CN110926644B - Three-wire system temperature measurement circuit - Google Patents
Three-wire system temperature measurement circuit Download PDFInfo
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- CN110926644B CN110926644B CN201911308657.3A CN201911308657A CN110926644B CN 110926644 B CN110926644 B CN 110926644B CN 201911308657 A CN201911308657 A CN 201911308657A CN 110926644 B CN110926644 B CN 110926644B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
- G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
- G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
- G01K7/20—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit
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- Measuring Temperature Or Quantity Of Heat (AREA)
Abstract
The invention discloses a three-wire temperature measuring circuit, which comprises 1) a voltage division circuit part consisting of a three-wire temperature sensor PT0, a relay and a resistor R0; 2) a subtraction amplification circuit section which performs operational amplification on the divided voltage; 3) and the MCU is used for performing analog-to-digital conversion on the input signal of the IN0 and controlling the K1 to open and close. Three cables connected into the three-wire temperature measuring resistor are identical in material, wire diameter and length; the relay controls the three-wire access state of the temperature sensor PT0, calculates the internal resistance of the connecting cable according to the data output difference of the K1 in two different access states of open loop and closed loop, and then carries out temperature compensation according to the internal resistance value. The invention has the advantages of scientific and reasonable structure, safe and convenient use, simple circuit, wide range of measurement and suitability for popularization and use.
Description
Technical Field
The invention relates to the technical field of temperature measuring circuits, in particular to a three-wire temperature measuring circuit.
Background
The thermal resistor is a commonly used temperature sensor, such as PT100, NTC30, etc., and the resistance value of the thermal resistor is monotonous with the measurement stability, so that the temperature to be measured can be calculated according to the resistance value of the thermal resistor. However, when the distance between the sensor mounting position and the measuring instrument is long, the wire resistance of the connection cable causes a large measurement error. A three-wire wiring method may be employed in order to eliminate the influence of wiring resistance.
The general practice is to adopt a single constant current source or a double constant current source method, and the Chinese patent No. ZL03263202.9 discloses a thermal resistance temperature measuring circuit, namely a single constant current source method, but most of the methods are complex in circuit and relatively small in measuring range.
Disclosure of Invention
The invention provides a three-wire temperature measuring circuit which can effectively solve the problems that most circuits are complex and the measuring range is relatively small in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: the circuit comprises 1) a voltage division circuit part consisting of a three-wire temperature sensor PT0, a relay and a resistor R0; 2) a subtraction amplification circuit section which performs operational amplification on the divided voltage; 3) MCU for analog-to-digital conversion of IN0 input signal and controlling K1 to open and close;
three cables connected with the three-wire temperature measuring resistor are required to be identical in material, wire diameter and length; the relay controls the three-wire access state of the temperature sensor PT0, calculates the internal resistance of the connecting cable according to the data output difference of the K1 in two different access states of open loop and closed loop, and then carries out temperature compensation according to the internal resistance value. Compared with the prior art, the invention has the beneficial effects that: the invention has the advantages of scientific and reasonable structure, safe and convenient use, simple circuit, wide range of measurement and suitability for popularization and use.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
In the drawings:
fig. 1 is a schematic diagram of the circuit structure of the present invention.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
Example (b): as shown in fig. 1, the invention provides a technical solution, a three-wire temperature measuring circuit, which comprises a temperature sensor PT0, wherein the temperature sensor PT0 is connected in parallel with a normally open contact of an intermediate relay K1 and a resistor R0, a coil of the intermediate relay K1 is controlled to be closed through an end SW0, and the other end of the normally open contact of the intermediate relay K1 is connected in series with the resistor R0;
the resistor R0 is connected with the resistor R3 in series, the resistor R1, the resistor R2, the resistor R3, the resistor R4 and the LM358 operational amplifier form a subtraction amplifier, and the resistor R4 is connected with the voltage regulator tube D1 in series;
the resistor R1 and the resistor R2 are connected IN series, the output end of the LM358 operational amplifier is connected IN series with the resistor R5, and the output signal end is IN0 and is connected IN parallel with the capacitor C1.
According to the technical scheme, the resistor R0, the voltage regulator tube D1, the resistor R4, the LM358 operational amplifier and the capacitor C1 are all grounded.
According to the technical scheme, in one embodiment, the coil of the intermediate relay K1 has 5V voltage, the voltage of the resistor R1 is 2.38V, and the content of the capacitor C1 is 0.1 uF.
According to the technical scheme, the PT0 is a PT100 temperature sensor, and the resistance characteristic of the PT100 is that 135 degrees are 151R, -30 degrees are 88.04R, and 300 degrees are 213.79R (R represents ohm); k1 is a relay with model number of HF46F-5V,
the SW0 end is used for controlling the closing, and according to the technical scheme, R0 is 200R; the R1, R2, R3, R4 and LM358 operational amplifier form a subtraction amplifier; the output signal end is IN0, and is butted with an ADC sampling port (limit value is 3.3V), one embodiment is a selection chip STM32F103C8T6, the chip is provided with a plurality of ADC multichannel samplers, and meanwhile, the IO end output controls SW0 high and low level through triode amplification, so that the on and off of a relay are controlled.
