JP2008002853A - Cold contact compensation circuit, correction method of cold contact compensation circuit, and temperature measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that an inclination error occurs in forward voltage temperature characteristic and as a result, present temperature of a cold contact cannot be accurately specified. <P>SOLUTION: A cold contact compensation circuit 12 has a diode 21 for cold contact compensation which outputs voltage according to present temperature of the cold contact 2B of a thermocouple 2, a cold contact temperature detection part 23 which detects the temperature corresponding to the output voltage of the diode for cold contact compensation as the present temperature of the cold contact based on predetermined forward voltage temperature characteristic regarding the diode for cold contact compensation, and a compensation voltage creation part 25 which creates a compensation voltage corresponding to the detected present temperature of the cold contact. The circuit has a correction part 26 which corrects inclination of the predetermined forward voltage temperature characteristic (estimated characteristic after shift compensation) based on a band gap voltage value Vg corresponding to the absolute zero point of the diode for cold contact compensation and an output voltage value Vp corresponding to an arbitrary temperature of the diode for cold contact compensation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cold junction compensation circuit that compensates, for example, a DC voltage corresponding to the temperature of the cold junction with a DC voltage generated due to a temperature difference between the hot junction and the cold junction of a thermocouple, a calibration method for the cold junction compensation circuit, and The present invention also relates to a temperature measuring device provided with this cold junction compensation circuit.

  Conventionally, a temperature measuring device equipped with such a cold junction compensation circuit is provided with a thermocouple characteristic table (reference thermoelectromotive force table) in which temperatures are associated with each DC voltage in advance, and between the hot junction and the cold junction of the thermocouple. The compensation voltage corresponding to the current temperature of the cold junction is added from the cold junction compensation circuit to the DC voltage generated by the temperature difference of the temperature, and the temperature corresponding to the DC voltage of the addition result is read from the thermocouple characteristic table, This read temperature is detected and output as the current temperature of the hot junction.

  Further, such a cold junction compensation circuit outputs a voltage according to a compensation voltage table (reference thermoelectromotive force table) in which a compensation voltage is associated with each cold junction temperature and a current temperature of the cold junction of the thermocouple. Based on the cold junction compensation diode and the forward voltage temperature characteristics related to the cold junction compensation diode, the cold junction temperature detection detects the temperature corresponding to the output voltage of the cold junction compensation diode as the current temperature of the cold junction. And a compensation voltage generation unit that reads a compensation voltage corresponding to the current temperature of the cold junction detected by the cold junction temperature detection unit from the compensation voltage table and generates the readout compensation voltage ( For example, see Patent Document 1).

  According to such a conventional cold junction compensation circuit, the temperature corresponding to the output voltage of the cold junction compensation diode is detected as the current temperature of the cold junction based on the forward voltage temperature characteristic of the cold junction compensation diode. Since it did in this way, the present temperature of a cold junction can be detected using the linearity of the forward voltage temperature characteristic of a diode.

  Further, the forward voltage temperature characteristic used for specifying the current temperature of the cold junction from the output voltage of the cold junction compensation diode of the cold junction compensation circuit is as follows. Three or more arbitrary temperatures (excluding absolute zero) for each type, for example, output voltage values corresponding to −10 ° C., 25 ° C., 50 ° C., etc. are measured in advance, and output voltages corresponding to these three or more arbitrary temperatures A forward voltage temperature characteristic is created for each product type as a measured estimated characteristic by value, and the forward voltage temperature characteristic (actually estimated characteristic) created for each product type is averaged to average the forward voltage temperature characteristic common to the product. (Default characteristics) is used. Note that the slope of the forward voltage temperature characteristic (default characteristic) common to this product is constant.

