JP3365671B2 - Compensation method of cold junction temperature in glassy carbon-graphite thermocouple - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reduces an error based on a temperature difference between cold junctions in a glassy carbon-graphite thermocouple and obtains a highly accurate temperature measurement result. The present invention relates to a method of compensating for a cold junction temperature for obtaining a temperature. 2. Description of the Related Art Thermocouples are formed by joining different kinds of linear elements at their tips, and measuring the thermoelectromotive force generated by changing the temperature of the other contact while maintaining one contact at room temperature. It is useful as a member of a thermoelectric thermometer that measures the temperature of a temperature measuring object.
As the linear element, a metal material is mainly used. Usually, the linear element is inserted into a cylindrical magnetic protection tube to form a thermocouple. The temperature measurement range varies depending on the type of element material to be combined. [0003] However, the upper limit of the temperature measurement of a commercially available thermocouple is limited to about 1600 ° C for the R thermocouple which is considered to have the highest performance. For this reason, it was necessary to use a radiation thermometer to measure a high temperature around 2000 ° C.
Further, the protection tube of the thermocouple conventionally used has a drawback that even if it is a non-metallic one, its service temperature is at most about 1700 ° C. and it is easily eroded by a corrosive atmosphere, especially a fluorine-based gas. As a thermocouple which has solved the above-mentioned disadvantages, a tube-type thermocouple in which an element tube and an element rod are made of glassy carbon and graphite (Japanese Utility Model Publication No. 3-37243), and further improvements have been made. The element rod has a coefficient of thermal expansion of 3 × 10 ^-6 /
A glassy carbon-graphite thermocouple made of a graphite material having a temperature of not more than 100 ° C. and in which the connecting means of the element tube and the tip mounting portion of the element rod are fixed via a porous carbon adhesive layer (Japanese Utility Model Application Laid-Open No. 3-67).
No. 464), a large-diameter distal end having an end surface having substantially the same diameter as the inner diameter of the element tube and having a normal surface contact with the inner surface of the bottomed end portion is formed at the distal end of the element tube. Applicant has developed a glassy carbon-graphite thermocouple (Japanese Utility Model Application No. 5-71182) equipped with a spring-spring mechanism for crimping the enlarged diameter tip to the bottomed tip of the element tube. Proposed. [0005] In the above-mentioned glassy carbon-graphite thermocouple, the element tube made of glassy carbon and the lead wire terminal of the element rod made of graphite material are connected to the thermocouple. Since it becomes a cold junction, it is necessary to perform forced cooling so that both temperatures become equal. However, even when forced cooling is performed, there is a problem that a temperature difference occurs between the two terminals due to a difference in thermal conductivity between the element tube and the element rod, resulting in an error in a measured value. SUMMARY OF THE INVENTION It is an object of the present invention to correct the cold junction temperature of a glassy carbon element tube and a graphite element rod to reduce an error due to a temperature difference between cold junctions without forcibly cooling a lead terminal. It is an object of the present invention to provide a method for compensating a cold junction temperature in a glassy carbon-graphite thermocouple that always provides a highly accurate temperature measurement result. In order to achieve the above object, a method of compensating for a cold junction temperature in a glassy carbon-graphite thermocouple according to the present invention is to provide a lead terminal at a base end. A graphitic element having a vitreous carbonaceous element tube having a bottomed tip, and a lead terminal at a base end extending straight in the element tube with the tip contacting the bottomed tip. In a glassy carbon-graphite thermocouple composed of a rod, a metal thermocouple is connected to each base end of an element tube and an element rod to measure a cold junction temperature, and the cold junction temperature is measured using the cold junction temperature. The configuration is characterized in that the temperature is corrected during the operation. In the present invention, a copper lead wire connected to a lead wire terminal portion is used to extract the thermoelectromotive force of the thermocouple, and the temperature of each lead wire terminal portion is measured by a glassy carbonaceous element tube and a graphite element. This is done by a metal thermocouple, preferably a K thermocouple, connected to the proximal end of the bar. First, as shown in FIG. 1, when the thermoelectromotive force characteristics of the vitreous carbonaceous element tube 1 and the copper lead wire 2 are measured using the copper lead wire 2 as a negative electrode, the obtained thermoelectromotive force (E _C'C ) is obtained. The relationship of the temperature (T ₁ ) of the contact A is as shown in FIG. The thermoelectromotive force is generated when dissimilar substances are connected, and since the magnitude is a function of the temperature of the connection point, for example, the glassy carbonaceous element tube (GC) and the copper lead (Cu) When the thermoelectromotive force [E _GC-Cu (T)] generated at the contact is shown with reference to the lead wire when the contact temperature is T (° C.), the electromotive force measured between C′C in FIG. ) Expression. E _C′C (T ₁ ) = E _GC-Cu (T ₁ ) −E _GC-Cu (T _C ) (1) Similarly, as shown in FIG.
