1、 Scope of application of the standard

Applicable object: Low cost metal armored thermocouples (K, N, E, J, T type, etc.) with metal casing length ≥ 500 mm.

Temperature measurement range: -40 ℃~1100 ℃.

Calibration object: Newly manufactured, in use, and repaired armored thermocouples. ‌

2、 Core metrological characteristic requirements

Room temperature insulation resistance

The insulation resistance between thermoelectric electrodes and between electrodes and metal sleeves is ≥ 1000 M Ω· m (20 ± 15 ℃, humidity ≤ 80%). ‌

Allowable deviation of indication

According to the division number and temperature range classification (1 level/2 levels), for example:

K-type (-40~375 ℃): ± 1.5 ℃ (Level 1) or ± 2.5 ℃ (Level 2)

E-type (-40~375 ℃): ± 1.5 ℃ (Level 1) or ± 2.5 ℃ (Level 2)

Please refer to Appendix E of the specification for the tolerance table

Thermal response time (dynamic performance)

Requirement: ≤ 180 seconds (conventional diameter), ultra-fine armor wire needs to be verified through a precision constant temperature bath. ‌

3、 Calibration conditions and equipment

Environmental requirements

Temperature: 15~35 ℃, fluctuation ≤ 1 ℃/hour; Humidity: ≤ 85% RH

Standard configuration

Main standard: second-class standard platinum resistance thermometer or standard platinum rhodium 10 platinum thermocouple.

Electrical measuring equipment: 0.02 level or above digital multimeter.

Temperature field source: High temperature furnace (temperature field uniformity ≤ 1 ℃/60mm) or constant temperature bath. ‌

Supporting tools

Freezing point thermostat (reference terminal 0 ℃ control), compensation wire (correction value needs to be calibrated). ‌

4、 Calibration method and process

Calibration point selection

Covering the process temperature range of the tested equipment, distribute points at intervals of 150 ℃ (such as 500 ℃, 650 ℃, 800 ℃).

Prohibition of extrapolation method: Deviation cannot be calculated outside the measured temperature range. ‌

Operation steps

① Preprocessing: Check the appearance and insulation resistance. New couples do not require annealing (experimental results have shown that annealing affects approximately 10% tolerance). ‌

② Layout: The standard and the calibrated couple are placed at the center of the temperature equalizing block/tube furnace, with an insertion depth of ≥ 300mm.

③ Measurement: After constant temperature (fluctuation ≤ 0.2 ℃/min), read the thermoelectric potential values in reverse order (4 times/point average). ‌

④ Deviation calculation:

5、 Result processing and resumption management

Calibration certificate content

Indication deviation, expanded uncertainty, environmental parameters (temperature and humidity/atmospheric pressure), traceability validity statement. ‌

Uncertainty assessment

Including standard error, temperature field uniformity, repeatability and other components (see Appendix G of the specification for examples)

Resumption period

Regular use: 6 months

High frequency/harsh environment: 3 months

After repairing or replacing core components: calibrate immediately. ‌