JPH09250956A - Fixed point calibrating method for nobel metal thermocouple - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a thermoelectromotive force value at real melting point of Pd by performing argon displacement after the surroundings of a Pd part bridged to a hot junction is evacuated below 1pa after its temperature is lowered to a melting point or below with an electric furnace whose temperature is 1500 deg.C or above. SOLUTION: In an alumina tube 13, two thermoelectric couple element wires 26 are made to pass through an insulating tube 25, and an R thermoelectric couple 28 wherein a Pd wire 27 is attached to a hot junction of its tip in a bridging manner is inserted, and the part between the upper end opening and the insulating tube 25 is sealed with epoxy system double fluid bonding agent 29. And a zero junction of the R thermoelectric couple 28 is put in an ice point 30, and lead wires 31 are connected, respectively, for starting measurement for thermoelectromotive force with a fixed point correcting device. For example, after temperature of the electric furnace is set at 1545 deg.C and the inside of the device is deaerated with a vacuum pump, and a two-direction change-over valve 22 is changed to supply argon gas into the device with an argon gas supply pipe 23 for filling up, and the temperature at which the Pd wire 27 melts is measured with the thermoelectromotive force of the R thermoelectric couple 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed-point calibration method for precious metal thermocouples, and more particularly to improvement of a fixed-point calibration method for Pd points by a wire bridge method.

[0002]

2. Description of the Related Art In general, a fixed point calibration method for precious metal thermocouples includes
The wire bridge method is adopted. In the wire bridge method, as shown in FIGS. 4A and 4B, a thermocouple wire 40 to be inspected is passed through a two-hole insulating tube 41, and a noble metal wire as a sample wire, for example, a Pd wire 42 is attached to the hot junction at the tip. As shown in Fig. 4a, the method of attachment is to cut the tip of the thermocouple wire 40 and crimp it in the shape of "I" to fix it, and as shown in Fig. 4b, to the hot junction. There is a method of winding several times. In this way, the thermocouple 43 with the Pd wire 42 attached is inserted into the furnace of the Pd point heating furnace 44 shown in FIG. 5 which is adjusted to a temperature about 20 ° C. lower than the Pd melting point in advance, and from this point the thermoelectromotive force is measured. After the thermoelectromotive force value reaches a constant value, the furnace temperature is raised at a temperature rising rate of about 1 to 2 ° C./min. During this time, the thermoelectromotive force is continuously measured. When the Pd wire 42 melts, the thermoelectromotive force becomes constant for a short time, and the thermoelectromotive force at this point is read.

By the way, since such a wire bridge method is carried out in the atmosphere, the melted liquid phase Pd dissolves a large amount of oxygen and does not dissolve it in the solid phase. That is, in the wire bridge method, when the melting point is reached, oxygen forms a solid solution in the liquid phase portion and the melting point (freezing point) is lowered. It cannot be said that the melting point of pure Pd is measured, and the value is lower than the true value.

As another conventional fixed-point calibration method for precious metal thermocouples, a thermocouple 45 having a length of 600 mm, as shown in FIG.
Assembled using a 4-hole insulating tube 46 with a diameter of 4 mm, and injecting argon gas or an argon-oxygen mixed gas from one hole of the 4-hole insulating tube 46 toward the temperature measuring junction of the thermocouple, and then performing Pd by the wire bridge method. There is a method of measuring a fixed point.

However, in this method, it is doubtful that oxygen will be completely degassed when only argon gas is blown, and since argon gas at a low temperature is supplied to the tip, it is difficult to maintain thermal equilibrium, It is very doubtful that the true Pd melting point is being measured.

[0006]

Therefore, the present invention is to provide a fixed point calibration method for a noble metal thermocouple capable of obtaining a thermoelectromotive force value at the melting point of true Pd.

[0007]

A fixed point calibration method for a precious metal thermocouple according to the present invention for solving the above problems is a Pd point bridged at least to a hot junction in a fixed point calibration of a Pd point by a wire bridge method. After heating the temperature around the melting point to a temperature below the melting point in an electric furnace with a furnace temperature of 1500 ° C or higher, and applying a vacuum of 1pa or lower, argon replacement is performed, and P in an oxygen-free atmosphere.
The melting point of d is measured.

Further, as a method of making the hot junction of the precious metal thermocouple into a vacuum and an argon atmosphere, an alumina single-sealed tube in which a metallic flange is joined and integrated with alumina cement around the opening end and an O-ring are interposed. The thermocouple introduction pipe is fixed by tightening the bolts, and a cap having a passage leading to the vacuum pump and the argon gas supply pipe, and a flange portion capable of contacting the flange integrally joined to the opening end of the alumina piece-sealing tube, Bolt the flanges together via the O-ring, insert the thermocouple from the thermocouple introduction tube, and expose the hot junction of the precious metal thermocouple from the outlet of the thermocouple introduction tube in the alumina single-sided tube. Also, it is achieved by maintaining the airtightness by sealing the inlet of the thermocouple introduction tube with a resin or an adhesive.

Since the melting point of Pd is measured in the oxygen-free atmosphere as described above, the true temperature value of Pd melting can be obtained.

Further, since the flange is joined and integrated with the alumina end-sealed tube with alumina cement and the cap to which the thermocouple introduction tube is fixed is fixed by bolting the flange portions together, the thermocouple can be attached and detached. Although easy, the airtightness inside the alumina tube can be kept high.

[0011]

EXAMPLE An example of a fixed point calibration method for a precious metal thermocouple according to the present invention will be described. First, a fixed point calibration device for carrying out this method will be described with reference to FIG. 1. Reference numeral 1 is a piece-sealed tube made of alumina (inner diameter 40 mm, outer diameter 50 mm, length 500 mm), and a water-cooled tube 2 with a SUS flange 3 Is alumina cement 3
It is joined and integrated at a. Reference numeral 4 is a cap having a SUS flange 3 having a flange 7 tightened and fixed by a bolt 6 with an O-ring 5 interposed, and having a through hole 8 in the center. In the center of the alumina piece-sealing tube 1, an alumina spacer is concentrically provided with a thin diameter alumina piece-sealing tube (inner diameter 16 mm, outer diameter 20 mm, length 480 mm) 9 on the outer circumference.
A cap 12 having a through hole 11 is fitted to the upper end of the small diameter alumina piece-sealed tube 9 which is disposed through the tube 10. An alumina tube 13 having an inner diameter of 5 mm, an outer diameter of 8 mm, and a length of 600 mm is arranged in the thin alumina piece-sealing tube 9 penetrating the through hole 8 at the center of the cap 4 and the through hole 11 of the cap 12. It is centrally held by a flange 14 provided in multiple stages on the outer circumference. An O-ring 15 is provided in the opening edge concave portion 8a of the through hole 8 of the cap 4 penetrating the alumina tube 13.
, The pressing plate 16 fitted in the alumina tube 13 is clamped and fixed to the upper surface of the cap 4 by the bolt 17, the O ring 15 is compressed, and the space between the through hole 8 and the alumina tube 13 is sealed. Has been done. The cap 4 is provided with a passage 18 which communicates with the inside of the alumina piece-sealed tube 1.
A compound meter 19 is connected to the passage 18. Further, a passage 20 communicating with the inside of the single-sided tube 1 is separately provided in the cap 4, a suction pipe 21 connected to a vacuum pump (not shown) is connected to the passage 20, and a two-way switching valve 22 is provided in the middle of the suction pipe 21. An argon gas supply pipe 23 is connected via the.

Next, an example of a fixed point calibration method for a precious metal thermocouple according to the present invention using the fixed point construction device constructed as described above will be described.
The fixed point calibration of the Pd point will be described. In the alumina tube 13 of the fixed-point calibration device shown in FIG. 1, as shown in FIG. 2, a thermocouple element 26 having a wire diameter of 0.5 mm is attached to an alumina two-hole insulating tube 25 having a diameter of 3 mm and a length of 600 mm. Insert the R thermocouple 28, which consists of a Pd wire 27 with a wire diameter of 0.5 mm and a length of 15 mm attached to the hot junction at the tip by the bridge method, and insulates the upper end of the alumina tube 13 from the two holes. The tube 25 was sealed with an epoxy two-component adhesive 29. Then, the fixed point calibration device was set in an electric furnace (not shown), the zero contact point of the R thermocouple 28 was put at the freezing point 30, and the lead wire 31 was connected to each to start measurement of thermoelectromotive force with a voltmeter (not shown). .

The R thermocouple 28 has Zn and Au points preliminarily assigned values of 3.608 mV and 11.366 mV, respectively. After raising the furnace temperature of the electric furnace and sufficiently deaerating the inside of the device, that is, the alumina piece-sealed tube 1 at 1545 ° C (10 ^-3 Torr or less), switch the two-way switching valve 22 to supply argon gas. Argon gas was supplied and filled into the alumina piece-sealed tube 1 through the pipe 23, and the argon pressure was maintained in the range of 1.01 to 1.1 atm while observing the compound gauge 19. Next, the furnace temperature was raised at a rate of 1 ° C./min, and the temperature at which the Pd wire 27 was melted was measured by the thermoelectromotive force of the R thermocouple 28. The measured value is 1
It was 8.221 mV. After performing the same measurement twice,
The measured values were 18.223 mV and 18.222 mV.