Therefore, according to the conventional cold junction compensation circuit, as shown in FIG. 6, when the temperature measuring device having the cold junction compensation circuit is shipped, the forward direction of the cold junction compensation diode used in the cold junction compensation circuit is as shown in FIG. Based on the amount of shift of the voltage temperature characteristics, the default characteristics were calibrated according to the product type of the cold junction compensation diode, so based on the forward voltage temperature characteristics (estimated characteristics after shift calibration) The temperature corresponding to the output voltage of the cold junction compensation diode can be detected as the current temperature of the cold junction.
JP 2001-124636 A (see paragraph numbers “0024” to “0027” and FIG. 6)

  However, according to the above-described conventional cold junction compensation circuit, the forward voltage temperature characteristic (default characteristic) common to the products is used, and the forward voltage temperature according to the product type of the cold junction compensation diode as shown in FIG. The characteristic (default characteristic) shift amount is calibrated, and the temperature corresponding to the output voltage of the cold junction compensation diode is calculated based on the forward voltage temperature characteristic (estimated characteristic after shift calibration). Although the slope of the forward voltage temperature characteristics of the cold junction compensation diode differs depending on the product of the same type as well as the product type, a tilt error occurs and the cold junction is detected. An error also occurs in the temperature corresponding to the output voltage of the compensation diode, and as a result, the accurate current temperature of the cold junction cannot be detected. It is not possible to also obtain accurate compensation voltage, it is impossible to accurately measure the current temperature of the hot junction of the thermocouple as temperature measurement device.

  In addition, according to the conventional cold junction compensation circuit, in order to eliminate the tilt error of the cold junction compensation diode and improve the cold junction temperature measurement accuracy, an expensive cold junction compensation diode is used instead of an inexpensive cold junction compensation diode. Although it is conceivable to use a platinum wire thermal resistor, this leads to an increase in product cost.

  The present invention has been made in view of the above points, and an object of the present invention is to improve the cold junction temperature measurement accuracy by suppressing the inclination error of the forward voltage temperature characteristic of the cold junction compensation diode. As a result, an inexpensive cold junction compensation circuit capable of improving the temperature measurement accuracy of the hot junction, a calibration method for the cold junction compensation circuit, and a temperature measurement device including the cold junction compensation circuit are provided.

  In order to achieve the above object, the cold junction compensation circuit of the present invention includes a cold junction compensation diode that outputs a voltage according to the current temperature of the cold junction of the thermocouple, and a predetermined forward direction related to the cold junction compensation diode. Based on the voltage temperature characteristics, cold junction temperature detection means for detecting the temperature corresponding to the output voltage of the cold junction compensation diode as the current temperature of the cold junction, and the cold junction temperature detected by the cold junction temperature detection means A cold junction compensation circuit having compensation voltage generation means for generating a compensation voltage corresponding to a current temperature, wherein a band gap voltage corresponding to an absolute zero of the cold junction compensation diode and an arbitrary one of the cold junction compensation diodes Calibration means for calibrating the slope of the predetermined forward voltage temperature characteristic based on the output voltage corresponding to the temperature is provided.

  Therefore, according to the cold junction compensation circuit of the present invention, it is noted that the band gap voltage corresponding to the absolute zero degree of the cold junction compensation diode is a point at which the error converges even if the product type or the product itself is different. The slope of the predetermined forward voltage temperature characteristic is calibrated based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode. Therefore, even if an inexpensive cold junction compensation diode is used, cold junction temperature measurement is possible by using the forward voltage temperature characteristic that suppresses the tilt error of the forward voltage temperature characteristic of the cold junction compensation diode. The accuracy can be improved and an accurate compensation voltage corresponding to the current temperature of the cold junction can be generated. As a result, temperature measurement can be performed by using this compensation voltage. It is possible to improve the temperature measurement accuracy of the hot junctions in the device.

  Further, the calibration means of the cold junction compensation circuit of the present invention measures the output voltage of the cold junction compensation diode according to the current temperature of the cold junction, and the measurement result is used as an arbitrary temperature of the cold junction compensation diode. The output voltage may correspond to the above.

