A cold junction simulation compensation circuit

Abstract

The application provides a cold end analog compensation circuit for measuring the cold end temperature of a thermocouple. The cold end analog compensation circuit comprises: a first operational amplifier calculation circuit receiving a cold end temperature signal of the thermocouple and a first reference voltage to perform subtraction operation and output a first output signal, for eliminating the direct current bias voltage of the cold end temperature signal; a second operational amplifier calculation circuit receiving a temperature difference signal of the thermocouple and a second reference voltage to perform addition operation and output a second output signal, for making the second output signal in a positive voltage output range; and a third operational amplifier calculation circuit receiving the first output signal and the second output signal to perform weighted subtraction, for outputting a measured temperature signal whose voltage changes in proportion to the measured temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cold end compensation of thermocouple, and particularly relates to a cold end simulation compensation circuit. BACKGROUND

[0002] In temperature measurement applications, thermocouples are widely used due to their robustness, reliability and fast response. The structure of thermocouples is simple and can be designed according to specific applications. For example, in the food industry, it can be easily inserted into the product; in the process of metal heat treatment, it can be welded on the product.

[0003] In theory, the cold end of the thermocouple is measured at 0℃. However, usually the instrument is at room temperature when measuring, which results in that the cold end of the thermocouple cannot reach exactly 0℃. Since the temperature measurement principle of the thermocouple is to sum the cold end temperature of the thermocouple and the temperature corresponding to the measured potential difference between the cold and hot ends of the thermocouple to obtain the temperature of the hot end of the thermocouple, that is, the absolute temperature of the measured object, the above-mentioned cold end of the thermocouple cannot reach 0℃, which results in that the measured absolute temperature of the measured object is not equal to its actual temperature. This is the influence of the cold end temperature fluctuation on the measurement result of the thermocouple. In order to reduce the error, the compensation measure is cold end temperature compensation.

[0004] In the prior art, the cold end compensation technology mainly includes ice bath method, cold end temperature measurement method and compensation bridge method. For the cold end temperature measurement method, the existing cold end temperature measurement chip mostly includes a single-chip microcomputer, and outputs a digital signal through the operation of the single-chip microcomputer, such as a temperature measurement chip of MAX6675 type. However, in order to reduce the cost and the package, in some products that do not include a single-chip microcomputer, the cold end temperature measurement chip needs to be able to directly output an analog signal. In the current technology, a temperature measurement chip of LTC2997 type can realize similar functions, but the price of this type of chip is relatively high, and the package is relatively large.

[0005] In summary, in order to solve the above problems in the prior art, the technical field urgently needs a cold end compensation circuit scheme, which can overcome the deficiency that the thermocouple cannot measure the absolute temperature of the object without the participation of a single-chip microcomputer in processing digital signals, so that after cold end compensation, the circuit can output the absolute temperature signal of the measured object in the form of an analog signal. SUMMARY

[0006] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0007] To solve the above problems in the prior art, one aspect of the present application provides a cold end analog compensation circuit for measuring the cold end temperature of a thermocouple. The cold end analog compensation circuit comprises: a first operational amplifier calculation circuit receiving a cold end temperature signal of the thermocouple and a first reference voltage to perform subtraction operation and output a first output signal, for eliminating the direct current bias voltage of the cold end temperature signal; a second operational amplifier calculation circuit receiving a temperature difference signal of the thermocouple and a second reference voltage to perform addition operation and output a second output signal, for making the second output signal in a positive voltage output range; and a third operational amplifier calculation circuit receiving the first output signal and the second output signal to perform weighted subtraction, for outputting a measured temperature signal whose voltage changes in proportion to the measured temperature. By using the above cold end analog compensation circuit, the deficiency that the thermocouple cannot measure the absolute temperature of an object can be overcome without the need for a single-chip microcomputer to process digital signals, so that after cold end compensation, the circuit can output the absolute temperature signal of the measured object in the form of an analog signal.

