Primary transfer standard hygrometer, a cooled mirror dewpointmeter, has been successfully calibrated at NPL to a new low limit and can now offer traceable calibration to -90C dew point
For twenty years, Michell's humidity calibration systems have been maintained traceable to the premier national standards held by the National Physical Laboratory (NPL), London and the National Institute of Standards and Technology (Nist), Washington, USA.
For much of that time the lowest achievable humidity level claimed by both NPL and Nist has been -75C dew point, which is equivalent to one part per million of moisture in dry gas.
Recently NPL has extended its capability down to -90C dew point (0.1ppmV) and now offers a Ukas (United Kingdom Accreditation Service) calibration facility to that low level.
As part of a strategic investment into the capability to produce high performance hygrometry for the pure gas and semiconductor industry, Michell has had its primary transfer standard hygrometer, a S4000 TRS cooled mirror dewpointmeter, successfully calibrated at NPL to this new low limit and can now offer traceable calibration to -90C dew point on all of its low end hygrometer products.
Instruments to benefit from this extension of traceability are the Easidew, Transmet, Cermax and Pura product ranges.
Pura in particular is designed for use in high purity gas applications and is, Michell believes, the only such product to benefit from traceability to a National Standard down to 0.1ppmV (in the semiconductor industry known as 100 parts per billion).
Over the coming months Michell will be applying this extended measurement capability to its own Ukas accredited humidity calibration laboratory and expects to be able to offer Ukas calibrations to -90C dew point from early in 2004, giving a complete range from 100ppb to 25,000ppm (-90 to +20C dew point).
