the resistance of the constant resistor. When measuring small temperature ranges, this avoids the problem of a large difference between the resistance of the variable resistor and the platinum resistor, which would cause the temperature measurement circuit to lose accuracy, thereby improving the accuracy of the temperature measurement circuit.

[0080] 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 multi-range platinum resistance temperature measurement circuit, characterized in that: The circuit includes a constant current source, a single-pole double-throw switch, a reference circuit, a circuit to be tested, and a temperature measurement chip. The fixed end of the single-pole double-throw switch is connected to the constant current source, and the two moving ends of the single-pole double-throw switch are respectively connected to the reference circuit and the circuit to be tested, so that the single-pole double-throw switch controls different circuits to work, wherein: The reference circuit includes a constant resistor and a variable resistor, the circuit to be measured includes a platinum resistor to be measured and a variable resistor shared with the reference circuit, the constant resistor and the platinum resistor have a common end and are connected in series to the variable resistor, the other ends of the constant resistor and the platinum resistor are respectively connected to the two moving ends of the single-pole double-throw switch, the maximum resistance of the variable resistor is greater than the resistance of the platinum resistor at the maximum temperature measurement point, and the minimum resistance of the variable resistor is greater than the resistance of the constant resistor. The two ends of the constant resistor are respectively connected to the two ports of the first input end of the temperature measuring chip, the two ends of the platinum resistor are respectively connected to the two ports of the second input end of the temperature measuring chip, and the two ends of the variable resistor are also respectively connected to the two ports of the reference end of the temperature measuring chip; The variable resistor is a precision resistor network, including a plurality of precision resistors connected in series, and except for the last precision resistor, each of the remaining precision resistors is controlled by a single-pole single-throw switch to control whether to be connected to the circuit, thereby realizing variable resistance of the precision resistor network; A second multi-way selection switch is further provided between the constant resistor or the platinum resistor and the precision resistor network, for controlling whether the constant resistor or the platinum resistor is connected to the precision resistor network, the second multi-way selection switch having at least three selection terminals, one of which is connected to the constant resistor, and the other two selection terminals are connected to the platinum resistor; When the platinum resistor is a four-wire system, only one of the two selection terminals connected to the platinum resistor is used; when the platinum resistor is a three-wire system, both selection terminals connected to the platinum resistor are used simultaneously; A first multi-way selection switch is further provided between the precision resistor network and the temperature measurement chip, wherein the first multi-way selection switch is used to match the resistor network formed by the precision resistors currently connected to the circuit and output the voltage of the resistor network to the reference terminal of the temperature measurement chip; The variable resistor is a potentiometer with continuously adjustable resistance.

2. The multi-range platinum resistance temperature measurement circuit according to claim 1, characterized in that: The constant resistor and the variable resistor are low temperature coefficient resistors, and the temperature coefficient thereof is at least less than 5 PPM / °C.

3. The multi-range platinum resistance temperature measurement circuit according to claim 1, characterized in that: It also includes a microcontroller connected to the temperature measurement chip and used for controlling the entire temperature measurement circuit.

4. A temperature measurement method matching a multi-range platinum resistance temperature measurement circuit, characterized in that: The method uses the multi-range platinum resistance temperature measurement circuit according to any one of claims 1 to 3; the temperature measurement method comprises the following steps: S1: After selecting the temperature measurement range, calculate the platinum resistor resistance R corresponding to the highest temperature in the range, and control the resistance of the variable resistor so that the resistance of the variable resistor connected to the circuit is greater than or equal to R; S2: Control the single-pole double-throw switch to select the reference circuit, and at the same time close the selection end of the second multi-way selection switch connected to the constant resistor, and read the temperature measurement chip reading D0; S3: Control the single-pole double-throw switch to select the circuit to be tested, and at the same time close one of the two selection terminals of the second multi-way selection switch connected to the platinum resistor, and read the temperature measurement chip reading D1; S4: When the platinum resistance is a four-wire system, calculate the platinum resistance R PT Calculate according to the following formula: ； Where Rs represents the resistance of the constant resistor, R PT Indicates the resistance value of the platinum resistor.

5. The temperature measurement method of the multi-range platinum resistance temperature measurement circuit according to claim 4, characterized in that: When the platinum resistor is a three-wire platinum resistor, after steps S1 to S3, step S4 is performed: obtaining the calculated platinum resistor R PT The calculation formula is: ； S5: Control the single-pole double-throw switch to select the circuit to be tested, and at the same time close the other of the two selection terminals connected to the platinum resistor in the second multi-way selection switch, read the temperature measurement chip reading D2, and calculate the platinum resistor lead resistance R according to the same current in step S3 and step S5. L Calculate according to the following formula: ； The calculation formula of platinum resistance is obtained by subtracting formula (2) from formula (3): ； Where Rs represents the resistance of the constant resistor.

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