[0008] In one embodiment, the first operational amplifier calculation circuit in the above cold end analog compensation circuit performs scaling on the cold end temperature signal to output a first output signal whose voltage changes linearly with respect to the cold end temperature; the second operational amplifier calculation circuit performs scaling on the temperature difference signal to output a second output signal whose voltage changes linearly with respect to the temperature difference signal, wherein the slope of the second output signal is consistent with the slope of the first output signal, and the third operational amplifier calculation circuit performs subtraction operation on the second output signal and the first output signal with a weighting coefficient ratio of 1:1 to output a measured temperature signal whose voltage changes in proportion to the measured temperature.

[0009] In one embodiment, the slope of the second output signal in the above cold end analog compensation circuit is inconsistent with the slope of the first output signal, and the third operational amplifier calculation circuit performs weighted subtraction on the second output signal and the first output signal, wherein the weighting coefficient ratio of the second output signal and the first output signal is inversely proportional to the slope ratio of the second output signal and the first output signal, so that the coefficient of the cold end temperature signal and the coefficient of the temperature difference signal are consistent.

[0010] In one embodiment, the first operational amplifier calculation circuit in the above cold end analog compensation circuit comprises a first differential proportional amplification circuit, the inverting input terminal of the first differential proportional amplification circuit receives the cold end temperature signal, and the non-inverting input terminal receives the first reference voltage, wherein the first reference voltage is equal to the direct current bias voltage of the cold end temperature signal, and the cold end temperature signal is greater than the first reference voltage so that the first output signal is in a negative voltage output range.

[0011] In an embodiment, the slope of the cold junction temperature signal in the cold junction analog compensation circuit varies proportionally with the thermocouple cold junction temperature, and the direct current bias voltage depends on the electrical characteristics of a temperature sensing chip used to measure the cold junction temperature signal.

[0012] In an embodiment, the second operational amplifier calculation circuit in the cold junction analog compensation circuit includes a second differential proportional amplification circuit, the non-inverting input of the second differential proportional amplification circuit receives the temperature difference signal and the second reference voltage, the inverting input of the second differential proportional amplification circuit is connected to a resistor and the other end of the resistor is grounded, and the second differential proportional amplification circuit performs same-direction addition on the temperature difference signal and the second reference voltage, wherein the second reference voltage is set so that the second output signal is in a positive voltage output range.

[0013] In an embodiment, the third operational amplifier calculation circuit in the cold junction analog compensation circuit includes a third differential proportional amplification circuit, the inverting input of the third differential proportional amplification circuit receives the first output signal, and the non-inverting input of the third differential proportional amplification circuit receives the second output signal, and the third differential proportional amplification circuit performs weighted subtraction on the first output signal and the second output signal to obtain a measured temperature signal whose voltage varies proportionally with the measured temperature. BRIEF DESCRIPTION OF DRAWINGS

[0014] The above features and advantages of the present application can be better understood by reading the following detailed description of embodiments of the application in conjunction with the drawings, in which each component is not necessarily drawn to scale and components with similar relative functions or characteristics can have the same or similar reference numbers.

[0015] Figure 1 A circuit diagram of a cold junction analog compensation circuit according to an aspect of the present application is shown.

[0016] REFERENCE NUMERALS:

[0017] 100: cold junction compensation circuit;

[0018] 110: first differential proportional amplification circuit;

[0019] 120: second differential proportional amplification circuit;

[0020] 130: third differential proportional amplification circuit;

[0021] 111: first operational amplifier;

[0022] 121: second operational amplifier;

[0023] 131: third operational amplifier;

[0024] R1: first resistor;

[0025] R2: second resistor;

[0026] R3: third resistor;

[0027] R4: first feedback resistor;

[0028] R5: fifth resistor;

[0029] R6: sixth resistor;

[0030] R7: seventh resistor;

[0031] R8: third feedback resistor;

[0032] R9: second feedback resistor;

[0033] R10: tenth resistor;

[0034] R11: eleventh resistor;

[0035] R12: twelfth resistor;

[0036] VS1: negative power supply of first operational amplifier;

[0037] VS2: positive power supply of first operational amplifier;

[0038] VS3: negative power supply of second operational amplifier;

[0039] VS4: positive power supply of second operational amplifier;

[0040] VS5: negative power supply of third operational amplifier;

[0041] VS6: positive power supply of third operational amplifier;

[0042] VS7: first reference voltage; and

[0043] VS8: second reference voltage. DETAILED DESCRIPTION

[0044] The advantages and features of the present application will become apparent from specific non-limiting embodiments described hereinafter in conjunction with the accompanying drawings in which:

[0045] In the description of the present application, it should be noted that unless specifically stated and limited otherwise, the terms "mounting", "connected", "connecting" should be construed broadlyly, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0046] In addition, "upper", "lower", "left", "right", "top", "bottom", "horizontal", "vertical" used in the following description should be understood as the orientation shown in the section and the related drawings. The relative terms are only for the convenience of description, and do not mean that the device described thereby should be manufactured or operated in a particular orientation, and therefore should not be understood as a limitation on the present application.

