New double-probe microwave moisture sensors

Citation

(1998), "New double-probe microwave moisture sensors", Sensor Review, Vol. 18 No. 2. https://doi.org/10.1108/sr.1998.08718bad.009

New double-probe microwave moisture sensors

New double-probe microwave moisture sensors

Keywords Moisture Sensors Ltd, Sensors, Water content

UK-based Moisture Sensors Ltd has developed a new double-probe sensor head, designed to measure the moisture content in the continuous production of fluids, emulsions, powders and sawdust, granulates and pellets using modified microwave sensors which pass a harmless beam through the material to be measured (Plate 4).

The MX4DP sensors can be used to determine actual water content in percentage or grammes and to monitor drying as well as incoming materials. The microwave beam will not pass through metal, which can be used as a reflective surface for it, and only "sees" water molecules, so it is not affected by the material, its surface, temperature, colour or speed of movement. It passes completely through the product and can provide an accurate moisture profile of it.

A further advantage is its ability to differentiate between free, chemically bound and frozen water. It is thus possible to monitor defrosting and thawing very accurately.

Plate 4 Double-probe microwave moisture sensors

The system follows the same principle as the domestic microwave in using the rotational energy of water molecules to provide an attenuated signal but at an energy level so low that there is no effect on the material under measurement and complete safety for operational purposes. The range of sensors includes those of a remote, non-contact type; they can be set up in a variety of process locations.

The standard MX4 units produced by Moisture Sensors Ltd, which have been supplied to the timber, board, carpet, laminating and cereals processing industries, consist of transmitter/receiver heads with a separate control box which provides a 0 to 20mAmp analogue output signal monitored by an LCD display. This signal can be calibrated very easily and used, via a converter or microprocessor, to provide the controls, warning lamps or displays required for the process as well as for data recording.

Other special units have been built to order. They can be set up over conveyors or fitted into hoppers for powders and granulates or engineered into bypass pipework for continuous readings in liquids and emulsions.

The units are intended as continuous process tools rather than laboratory instruments but static analyser versions have also been produced for off-line sampling where continuous measurement is difficult.

For further information contact: Moisture Sensors Ltd, 1 Queen Street, Sandhurst, Kent TN18 5HY, UK. Tel: +44 (0) 1 580-850915; Fax: +44 (0) 1580-850945.