JPH10111188A - Automatic thermocouple calibration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermocouple calibrating device wherein a calibration value with high precision is obtained and its complex calculation is easily performed by using a comparison-calibration method wherein fixed-point calibration method is taken. SOLUTION: The device comprises an electric furnace 2 where a standard thermocouple which is going to be a reference and a to-be-calibrated thermocouple are set, an electric furnace control part which controls the electric furnace 2 to a set temperature, a calculation part 3, a display 5, and a printer 6. The calculation part 3, based on a calibration data near the known fixed-point temperature of the standard thermocouple and a calibration measurement value from the standard thermocouple and the to-be-calibrated thermocouple in the electric furnace 2, obtains a deviation approximate expression of the standard thermocouple and the to-be-calibrated thermocouple. In addition, the display 5 is allowed to display a in-furnace temperature, an error curve of each thermo couple, and a thermo-electromotive force table, and the printer 6 prints out a heard copy of them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocouple calibration device.

[0002]

2. Description of the Related Art Conventionally, thermocouples are calibrated by the Nippon Electric Instrument Calibration Laboratory using a comparative verification method, and based on the passed thermocouple as a reference, the thermocouple to be calibrated and the thermocouple to be calibrated are simultaneously placed in an electric furnace or the like. Then, the thermoelectromotive force corresponding to the test temperature was measured, and calibration was performed by the comparative calibration method.

[0003] However, the maximum accuracy guaranteed by the Nippon Keiki Keiki Testing Laboratory for thermocouples verified using the comparative calibration method is ± 0.01.
When converted to a temperature of mV, the accuracy of the R thermocouple is as coarse as ± 0.6 to 0.7 ° C., and the accuracy of a general-purpose thermocouple calibrated based on this is even lower.

In addition, complicated calculations are required to obtain the error characteristics from the measured values in accordance with the JIS thermoelectromotive force table (electromotive force / temperature correspondence table). It took a lot of trouble. In recent years, the use of computers has become common, and calculations using computers have been attempted.However, there is no software developed for thermocouple calibration, and each individual has to work hard. It is the current situation.

[0005]

However, in response to the progress of modern science and technology, the demand for accuracy required for temperature measurement is increasing, and the reliability of the measuring instrument itself is inevitably improved, that is, There is an increasing demand for higher calibration accuracy. Therefore, it is not sufficient to use the conventional comparative calibration method alone, and it is effective to incorporate a temperature correction in consideration of the fixed-point calibration method, but this requires extremely complicated arithmetic processing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermocouple calibrator which can obtain a highly accurate calibration value by a comparative calibration method in which a fixed-point calibration method is added and can easily execute complicated calculations. is there.

[0007]