[0047] It can be understood that although the terms "first", "second", "third" and the like are used herein to describe various components, regions, layers and / or parts, these components, regions, layers and / or parts should not be limited by these terms, and these terms are only used to distinguish different components, regions, layers and / or parts. Therefore, the first component, region, layer and / or part discussed below can be referred to as the second component, region, layer and / or part without departing from some embodiments of the present application.

[0048] As described above, the temperature measurement of the thermocouple is measured at 0℃ as the standard of the cold end. However, usually the instrument is below room temperature when measuring, which results in that the cold end of the thermocouple cannot reach exactly 0℃, so that the absolute temperature of the measured object measured by the thermocouple is not equal to its actual temperature, and cold end compensation needs to be performed. In the prior art, the chip for measuring the cold end temperature in the method of cold end compensation mostly includes a single-chip microcomputer, and outputs a digital signal through the operation of the single-chip microcomputer. However, in order to reduce the cost and the package, in some products that do not include a single-chip microcomputer, the cold end temperature measurement chip needs to be able to directly output an analog signal.

[0049] In order to solve the above problems existing in the prior art, the present application provides a cold end analog compensation circuit, which can overcome the deficiency that the thermocouple cannot measure the absolute temperature of an object without the participation of a single-chip microcomputer in processing a digital signal, so that after cold end compensation, the circuit can output the absolute temperature signal of the measured object in the form of an analog signal.

[0050] For details, please refer to Figure 1 , Figure 1 The circuit diagram of the cold end analog compensation circuit according to an aspect of the present application is shown.

[0051] In some embodiments of the present application, asFigure 1 The cold end analog compensation circuit 100 shown includes a first operational amplifier calculation circuit, a second operational amplifier calculation circuit, and a third operational amplifier calculation circuit. The cold end analog compensation circuit 100 can be used to measure the hot end temperature of a plurality of different types of thermocouples, such as the hot end temperature of a K-type thermocouple, an S-type thermocouple, and the like.

[0052] In order to more clearly introduce the cold end analog compensation circuit 100 protected by the present application, the following will introduce in detail an embodiment in which the compensation circuit 100 is applied to cold end compensation for temperature measurement of a K-type thermocouple.

[0053] In the embodiment shown in the present application Figure 1 In the embodiment shown in the present application

[0054] Those skilled in the art should understand that the type of temperature measurement chip used in the present application is not limited to the type mentioned in the above embodiment, and those skilled in the art can select different types of temperature measurement chips according to the type of thermocouple to be measured in actual application, for example, the LM20 series of Texas Instruments and the MCP9700 of MICROCHIP can be used to measure the cold end temperature of different types of thermocouples and output the cold end temperature signal of the thermocouple.

[0055] In the embodiment, the temperature measurement chip TC1047A can be placed at the cold end of the K-type thermocouple, about 20 mm away from the cold end of the K-type thermocouple, and the TC1047A can more accurately measure the cold end temperature of the K-type thermocouple. The signal output by the TC1047A is y=500mV+10mV*T1, where T1 is the current temperature of the TC1047A, that is, the current temperature of the cold end of the K-type thermocouple measured by the temperature measurement chip, 500mV is the direct current bias of the temperature measurement chip TC1047A, and 10mV / ℃ is the output voltage slope. The cold end temperature signal of the K-type thermocouple is the signal y=500mV+10mV*T1 output by the TC1047A.

