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Temperature and humidity measurements

Temperature fixed-point cells

Range: -189 °C to +1492 °C

UKAS accredited calibration of temperature fixed-point cells

NPL can calibrate a range of temperature fixed-point cells for use in the subsequent calibration of SPRTs and thermocouples. We provide UKAS (ISO 17025) accredited calibration of temperature fixed-point cells. These are compared against NPL national standards, either by direct inter-comparison or via calibrated reference thermometers.

For the pure-metal fixed-point cells, this service meets the requirements of the ITS-90 for local realisation, traceable to NPL’s national standards.

Furthermore, calibration of high temperature, eutectic temperature fixed-points are also available.

ITS-90 fixed point cells

NPL calibrates Ar (-189.3442 °C), Hg (-38.8344 °C), H2O (0.01 °C), Ga (29.7646 °C), In (156.5985 °C), Sn (231.928 °C), Zn (419.527 °C), Al (660.323 °C), Ag (961.78 °C) and Cu (1084.62 °C) fixed-point cells, in both open and sealed configurations.

The uncertainties achievable are as low as ±0.00007 °C at H2O, ±0.0006 °C at Sn and ±0.004 °C at Ag. 

These are additionally certified under the CIPM Mutual Recognition Agreement (MRA), excluding Cu.

High temperature fixed-points 

These fixed-points provide reference temperatures for thermocouples, above those specified in the ITS-90. They are made from a eutectic alloy of metal and carbon. At NPL, the Co-C (1324 °C) and Pd-C (1492 °C) cells can be calibrated.

The calibration uncertainties are typically ±0.44 °C at Co-C and ±0.65 °C at Pd-C.

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