  Therefore, according to the cold junction compensation circuit of the present invention, the calibration unit measures the output voltage of the cold junction compensation diode according to the current temperature of the cold junction, and the measurement result is used as the cold junction compensation diode. The output voltage corresponding to the arbitrary temperature is obtained using the cold junction compensation diode that is actually used regardless of the product type of the cold junction compensation diode. Therefore, it is possible to acquire the forward voltage temperature characteristic of the cold junction compensation diode that has an extremely small inclination error as compared with the conventional case.

  The arbitrary temperature of the cold junction compensation circuit of the present invention may correspond to the ambient temperature of the cold junction compensation circuit.

  Therefore, according to the cold junction compensation circuit of the present invention, since the arbitrary temperature corresponds to the ambient temperature of the cold junction compensation circuit, the output at the ambient temperature of the cold junction compensation circuit actually used is output. In order to acquire the voltage, it is possible to acquire the forward voltage temperature characteristic of the cold junction compensation diode in accordance with the operating environment temperature of the cold junction compensation circuit.

  In order to achieve the above object, the cold junction compensation circuit calibration method of the present invention includes a cold junction compensation diode that outputs a voltage according to the current temperature of the cold junction of the thermocouple, and a cold junction compensation diode. Based on the predetermined forward voltage temperature characteristics involved, a cold junction temperature detection means for detecting the temperature corresponding to the output voltage of the cold junction compensation diode as the current temperature of the cold junction, and detected by the cold junction temperature detection means A cold junction compensation circuit calibration method comprising compensation voltage generation means for generating a compensation voltage corresponding to the current temperature of the cold junction, a band gap voltage corresponding to absolute zero of the cold junction compensation diode, The slope of the predetermined forward voltage temperature characteristic is calibrated based on the output voltage corresponding to the arbitrary temperature of the cold junction compensation diode.

  Therefore, according to the cold junction compensation circuit calibration method of the present invention, the band gap voltage corresponding to the absolute zero degree of the cold junction compensation diode is a point at which the error converges even if the product type or the product itself is different. In particular, based on the band gap voltage corresponding to the absolute zero of the cold junction compensation diode and the output voltage corresponding to the arbitrary temperature of the cold junction compensation diode, the slope of the predetermined forward voltage temperature characteristic is determined. Even if an inexpensive cold junction compensation diode is used, the forward voltage temperature characteristic that suppresses the slope error of the forward voltage temperature characteristic of the cold junction compensation diode is used. By improving the junction temperature measurement accuracy, an accurate compensation voltage corresponding to the current temperature of the cold junction can be generated. As a result, this compensation voltage can be used. In it is possible to improve the temperature measurement accuracy of the hot junction at a temperature measuring device.

  In order to achieve the above object, the temperature measuring device of the present invention includes a cold junction compensation diode that outputs a voltage in accordance with the current temperature of the cold junction of the thermocouple, and a predetermined order related to the cold junction compensation diode. Based on the directional voltage temperature characteristics, cold junction temperature detection means for detecting the temperature corresponding to the output voltage of the cold junction compensation diode as the current temperature of the cold junction, and the cold junction detected by the cold junction temperature detection means A cold junction compensation circuit having a compensation voltage generating means for generating a compensation voltage corresponding to the current temperature of the thermocouple, and the DC voltage generated according to a temperature difference between the hot junction and the cold junction of the thermocouple A temperature measuring device that adds the compensation voltage corresponding to the current temperature of the cold junction generated by a junction compensation circuit and detects the current temperature of the hot junction according to a DC voltage as a result of the addition. The compensation circuit calibrates the predetermined forward voltage temperature characteristic based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode. It has a calibration means.

  Therefore, according to the temperature measurement device of the present invention, focusing on the fact that the band gap voltage corresponding to the absolute zero degree of the cold junction compensation diode is the point where the error converges even if the product type or product itself is different, Based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode on the cold junction compensation circuit side and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode, the predetermined forward voltage temperature characteristic Since the slope is calibrated, even if an inexpensive cold junction compensation diode is used, the forward voltage temperature characteristic that suppresses the slope error of the forward voltage temperature characteristic of the cold junction compensation diode can be used. In order to improve the cold junction temperature measurement accuracy, an accurate compensation voltage corresponding to the current temperature of the cold junction is generated, and as a result, using this compensation voltage, It is possible to improve the temperature measurement accuracy of the point.

