CN113375826A - Temperature measurement circuit capable of eliminating line resistance influence - Google Patents

Temperature measurement circuit capable of eliminating line resistance influence Download PDF

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Publication number
CN113375826A
CN113375826A CN202110733119.XA CN202110733119A CN113375826A CN 113375826 A CN113375826 A CN 113375826A CN 202110733119 A CN202110733119 A CN 202110733119A CN 113375826 A CN113375826 A CN 113375826A
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China
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resistor
pin
operational amplifier
thermistor
inverting input
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CN202110733119.XA
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Chinese (zh)
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马嫣
杨垒
高捷
张朝
周在伟
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Shandong Renke Measurement And Control Technology Co ltd
Shandong Institute of Metrology
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Shandong Renke Measurement And Control Technology Co ltd
Shandong Institute of Metrology
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Priority to CN202110733119.XA priority Critical patent/CN113375826A/en
Publication of CN113375826A publication Critical patent/CN113375826A/en
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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
    • G01K7/22—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 non-linear resistance, e.g. thermistor
    • G01K7/24—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 non-linear resistance, e.g. thermistor in a specially-adapted circuit, e.g. bridge circuit

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)

Abstract

The invention relates to the technical field of thermistor temperature measurement, and solves the problem of temperature measurement errors caused by wire resistance in the prior art. A temperature measuring circuit capable of eliminating line resistance influence comprises a constant current source circuit, a three-wire thermistor R13 and an arithmetic circuit, wherein the arithmetic circuit comprises a resistor R5, a resistor R8, a resistor R2 and an operational amplifier U1.2, a pin 1 of the thermistor R13 is connected with a first end of a resistor R5, a second end of a resistor R5 is connected with an inverting input end of the operational amplifier U1.2, a pin 2 of the thermistor R13 is connected with a first end of the resistor R8, a second end of the resistor R8 is connected with a non-inverting input end of the operational amplifier U1.2, a pin 3 of the thermistor R13 is connected with the constant current source circuit, a first end of the resistor R2 is connected with an inverting input end of the operational amplifier U1.2, a second end of the resistor R2 is connected with an output end of the operational amplifier U1.2, resistances of the resistors R5, the resistor R2 and the resistor R8 are equal, and a first end of the resistor R5 is connected with the constant current source circuit.

