Michal J. Chojnacky (83 K to 962 ºC)
Fees are subject to change without notice.
NIST provides calibration services for standard platinum resistance thermometers (SPRTs) from 13.8 K to 1235 K. Both long-stem and capsule-type SPRTs are calibrated, providing direct access to the International Temperature Scale of 1990 (ITS-90). There are eleven temperature subranges over which an SPRT may be calibrated according to the ITS-90 definitions. From 13.8 K to 83.8 K, SPRT calibrations are performed by comparison with a set of NIST reference thermometers. From 83.8 K to 962 °C, calibrations are performed using the ITS-90 defining fixed points as described in NIST Technical Note 1265. Expanded uncertainties, as described in NISTIR 5319, for SPRT calibrations are given in Table 6.3. The comparison calibration of rhodium-iron resistance thermometers (RIRTs) in the temperature range from 0.65 K to 26 K, using the NIST-maintained ITS-90, is based on a set of reference capsule-type RIRTs. The expanded uncertainty of those calibrations is given in Table 6.4. Extended range RIRT calibrations, for temperatures greater than 26 K and up to 83.8 K, are accomplished by comparison with reference capsule SPRTs in the range 26 K to 83.8 K.
Table 6.3. Maximum Expanded Uncertainties of SPRTs at NIST
To qualify for testing, either long-stem or capsule SPRTs must meet two conditions. They must meet the ITS-90 criteria of W (Hg) < 0.844 235 or W (Ga) > 1.118 07, and for use above 660 °C the criterion of W (Ag) > 4.2844. Second, they must be compatible with the NIST calibration equipment. It is important that, insofar as possible, resistance thermometers be protected from any mechanical shock that could alter their calibration. For shipment, the thermometer should be softly supported within a case but not be free to rattle. This necessitates the use of packing material that does not become compacted. The thermometer case should be softly packed inside a shipping container. The shipping container must be sufficiently rigid and strong that it will not appreciably deform under the treatment usually given by common carriers. Styrofoam is not sufficiently rigid to be used as an outside container. Similarly, mailing tubes are unacceptable. Thermometers will not be returned in containers that are obviously unsuitable, such as those closed by nailing. Suitable containers will be provided when a thermometer shipping container is not satisfactory for re-use.
Special tests (e.g., certification, prototype testing) of various resistance thermometers and thermometric fixed-point devices may be made by prior arrangement with the specified technical contacts. Fixed-point cells may be sent to NIST for certification by the method of direct comparison with the applicable NIST laboratory standard fixed-point cell.
Special tests (e.g., calibration, prototype testing) of various cryogenic resistance thermometers may be made by prior arrangement with the specified technical contact. Cryogenic resistance thermometers may be calibrated over the temperature range from 0.65 K to 84 K.
The purpose of this Measurement Assurance Program (MAP) is to assure the accuracy of the calibration of temperature standards (83 K to either 420 °C or 661 °C) conducted by participating laboratories when using platinum resistance thermometry. Other temperature ranges are available upon request.
The MAP transport standard consists of sets of three commercial SPRTs packaged in a special shock-proof shipping container (mechanical shock may shift calibration values). These SPRTs are used to assess both the reproducibility and the uncertainty of calibrations performed by the participating laboratory.
MAP participants should use the techniques described in NIST Technical Note 1265 and ITS-90 fixed-point cells, or use an SPRT previously calibrated by NIST. In order to achieve high accuracy, SPRTs used as standards should be either metal sheathed or of the matte-finish glass-sheathed type to avoid systematic errors arising from light-pipe effects in the glass sheath. The participant must have a triple point of water cell and an appropriate resistance bridge.
NIST provides worksheets on which the participant records data. The participant calculates the thermometer constants from experimental data, records them, and prepares tables of either resistance ratio or resistance versus temperature. These completed worksheets and the participant's calibration reports are sent to NIST with the return of the MAP SPRTs.
The SPRTs are recalibrated upon return to NIST and the participant's data are compared with NIST's calibration results. NIST provides a plot of the participating laboratory's temperature deviation from NIST values and a written analysis of the data, including any pertinent observations. In a typical MAP transfer, the participant makes measurements over a period of 1 to 2 months. A typical turnaround time from the date NIST receives the participant's data until a test report is sent to the participant is 4 to 6 weeks. Former participants in the MAP have had expanded uncertainties that ranged from about 1 mK to several tens of millikelvins.
No rigid recommendations can be given concerning how often a participant should utilize the temperature MAP service. Experience has indicated that when temperature measurements are in a state of statistical control, as evidenced by in-house check standards and control charts used to monitor the measurement process, the participant should be able to go at least 3 years between transfers from NIST without significantly degrading the confidence in the correctness of the measurements.
Among other NIST Services for Temperature Calibration Laboratories, NIST provides Standard Reference Materials for use as defining fixed points of the ITS-90 and as secondary reference points.
NIST Certification of ITS-90 Fixed-Point Cells From 83.8058 K to 1234.93 K: Methods and Uncertainties, G. F. Strouse, TEMPMEKO, (Jan. 2005).
NIST Implementation and Realization of the ITS-90 Over the Range 83 K to 1235 K. Reproducibility, Stability, and Uncertainties, G. F. Strouse, Temperature. Its Measurement and Control in Science and Industry, J. F. Schooley, Ed., 6, 169-174, Amer. Inst. Phys., New York, NY (1992).
Realization of the ITS-90 Below 83.8 K at the National Institute of Standards and Technology, E. R. Pfeiffer, Temperature. Its Measurement and Control in Science and Industry, J. F. Schooley, Ed., 6, 155-160, Amer. Inst. Phys., New York, NY (1992).
The International Temperature Scale of 1990 (ITS-90), H. Preston-Thomas, Metrologia 27, 3-10 (1990); Metrologia 27, 107 (1990).
NBS Measurement Services: Platinum Resistance Thermometer Calibrations, B. W. Mangum, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-22 (1988).
Reproducibility of Some Triple Point of Water Cells, G. T. Furukawa and W. R. Bigge, Temperature, Its Measurement and Control in Science and Industry 5, 291, Amer. Inst. Phys., New York, NY (1982).
Standard Reference Materials: Application of Some Metal SRM's as Thermometric Fixed Points, G. T. Furukawa, J. L. Riddle, W. R. Bigge, and E. R. Pfeiffer, Natl. Bur. Stand. (U.S.), Spec. Publ. 260-77 (Aug. 1982).
A Measurement Assurance Program-Thermometer Calibration, G. T. Furukawa and W. R. Bigge, in Natl. Conference on Testing Laboratory Performance, Evaluation, and Accreditation, Natl. Bur. Stand. (U.S.), Spec. Publ. 591, 137 (Aug. 1980).
Determination of the Triple-Point Temperatures of Gallium, B. W. Mangum and D. D. Thornton, Metrologia 15, 201-215 (1979).
Platinum Resistance Thermometry, J. L. Riddle, G. T. Furukawa, and H. H. Plumb, Natl. Bur. Stand. (U.S.), Monogr. 126 (Apr. 1973).