On the other hand, as a conventional example, the fixed point calibration device shown in FIG. 3 excluding the upper part of the fixed point calibration device of FIG.
When the temperature at which is melted is measured with the thermoelectromotive force of the R thermocouple 28 three times, the measured values are 18.201mV, 18.198mV, 18.204
mV.

As can be seen from the results of the fixed point calibration of the Pd point in the above-mentioned embodiment and the conventional example, the measured value of the conventional example is low. When the Pd wire is melted, oxygen is solid-dissolved in the liquid phase portion to lower the melting point. In contrast to this, the measured value of the example is high,
When melting the Pd wire, there is no oxygen in the fixed point calibration device,
Moreover, since the internal pressure is kept within the range of 1.01 to 1.1 atm, the oxygen gas that permeates into the alumina piece-sealed tube 1 of the fixed point calibration device is blocked, and oxygen does not form a solid solution in the liquid phase portion of Pd. , Because the melting point never decreases,
This gives the true temperature value for Pd melting.

[0016]

As can be seen from the above description, according to the fixed point calibration method for a noble metal thermocouple of the present invention, the true Pd melting temperature can be obtained without the influence of oxygen during Pd melting.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a fixed point calibration device for carrying out a fixed point calibration method for a precious metal thermocouple according to the present invention.

FIG. 2 is a diagram showing a state in which a fixed-point calibration method for a precious metal thermocouple according to the present invention is carried out using the fixed-point calibration device shown in FIG.

3 is a diagram showing a state in which a conventional fixed-point calibration method for a precious metal thermocouple is carried out using the fixed-point calibration device excluding the upper part of the fixed-point calibration device in FIG.

FIG. 4 shows how to attach the Pd wire in the wire bridge method of the conventional fixed-point calibration method for precious metal thermocouples.
Is a bridge method in which the tip of a thermocouple wire is pierced and crimped in my form, and b is a method of winding it around a hot contact portion several times.

FIG. 5 is a diagram showing an outline of a conventional Pd point heating furnace.

FIG. 6 is a diagram showing another conventional fixed-point calibration method for a precious metal thermocouple.

[Explanation of symbols]

 1 Alumina piece-sealed tube 2 Water-cooled tube 3 SUS flange 3a Alumina cement 4, 12 Cap 5, 15 O-ring 6 Bolt 7, 14 Flange 8, 11 Through hole 9 Small diameter alumina piece-sealed tube 10 Alumina spacer 13 Alumina tube 16 Presser plate 17 Bolts 18, 20 Passage 19 Compound meter 21 Suction pipe 22 Two-way selector valve 23 Argon supply pipe 25 Alumina two-hole insulating pipe 26 Thermocouple element wire 27 Pd wire 28 R thermocouple 29 Epoxy Two-component adhesive 30 Freezing point 31 Lead wire

Claims (2)

[Claims] 1. In a fixed point calibration method of a Pd point by a wire bridge method, at least a P bridged to a hot junction is used.
The melting point of Pd should be measured in an oxygen-free atmosphere after making the area around the d part an electric furnace with a furnace temperature of 1500 ° C or higher and a temperature of the melting point or lower, then applying a vacuum of 1 pa or lower, then performing argon replacement. Fixed-point calibration method for precious metal thermocouples. 2. A method of placing a hot junction of the precious metal thermocouple in a vacuum and an argon atmosphere by using an alumina piece-sealed tube in which a metal flange is integrally joined with alumina cement around the opening end and an O-ring. The thermocouple introduction pipe is fixed by bolting, and a cap having a passage leading to the vacuum pump and the argon gas supply pipe, and a flange portion capable of contacting the flange integrally joined to the opening end of the alumina piece sealing tube is provided. , The flange parts are bolted together through the O-ring, and the thermocouple is further inserted from the thermocouple introduction tube to expose the hot junction of the precious metal thermocouple from the outlet of the thermocouple introduction tube in the alumina single-sided tube.
The hot junction of the noble metal thermocouple is held in an airtight alumina tube by sealing the inlet of the thermocouple introduction tube with a resin or an adhesive.
Fixed-point calibration method for the described precious metal thermocouple.