Why we use capacitive sensors for humidity measurement and control

Ten reasons CTS chambers use capacitive sensors instead of pychrometric (wet sock) sensors for humidity measurements and control.

1.    The measurement tolerance of our capacitive sensors is < 1% r.h. In practical application for environmental chambers capacitive sensors produce better accuracy than pychrometric sensors. We calibrate the sensor with a PTB or equivalent calibrated dew point mirror.
   
2.    Capacitive sensors can measure negative dew points effectively where psychrometric cannot. For full range rh measurement in a well controlled environmental chamber capacitive sensors span measurements beyond that which pyschrometric can.

3.    No maintenance is required for the capacitive sensors. Psychrometric sensors need changing of the “wet sock” and a consistent type and quality of socks.

4.    You do not have to humidify the capacitive sensor before each measurement. For psychrometric sensors clean demineralised water must be introduced before measurement so the system needs a water supply (pumps, pipes, water tray, measuring lag etc. are all factors).

5.    Capacitive sensors perform better over extended test periods for a mixture of reasons including those already mentioned.

6.    Capacitive sensor technology is well developed and established, older chamber designs still using pyschrometric have not taken advantage of developments in capacitive sensor technology and reliability. Amongst the “better” chamber manufacturers only CTS has capacitive as standard measurement rather than the opposite, others consider it an additional cost.

7.    Capacitive sensors are now used worldwide for humidity measurement, its technology (and our premium sensor provider Rotronic) is extremely well established and respected.

8.    In the rare case of capacitive sensor failure it can be changed very easily. Psychrometric sensor failures or faults can be caused by a mixture of reasons (mineral deposits, dry sock etc.

9.    In CTS chambers the capacitive sensor is installed in a small enclosure within the test space to avoid drops from the ceiling. It is thus also less subject to accidental damage and droplet humidity errors.

10.    Capacitive devices sense moisture directly from the chamber atmosphere and are therefore virtually immune to the risk of mineral build up. Because “wet sock” psychrometric systems must always use water the chances of slow mineral build up and subsequent measurement drift are significant.

If you have any questions about this subject please contact info@qtpe.co.uk