[0056] Generally, temperature sensing chips require a larger signal output voltage slope to improve accuracy. Therefore, the cold junction temperature signal of the K-type thermocouple output by the TC1047A temperature sensing chip can be reduced by a certain factor through the first operational amplifier calculation circuit, that is, the slope of the cold junction temperature signal is adjusted, and a subtraction operation is performed with the first reference voltage to output the first output signal, which is used to eliminate the DC bias voltage of the cold junction temperature signal.

[0057] like Figure 1 As shown, in some embodiments of the present invention, the first operational amplifier calculation circuit can be a differential proportional amplifier circuit. The cold junction temperature signal output by TC1047A is used as the first input signal Vin1, which is connected to the inverting input terminal of the first operational amplifier 111 in the first differential proportional amplifier circuit 110 through the third resistor R3. The first reference voltage VS7 is used as the second input signal Vin2, which is connected to the non-inverting input terminal of the first operational amplifier 111 through the first resistor R1. The output terminal of the first operational amplifier 111 is connected back to its inverting input terminal through the first feedback resistor R4.

[0058] In practical applications, the inherent structure of operational amplifiers can lead to a bias voltage at their input terminals. This bias voltage can easily interfere with or overwhelm small signals during transmission. Generally, the first reference voltage Vin1 can be set equal to the DC bias voltage in the temperature sensing chip. The cold junction temperature signal can be set to be greater than the first reference voltage Vin1, ensuring that the first output signal of the first differential proportional amplifier circuit 110 is in the negative voltage output range for subsequent calculations. Based on the operating principle of the first differential proportional amplifier circuit 110, the second input signal Vin2 (first reference voltage VS7) is subtracted from the first input signal Vin1 (cold junction temperature signal), thereby reducing the DC bias in the temperature sensing chip using the applied first reference voltage VS7.

[0059] To ensure that the resistances of the two input terminals of the first operational amplifier 111 in the first differential proportional amplifier circuit 110 to ground are balanced, and to avoid reducing the common-mode rejection ratio, the first resistor R1 can be set to be equal to the third resistor R3, and the second resistor R2 can be set to be equal to the first feedback resistor R4. That is, the ratio of the second resistor R2 to the first resistor R1 is the same as the ratio of the first feedback resistor R4 to the third resistor R3.

[0060] In some embodiments, the resistance of the first resistor R1 can be set to 25k, the resistance of the second resistor R2 can be set to 3.9k, the resistance of the third resistor R3 can be set to 25k, and the resistance of the first feedback resistor R4 can be set to 3.9k. The inverting input terminal of the first differential proportional amplification circuit 110 is connected to the cold end temperature signal Vin1 of the K-type thermocouple, which is 500mV+10mV×T1, and the non-inverting input terminal is connected to the first reference voltage VS7 of 500mV. According to the working principle of the first differential amplification circuit 110, the first output signal output at the output terminal of the first differential amplification circuit 110 can be By setting the resistance of R1, R2, R3, and R4 as described above, the first output signal output by the first differential proportional amplification circuit 110 can be

[0061] In this embodiment, after passing through the first differential proportional amplification circuit 110, the slope of the cold end temperature signal of the K-type thermocouple measured by the temperature measuring chip TC1047A is reduced from 10mV / °C when input to the first slope -1.56mV / °C when output, and as can be seen from the output result Vout1, the DC bias 500mV in the temperature measuring chip signal is removed by the first differential proportional amplification circuit 110.

[0062] Please continue to read Figure 1 Since the output voltage slope of the K-type thermocouple itself is small, the temperature difference signal between the cold end and the hot end of the K-type thermocouple can be amplified by a certain multiple by the second operational amplifier calculation circuit, i.e., the slope of the temperature difference signal is adjusted, and a second reference voltage is added to output a second output signal, so that the second output signal is in a positive voltage output range.

[0063] The slope of the temperature difference signal output by the thermocouple is related to the type of the thermocouple. Since the temperature difference between the cold end and the hot end of the K-type thermocouple is measured in this embodiment, the temperature difference signal output by the K-type thermocouple is z=0.04mV×T2, where 0.04mV is the output voltage slope of the K-type thermocouple itself, and T2 is the temperature difference between the hot end and the cold end of the K-type thermocouple. The second operational amplifier calculation circuit can add a plurality of non-inverting input signals at the non-inverting input terminal of the second differential proportional amplification circuit 120.