The relationship between the thermoelectromotive force (E _F'F ) obtained by measuring the thermoelectromotive force characteristics of the copper lead wire 2 and the copper lead wire 2 as the negative electrode and the temperature (T ₂ ) of the contact D is as shown in FIG. . Therefore, the electromotive force [E generated at the contact point between the graphite element rod (GP) and the copper lead wire (Cu) [E
_GP-Cu (T)] when the contact temperature is T (° C.) and the lead wire is used as a reference, the electromotive force measured between F′F in FIG.
Equation (2) shows the result. E _F'F (T ₂ ) = E _GP-Cu (T ₂ ) −E _GP-Cu (T _C ) (2) When actually operating using a glassy carbon-graphite type thermocouple, Is measured by connecting a copper lead wire 2 to each lead wire terminal portion of the vitreous carbonaceous element tube 1 and the graphite element rod 3 as shown in FIG. In this case, assuming that the temperature of the contact H between the glassy carbonaceous element tube 1 and the copper lead wire 2 is t ₀ (° C.), the electromotive force generated at this contact H is −E _GC-Cu (t ₀ ). is there. If the temperature of the contact I between the graphite element rod 3 and the copper lead wire 2 is t ₁ (° C.), the electromotive force generated at this contact I is E _GP-Cu
(t ₁ ). When the electromotive force generated at the contact point G between the graphitic element rod 3 and the vitreous carbon element tube 1 is represented by E _GC-GP (T) based on the graphitic element rod, the contact point G (temperature measuring contact)
E a in electromotive force generated measuring junction temperature of T _h (° C.)
_GC-GP (T _h ). Therefore, the electromotive force measured between J′J is as shown in equation (3). E _J'J (T _h , t ₀ , t ₁ ) = E _GP-Cu (t ₁ ) + E _GC-GP (T _h ) −E _GC-Cu (t ₀ ) (3) By transforming equation (3) using equations (1) and (2), equation (4) is obtained. E _GC-GP (T _h ) = E _J′J (T _h , t ₀ , t ₁ ) + E _C′C (t ₀ ) + E _GC-Cu (T _C ) −E _F′F (t ₁ ) −E _GP-Cu (T _C ) (4) E _GC-Cu (T _C ) and E _GP-Cu (T _C ) are constants of unknown size. Therefore, Equation (5) is used. E _GC-Cu (T _C ) −E _GP-Cu (T _C ) = C _Tc (constant) (5) E _C′C (t ₀ ) and E _F′F (t ₁ ) are respectively It can be obtained from the relationship between FIG. 2 and FIG. Also, E
_J′J (T _h, t ₀ , t ₁ ) is an electromotive force to be measured. Therefore, first, the temperature (T _h ) of the temperature measurement contact G is changed to change the temperature of the contact H [t ₀ (° C.)] and the temperature of the contact I [t ₁ (° C.) in FIG.
], And the electromotive force [E _J'J (mV)] between _J'J is measured. From this measurement result, the relationship between the temperature measuring junction temperature [ _Th (° C.)] and [E _GC-GP ( _Th ) −C _TC ] is obtained by the following equation (6). _Th = f [E _GC-GP (T _h ) -C _TC ] (6) Therefore, the glassy carbon of the present invention
The method of compensating the cold junction temperature in the graphite thermocouple is performed in the following order in the connection structure of FIG. (1) Temperature of contact H between glassy carbonaceous element tube 1 and copper lead wire [t ₀ (° C.)], graphitic element rod 3 and copper lead wire 2
The temperature [t ₁ (° C.)] and the electromotive force [E _J'J (mV)] between J and J are measured. (2) Utilizing the relationship between FIG. 2 and FIG. 4, t ₀ and t ₁ to E _{c ′} are measured by a metal thermocouple attached to each base end of the vitreous carbonaceous element tube and the graphite element rod. _c (t ₀ ) and E
_{Find F'F} (t ₁ ). (3) E _GC-GP (T _h ) −C _Tc = E _J′J + E _C′C (t ₀ ) −E
_{Find F'F} (t ₁ ). (4) (6) displays seek measuring junction temperature T _h from the equation. [0016] Thus, by measuring the lead terminal portion temperature of the glassy carbonaceous element tube [t ₀ (° C.)] and the lead wire terminal portion temperature of the graphite element rod [t ₁ (° C.)], corrected To obtain the temperature measurement junction temperature [ _Th (° C)
] Can be measured with high accuracy. According to the present invention, the temperatures of the base ends of the vitreous carbon-graphite thermocouple in the element tube and the element rod are measured via the metal thermocouple, and the cold junction temperature is utilized. By performing the correction, the error due to the temperature difference between the cold junctions can be effectively reduced without forcibly cooling the terminal portion during the temperature measurement operation. Therefore, high-precision temperature measurement can always be performed over a wide temperature measurement range. FIG. 6 shows a method of compensating a cold junction temperature according to the present invention.
