iso17025

Reducing UKAS calibration uncertainties

At Rotronic UK our UKAS laboratory have worked hard to make a name for itself in high quality calibrations and service. Thanks to constant improvements in measurement procedures the laboratory is growing into one of the most advanced commercial facilities in this specialised field. The ISO 17025 accredited calibration of humidity and temperature sensors and dew point instruments confirms performance and is increasingly a requirement of industry regulations and company quality management systems. The UKAS laboratory at Rotronic UK has spent the last two years increasing confidence in the calibrations performed and as a consequence lowering the Calibration and Measurement Capability (CMC) of the laboratory. Significant improvements have been made in the measurement procedures for dew point and temperature in air, enabling the following UKAS Accredited CMCs:

Dew/Frost point measurement (°Cdp/fp) • -60 to -40 °Cfp; uncertainty ±0.14 °Cfp • -40 °Cfp to +60 °Cdp; uncertainty ±0.11 °Cdp • +60 °Cdp to 70 °Cdp; uncertainty ±0.12 °Cdp

Temperature in air/ °C • -60 °C to 0 °C; uncertainty ±0.08 °C to 0.06 °C • 0 °C to +70 °C; uncertainty ±0.05 °C • +70 °C to +150 °C; uncertainty ±0.07 °C to 0.16 °C

Relative Humidity (RH)/%rh In the laboratory RH is derived from vapour pressure formulations. Improvements in dew point and temperature in air CMCs therefore affect the RH CMCs profoundly. The improvement lies in the range 0 to 70 °C; in the worst case RH CMC is ±1.0 %rh. In all parts of the HC2-S specified range covered by the accreditation the CMC is better than the specification of the probe. This is the first time this has been achieved. With the new temperature in air calibration range (-60 °C to +150 °C) and new dew/frost point calibration range (-60 °Cdp and up to +70 °Cdp) the laboratory’s RH calibration range has been extended up to 70 °C and 98 %rh. For example, at the new upper limit of 70 °C/98 %rh the CMC is ±0.6%rh and with these levels of calibration measurement uncertainty and range of accredited calibration services the purpose-built laboratory is one of the most advanced commercial facilities in the world.

Dr. Jeremy Wingate
Rotronic UK

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