Where the equipment is required to maintain a predetermined level of humidity, a humidistat may be used instead of, or in addition to, a thermostat. The function will normally be to operate an electrical switch.
Mechanical humidistats employ materials which change dimension with humidity, such as animal hair, plastics, cellulosics, etc. These can work a switch directly.
Electronic humidistats generally depend on the properties of a hygroscopic salt. The signal has to be measured and amplified.
Posted in Refrigeration and Air Conditioning