[0064] Specifically, it includes Figure 1In the second differential proportional amplification circuit 120, the temperature difference signal outputted by the K-type thermocouple is taken as the third input signal Vin3, and is inputted into the non-inverting input terminal of the second operational amplifier 121 in the second differential proportional amplification circuit 120 through the eleventh resistor R11. Meanwhile, the second reference voltage VS8 is taken as the fourth input signal Vin4, and is inputted into the non-inverting input terminal together with the third input signal Vin3 (the temperature difference signal) through the twelfth resistor R12. The inverting input terminal of the second operational amplifier 121 is grounded through the tenth resistor R10, and the output terminal is connected back to the inverting input terminal through the second feedback resistor R9. Similarly, in order to ensure the resistance balance between the two input terminals of the second operational amplifier 121 in the second differential proportional amplification circuit 120, and to avoid reducing the common-mode rejection ratio, the tenth resistor R10 can be equal to the eleventh resistor R11, and the twelfth resistor R12 can be equal to the second feedback resistor R9, i.e. the ratio of the twelfth resistor R12 to the eleventh resistor R11 is the same as the ratio of the second feedback resistor R9 to the tenth resistor R10.

[0065] In some embodiments, the resistance value of the tenth resistor R10 can be set as 1k, the resistance value of the thirteenth resistor R13 can be set as 1k, the resistance value of the twelfth resistor R3 can be set as 39k, and the resistance value of the second feedback resistor R9 can be set as 39k. The third input signal Vin3 inputted into the non-inverting input terminal of the second differential proportional amplification circuit 120 is the temperature difference signal Vin3 = 0.04mV x T2 outputted by the cold and hot terminals of the K-type thermocouple, and the fourth input signal Vin4 can be set as the second reference voltage VS8 of 1250mV. Since the temperature difference signal outputted by the thermocouple can be a negative voltage, and the comparison circuit connected in the rear stage of the cold-end analog compensation circuit 100 does not support negative voltage input, in order to ensure that the signal outputted finally by the cold-end analog compensation circuit 100 is not a negative voltage, the second output voltage of the second operational amplifier calculation circuit can be raised, so as to ensure that the output value of the subsequent third operational amplifier calculation circuit is not a negative voltage. In this embodiment, the signal outputted by the K-type thermocouple can be adjusted to the positive voltage output range by setting a direct current bias with a value of 1250mV as the second reference voltage VS8.

[0066] Those skilled in the art can understand that the second reference voltage VS8 includes but is not limited to the 1250mV mentioned in the above embodiments, and the value of the second reference voltage VS8 can be adjusted according to the type of the thermocouple. For the K-type thermocouple in this embodiment, the second reference voltage VS8 can be set as 1250mV. Moreover, the second reference voltage VS8 does not have to be a fixed value, and it can be a range interval. For example, it is reasonable to set the second reference voltage VS8 of the K-type thermocouple in the above embodiments in the range interval of 1200mV-1300mV.

[0067] According to the working principle of the in-phase addition realized by the second differential proportional amplification circuit 120, the second output signal output by the second differential proportional amplification circuit 120 By inputting the resistance values of R9, R10, R11 and R12 and the input values of Vin3 and Vin4, it can be obtained that the second output signal output by the second differential proportional amplification circuit 120 can be specifically After the processing of the second differential proportional amplification circuit 120, the slope of the temperature difference signal of the K-type thermocouple is expanded from 0.04 mV / ℃ at the input to 1.56 mV / ℃ at the output, and it can be seen from the above output result Vout2 that the temperature difference signal of the K-type thermocouple output by the second differential proportional amplification circuit 120 is in the positive voltage output range.

[0068] In the above embodiment of the present application, since the cold end temperature signal of the thermocouple is obtained by the temperature measurement chip, the output voltage slope of the temperature measurement chip can be considered as the slope of the cold end temperature signal of the thermocouple. The temperature difference signal between the cold end and the hot end of the thermocouple is also a signal whose output voltage is proportional to the measured temperature, so the slope of the temperature difference signal is the output voltage slope of the thermocouple itself.