  According to the cold junction compensation circuit of the present invention configured as described above, the band gap voltage corresponding to the absolute zero degree of the cold junction compensation diode is a point at which the error converges even if the product type or the product itself is different. In particular, based on the band gap voltage corresponding to the absolute zero degree of the cold junction compensation diode and the output voltage corresponding to the arbitrary temperature of the cold junction compensation diode, the inclination of the predetermined forward voltage temperature characteristic is determined. Even if an inexpensive cold junction compensation diode is used, the cold voltage compensation characteristics can be reduced by using the forward voltage temperature characteristic that suppresses the slope error of the forward voltage temperature characteristic of the cold junction compensation diode. By improving the junction temperature measurement accuracy, an accurate compensation voltage corresponding to the current temperature of the cold junction can be generated. As a result, by using this compensation voltage, It can be in degrees measuring device to improve the temperature measurement accuracy of the hot junction.

  Further, according to the calibration method of the cold junction compensation circuit of the present invention, the band gap voltage corresponding to the absolute zero of the cold junction compensation diode is a point where the error converges even if the product type or the product itself is different. Pay attention and calibrate the slope of the predetermined forward voltage temperature characteristics based on the band gap voltage corresponding to the absolute zero of the cold junction compensation diode and the output voltage corresponding to the arbitrary temperature of the cold junction compensation diode. Therefore, even if an inexpensive cold junction compensation diode is used, the cold junction can be obtained by using the forward voltage temperature characteristic that suppresses the slope error of the forward voltage temperature characteristic of the cold junction compensation diode. The accuracy of temperature measurement can be improved, and an accurate compensation voltage corresponding to the current temperature of the cold junction can be generated. It is possible to improve the temperature measurement accuracy of the hot junctions in the measuring device.

  Also, according to the temperature measuring device of the present invention, focusing on the fact that the band gap voltage corresponding to the absolute zero of the cold junction compensation diode is a point where the error converges even if the product type or the product itself is different, Based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode on the cold junction compensation circuit side and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode, a slope of the predetermined forward voltage temperature characteristic Therefore, even if an inexpensive cold junction compensation diode is used, by using the forward voltage temperature characteristic that suppresses the slope error of the forward voltage temperature characteristic of the cold junction compensation diode, The accuracy of cold junction temperature measurement is improved, and an accurate compensation voltage corresponding to the current temperature of the cold junction is generated. As a result, by using this compensation voltage, It is possible to improve the degree measurement accuracy.

  Hereinafter, a temperature measuring apparatus showing an embodiment related to the cold junction compensation circuit of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing a schematic configuration inside the temperature measuring apparatus according to the present embodiment.

  A temperature measuring device 1 shown in FIG. 1 is a device that is connected to the cold junction 2B side of the thermocouple 2 in order to measure the current temperature of the object on the hot junction 2A side of the thermocouple 2 and includes the hot junction 2A and the cold junction 2B. Generated by a DC voltage generation circuit 11 that generates a DC voltage according to a temperature difference between the contacts 2B, a cold junction compensation circuit 12 that generates a compensation voltage corresponding to the current temperature of the cold junction 2B, and a DC voltage generation circuit 11 The DC voltage adding circuit 13 for adding the DC voltage thus generated and the compensation voltage generated by the cold junction compensation circuit 12, and a hot junction side storage unit storing and managing a table in which the temperature of the hot junction 2A is associated with each DC voltage value. 14 and the temperature corresponding to the DC voltage value as the addition result of the DC voltage adding circuit 13 are read from the table in the hot junction side storage unit 14, and the read temperature is detected as the current temperature of the hot junction 2A. Output the result And a contact temperature measuring circuit 15.

