Sensors & Transducers


Oxygen sensor for the process industry

April 2005 Sensors & Transducers

LTH Electronics has designed a dissolved oxygen sensor for the process industries. The ProcessProbe has a robust reinforced membrane, it has a simple cartridge membrane replacement, flat-face obstructionless measurement and has proven performance. Waste treatment, sewerage aeration, rivers, reservoirs and boreholes are suitable applications for this instrument.

The construction of the sensor provides a measurement system that is good for use in variable flow conditions or applications of extended duration. The sensor comprises of a silver anode tube positioned over a glass rod into which is fused the platinum cathode. The tip of the glass rod is ground to a precise hemispherical curve that supports the membrane and ensures an optimum pressure is maintained between the membrane and the cathode.

With most oxygen sensors the output is lower in stagnant solutions than in agitated ones. This is due to the sensor consuming oxygen and creating a depletion layer in the proximity of the cathode. In a stagnant solution, if the sample is not updated faster than the sensor, consumption of the oxygen results in lower measured output. A high degree of flow dependence occurs with sensors that have large cathodes or thin and highly permeable membranes.

The membrane construction of the ProcessProbe consists of a thin PTFE layer and a relatively thick steel mesh reinforced silicon layer. The silicon layer is highly permeable to oxygen and provides an oxygen reservoir. The double thick PTFE/silicon membrane therefore acts as an effective buffer against disturbances caused by flow variation. This provides a robust membrane assembly, which has virtually no flow dependence.

For simple maintenance the membrane is supplied as a cartridge, which is held in place by a screw-on sleeve. The cartridge is filled with electrolyte and any entrapped air is forced out when it is gripped between the thumb and forefinger.

For more information contact Keith Watson, Temperature Controls, 011 791 6000, [email protected], www.tempcon.co.za



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