Description

Temperature measurement circuit capable of eliminating line resistance influence
Technical Field
The invention relates to the technical field of thermistor temperature measurement, in particular to a temperature measurement circuit capable of eliminating the influence of wire resistance.
Background
The probe of the temperature measuring device is connected to the acquisition circuit through the wire, and for the measuring device which calculates the temperature by measuring the resistance value of the thermistor, the wire resistance of the wire can be counted into the resistance value of the thermistor, so that the composition measurement of the thermistor is inaccurate, and further the temperature calculation is inaccurate, thereby causing measurement errors.
Disclosure of Invention
The invention provides a temperature measuring circuit capable of eliminating the influence of wire resistance, and solves the problem of temperature measurement error caused by the wire resistance of a wire connected with a thermistor in the prior art.
A temperature measuring circuit capable of eliminating line resistance influence comprises a constant current source circuit, a three-wire thermistor R13 and an arithmetic circuit, wherein the arithmetic circuit comprises a resistor R5, a resistor R8, a resistor R2 and an operational amplifier U1.2, a pin 1 of the thermistor R13 is connected with a first end of a resistor R5, a second end of a resistor R5 is connected with an inverting input end of the operational amplifier U1.2, a pin 2 of the thermistor R13 is connected with a first end of the resistor R8, a second end of the resistor R8 is connected with a non-inverting input end of the operational amplifier U1.2, a pin 3 of the thermistor R13 is connected with the constant current source circuit, a first end of the resistor R2 is connected with an inverting input end of the operational amplifier U1.2, a second end of the resistor R2 is connected with an output end of the operational amplifier U1.2, resistances of the resistors R5, the resistor R2 and the resistor R8 are equal, and a first end of the resistor R5 is connected with the constant current source circuit. When the invention is used, the thermistor R13 exchanges heat with an object to be measured, the resistance value of the thermistor R13 changes along with the change of temperature, because the resistance values of the three resistors R5, R2 and R8 are equal, the output signal of the arithmetic circuit is only related to one variable of the resistance value of the thermistor R13 and is unrelated to the wire resistance of a wire connected to the thermistor R13, the interference of the wire resistance on a measurement structure is eliminated, the measurement error caused by the wire resistance is eliminated, and the measurement accuracy is improved.
Further, the constant current source circuit comprises a resistor R9 and an operational amplifier U1.1, a first end of the resistor R9 is connected with an inverting input end of the operational amplifier U1.1, a second end of the resistor R9 is grounded, the inverting input end of the operational amplifier U1.1 is connected with a pin 3 of the thermistor R13, a non-inverting input end of the operational amplifier U1.1 is connected with a reference voltage circuit, and an output end of the operational amplifier U1.1 is connected with a first end of the resistor R5. The stable current generated by the constant current source circuit enables the voltage of the thermistor R13 to be only related to the resistance value of the thermistor, so that the resistance value of the thermistor R13 can be calculated through the output of the operation circuit, and the temperature of the thermistor can be further calculated.
Further, the reference voltage circuit comprises a resistor R1 and a voltage reference chip U4, a first end of the resistor R1 is connected with the 3.3V direct current supply circuit, a second end of the resistor R1 is connected with a cathode of the voltage reference chip U4, a reference electrode of the voltage reference chip U4 is connected with a second end of the resistor R1, an anode of the voltage reference chip U4 is grounded, and a second end of the resistor R1 is connected with a non-inverting input end of the operational amplifier U1.1.
Further, the AD conversion circuit comprises an AD conversion circuit and a singlechip U9, the AD conversion circuit comprises a capacitor C17, an AD conversion chip U5, a capacitor C2 and a resistor R12, a pin 1 of the AD conversion chip U5 is connected with a second end of the resistor R1, a pin 2 of the AD conversion chip U5 is grounded, a first end of a capacitor C17 is connected with a pin 1 of the AD conversion chip U5, a second end of a capacitor C17 is connected with a pin 2 of the AD conversion chip U5, a pin 3 of the AD conversion chip U5 is connected with an inverting input end of the amplifier U1.1, a pin 4 of the AD conversion chip U5 is connected with an output end of the amplifier U1.2, a pin 5 of the AD conversion chip U5 is connected with a pin 27 of the singlechip U9, a pin 6 of the AD conversion chip U5 is connected with a pin 26 of the singlechip U9, a first end of the resistor R12 is connected with a pin 6 of the AD conversion chip U5, a second end of the resistor R12 is connected with a pin 3.V 3 and a DC power supply circuit V5733, the DC conversion chip U5733.3 is connected with the DC conversion chip U5733, a first terminal of the capacitor C2 is connected to the 7 pin of the AD conversion chip U5, and a second terminal of the capacitor C2 is grounded.
Further, the thermistor comprises a positive temperature coefficient platinum thermistor.
According to the technical scheme, the invention has the following advantages:
when the invention is used, the thermistor R13 exchanges heat with an object to be measured, the resistance value of the thermistor R13 changes along with the change of temperature, because the resistance values of the three resistors R5, R2 and R8 are equal, the output signal of the arithmetic circuit is only related to one variable of the resistance value of the thermistor R13 and is unrelated to the wire resistance of a wire connected to the thermistor R13, the interference of the wire resistance on a measurement structure is eliminated, the measurement error caused by the wire resistance is eliminated, and the measurement accuracy is improved.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts.
FIG. 1 is a circuit diagram of the present invention;
FIG. 2 is a wiring diagram of a thermistor R13 according to the present invention;
FIG. 3 is a diagram of an AD conversion circuit according to the present invention;
fig. 4 is a wiring diagram of the singlechip U9 of the invention.
Detailed Description
In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the embodiments described below are only a part of embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given in the present patent without making any creative effort, shall fall within the scope of protection of the present patent.