Means for Solving the Problems First, the present invention provides a highly accurate fixed point temperature (fixed point measurement of zinc, aluminum, silver and copper or gold: guaranteed accuracy of ± 0.1
° C), a deviation value (unit: mV) at four fixed-point temperatures is obtained from the JIS thermoelectromotive force table based on the measurement data of the R-type standard thermocouple obtained by the calibration at (° C), and the thermoelectromotive force deviation of this standard thermocouple is calculated. Approximate by a higher-order polynomial and find the coefficient. Then, an electromotive force table of the standard thermocouple is calculated and created from the deviation approximation formula and the JIS electromotive force table. Next, the calibration of the thermocouple to be calibrated is performed using the standard thermocouple as a reference. A tubular precision electric furnace is used to set the temperature environment for improving the measurement accuracy, and a plurality of fixed-point temperatures (the fixed-point temperatures are desirably equidistant for easy calculation and uniform interpolation accuracy).
The temperature of the electric furnace is sequentially controlled at each fixed point temperature (strictly speaking, the temperature near the fixed point), the electromotive force of the reference thermocouple and the thermocouple to be calibrated at the temperature is measured, and this value and the reference standard thermocouple are measured. The deviation data from the JIS electromotive force table of the thermocouple to be calibrated at the fixed point temperature is obtained using the deviation value at the fixed point temperature. Then, the deviation data at the fixed point temperature is approximated by a higher-order polynomial as in the case of the standard thermocouple, coefficients are obtained, and a deviation expression showing the characteristics of the thermocouple to be calibrated is obtained. An error regression calculation is performed based on the deviation formula and the JIS thermoelectromotive force table to obtain a thermoelectromotive force table of the thermocouple to be calibrated.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The calibration operation of the present invention will be described with reference to the overall system diagram of FIG. 1 and the flowchart of FIG.
Since the calibration test of the standard thermocouple at the Nippon Electric Keiki Inspection Laboratory is a fixed point calibration using the actual metal freezing point,
An extremely high measurement value is obtained for the accuracy of the fixed point temperature. First, the calculation unit inputs electromotive force measurement data of a thermocouple at a fixed point temperature (freezing point of Zn, Al, Ag, and Cu) obtained by the Nippon Electric Keiki Inst. In part 3 with the JIS thermoelectromotive force table
A deviation (unit: mV) at the fixed point temperature is obtained, and the thermoelectromotive force deviation of the standard thermocouple is approximated by a higher-order polynomial to obtain a coefficient. Then, based on the deviation approximation formula and the JIS electromotive force table, the electromotive force table of the standard thermocouple is calculated and created and stored in the memory (step 13). The data sheet output to the printer 6 in step 14 is the data sheet of FIG. The deviation equation is based on the output electromotive force of a standard thermocouple used as a reference.
This is for correcting the thermoelectromotive force table of FIG. On the other hand, on the electric furnace side, a standard thermocouple and a thermocouple to be calibrated are first set in the tubular precision electric furnace 2 in step 1. Multiple fixed-point temperatures (eg, 200 ° C, 400 ° C, 600
℃, 800 ℃, 1000 ℃ is desirable at equal intervals)
Set the order in which multiple fixed-point temperatures are realized. In the data sheet of FIG. 3, the upper table is Z
It is the data of the standard thermocouple at the freezing point of n, Al, Ag, and Cu. The value of the mV unit of the left column is the electromotive force value of the standard thermocouple verified by Nippon Electric Keiki Inspection, and the column with ITS-90. Is the standard value of the thermoelectric power of JIS, and the deviation and the value in a certain column are the deviation between the electromotive force value of the standard thermocouple and the standard value of the thermoelectromotive force table of JIS. It shows the temperature error when the electromotive force value of the thermocouple is read as it is on the JIS thermoelectromotive force table. The middle graph is a graph showing a temperature error characteristic corresponding to the temperature of the reference thermocouple.
The lower table shows the values of the thermoelectromotive force of the reference thermocouples at the respective temperatures of 0 ° C. to 1090 ° C. arranged at intervals of 10 ° C. in the horizontal direction and at 100 ° C. in the vertical direction.

In step 3, the heater of the electric furnace is turned on to raise the temperature to a fixed point temperature at which measured values are taken. If the furnace temperature stabilizes at the fixed point temperature (± 0.3 ° C./5 minutes) in step 4, the operation state of the standard thermocouple is stabilized in step 5 (± 0.5
(μV / 20 minutes), and the measured values (thermoelectromotive force μV) of both the standard thermocouple and the thermocouple to be calibrated are taken in step 6. In step 7, the stability during the data fetch operation is confirmed, and when the value of the standard thermocouple deviates from ± 0.5 μV, the process returns to step 6 and data fetch is performed again. When the value is obtained in a stable state, the process returns to step 4 until the measurement at all fixed-point temperatures is completed in step 8, and the acquisition of data is repeated. When the last measurement is completed, the heater is turned off in step 9 and
When the temperature is lowered, the thermocouple to be calibrated is removed in step 10 and the measurement at the fixed point temperature using the electric furnace is completed.

On the other hand, when the data of the reference thermocouple and the thermocouple to be calibrated at each fixed-point temperature are fetched, the arithmetic unit 3 operates in step 15 as follows. First, the fixed-point temperature realized in the electric furnace was measured with an electric furnace thermometer (R thermocouple) and controlled to the fixed-point temperature, so it was not the exact fixed-point temperature T but its nearby temperature T + △ (this is the sign of the plus or minus sign). Possible small value)
It is. In step 16, the electromotive force value a of the reference thermocouple at the fixed point temperature T is read out from the RAM (this is calculated and calculated based on the data calibrated by the Nippon Electric Keiki Inspection Center, so the reliability is high and the fixed point And the difference b'- between the electromotive force a 'of the reference thermocouple measured at the temperature near the fixed point T + △ and the electromotive force b' of the thermocouple to be calibrated. a 'is calculated.
Since the difference between the two can be considered to be equal both at the fixed point temperature T and at the nearby T + △, the electromotive force b of the thermocouple to be calibrated at the fixed point temperature T is a + (b′−a ′). Therefore, the temperature value corresponding to this electromotive force value is stored in the ROM
Is read from the JIS thermoelectromotive force table stored in the table. Then, the difference between the value and the fixed-point temperature T is calculated and determined as a temperature error at the fixed-point temperature T of the thermocouple to be calibrated, and the temperature is sequentially controlled to each fixed-point temperature. Find the deviation data of Then, the deviation data at the plurality of fixed-point temperatures is approximated by a higher-order polynomial as in the case of the standard thermocouple, coefficients are obtained, and a deviation expression indicating the characteristics of the thermocouple to be calibrated is obtained. This deviation formula and JI
An error regression calculation is performed from the thermoelectromotive force table of S to obtain a thermoelectromotive force table of the thermocouple to be calibrated. In step 17, those values are stored as calibration data in an electronic recording medium such as a magnetic disk. FIG. 4 shows the result of reading out the values at step 18 and printing out the deviation value of the fixed point temperature. In FIG. 4, the reference thermocouple temperature and the reference thermocouple electromotive force are the values of the electromotive force table of the standard thermocouple read from the memory, and the test thermocouple electromotive force is the value of the temperature near the fixed point. The electromotive force value a 'of the reference thermocouple measured in the electric furnace
The difference (b'-a ') between the electromotive force value b' of the thermocouple to be calibrated and
This is the electromotive force value at the fixed point temperature of the thermocouple to be calibrated, which is calculated by adding to the electromotive force value of the reference thermocouple at the fixed point temperature.
The temperature value read from the JIS thermoelectromotive force table for this value is described as a test thermocouple temperature, and the difference between this value and the fixed point temperature is described as a temperature error of the thermocouple to be calibrated.