[0069] Generally, since the output voltage slope of the temperature measurement chip is greater than the output voltage slope of the thermocouple itself, the present application obtains the first output signal whose output voltage linearly changes with the first slope with respect to the cold end temperature of the thermocouple by reducing the output voltage slope of the temperature measurement chip by a certain multiple through the first differential proportional amplification circuit 110, and obtains the second output signal whose output voltage linearly changes with the second slope with respect to the temperature difference between the cold end and the hot end of the thermocouple by expanding the output voltage slope of the temperature difference signal between the cold end and the hot end of the thermocouple by a certain multiple through the second differential proportional amplification circuit 120.

[0070] When the first slope value in the first output signal and the second slope value in the second output signal are consistent, that is, the absolute values of the first slope and the second slope are consistent. In some embodiments, the third operational amplifier calculation circuit can perform a subtraction operation on the second output signal and the first output signal with a weighting coefficient ratio of 1:1 to output a measurement temperature signal whose output voltage changes in proportion to the measured temperature.

[0071] For details, please continue to refer to Figure 1In some embodiments of the present application, the third operational amplifier calculation circuit can comprise a third differential proportional amplification circuit 130. The first output signal Voutl outputted by the first differential proportional amplification circuit 110 is taken as the input signal of the inverting input terminal of the third operational amplifier 131 in the third differential proportional amplification circuit 130. The second output signal Vout2 outputted by the second differential proportional amplification circuit 120 is taken as the input signal of the non-inverting input terminal of the third operational amplifier 131 in the third differential proportional amplification circuit 130. The second output signal Vout2 is connected to the non-inverting input terminal of the third operational amplifier 131 through a fifth resistor R5, and the non-inverting input terminal is grounded through a sixth resistor R6. The first output signal Voutl is connected to the inverting input terminal of the third operational amplifier 131 through a seventh resistor R7. The output terminal of the third operational amplifier 131 is connected back to its inverting input terminal through a third feedback resistor R8.

[0072] Since the first output signal Voutl is in the negative voltage range, the second output signal Vout2 is in the positive voltage range, and the absolute values of the first slope and the second slope are consistent, by performing the difference of the same proportional weighting coefficients on the first output signal Voutl and the second output signal Vout2 through the third differential proportional amplification circuit 130, the actual temperature signal of the measured object whose voltage changes in proportion to the measured temperature, that is, the temperature signal of the hot end of the K-type thermocouple, can be obtained.

[0073] For example, in the above-mentioned embodiment, the first slope in the first output signal is -1.56, the second slope in the second output signal is 1.56, and the slope values of the two are consistent in size but opposite in sign. At this time, the differential proportional amplification circuit 130 of the third operational amplifier calculation circuit can adjust the first slope and the second slope by a weighting coefficient ratio of 1:1. For example, the resistance value of the fifth resistor R5 in the differential proportional amplification circuit 130 can be set to 10k, the resistance value of the sixth resistor R6 can be set to 5k, the resistance value of the seventh resistor R7 can be set to 10k, and the resistance value of the third feedback resistor R8 can be set to 5k. The output signal Vout of the third differential proportional amplification circuit 130 By taking the resistance values of R5, R6, R7, and R8 set above, it can be obtained that the hot end temperature signal Vout of the thermocouple outputted by the third differential proportional amplification circuit 130 is Vout = 0.5 x [1250mV + 1.56mV x (T2 + Tl)]. The weighting ratio of the first slope and the second slope is 0.5:0.5, that is, 1:1. Tl + T2 in the output signal Vout of the third differential proportional amplification circuit 130 is the actual temperature of the hot end of the thermocouple. Those skilled in the art can directly find the hot end temperature value Tl + T2 corresponding to the hot end voltage signal of the K-type thermocouple outputted by the third differential proportional amplification circuit 130 from the K-type thermocouple graduation table of the national standard.

[0074] Preferably, in other embodiments, for the convenience of calculation, the third operational amplifier calculation circuit in the cold end simulation compensation circuit 100 protected by the present application can also select a unit differential proportional amplification circuit. Also in the case where the absolute values of the first slope of the first output signal and the second slope of the second output signal are equal, the resistance values of the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, and the third feedback resistor R8 can be set to be the same, for example, all four resistors are set to 10k. The hot end temperature signal of the thermocouple output by the unit differential proportional amplification circuit is Vout = Vout2-Vout1 = 1250mV + 1.56mV x (T2+T1). The weighted ratio of the second slope and the first slope is directly 1:1. T1+T2 in the output signal Vout of the unit differential proportional amplification circuit is the actual temperature of the hot end of the thermocouple, which can be directly found by a person skilled in the art through the K-type thermocouple scale table of the national standard.

