ANORDNING FOER AUTOMATISK STYRNING AV ELEKTRISKT UPPHETTADE FORDONSRUTOR

摘要

A grid of heating conductors for defrosting applied to the window of a vehicle is connected to a source of electrical energy through a relay-operated switch. This switch is closed either in response to a drop in the resistance between two conductors or electrodes mounted in spaced relation on an insulating support such as the window (the drop occurring by accumulation of moisture on the support and between the conductors) or in response to a drop in temperature at or near the window. For this purpose the resistance between the two conductors over the surface of the support may be paralleled by a thermostatic switch which closes with drop in temperature, both this resistance and the thermostatic switch being in the input to a trigger circuit controlling the relay to energize it in response to a decline in resistance at that input. Alternatively the trigger circuit may include thermistors which sense the drop in temperature and set the trigger circuit to the condition which energizes the relay.