Example 1
As shown in fig. 1 to 4, the temperature measuring circuit capable of eliminating the influence of the line resistance includes a constant current source circuit, a three-wire thermistor R13, an arithmetic circuit, an AD conversion circuit, and a single chip microcomputer U9, where the thermistor R13 is specifically PT100, and PT100 is a positive temperature coefficient platinum thermistor. The resistor R14, the resistor R15 and the resistor R16 are resistors of lead wires connected with the thermistor R13, and in practice, the three lead wires of the PT100 are of the same length, the same material and the same diameter, so that the resistors have the same resistance, that is, the resistances of the resistor R14, the resistor R15 and the resistor R16 are equal.
The operational circuit comprises a resistor R5, a resistor R8, a resistor R2 and an operational amplifier U1.2, wherein a pin 1 of a thermistor R13 is connected with a first end of a resistor R5, a second end of the resistor R5 is connected with an inverting input end of the operational amplifier U1.2, a pin 2 of a thermistor R13 is connected with a first end of a resistor R8, a second end of the resistor R8 is connected with a non-inverting input end of the operational amplifier U1.2, a pin 3 of the thermistor R13 is connected with a constant current source circuit, a first end of the resistor R2 is connected with an inverting input end of the operational amplifier U1.2, a second end of the resistor R2 is connected with an output end of the operational amplifier U1.2, resistance values of the resistor R5, the resistor R2 and the resistor R8 are equal, and a first end of the resistor R5 is connected with the constant current source circuit. When the invention is used, the thermistor R13 exchanges heat with an object to be measured, the resistance value of the thermistor R13 changes along with the change of temperature, because the resistance values of the three resistors R5, R2 and R8 are equal, the output signal of the arithmetic circuit is only related to one variable of the resistance value of the thermistor R13 and is unrelated to the wire resistance of a wire connected to the thermistor R13, the interference of the wire resistance on a measurement structure is eliminated, the measurement error caused by the wire resistance is eliminated, and the measurement accuracy is improved.
The constant current source circuit comprises a resistor R9 and an operational amplifier U1.1, the operational amplifier U1.1 and the operational amplifier U1.2 adopt TP5532, the first end of the resistor R9 is connected with the inverting input end of the operational amplifier U1.1, the second end of the resistor R9 is grounded, the inverting input end of the operational amplifier U1.1 is connected with the 3 pins of the thermistor R13, the non-inverting input end of the operational amplifier U1.1 is connected with a reference voltage circuit, and the output end of the operational amplifier U1.1 is connected with the first end of the resistor R5. The stable current generated by the constant current source circuit enables the voltage of the thermistor R13 to be only related to the resistance value of the thermistor, so that the resistance value of the thermistor R13 can be calculated through the output of the operation circuit, and the temperature of the thermistor can be further calculated.
The reference voltage circuit comprises a resistor R1 and a voltage reference chip U4, wherein the first end of the resistor R1 is connected with the 3.3V direct current supply circuit, the second end of the resistor R1 is connected with the cathode of the voltage reference chip U4, the reference pole of the voltage reference chip U4 is connected with the second end of the resistor R1, the anode of the voltage reference chip U4 is grounded, and the second end of the resistor R1 is connected with the non-inverting input end of the operational amplifier U1.1.
The AD conversion circuit comprises a capacitor C17, an AD conversion chip U5, a capacitor C2 and a resistor R12, the AD conversion chip U5 adopts CS1237, a pin 1 of the AD conversion chip U5 is connected with a second end of the resistor R1, a pin 2 of the AD conversion chip U5 is grounded, a first end of the capacitor C17 is connected with a pin 1 of the AD conversion chip U5, a second end of the capacitor C17 is connected with a pin 2 of the AD conversion chip U5, a pin 3 of the AD conversion chip U5 is connected with an inverting input end of the operational amplifier U1.1, a pin 4 of the AD conversion chip U5 is connected with an output end of the operational amplifier U1.2, a pin 5 of the AD conversion chip U5 is connected with a pin 27 of the singlechip U5, a pin 6 of the AD conversion chip U5 is connected with a pin 26 of the singlechip U9, a first end of the resistor R12 is connected with a pin 6 of the AD conversion chip U5, a second end of the resistor R12 is connected with a pin 3.3V 3 and a direct current supply circuit of the AD conversion chip U583 is connected with a direct current supply circuit, a first terminal of the capacitor C2 is connected to the 7 pin of the AD conversion chip U5, and a second terminal of the capacitor C2 is grounded.
The working principle is as follows: the 2.5V reference voltage output by the voltage reference chip U4 is applied to the non-inverting input terminal of the operational amplifier U1.1, the feedback loop is composed of a resistor R9 and a thermistor R13, and the amplification factor is
Figure DEST_PATH_IMAGE002
Wherein R is the resistance of the resistor R14, the resistor R15 and the resistor R16.
The output voltage at the output end of the operational amplifier U1.1 is
Figure DEST_PATH_IMAGE004
Where Ui is the voltage VREF at the second terminal of resistor R1.
The first end of the wire resistor R14 is connected with the thermistor R13, the first end of the wire resistor R15 is connected with the thermistor R13, and the voltage Uo1 at the second end of the wire resistor R14 and the voltage Uo2 at the second end of the wire resistor R15 are respectively
Figure DEST_PATH_IMAGE006
Figure DEST_PATH_IMAGE008
At this time
PT_OUT=
Figure DEST_PATH_IMAGE010
The amplification factor of the non-inverting input end of the operational amplifier U1.2 is
Figure DEST_PATH_IMAGE012
The inverse input end of the operational amplifier U1.2 has the amplification factor of
Figure DEST_PATH_IMAGE014
The output voltage of the operational amplifier U1.2 is
Figure DEST_PATH_IMAGE016
R9 and Ui are both constant values, PT _ MIDOUT is only related to the variable R13, and R13 is the resistance value of the thermistor R13.
The terms "first," "second," "third," "fourth," and the like in the description and in the claims and drawings, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (5)