According to the technical scheme, the R1, the R2, the R3, the R4 and the LM358 operational amplifier form a subtraction amplifier, and the requirements that R1 is equal to R2, R3 is equal to R4, R1 is equal to R2 is equal to 1:3.0 are met; the 2.38V voltage at the input end of the subtraction amplifier R1 is formed by a 220R and a 200R resistor voltage division 5.0V power supply; the resistance of PT100 at 300 degrees is 213.79R, the IN0 output is close to 0;
according to the technical scheme, the zero point needs to be corrected before leaving a factory;
PT100 resistance 213.79R at 300 degrees, 2.42V at the input end of R3;
PT100 resistance 88.04R at 30 degrees, 3.47V at input R3;
according to the technical scheme, the access state of the three wires is controlled by the relay, the internal resistance of the connecting cable is calculated according to the difference of data output in different access states, and then temperature compensation is carried out according to the internal resistance.
According to the technical scheme, the internal resistance of the cable is calculated as follows:
1) a three-wire system temperature sensor PT0 is connected according to the figure 1, and three wires of the three-wire cable are required to be the same in quality and diameter;
2) opening the relay K1, and measuring the voltage u1 at the input end of the R3;
3) closing the relay K1, measuring the voltage u1 at the input end of R3;
4) assuming that the internal resistance of each wire in the cable is r, the resistance value of PT100 is Rx;
therefore, there is a calculation formula:
u1/R0＝5.0/(2*r+Rx+R0)；u2/R0＝5.0/(1.5*r+Rx+R0)；
therefore, there are: r2 (5.0/u1-5.0/u2) R0;
rx 5.0R 0/u 2-1.5R-R0 can be calculated according to the calculated R;
therefore, the K1 can be kept closed in the test, the voltage u2 at the input end of the R3 is measured in real time, and then the resistance Rx of the PT100 is accurately calculated according to the formula so as to calculate the measured temperature, wherein the calculation is finished by an STM32F103C8T6 chip in the embodiment.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. A three-wire system temperature measurement circuit is characterized in that: comprises 1) a voltage division circuit part consisting of a three-wire temperature sensor PT0, an intermediate relay K1 and a resistor R0; 2) a subtraction amplification circuit section which performs operational amplification on the divided voltage; 3) the MCU is used for carrying out analog-to-digital conversion on an IN0 input signal and controlling the opening and closing of the intermediate relay K1;
three cables connected into the three-wire temperature measuring resistor are identical in material, wire diameter and length; the intermediate relay K1 controls the access state of three wires of the temperature sensor PT0, the internal resistance of the connecting cable is calculated according to the difference of data output of the intermediate relay K1 in two different access states of open loop and closed loop, and then temperature compensation is carried out according to the internal resistance;
the resistor R1 and the resistor R2 are connected IN series, the output end of the LM358 operational amplifier is connected with the resistor R5 IN series, and the output signal end is IN0 and is connected with the capacitor C1 IN parallel;
the resistor R0, the voltage regulator tube D1, the resistor R4, the LM358 operational amplifier and the capacitor C1 are all grounded;
the coil of the intermediate relay K1 has 5V voltage;
PT0 is a PT100 temperature sensor, K1 is an intermediate relay, and the model is HF 46F-5V;
the SW0 end of the intermediate relay K1 is controlled to be closed, and the R1, the R2, the R3, the R4 and the LM358 operational amplifier form a subtraction amplifier; the output signal end is IN0, the sampling port of the ADC is butted, the STM32F103C8T6 chip is provided with a plurality of samplers with multiple ADC channels, meanwhile, the IO end outputs, and the SW0 high and low levels of the intermediate relay K1 are controlled through triode amplification, so that the opening and closing of the intermediate relay K1 are controlled;
the internal resistance of the cable is calculated as follows:
1) a three-wire temperature sensor PT0 is connected, and three wires of the three-wire cable are required to be the same in quality and diameter;
2) disconnecting the intermediate relay K1, and measuring the voltage u1 of the input end of the resistor R3;
3) closing the intermediate relay K1, and measuring the voltage u2 at the input end of the resistor R3;
4) assuming that the internal resistance of each wire in the cable is r, the resistance value of PT100 is Rx;
therefore, there is a calculation formula:
u1/R0＝5.0/(2*r+Rx+R0)；u2/R0＝5.0/(1.5*r+Rx+R0)；
therefore, there are: r2 (5.0/u1-5.0/u2) R0;
rx 5.0R 0/u 2-1.5R-R0 can be calculated according to the calculated R;
therefore, the intermediate relay K1 can be kept closed in the test, the voltage u2 at the input end of the resistor R3 can be measured in real time, and the resistance Rx of the PT100 can be accurately calculated according to the formula, so that the measured temperature can be calculated.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201911308657.3A CN110926644B (en) | 2019-12-18 | 2019-12-18 | Three-wire system temperature measurement circuit |
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| CN201911308657.3A CN110926644B (en) | 2019-12-18 | 2019-12-18 | Three-wire system temperature measurement circuit |
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| CN110926644A CN110926644A (en) | 2020-03-27 |
| CN110926644B true CN110926644B (en) | 2021-11-30 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| DE10359988A1 (en) * | 2003-12-19 | 2005-07-14 | Siemens Ag | Measuring device, in particular temperature transmitter |
| CN201464101U (en) * | 2009-07-28 | 2010-05-12 | 依诺维信科技（天津）有限公司 | Bridge cable force temperature sensor |
| CN201575872U (en) * | 2009-12-03 | 2010-09-08 | 上海梅山钢铁股份有限公司 | Compensating circuit of thermal resistor capable of implementing temperature measurement correction |
| CN203241165U (en) * | 2013-05-17 | 2013-10-16 | 山东神戎电子股份有限公司 | Thermal resistor temperature measurement circuit based on three-wire system |
| CN205940797U (en) * | 2016-07-20 | 2017-02-08 | 武汉纵畅信息技术有限公司 | Range ability adjustable temperature sensor treatment circuit |
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