Ceramic Moisture Sensor

Citation

(2005), "Ceramic Moisture Sensor", Sensor Review, Vol. 25 No. 2. https://doi.org/10.1108/sr.2005.08725bad.006

Ceramic Moisture Sensor

Ceramic Moisture Sensor

Keywords: Moisture, Moisture measurement, Sensors

Michell Instruments' latest Ceramic Moisture Sensor (see Plate 6) has been designed using a 360° development process which looked at the needs of all potential stakeholders in the product; from the technical requirements of the customer, through ease of manufacturing and service, to the look and feel of the instrument to the user.

All Michell's Impedance instruments use the Advanced Ceramic Moisture Sensor. Backed by over 30 years' experience in humidity measurement, Michell's latest generation impedance dew-point sensor combines fast response and high repeatability with long-term stability and resistance to contamination.

Plate 6 Michell Instruments' latest Ceramic Moisture Sensor responds very rapidly to changes in applied moisture

Operation of the sensor depends upon the adsorption of water vapour into a porous non-conducting “sandwich” between two conductive layers built on top of a base ceramic substrate. The active sensor layer is very thin – less than 1mm (a millionth of a metre) and the porous top conductor that allows transmission of water vapour into the sensor is less than 0.1mm thick. Therefore the sensor responds very rapidly to changes in applied moisture, both when being dried (on process start-up) and when called into action if there is moisture ingress into a process.

Despite this extreme sensitivity to changes in moisture content, the Michell Ceramic Moisture Sensor is incredibly rugged due to the nature of its construction. To protect the sensor further against contaminants and large particulates it is housed in a protective sintered stainless steel guard.

Michell's Ceramic Moisture Sensor has been proven time and again in virtually every application, from pure gases to corrosive processes. The sensor can withstand the most aggressively acid media – for example virtually 100 per cent hydrogen sulphide – conditions in which no other humidity sensor will survive. If oil, other liquids or solid matter contaminate the sensor, it can be safely cleaned using distilled water, high purity solvent such as acetone, or a combination of the two. This cleaning process will not damage the sensor or affect its calibration accuracy, provided our recommended procedures are observed.

The Ceramic Moisture Sensor handles not only high gas pressures, but also rapid changes in pressure, without damage. Some less robust dew-point sensors will be damaged by rapid pressurisation/de-pressurisation due to the inferior method of construction. The Ceramic Moisture Sensor is constructed in such a way that virtually instantaneous pressurisation right up to the 30MPa (300 bar) limit will not cause failure.

All Ceramic Moisture Sensors are calibrated over the full dew point range from -100 to +20°C dew point using state-of-the-art computer controlled humidity generators with mass flow controller operation. Each sensor is individually calibrated at 10°C dew point intervals with the exact calibration data stored in an on-board processor memory. This ensures both the optimum calibration accuracy and makes re-certification very easy to perform, allowing you to maintain conformance with your own quality assurance requirements.

For further information 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