[0075] Those skilled in the art can understand that in actual application, the absolute values of the first slope and the second slope described in the above embodiments can allow a certain deviation therebetween, as long as the deviation between the two slope values is within a set range, which belongs to the technical solution protected by the present application and can also be used to execute the technical solution protected by the present application.

[0076] Optionally, in other embodiments of the present application, when the first slope value of the first output signal and the second slope value of the second output signal are inconsistent, that is, the absolute values of the first slope and the second slope are inconsistent. In these embodiments, the third operational amplifier calculation circuit can perform weighted subtraction on the second output signal and the first output signal. The third operational amplifier calculation circuit adjusts the weighted coefficient ratio of the first output signal and the second output signal, so that the weighted coefficient ratio is inversely proportional to the slope ratio of the first output signal and the second output signal, thereby realizing the consistency of the coefficient of the cold end temperature signal in the first output signal and the coefficient of the temperature difference signal in the second output signal.

[0077] Specifically, as shown in Figure 1 In an embodiment, assuming that the first output signal Vout1 is -2T1 and the second output signal Vout2 is 1.25+T2, wherein the first slope is the coefficient -2 of the cold end temperature signal T1 included in the first output signal, the second slope is the coefficient 1 of the temperature difference signal T2 included in the second output signal, and the ratio of the first slope to the second slope is 2:1. The resistance value relationship between the eighth resistor R8 and the seventh resistor R7 in the third differential amplification circuit 130 can be set as The resistance relationship of the sixth resistor R6 and the fifth resistor R5 is R6=2R5. According to the working principle of the differential amplification realized by the third differential proportional amplification circuit 130, and substituting the relationship among the resistors R5, R6, R7, and R8, the output signal of the third differential proportional amplification circuit 130 is In the formula of the output signal of the third differential proportional amplification circuit 130, since the corresponding weighting coefficient ratio of the first output signal Voutl and the second output signal Vout2 is 0.5:1=1:2, which is exactly the inverse relationship of the ratio of the first slope and the second slope 2:1, the coefficient of the cold end temperature signal Tl in the first output signal and the coefficient of the temperature difference signal T2 in the second output signal are consistent, and the common factor can be extracted to obtain the actual temperature Tl+T2 of the hot end of the thermocouple.

[0078] In the cold end simulation compensation circuit 100 protected by the present application, each operational amplifier, i.e. the first operational amplifier 111, the second operational amplifier 121, and the third operational amplifier 131, can select an operational amplifier model that is a double power supply precision operational amplifier with an offset voltage less than 25uV, such as OP07C. The first operational amplifier 111 in the first differential proportional amplification circuit 110 includes a positive power supply VS2 and a negative power supply VS1. The second operational amplifier 121 in the second differential proportional amplification circuit 120 includes a positive power supply VS4 and a negative power supply VS3. The third operational amplifier 131 in the third differential proportional amplification circuit 130 includes a positive power supply VS6 and a negative power supply VS5. Since the temperature measuring chip used to measure the cold end temperature of the K-type thermocouple is TC1047A, and the output of the TC1047A input after the differential proportional circuit is a negative voltage, a double power supply operational amplifier is required because a single power supply cannot provide a negative voltage output.

[0079] Those skilled in the art should also understand that the resistance values of all resistors in the first differential proportional amplification circuit 110, the second differential proportional amplification circuit 120, and the third differential proportional amplification circuit 130 mentioned in the above embodiments are not unique and are not limited to the resistance values mentioned in the embodiments. Those skilled in the art can select appropriate resistance values for each amplification circuit according to the type of thermocouple selected for cold end compensation, the type of temperature measuring chip used for cold end temperature measurement, and the slope value to be adjusted.

