Thermometry and humidity calibration services

ITS-90 calibration between 13.8033 K and 1234.93 K

In the range between 13.8033 K and 1234.93 K the ITS-90 is defined by the standard platinum resistance thermometer (SPRT), when the latter is calibrated at specific sets of defining fixed points, called temperature fixed points, and is used with specified reference and deviation functions for interpolation at intervening temperatures. The defining temperature fixed points are listed in the following table.

The ITS-90 contains a number of overlapping subranges. The calibration of a particular SPRT involves selecting the range over which the thermometer will be used, or the maximum range over which the SPRT may be operated in accordance with the recommendations of the manufacturer. SPRTs may be broadly classified into two types: capsule thermometers (CSPRT) and long-stem thermometers (LSPRT). Capsule thermometers are used primarily between 13.8 K and 273 K and, by the nature of their construction, generally become an integral part of the apparatus in which they are used to determine temperature. Long-stem SPRTs (25 Ω at 0 °C) normally operate between 84 K and 660 °C. The high-temperature platinum resistance thermometer (HTPRT) (0.25 to 2.5 Ω at 0 °C) may be operated to 961.78 °C.

Calibration of temperature fixed-point cells

The following services are provided for calibrating temperature fixed-point cells. The corresponding ITS-90 temperature is shown in the table above. Each calibration includes the measurement of: 1) a complete freezing/melting curve; 2) an immersion profile; 3) two simultaneous realizations of the NRC reference cell and client cell in two separate cryostats, furnaces or calibration baths. Note that for the argon fixed point the cryostat is to be provided by the client and the immersion profile is not collected.

Long-stem SPRTs and HTPRTs

The following services are provided for long-stem SPRTs and HTPRTs. The temperature ranges are as shown for each calibration.

Platinum-rhodium thermocouples

Standard platinum 10 percent rhodium/platinum thermocouples (type S) must be at least 90 cm long and made of wire not less than 0.35 mm in diameter. It is recommended that a standard thermocouple be at least 120 cm long and be shipped as bare unstrained wire. This is to facilitate the annealing of the thermocouple wire at high temperature (1300 °C) by electrical heating prior to assembly. Platinum 13 percent rhodium/platinum thermocouples (type R) of the same construction will also be calibrated under A33-03-03-03.

Thermocouples, thermistors and resistance thermometers (including laboratory grade digital thermometers)

This category includes both individual sensors (thermocouples, thermistors, industrial resistance temperature detectors) and various digital instruments that read directly in terms of temperature. Calibrations are performed by comparison against SPRTs or standard thermocouples that determine the calibration temperature. The comparison facilities include a variety of baths, furnaces and cryostats. Each calibration involves A33-03-04-01 and one or more of A33-03-04-02 to A33-03-04-05.

Radiation thermometers

Radiation thermometers (RTs) are calibrated using a wide variety of variable temperature blackbody sources (VTBBs) covering a total range of -40 °C to 2500 °C. For temperatures below 1000 °C, the blackbodies are measured with a standard platinum resistance thermometer (SPRT) or a Au: Pt standard thermocouple traceable to the NRC realization of the international temperature scale of 1990 (ITS-90). For temperatures over 1000 °C, the blackbody is measured with a radiance temperature transfer standard calibrated in accordance with the ITS-90. Radiation thermometers with a field-of-view (spot size) up to and including 20 mm may be calibrated in this manner. RT calibrations using fixed point blackbody sources (FPBBs) are also available using indium, tin, zinc, aluminium, and silver FPBBs. Other radiation thermometers may be calibrated by special arrangement.

Humidity

Dew point hygrometers and relative humidity sensors

Hygrometers scaled in the units of dew point (or frost point) can be calibrated in the dew-point range from -35 °C to 30 °C. Each calibration involves A33-03-06-00 and one or more of A33-03-06-01.

Hygrometers scaled in the units of relative humidity can be calibrated in the relative humidity range from 10 % rh to 95 % rh at air temperatures ranging from 10 °C to 30 °C. Each calibration involves A33-03-06-00 and one or more of A33-03-06-01 or A33-03-06-02.