When deviation data of the thermoelectromotive force at a plurality of fixed-point temperatures is obtained, an approximate expression (higher-order polynomial) indicating the deviation characteristic of the thermocouple to be calibrated is calculated based on the data, and is used as a reference in FIG. Similar to the data sheet of the standard thermocouple, a graph display of the error characteristics of the thermocouple to be calibrated and a thermoelectromotive force table can be obtained. Also, as an option, the IS
A grade sheet corresponding to O-9000 can be attached.

[0012]

FIG. 5 shows a thermocouple automatic calibration furnace according to the present invention using a tubular precision electric furnace. A is a plan view, B is a tube axial direction side view, and C is a tube longitudinal direction side view. Thermocouple automatic calibration furnace 11
Is composed of platinum furnace 13, Kanthal furnaces 14, 15 and gantry 12,
The size is 1200mm x 710mm x 1750mm. 16 is a thermocouple holding rod, 17 is a soaking tube for a platinum furnace, and 18 and 19 are soaking tubes for a Kanthal furnace. FIG. 6 shows an electric furnace control device 20 according to the present invention.
Is a program controller, 22 is a heater ammeter, 23 is a temperature recorder, 24 is a power receiving lamp, 25 is a primary voltmeter, and 26 is a breaker. 21, 22, 26 are integrated into one unit and are provided for each of the three furnaces. FIG. 7 shows a data processing apparatus of the present invention, in which 31 is a display, 32
Is a laser printer, 33 is a computer constituting an arithmetic unit, 35 is a scanner, 36 is an uninterruptible power supply, and 37 is an input means (keyboard).

The heating temperature range of the platinum furnace is 200 to 1500 ° C., the furnace temperature stability is ± 0.15 ° C./60 minutes, and the soaking temperature is 140 ° C.
Within ± 0.5 ° C within ± 100mm of core center at 0 ° C, heating element is 8mm W × 0.2mmt with platinum-rhodium alloy (80 Pt 20 Rh)
You are using This platinum furnace uses three R thermocouples as control thermocouples. The heating method is a horizontal three-segment heater heating method. The size of the furnace is 320 mmφ x 780 mm. The inner diameter of the soaking tube 17 is 20 mmφ. The number of possible thermocouples is 4.0 mmφ in outer diameter
The maximum number is 3 when using the insulating tube.

The heating temperature range of the Kanthal furnace is 200 to 1100
℃, furnace temperature stability is ± 0.15 ℃ / 60min, soaking temperature is 1100 ℃, furnace temperature is within ± 0.5 ℃ within ± 100mm, and heating element is Kanthal A-1 6.0mmφ. ing. The control thermocouple of this Kanthal furnace is R thermocouple and each uses 3 thermocouples.
The heating method is a horizontal three-division heater heating method, the size of the furnace is 200 mmφ x 780 mm, the inner diameter of the soaking tubes 18 and 19 is 40 mmφ, and the number of thermocouples that can be calibrated is up to 6 when the sheath outer diameter is 1.0 mmφ. It is. The control system of the control panel is a controller communication general control system, the power supply is AC three-phase 200V, 50Hz, and the temperature recorder adopts a recorder with an overheat alarm setting function.