  The hot junction side storage unit 14 stores and manages a table in which the temperature of the hot junction 2A is associated with each DC voltage value, that is, a reference thermoelectromotive force table corresponding to the material of the thermocouple 2.

  The cold junction compensation circuit 12 outputs a voltage according to the current temperature on the cold junction 2B side in order to detect the current temperature of the cold junction 2B, and the forward voltage of the cold junction compensation diode 21. The forward voltage temperature characteristic storage unit 22 storing the temperature characteristics and the forward voltage stored in the forward voltage temperature characteristic storage unit 22 with the temperature of the cold junction 2B corresponding to the output voltage value of the cold junction compensation diode 21. A cold junction temperature detection unit 23 that reads out from the temperature characteristics and detects the read temperature as the current temperature of the cold junction 2B; and a compensation voltage storage unit 24 that stores and manages a compensation voltage value for each temperature of the cold junction 2B. A compensation voltage value corresponding to the temperature of the cold junction 2B detected by the cold junction temperature detection unit 23 is read from the compensation voltage storage unit 24, and a compensation voltage is generated based on the read compensation voltage value. The voltage generation unit 25 and the calibration unit 26 that calibrates the forward voltage temperature characteristic stored in the forward voltage temperature characteristic storage unit 22, and the compensation voltage generation unit 25 converts the generated compensation voltage into a DC voltage addition circuit. 13 is input. It is assumed that the cold junction compensation diode 21 is in substantially the same temperature environment as the cold junction 2B.

  The compensation voltage storage unit 24 stores and manages a table in which a DC voltage value (compensation voltage value) is associated with each temperature, that is, a reference thermoelectromotive force table corresponding to the material of the thermocouple 2.

  The forward voltage temperature characteristic storage unit 22 stores a forward voltage temperature characteristic (default characteristic) common to products before the temperature measurement device 1 is shipped from the factory, that is, before calibration.

  Further, the calibration unit 26 calculates the output voltage value of the cold junction compensation diode 21 corresponding to the absolute zero (for example, −273.15 degrees) inherent to the metal used for the cold junction compensation diode 21, that is, the band gap voltage value Vg. It is a memory management. When the cold junction compensation diode 21 is a silicon diode, the band gap voltage value Vg is about 1.2V.

  Further, the calibration unit 26 uses the default characteristics stored in the forward voltage temperature characteristic storage unit 22 at the time of shipment from the factory as the product type of the cold junction compensation diode 21 used in the cold junction compensation circuit 12 as shown in FIG. The estimated characteristic after shift calibration is created by calibrating based on the shift amount corresponding to the shift amount, and the estimated characteristic after shift calibration is stored and updated in the forward voltage temperature characteristic storage unit 22.

  Further, the calibration unit 26 stores and updates the estimated characteristics after shift calibration in the forward voltage temperature characteristic storage unit 22, and then outputs the output voltage value Vp of the cold junction compensation diode 21 and the output voltage through the cold junction temperature detection unit 23. An arbitrary temperature corresponding to the value Vp (the current temperature of the cold junction 2B) is measured, and the output voltage value Vp corresponding to the arbitrary temperature and the band gap voltage value Vg corresponding to the absolute zero during storage are used ( The inclination for calibration of the forward voltage temperature characteristic is calculated based on the equation of output voltage Vp at arbitrary temperature−band gap voltage Vg) / (arbitrary temperature−absolute zero degree).

  Then, after calculating the calibration inclination, the calibration unit 26 calibrates the inclination of the post-shift calibration estimated characteristic stored in the forward voltage temperature characteristic storage unit 22 based on the calibration inclination, and calibrates the inclination. The estimated characteristics after shift calibration are stored and updated in the forward voltage temperature characteristics storage unit 22 as estimated characteristics after tilt calibration (see FIG. 3).

  As a result, the cold junction temperature detection unit 23 of the cold junction compensation circuit 12 outputs the output voltage of the cold junction compensation diode 21 based on the estimated characteristics after inclination calibration stored in the forward voltage temperature characteristic storage unit 22 during operation. Accordingly, the current temperature on the cold junction 2B side is detected.