1. A temperature measuring circuit capable of eliminating line resistance influence is characterized by comprising a constant current source circuit, a three-wire thermistor R13 and an arithmetic circuit, wherein the arithmetic circuit comprises a resistor R5, a resistor R8, a resistor R2 and an operational amplifier U1.2, a pin 1 of the thermistor R13 is connected with a first end of a resistor R5, a second end of a resistor R5 is connected with an inverting input end of the operational amplifier U1.2, a pin 2 of the thermistor R13 is connected with a first end of the resistor R8, a second end of the resistor R8 is connected with a non-inverting input end of the operational amplifier U1.2, a pin 3 of the thermistor R13 is connected with the constant current source circuit, a first end of the resistor R2 is connected with an inverting input end of the operational amplifier U1.2, a second end of the resistor R2 is connected with an output end of the operational amplifier U1.2, resistors R5, R2 and R8 are equal in resistance, and a first end of the resistor R5 is connected with the constant current source circuit.
2. The temperature measuring circuit capable of eliminating the influence of the wire resistance according to claim 1, wherein the constant current source circuit comprises a resistor R9 and an operational amplifier U1.1, a first end of the resistor R9 is connected with an inverting input end of the operational amplifier U1.1, a second end of the resistor R9 is grounded, the inverting input end of the operational amplifier U1.1 is connected with the 3 pin of the thermistor R13, a non-inverting input end of the operational amplifier U1.1 is connected with a reference voltage circuit, and an output end of the operational amplifier U1.1 is connected with a first end of the resistor R5.
3. The temperature measuring circuit capable of eliminating the influence of the wire resistance according to claim 2, wherein the reference voltage circuit comprises a resistor R1 and a voltage reference chip U4, a first end of the resistor R1 is connected to the 3.3V dc supply circuit, a second end of the resistor R1 is connected to a cathode of the voltage reference chip U4, a reference electrode of the voltage reference chip U4 is connected to a second end of the resistor R1, an anode of the voltage reference chip U4 is grounded, and a second end of the resistor R1 is connected to a non-inverting input terminal of the operational amplifier U1.1.
4. The temperature measuring circuit capable of eliminating the influence of line resistance according to claim 1, 2 or 3, further comprising an AD conversion circuit and a single chip microcomputer U9, wherein the AD conversion circuit comprises a capacitor C17, an AD conversion chip U5, a capacitor C2 and a resistor R12, a pin 1 of the AD conversion chip U5 is connected with a second end of the resistor R1, a pin 2 of the AD conversion chip U5 is grounded, a first end of the capacitor C17 is connected with a pin 1 of the AD conversion chip U5, a second end of the capacitor C17 is connected with a pin 2 of the AD conversion chip U5, a pin 3 of the AD conversion chip U5 is connected with an inverting input end of the operational amplifier U1.1, a pin 4 of the AD conversion chip U5 is connected with an output end of the operational amplifier U1.2, a pin 5 of the AD conversion chip U5 is connected with a pin 27 of the U9, a pin 6 of the AD conversion chip U5 is connected with a pin 26 of the single chip microcomputer U9, a first end of the resistor R12 is connected with the pin 5 of the single chip U5, the second end of the resistor R12 is connected with a 3.3V direct current supply circuit, the pin 7 of the AD conversion chip U5 is connected with the 3.3V direct current supply circuit, the first end of the capacitor C2 is connected with the pin 7 of the AD conversion chip U5, and the second end of the capacitor C2 is grounded.
5. The temperature measuring circuit capable of eliminating the influence of the wire resistance according to claim 1, 2 or 3, wherein the thermistor comprises a positive temperature coefficient platinum thermistor.
CN202110733119.XA 2021-06-30 2021-06-30 Temperature measurement circuit capable of eliminating line resistance influence Withdrawn CN113375826A (en)

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CN202110733119.XA CN113375826A (en) 2021-06-30 2021-06-30 Temperature measurement circuit capable of eliminating line resistance influence

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Application publication date: 20210910