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Whitepapers / Thermocouple Standards & Calibrations
Nanmac Corporation
Quality • Performance • Solutions
Nanmac Notes
Subject: Thermocouple Standards and Calibrations • No. 92-3
Thermocouple Standards

As shown in Table I, there are seven thermocouple standards applicable to heat treating furnaces. These include Reference Standard, Primary Standard, Secondary Standard, Temperature Uniformity Test Standard, System Accuracy Test plus Working and Load Standards. This chart summarizes the type of thermocouples which can be used for each category in addition to calibration frequency and accuracy requirements. These standards were established by SAE (Society of Automotive Engineers) specification SAE-AMS-2750 Rev. C in 1990. This specification has been adopted by the U.S. Department of Defense. It is a valuable reference and we suggest that anyone who manufactures or uses heat treating furnaces should have a copy of this specification in their Quality Control Department.

Table I
Outline of Sensors
NomenclatureDescriptionCalibrationUse/Max Error Limit
PeriodAgainstCorrection Factor (°F)
Reference StandardPlatinum Platinum-Rhodium5 yearsNIST Reference StandardPrimary Standard Calibration None
Primary StandardPlatinum Platinum-Rhodium3 yearsReference StandardSecondary Standard Calibration ±2.7° or ±0.25%**
Secondary StandardBase or noble metal1 year base 2 years noblePrimary StandardTest Sensor Calibration base: ±2° or ±0.4%** noble: ±2.7° or ±0.25%**
Temperature Uniformity TestBase of noble metal3 months base 6 months noblePrimary or Secondary StandardTemperature Uniformity Tests ±4° or ±0.75%**
System Accuracy TestBase of noble metal3 months base 6 months noblePrimary or Secondary StandardSystem Accuracy Tests ±2° or ±0.4%**
WorkingBase of noble metalBefore installationPrimary or Secondary StandardInstallation in Equipment Class 1: ±2° or ±0.4%** Class 2: ±4° or ±0.75%**
LoadBase of noble metal3 months N, R, S 6 months otherPrimary or Secondary StandardInsertion in Loads ±4° or ±0.75%**
* Sensors of Equivalent or Greater Accuracy are Acceptable
** Percent of Reading, if Greater Than Correction Factor in Degrees
Aerospace Material Specification - SAE AMS-2750 Rev. C. issued 1980-04-15, Revised 1990-04-01
Superceding AMS-2750B. Society of Automotive Engineers, Inc., 400 Commonwealth Drive, Warrendale, PA 15096 (1990).
Calibration Services

Nanmac's calibration laboratory will calibrate bare or insulated thermocouple wire, assembled thermocouples, RTD's, hermistors and instruments. All of our calibration equipment is calibrated against National Institute of Standards and Technology (NIST) standards. Our calibration data are traceable to NIST standards. Calibration costs are listed in the chart below. The maximum temperature range of our standard services is 2,100 degrees Fahrenheit.

  1. All temperature sensors must be at least 12 inches long to minimize conduction errors.
  2. Calibrations to 2,950°F can be made on a special basis (contact factory for details). Also, calibrations at cryogenic ranges can also be made on a special basis.
  3. Your instruments and sensors can also be calibrated and certified (contact factory for details).
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