The unique Installation for calibration of tungsten-rhenium thermocouples
was developed by Obninsk Thermoelectric Company (OTC, Ltd)
Russian Federal Agency for Intellectual Property, Patents and Trademarks took positive decision to issue the patent for invention “The unit for calibration of high-temperature thermocouples” (temperature range 1200-2200 ℃). Patent owner is OTC, Ltd., the authors are Anatoly Ulanovskiy, (managing director), Roman Maletsky (scientific worker). The unit was developed under a Grant contract with the Russian Foundation for innovations promotion.
The invention is used as a part of the installation certified by the specialists of The D.I. Mendeleev All-Russian Institute for Metrology (VNIIM) (Russia, Saint-Petersburg). Certification was made with the help of a reference radiation pyrometer of the first grade.
The Installation reproduces the set temperature values with high accuracy and has the maximum deviation of 3.5 degrees from the reading of reference pyrometer at the point 2200 °C, having acceptable deviation value 5.5 degrees. Time instability of maintaining the temperature was 1.2 degrees at the point 1800 ℃. Certification was carried out in accordance with the requirements of Russian state standards GOSTR 8.568-2017 and PMA 241.031.001405-2019.
The Installation is the Russia’s the only one unit for tungsten-rhenium thermocouples calibration within the temperature range from 1700 ℃ to the upper limit of long-term use of such thermocouple. The installation can be used in serial production of W-Re thermocouples. It is relatively easy to maintain and operate with this installation. It has low electrical power in comparison with vacuum installations and furnaces having reference black bodies. Up to 10 thermocouples can be calibrated simultaneously.
Calibration cost per a thermocouple is several times less than calibration in vacuum furnace. The upper calibration temperature is limited only by the insulating properties of high-temperature ceramics. The insulation resistance value of the oxide ceramics usually falls down by an order of magnitude when temperature increases by every 200 degrees.
Each type of ceramics has its own upper limit of the operating range. Aluminum oxide (corundum) has the limit temperature of 1700-1900 ℃, depending on the material quality and purity, boron nitride (hexagonal and pyrolytic) - up to 1800 ℃, leucosapphire - up to 1950 ℃, hafnium or yttrium oxide up to 2200 ℃, beryllium oxide up to 2300-2400℃ (it isn't used in conventional laboratories due to toxicity). Thermocouple calibration is performed in an inert gas media (argon) within protective tungsten tube, which restricts graphite vapor transfer to working junctions of the thermocouples and surface of the insulating tubes.
The design of the furnace and graphite electric heater also allow to install a high-temperature fixed-point (Me-C) inside the furnace working space: Rh-C (1657 ℃); Pt-C (1738℃); Cr3C2-C (1811℃); Ru-C (1953℃); Ir-C (2290℃); Re-C (2474℃), - for calibration a single thermocouple against melting-freezing temperature of Me-C alloy. Total error will not exceed one degree in the operating temperature range.
Metrological laboratory of Obninsk Thermoelectric Company is certified in Russian calibration system (Register No. 001473) for the right to calibrate all thermocouple types according to Russian state standard GOST 6616-94 including digital secondary devices for measuring and regulating temperature. An individual reference table for any thermocouple can be obtained in the operating temperature range or in the range specified by a customer. Calibration Certificate will be issued.
- Comparison the reference temperature defined by a type B reference platinum-rhodium thermocouple with the readings of thermocouples being calibrated in the temperature range 600-1700 °C;
- Comparison the readings of non-contact radiation pyrometer with the readings of tungsten-rhenium thermocouples being calibrated in the temperature range 1200-2200 °C;
- Calibration in reference temperature of melting-freezing points of eutectic metal carbide alloys (fixed points «Me-C»): Pd-C (1492 °C); Pt-C (1738 ºC); Cr3С2-С (1827°C); Ru-C (1953 ºС); Ir-C (2290 ºC); Re-C (2474 ºC).
The reference fixed points will appear when calibration orders be received. Calibration is performed using the Program for Automatic Calibration of Thermocouples (PACT), registered in the Russian state registry of computer programs (certificate No. 2016614991, dated 12.05.2016).
Outlook of the Installation for a high-temperature thermocouples calibration
and its Certificate No. 2411/0042-2020, dated 13.01.2020: