Control your environment

Citation

(2003), "Control your environment", Sensor Review, Vol. 23 No. 4. https://doi.org/10.1108/sr.2003.08723daf.004

Control your environment

Control your environment

Precise humidity verification of environmental chambers

Keywords: Humidity, Sensors

Environmental chambers are widely used for the testing of a huge range of products, such as electronic equipment, pharmaceuticals and food packaging. Historically, wet/dry bulb psychrometers and capacitive relative humidity probes have been used for both the control and validation of such chambers. However, neither is particularly suitable for the highest level of validation of chamber performance. Now, for the first time there exists an alternative in the form of a cooled mirror transmitter offering improved measurement capability and a flexibility that can be applied over a wide range of environmental conditions with ease.

In the past, a cooled mirror dew-point hygrometer was regarded as an expensive laboratory reference device that would be used for the calibration of lower specification instruments, such as psychrometers and RH sensors. Limitations in electronics and in the design of early cooled mirror sensors rendered them inflexible when presented with extremes of temperature and humidity. The design and development of Optidew has addressed these limitations and resulted in a cooled mirror dew-point hygrometer that is 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 (Plate 4).

Plate 4 Optidew

The pedigree of the cooled mirror dew-point hygrometer as a calibration reference device is well established and Optidew follows in the long tradition. 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 makes it suitable for verification of chamber performance, humidity profiling and for the calibration of chamber humidity control loop sensors.

But can Optidew replace those psychrometers and RH probes as the main measurement and control device for an environmental chamber? The results of independent tests suggest that this is possible. The combination of Optidew's own intelligent control system and the improved sophistication of microprocessor based environmental chambers means that such an advanced, fundamentally-based measurement system can now be applied with success to the control of enclosed environments.

For further information, please contact: Michell Instruments Limited at Nuffield Close, Cambridge, CB4 1SS. Tel: 01223 434800; Fax: 01223 434895; E-mail: info@michell.co.uk, Web site: www.michell-instruments.com