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Thermocouples, Thermocouple Materials, Thermometer Indicators
C. Dawn Cross (32110C-32147C)
Please contact the technical staff before shipping instruments or standards to the address listed below.
Fees are subject to change without notice.
NOTE: Due to the extra time involved in calibrating sheathed thermocouples, a surcharge of 20% of the cost of calibrating bare-wire thermocouples will be added to the relevant fees listed above.
Calibration services for all commonly used types of thermocouples are provided by NIST from -196 °C to 1750 °C depending upon the wire or thermocouple type. The thermocouples are calibrated by one or a combination of three general methods, depending on the thermocouple type, the temperature range, and the uncertainty required. All three methods provide traceability to the ITS-90. In the first method, thermocouples are calibrated by comparison with a reference thermocouple maintained at NIST. In the second method, thermocouples are calibrated by comparison with a standard platinum resistance thermometer. In the third method, thermocouples are calibrated at four defining fixed-point temperatures on the ITS-90: the freezing points of Zn, Al, Ag, and Au. Below 0 °C, the thermocouple calibration is performed in a cryostat; above 0 °C, stirred liquid baths, metal freezing-point cells, and electric tube-type furnaces are employed for the calibrations. Vacuum or inert gas furnaces are also available for testing thermocouples.
Only the bare wires are required to perform the thermocouple calibrations. It is preferable not to send insulating and protecting tubes as the rate of breakage of these in shipment is high. If the thermocouple is furnished mounted (as in a protection tube assembly), a nominal charge will be made for dismantling the mounting and the various parts will be returned to the sender without reassembling them. Minimum thermocouple length requirements listed in the Service ID Number tables are exclusive of lead wire. Lead wires (for connections) should not be sent with thermocouples. All thermocouple calibration data furnished in reports will be on the basis of a reference junction temperature of 0 °C (32 °F). The calibration results will be given in °C or °F, as requested by the customer. The calibration of a thermocouple will not be undertaken if it will likely not yield the specified expanded uncertainty or if it possesses unusual characteristics that would prevent the performance of the calibration or test at a reasonable cost. Only unused base-metal thermocouples and thermocouple materials will be accepted for test.
All uncertainties are expressed as expanded uncertainties and vary with test temperature. In cases where a range of temperatures is given, the stated expanded uncertainty is the maximum of the expanded uncertainties over this range of temperatures.
For requirements not covered by calibrations described above, special arrangements may be made by consulting one of the specified staff members.
ASTM Standard E 220-86(96), Standard Method for Calibration of Thermocouples by Comparison Techniques, Annual Book of ASTM Standards 14.03, 94, Amer. Soc. For Test. and Matls., Philadelphia, PA (1997).
ASTM Standard E 230-96, Standard Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples, Annual Book of ASTM Standards 14.03, 106, Amer. Soc. for Test. And Matls., Philadelphia, PA (1997).
ASTM Standard E 1751-95, Standard Guide for Temperature Electromotive Force (EMF) Tables for Non-Letter Designated Thermocouple Combinations, Annual Book of ASTM Standards 14.03, 456, Amer. Soc. For Test And Matls., Philadelphia, PA (1996).
International Electrotechnical Commission Standard, Thermocouples, Part I: Reference Tables, IEC Publication 584- 1, Intl. Electrotech. Com., (1994).
Assessment of Uncertainties of Thermocouple Calibrations at NIST, D. Ripple, G. W. Burns, and M. G. Scroger, NISTIR 5340 (1994).
Manual on the Use of Thermocouples in Temperature Measurement, ASTM MNL 12, Amer. Soc. for Test. And Matls., Philadelphia, PA (1993).
Temperature-Electromotive Force Reference Functions and Tables for the Letter-Designated Thermocouple Types Based on the ITS-90, G. W. Burns, M. G. Scroger, G. F. Strouse, M. C. Croarkin, and W. F. Guthrie, Natl. Inst. Stand. Technol. Mongr. 175 (1993).
The International Temperature Scale of 1990 (ITS-90), H. Preston-Thomas, Metrologia 27, 3-10 (1990), Metrologia 27, 107 (1990).
NIST Measurement Services: The Calibration of Thermocouple and Thermocouple Materials, G. W. Burns and M. G. Scroger, Natl. Inst. Stand. Technol. Spec. Publ. 250-35 (April 1989).