B b sensors con tps fl l5 dew point controller and surface sensor b b sensors con tps fl l5 this hygrostat humidistat is designed for the monitoring and control of the relative humidity of an enclosed space when the device senses dew formation or condensation on cooled objects and the value exceeds an approximate limit of 94 rh the controller opens a relay contact and trips a safety function static switch contact the resultant output signal may thus be used to operate a heater dehumidifie