B b sensors tw2001 c hygrostat humidity switch reversible contacts b b sensors tw2001 c an electromechanical hygrostat that functions as a relative humidity regulator for controlling humidification dehumidification equipment measurement is carried out by using a hygroscopic polyamide band attached to a spring that changes length depending on humidity levels a rotary switch adjusts the switching point between 10 and 80 rh suitable for applications such as air dryer humidifier dehumidifi