  The cold junction temperature detection means described in the claims is the cold junction temperature detection section 23 and the forward voltage temperature characteristic storage section 22, the compensation voltage generation means is the compensation voltage generation section 25 and the compensation voltage storage section 24, and the calibration means is the calibration section. 26.

  Next, operation | movement of the temperature measuring apparatus 1 which shows this Embodiment is demonstrated.

  First, the operation at the time of calibrating the forward voltage temperature characteristic inside the cold junction compensation circuit 12 of the temperature measuring device 1 will be described. FIG. 4 is a flowchart showing the processing operation related to the forward voltage temperature characteristic calibration processing of the cold junction compensation circuit 12 according to the present embodiment.

  First, when the temperature measuring device 1 is shipped from the factory, the calibration unit 26 in the cold junction compensation circuit 12 stores the forward voltage temperature characteristic storage unit 22 based on the shift amount corresponding to the product type of the cold junction compensation diode 21. The stored default characteristics are shift calibrated to create estimated characteristics after shift calibration (step S11), and the created post-shift calibrated estimated characteristics are stored and updated in the forward voltage temperature characteristic storage unit 22 (step S12).

  When the calibration unit 26 stores and updates the estimated characteristics after shift calibration, based on the estimated characteristics after shift calibration, the current output voltage value Vp of the cold junction compensation diode 21 through the cold junction temperature detection unit 23 and the output voltage value thereof. The current temperature of the cold junction 2B corresponding to Vp is acquired (step S13).

  When the calibration unit 26 acquires the current temperature and the output voltage value Vp of the cold junction 2B, the calibration unit 26 uses the current temperature and the output voltage value Vp of the cold junction 2B and the absolute zero and the band gap voltage value Vg stored. Based on (output voltage value Vp−bandgap voltage value Vg) / (current temperature−absolute zero degree), a calibration gradient is calculated (step S14).

  Further, after calculating the calibration inclination, the calibration unit 26 calibrates the post-shift calibration estimated characteristic stored in the forward voltage temperature characteristic storage unit 22 based on the calibration inclination to obtain the estimated characteristic after tilt calibration. Create (step S15).

  When the calibration unit 26 creates the estimated characteristic after tilt calibration, the calibration unit 26 updates the estimated characteristic after tilt calibration in the forward voltage temperature characteristic storage unit 22 (step S16), and ends this processing operation.

  As a result, the forward voltage temperature characteristic (estimated characteristic after slope calibration) stored in the forward voltage temperature characteristic storage unit 22 uses the band gap voltage Vg of absolute zero inherent to the metal related to the cold junction compensation diode 21. Therefore, the conventional tilt error can be suppressed to the minimum, and the temperature measurement accuracy of the cold junction compensation diode 21 is improved.

  Next, the operation of the temperature measuring apparatus 1 that has performed such calibration of the forward voltage temperature characteristic will be described.

  The DC voltage generation circuit 11 inside the temperature measuring device 1 generates a DC voltage according to the temperature difference between the hot junction 2A and the cold junction 2B of the thermocouple 2 and supplies this DC voltage to the DC voltage addition circuit 13.

  The cold junction temperature detection unit 23 in the cold junction compensation circuit 12 detects the output voltage of the cold junction compensation diode 21 according to the current temperature of the cold junction 2B, and the forward voltage temperature characteristic storage unit 22 stores the forward voltage. Based on the directional voltage temperature characteristics, the temperature corresponding to this output voltage value is detected as the current temperature of the cold junction 2B.

  The compensation voltage generation unit 25 reads a compensation voltage value corresponding to the current temperature of the cold junction 2B detected by the cold junction temperature detection unit 23 from the compensation voltage storage unit 24, and generates a compensation voltage based on the read compensation voltage value. The generated compensation voltage is supplied to the DC voltage adding circuit 13.