[0080] In summary, the application provides a cold end simulation compensation circuit, which can provide a thermocouple cold end temperature signal through a temperature measuring chip without the need of a single-chip microcomputer to process digital signals, and convert the cold end temperature signal into a signal slope same as the thermocouple through an operational amplifier circuit, so as to compensate the cold end temperature signal of the thermocouple, overcome the deficiency that the thermocouple cannot measure the absolute temperature of an object, and enable the circuit to output the absolute temperature signal of the measured object in the form of an analog signal after cold end compensation.

[0081] The foregoing description of the present disclosure has been provided for the purposes of illustrating and describing the present disclosure but is not intended to be limiting; modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that changes can be made in the particular embodiments of the disclosure disclosed which are within the scope and spirit of the disclosure, with the scope of the present disclosure being indicated by the appended claims.

Claims

1. A cold junction simulation compensation circuit for measuring the cold junction temperature of a thermocouple, characterized in that, The application relates to a temperature measurement circuit, comprising: a first operational amplifier calculation circuit receiving a cold end temperature signal of a thermocouple and a first reference voltage to perform subtraction operation and output a first output signal, which is used to eliminate a direct current bias voltage of the cold end temperature signal; a second operational amplifier calculation circuit receiving a temperature difference signal of the thermocouple and a second reference voltage to perform addition operation and output a second output signal, which is used to make the second output signal in a positive voltage output range; and a third operational amplifier calculation circuit receiving the first output signal and the second output signal to perform weighted subtraction, which is used to output a measurement temperature signal whose voltage changes in proportion to a measured temperature. The first operational amplifier calculation circuit performs scaling on the cold end temperature signal and outputs the first output signal whose voltage changes linearly with respect to the cold end temperature signal; 2. The cold-junction simulation compensation circuit of claim 1, wherein, The second operational amplifier calculation circuit performs scaling on the temperature difference signal and outputs the second output signal whose voltage changes linearly with respect to the temperature difference signal, wherein a slope value of the second output signal is consistent with a slope value of the first output signal, The third operational amplifier calculation circuit performs subtraction operation on the second output signal and the first output signal with a weighted coefficient ratio of 1:1 to output the measurement temperature signal whose voltage changes in proportion to the measured temperature. The slope value of the second output signal is inconsistent with the slope value of the first output signal, 3. The cold-junction simulation compensation circuit of claim 2, wherein, The third operational amplifier calculation circuit performs weighted subtraction on the second output signal and the first output signal, wherein a weighted coefficient ratio of the first output signal and the second output signal is inversely proportional to a slope ratio of the first output signal and the second output signal, so that a coefficient of the cold end temperature signal and a coefficient of the temperature difference signal are consistent. The first operational amplifier calculation circuit comprises a first differential proportional amplification circuit, an inverting input end of the first differential proportional amplification circuit receiving the cold end temperature signal, and a non-inverting input end receiving the first reference voltage, wherein the first reference voltage is equal to the direct current bias voltage of the cold end temperature signal, and the cold end temperature signal is greater than the first reference voltage to make the first output signal in a negative voltage output range.

4. The cold-junction simulation compensation circuit of claim 1, wherein, The slope of the cold end temperature signal changing in proportion to the cold end temperature of the thermocouple, and the direct current bias voltage depend on electrical characteristics of a temperature measurement chip used for measuring the cold end temperature signal.

5. The cold-junction simulation compensation circuit of claim 4, wherein, The second operational amplifier calculation circuit comprises a second differential proportional amplification circuit, a non-inverting input end of the second differential proportional amplification circuit receiving the temperature difference signal and the second reference voltage, an inverting input end being connected with a resistor and the other end of the resistor being grounded, and the second differential proportional amplification circuit performing same-direction addition on the temperature difference signal and the second reference voltage, wherein the second reference voltage is set to make the second output signal in a positive voltage output range.

6. The cold-junction simulation compensation circuit of claim 1, wherein, ​ 7. A cold finger analog compensation circuit as claimed in claim 2 or 3, characterized in that, The third operational amplifier calculation circuit includes a third differential proportional amplification circuit, the reverse input end of the third differential proportional amplification circuit receives the first output signal, the non-inverting input end receives the second output signal, and weighted subtraction is performed on the first output signal and the second output signal to obtain a measurement temperature signal whose voltage changes in proportion to the measurement temperature.

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