This will be specifically described based on the embodiment shown in FIG. In FIG. 6, reference numeral 4 denotes a glassy carbon-graphite type thermocouple, which is a glassy carbonaceous element tube 1 having a bottomed distal end provided with a lead terminal at a base end, and having the distal end having the above-mentioned end. The inside of the element tube 1 extends straight in a state where the element tube 1 is brought into pressure contact with the bottom end portion, and is integrally formed by a graphite element rod 3 having a lead terminal portion at a base end portion. This structure is the same as the structure described in Japanese Utility Model Application No. 6-71182 (FIG. 1). The glassy carbon-graphite thermocouple 4 is inserted and fixed by a support jig 8 at an end of a closed heating furnace 7 provided with an argon gas introduction pipe 5 and an argon gas discharge pipe 6, and a glass is attached to the other end. The radiation thermometer 9 was placed in a state where the tip of the bottom of the carbon-graphite-based thermocouple 4 was opposed to the bottomed end of the thermocouple 4. Copper lead wires 2 are connected to the lead terminals of the graphite element rod 3 and the vitreous carbon element tube 1, respectively, and connected to the recording apparatus 10, and the base of the graphite element rod 3 is separately provided. The K thermocouple 11 connected to the end and the K thermocouple 12 connected to the base end of the vitreous carbonaceous element tube 1 were connected to the recording device 10, respectively. Copper lead 2
The portions of the supporting jig 8 from which the K thermocouples 11 and 12 are led out were sealed with a hermetic seal. In the above condition, the temperature of the heating furnace 7 is set to 1000 to
The temperature was varied in the range of 2000 ° C., and the temperature measurement contact temperature [T (° C.)] measured with a radiation thermometer at this time, and the thermoelectromotive force [Eob (m) of a glassy carbon-graphite thermocouple measured with a copper lead wire were used.
V)], the cold junction temperature of the glass-like carbonaceous element tube measured at K thermocouple [t ₀ (° C.)] and the cold junction temperature of the graphite element rod [t ₁ (° C.)], corrected heat electromotive force [Ec (mV)], the calculated value of the temperature measuring junction temperature [ _Th (° C)] and the error [(T- _Th )
/ T (%)] are shown in Tables 1 and 2. Tables 3 and 4 show data when the cold junction temperature was not corrected according to the present invention. [Table 1] [Table 2] [Table 3] [Table 4] As is apparent from consideration of the results of Tables 1 and 2 and Tables 3 and 4, the temperature measurement error can be reduced from about ± 1.5% to ± 0.5% by applying the cold junction temperature compensation method of the present invention. It was recognized that it could be reduced to about 8%. As described above, according to the method of correcting the cold junction temperature according to the present invention, the cold junction temperature of the vitreous carbonaceous element tube and the graphitic element rod in the vitreous carbon-graphite thermocouple is reduced. By measuring through a metal thermocouple and using this to correct the cold junction temperature, it is possible to reduce the temperature measurement error based on the temperature difference between the cold junctions and always obtain highly accurate temperature measurement results. It becomes possible. In addition, since the forced cooling of the cold junction is not required, the device can be simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a connection explanatory diagram in which a contact A is formed by a glassy carbonaceous element tube and a copper lead wire. FIG. 2 is a graph showing the relationship between the temperature of a contact A in FIG. 1 and the thermoelectromotive force. FIG. 3 is an explanatory diagram of connection in which a contact D is constituted by a graphite element rod and a copper lead wire. FIG. 4 is a graph showing a relationship between a temperature of a contact point D and a thermoelectromotive force in FIG. 3; FIG. 5 is an explanatory diagram of connection of a glassy carbon-graphite thermocouple according to the present invention. FIG. 6 is an explanatory sectional view showing a temperature measuring device used in an example of the present invention. [Description of Signs] 1 Vitreous carbon element tube 2 Copper lead wire 3 Graphite element rod 4 Glassy carbon-graphite thermocouple 5 Argon gas introduction pipe 6 Argon gas discharge pipe 7 Heating furnace 8 Supporting jig 9 Radiation temperature Total 10 Recording device 11 K thermocouple 12 K thermocouple

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 62-5664 (JP, U) JP-A 3-676464 (JP, U) JP-A 26-10093 (JP, Y1) 505504 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01K 7/12 G01K 7/02 H01L 35/22

Claims (1)

(57) Claims 1. A vitreous carbonaceous element tube having a bottomed tip provided with a lead terminal at a base end, and a tip contacting the bottomed tip. In a glassy carbon-graphite-based thermocouple consisting of a graphitic element rod provided with a lead terminal at the base end extending straight in the element tube in a state in which the element tube and the element rod A method of compensating a cold junction temperature in a glassy carbon-graphite thermocouple, wherein a cold junction temperature is measured by connecting a metal thermocouple, and the temperature between the cold junctions is corrected using the cold junction temperature. .