  The DC voltage adding circuit 13 adds the DC voltage generated by the DC voltage generating circuit 11 and the compensation voltage generated by the compensation voltage generating unit 25, and the DC voltage that is the addition result is added to the hot junction temperature measuring circuit 15. To supply.

  The hot junction temperature measurement circuit 15 reads the temperature corresponding to the DC voltage value of the DC voltage from the hot junction storage unit 14, and measures and outputs the read temperature as the current temperature of the hot junction 2A.

  As a result, according to the temperature measuring apparatus 1, the forward voltage temperature characteristics (estimated characteristics after tilt calibration) stored in the cold junction compensation circuit 12 have a small tilt error using the band gap voltage value Vg. Therefore, by using this forward voltage temperature characteristic (estimated characteristic after tilt calibration), the temperature measurement accuracy can be greatly improved.

  According to the present embodiment, paying attention to the fact that the band gap voltage value Vg corresponding to absolute zero of the cold junction compensation diode 21 is a point where the error converges even if the product type or the product itself is different. Based on the band gap voltage value Vg corresponding to the absolute zero of the compensation diode 21 and the output voltage value Vp corresponding to the ambient temperature of the cold junction compensation diode 21 when the temperature measuring device 1 is shipped from the factory, for example, in a predetermined order. Since the inclination of the directional voltage temperature characteristic (forward voltage temperature characteristic after shift calibration) is calibrated, even if an inexpensive cold junction compensation diode 21 is used, the forward voltage temperature characteristic of the cold junction compensation diode 21 is used. By using the forward voltage temperature characteristics (estimated characteristics after tilt calibration) that suppresses the tilt error, the cold junction temperature measurement accuracy is improved and the cold junction 2 Current generates accurate compensation voltage corresponding to the temperature, as a result, by using this compensation voltage, it is possible to improve the temperature measurement accuracy of the hot junction as the temperature measuring device 1.

  According to the present embodiment, when calculating the slope of the forward voltage temperature characteristic of the cold junction compensation diode 21, the output voltage value Vp of the cold junction compensation diode 21 corresponding to the current temperature of the cold junction 2B is measured. Since the cold junction compensation diode 21 that is actually used is used to obtain the output voltage value of the current temperature regardless of the product type of the cold junction compensation diode 21, the output voltage value of the current temperature is much higher than in the past. The forward voltage temperature characteristic of the cold junction compensation diode 21 with little error can be acquired.

  In the above embodiment, when calculating the slope of the forward voltage temperature characteristic of the cold junction compensation diode 21, the cold junction compensation diode according to the current temperature of the cold junction 2B corresponding to the room temperature at the time of shipment from the factory. Although the output voltage value of 21 is measured, it is needless to say that the output voltage value is not limited to room temperature, and can cope with various environmental temperatures.

  In the above embodiment, when the inclination of the forward voltage temperature characteristic of the cold junction compensation diode 21 is calibrated at the time of shipment from the factory, the default characteristic is the estimated characteristic after shift calibration based on the shift amount corresponding to the product type. After creation, the estimated characteristics after shift calibration are created based on the slope for calibration, but the estimated characteristics after shift calibration corresponding to the product type are stored in advance, not from the default characteristics. In this case, the shift calibration processing operation is not necessary.

  According to the present invention, even if an inexpensive cold junction compensation diode is used, by using the forward voltage temperature characteristic in which the inclination error of the forward voltage temperature characteristic of the cold junction compensation diode is suppressed, The temperature measurement accuracy can be improved, and an accurate compensation voltage corresponding to the current temperature of the cold junction can be generated. As a result, by using this compensation voltage, the temperature measurement accuracy of the hot junction can be improved in the temperature measurement device. Since improvement can be aimed at, it is useful for the temperature measuring device which uses the cold junction compensation circuit using a thermocouple, for example.

