Miniature metallised polypropylene film capacitors
26 Jan 2000
Passive Components
Avnet Kopp
BC Components' capacitive humidity sensor operates by sensing changes in capacitance of a thin-film polymer membrane as it absorbs moisture from its surroundings. Compared with many alternatives, the company claims it is simple to operate, highly reliable and fast. It also has long-term characteristics unaffected by condensation of water on the membrane surface and other aggressive pollutants in the air.
Applications are home hygrometers, weather stations, air-conditioners, climate controllers and tumble dryers.
Designed for a measuring range between 10% and 90% relative humidity the sensor's relatively linear characteristic allows it to be easily incorporated into simple, inexpensive measuring circuitry.
The sensor is made up of a polymer film coated on both sides with a very thin air-permeable gold layer to form a capacitive element. The film is clamped between spring contacts inside a perforated plastic housing and changes in relative humidity (RH) cause a change in dielectric constant of the polymer film leading to a change of sensor capacitance. BC Components says the relationship between sensor capacitance and relative humidity is a rather simple one which means that the sensor can easily be incorporated into an electrical measuring circuit.
Sensor specifications are: humidity range 10 to 90% RH; capacitance (+25°C, 43% RH, 100 kHz), 122 ±15% pF; sensitivity between 12 and 75% RH, 0,4 ±0,05 pF/% RH; frequency range, 1 to 1000 kHz; response time between 10 and 43% RH, <3 min and between 48 and 90% RH, <5 min; operating and storage temperature range, -25 to +85°C.
The units measure 20,0 x 15,5 x 5,0 mm with lead distance 5,08 mm.
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