The apparatus of this embodiment can drive and control three furnaces at the same time, not only can monitor the temperature of the furnace with a temperature recorder, but also monitor the temperature inside the three furnaces by operating the mouse as needed. It has a function to display it on the display. Connect multiple thermocouples to be calibrated to each furnace (standard type can connect 7 thermocouples to be calibrated in addition to the standard thermocouple)
The thermo-electromotive force signals from each thermocouple can be sequentially taken into the arithmetic processing unit via a scanner (in this embodiment, up to 40 channels). The thermocouples that can be calibrated are not limited to the R-type thermocouples, and can correspond to various thermocouples such as S, B, K, E, J, T, and N. Calibration test temperature (200 ℃, 400 ℃,
5 steps (600 ° C., 800 ° C., 1000 ° C.) have been described as an example, but the present invention is not limited to this and can be set arbitrarily, such as 8 steps. The method of calculating the deviation formula consisting of higher-order polynomials from the deviation values at multiple fixed-point temperatures obtained by measurement is S
VD, Glavens, Householder, Lu decomposition and other methods can be selected. For example, it can be performed by the Lu decomposition method using commercially available calculation software LABVIEW (registered trademark of Japan National Instruments Co., Ltd.).

[0016]

According to the present invention, the operation can be performed while visually confirming the stable state of the electric furnace and the stable state of the standard thermocouple during the calibration test on a display and a recording device, and a highly reliable calibration can be realized. Then, since the deviation of the standard thermocouple as a reference is determined based on the thermoelectromotive force value at a fixed point temperature obtained by the Nippon Electric Keiki Inspection Laboratory, the accuracy of the reference itself is high and the calibration accuracy is improved. In addition, since the characteristics of the standard thermocouple and the thermocouple to be calibrated can be obtained in the form of a deviation equation, accurate approximations can be obtained for the temperatures between the values in the electromotive force table, and accurate calibration can be realized. Accurate measurement is possible even with normal measurement using a calibration thermocouple. In addition, since complicated calculations are performed using a computer, the efficiency of each stage is guaranteed, for example, the time can be reduced and energy can be saved as compared with the conventional calibration time.

[0017]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall system of the present invention.

FIG. 2 is a flowchart of a calibration operation according to the present invention.

FIG. 3 is a data sheet for a standard thermocouple used as a reference processed and printed out by the calculation unit of the present invention.

FIG. 4 is a calibration test report of a standard thermocouple to be calibrated, which has been processed and printed out by the arithmetic unit of the present invention.

FIG. 5 is an example of a thermocouple automatic calibration furnace used in the present invention, wherein A is a plan view, B is a tube axial side view, and C is a tube longitudinal direction side view.

FIG. 6 is a front view showing the electric furnace control device 20 of the present invention.

FIG. 7 is a front view showing the data processing device of the present invention.

[Explanation of symbols]

 1,21 Program controller for electric furnace control 2,11 Electric furnace for thermocouple calibration 3,33 Arithmetic processing unit (computer) 4,37 Input means 5,31 Display 6,32 Printer 13 Platinum furnace 14,15 Kanthal furnace 22 heater ammeter 23 temperature recorder

Claims (3)

[Claims] An electric furnace in which a standard thermocouple as a reference and a thermocouple to be calibrated can be installed, an electric furnace control unit for controlling the electric furnace to a set temperature, a calculation unit, a display, and a printer, The calculation unit calculates the approximation formula of the deviation between the standard thermocouple and the thermocouple to be calibrated based on the calibration data of the known fixed point temperature of the standard thermocouple and the calibration measurement value from the standard thermocouple and the thermocouple to be calibrated in the electric furnace. Means for obtaining, means for displaying the furnace temperature and the error curve of each thermocouple and the thermoelectromotive force table on the display,
Means for printing out the data as a hard copy to the printer. 2. A means for inputting calibration data at a plurality of fixed-point temperatures of a standard thermocouple, a means for obtaining a deviation from a thermoelectromotive force table of JIS based on the data, and an approximation by a higher-order polynomial from the deviation value. Means for determining the coefficient by using
2. The calculation unit according to claim 1, further comprising means for calculating a thermoelectromotive force table of the standard thermocouple from the S thermoelectromotive force table. 3. A means for calculating a deviation of a thermocouple to be calibrated from measured thermoelectromotive force data of a standard thermocouple and a thermocouple to be calibrated at the same temperature and a thermoelectromotive force table of the standard thermocouple,
A means for calculating a coefficient by approximating the deviation value at a plurality of temperatures by a higher-order polynomial; and a means for calculating a thermoelectromotive force table of the thermocouple to be calibrated from the approximation formula and a JIS thermoelectromotive force table. The operation unit according to 1.