New chamber validator

Historically, wet/dry bulb psychrometers and capacitive relative humidity probes have been used both for the control and validation of environmental chambers.

However, according to Michell Instruments, neither is particularly suitable for the highest level of validation of chamber performance and the company has now introduced an alternative in the form of a cooled mirror transmitter which it claims offers improved measurement capability and a flexibility that can be applied over a wide range of environmental conditions. In the past, says Michell, a cooled mirror dew-point hygrometer was regarded as an expensive laboratory reference device used for the calibration of lower specification instruments, such as psychrometers and relative humidity sensors. Limitations in electronics and in the design of early cooled mirror sensors rendered them inflexible when presented with extremes of temperature and humidity. Addressing these limitations, Michell has introduced Optidew, a cooled mirror dew-point hygrometer that is said to be stable, fast responding and accurate over the whole operating range of an environmental chamber, from the driest conditions (typically -40°C dew point) to saturation at the highest operating temperatures, automatically and without any need for user intervention. The company says four-wire resistance temperature measurement, precision digital control and high quality sensor components with a corrosion-resistant hard gold mirror ensure reliable and accurate performance. Calibration traceability to International Standards (NPL and NIST primarily) along with the option for direct UKAS calibration make it suitable for verification of chamber performance, humidity profiling and for the calibration of chamber humidity control loop sensors. Michell claims that independent tests suggest it is possible to use Optidew to replace psychrometers and rh probes as the main measurement and control device for an environmental chamber.