DAkkS calibration of resistance thermometers

eXacal-prt-kalibrieren

DAkkS calibration of resistance thermometers

The DAkkS calibration of ITS-90 standard thermometers, resistance thermometers (Pt100, Pt125, SPRT, etc.) and measurement devices with direct displays is based on ITS-90 fixed points. It is also possible to perform calibrations using the reference method in liquid baths or in calibration furnaces.

  • Full-range DAkkS calibration from the triple point of argon to the freezing point of aluminium
  • The latest temperature fixed points are used (ISO tower)
  • Triple set of temperature fixed points available
  • Reference calibration from -80°C to 660°C
  • Turnaround time of five working days
  • Temperature sensors from a length of 300mm can be calibrated
  • DAkkS calibration certificate from -190°C to 660°C
  • Temperature sensors and measurement devices with direct displays

DAkkS-permitted uncertainty: Calibration to temperature fixed points

Fixed point

Temperature

Triple point

Melting point

Freezing point

Argon

-189.3442 °C

5.0 mK

Mercury

-38.8344 °C

3.5 mK

Water

0.01 °C

2.5 mK

Gallium

29.7646 °C

2.5 mK

Indium

156.5985 °C

5.5 mK

Tin

231.928 °C

7.0 mK

3.0 mK

Zinc

419.527 °C

12.0 mK

3.0 mK

Aluminium

660.323 °C

20.0 mK

5.0 mK

DAkkS-permitted uncertainty: Comparison calibration

Range

Process

Uncertainty

-80 °C to -60 °C

Liquid bath with compensator block

15 mK

-60 °C to 90 °C

10 mK

 Calibration to temperature fixed points

Klasmeier’s calibration service calibrates resistance thermometers (Pt 100, Pt 25, Pt 1000, standard working thermometers, etc.) using ITS 90 temperature fixed points. Both ITS-90 standard thermometers and reference thermometers (Pt 100) can be calibrated to the temperature fixed points. The order of fixed points on which the calibration is based is derived from SPRT’s falling temperatures. In order to rule out thermometer drift, the triple point of water is determined after each fixed point measurement, thus controlling the temperature sensor drift. In addition, each resistance thermometer is fully annealed prior to calibration at the highest temperature used and thus annealing drift determined using the triple point of water. Self-heating errors and the effects of hydrostatic pressure are investigated and taken into account during calibration. For non-standard thermometers, the hysteresis and ITS-90 reference curve are also checked. The DAkkS calibration certificate issued is recognised internationally and can also be used abroad.

Low immersion depth from 300mm

The use of narrow and high temperature fixed points, together with the modern ISO tower, enables ITS 90 standard thermometers (SPRTs as Pt 100 or Pt 25) and industrial reference thermometers (Pt 100) to be calibrated from an immersion depth of 300 mm with excellent uncertainties.

Comparison of SPRTs with IPRTs at temperature fixed points

When calibrating reference thermometers to ITS 90 temperature fixed points, the question of which are the necessary fixed points is often raised. In order to ensure that the number of ITS 90 temperature fixed points are also sufficient in the higher temperature ranges, Klasmeier’s calibration service has performed comprehensive experiments using ISOTECH sensors of the types 935-14-72 and 935-14-95 and eXacal sensors. The following graphic shows a comparison between a standard thermometer (SPRT) and a reference thermometer 935-14-95 based on the results of our experiments. The temperature difference shows that the maximum deviation on the reference curve of approx. 25 mK falls within the limit of uncertainty.

sprt_vs_prt

For DAkkS calibrations at high temperatures, the reference curve is also tested for plausibility in addition to the experiments set out above. The test temperature in this context falls between the fixed point temperatures.

Typical uncertainties

Typical uncertainties for reference thermometers are available here:   >>further information