Plant & Works Engineering

Dew point measurement with capacitive polymer sensors

Published:  30 June, 2007

Dew point measuring devices detect the formation of moisture in compressed air systems - one of the greatest risks to process reliability. By using capacitive polymer sensors, a new generation of measuring devices achieves a faster response time and produces results that are noticeably more reliable.

Unlike the conventional open-pored aluminium sensors, the capacitive polymer sensors of the dew point measuring devices, which are developed and offered by Beko Technologies Ltd, the compressed-air specialist, function with a closed condenser.

The cover electrode is penetrated solely by water vapour (and not by further particles which possibly exist in the air) by way of diffusion. The vapour accumulates reversibly on the polymer, whereby the capacity of the sensor changes.

On the even surface of the capacitive sensor, dust, dirt, oil and other substances may, in the worst case, settle but not enter the sensor. Misinterpretations are thus reduced to an absolute minimum, as merely the indiffused water vapour exerts influence on the measuring effect.

A further special advantage of the new devices made by Beko Technologies consists in their extremely short response time, compared with devices where aluminium oxide sensors are used. In the polymer sensor, droplet formation does not exist, as water enters and exits exclusively in the form of vapour. This means the adaption time is shorter, a change in the humidity conditions will be indicated very quickly. At an incoming flow of more than three litres per minute, the response time amounts to just about 15 seconds.

With three versions in all, two stationary and one mobile model, the Beko devices cover a pressure dew point measuring range of -80  to up to 50 C. While the first stationary system with a PDP range of -10 to up to 50 C is particularly suitable  for the application subsequent to refrigeration drying, the second permanent installation device with a PDP measuring range between -80 and 20 C is the right choice for the combination with membrane and absorption dryers.

The mobile measuring device is suitable for the entire range of the aforementioned temperatures and can be connected safely and easily at any point in the pipework, using a quick coupling.

All three models are ready-to-use when supplied, with the stationary versions prepared (ready-for-connection) for wall mounting. They only need to be connected with the electric mains using the plug. The mobile device has an internal, rechargeable storage battery with a long service life. Dataloggers are available for all models, should the results need to be recorded and studied.

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