It is a block diagram which shows schematic structure inside the temperature measuring device which shows embodiment in connection with the cold junction compensation circuit of this invention. It is explanatory drawing which shows directly the calibration content of the forward voltage temperature characteristic inside the cold junction compensation circuit in connection with this Embodiment. It is explanatory drawing which shows directly the forward voltage temperature characteristic (estimated characteristic after inclination calibration) inside the cold junction compensation circuit in connection with this embodiment. It is a flowchart which shows the processing operation in connection with the forward voltage temperature characteristic calibration process of the cold junction compensation circuit in connection with this Embodiment. It is explanatory drawing which shows directly the forward voltage temperature characteristic (default characteristic) inside the conventional cold junction compensation circuit. It is explanatory drawing which shows straightly the calibration content of the forward voltage temperature characteristic inside the conventional cold junction compensation circuit, and the inclination error of the forward voltage temperature characteristic (estimated characteristic after shift calibration).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Temperature measuring device 2 Thermocouple 2A Hot junction 2B Cold junction 11 DC voltage generation circuit (temperature measuring device)
12 Cold junction compensation circuit 13 DC voltage addition circuit (temperature measuring device)
14 Warm junction side storage (temperature measuring device)
15 Hot junction temperature measurement circuit (temperature measurement device)
21 Cold junction compensation diode 22 Forward voltage temperature characteristic storage unit (cold junction temperature detection means)
23 Cold junction temperature detector (Cold junction temperature detection means)
24 Compensation voltage storage unit (compensation voltage generation means)
25 Compensation voltage generator (compensation voltage generator)
26 Calibration section (calibration means)

Claims (5)

Based on the cold junction compensation diode that outputs a voltage according to the current temperature of the cold junction of the thermocouple, and a predetermined forward voltage temperature characteristic related to the cold junction compensation diode, the output voltage of the cold junction compensation diode is Cold junction temperature detection means for detecting the corresponding temperature as the current temperature of the cold junction, and compensation voltage generation means for generating a compensation voltage corresponding to the current temperature of the cold junction detected by the cold junction temperature detection means A cold junction compensation circuit comprising:
Calibration means for calibrating the slope of the predetermined forward voltage temperature characteristic based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode A cold junction compensation circuit comprising: The calibration means includes
The output voltage of the cold junction compensation diode according to the current temperature of the cold junction is measured, and the measurement result is set as an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode. The cold junction compensation circuit described. The arbitrary temperature is
The cold junction compensation circuit according to claim 1, wherein the cold junction compensation circuit corresponds to an ambient temperature of the cold junction compensation circuit. Based on the cold junction compensation diode that outputs a voltage according to the current temperature of the cold junction of the thermocouple, and a predetermined forward voltage temperature characteristic related to the cold junction compensation diode, the output voltage of the cold junction compensation diode is Cold junction temperature detection means for detecting the corresponding temperature as the current temperature of the cold junction, and compensation voltage generation means for generating a compensation voltage corresponding to the current temperature of the cold junction detected by the cold junction temperature detection means A cold junction compensation circuit calibration method comprising:
Calibrating the slope of the predetermined forward voltage temperature characteristic based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode; A method for calibrating a cold junction compensation circuit. Based on the cold junction compensation diode that outputs a voltage according to the current temperature of the cold junction of the thermocouple, and a predetermined forward voltage temperature characteristic related to the cold junction compensation diode, the output voltage of the cold junction compensation diode is Cold junction temperature detection means for detecting the corresponding temperature as the current temperature of the cold junction, and compensation voltage generation means for generating a compensation voltage corresponding to the current temperature of the cold junction detected by the cold junction temperature detection means The compensation corresponding to the current temperature of the cold junction generated by the cold junction compensation circuit is applied to a DC voltage generated according to the temperature difference between the hot junction and the cold junction of the thermocouple. A temperature measuring device that adds a voltage and detects a current temperature of the hot junction according to a DC voltage of the addition result,
The cold junction compensation circuit is:
Calibration means for calibrating the slope of the predetermined forward voltage temperature characteristic based on a band gap voltage corresponding to absolute zero of the cold junction compensation diode and an output voltage corresponding to an arbitrary temperature of the cold junction compensation diode A temperature measuring device comprising:

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