Level sensing device for dielectric liquids

Claim 1

A device for sensing the presence of a dielectric liquid at a predetermined level in a tank, comprising first and second bimetallic strips having substantially identical thermal characteristics, each of said strips bearing an electric contact, said contacts forming a low resistance electrical path when said contacts are closed and a high resistance electrical path when said contacts are opened, said strips being adapted to be disposed in said tank in contact with the dielectric fluid at a level equal to said predetermined level; a source of electric current; a resistor connected between a switching element and one of said contacts and disposed in heat exchange proximity for heating said second strip; a timer circuit for periodically operating said switching element to provide current flow through said resistor; and a memory circuit having a signal input connected to the other of said contacts and an enabling input responsive to said timer circuit, said memory circuit providing an electrical output signal only when enabled by said timing circuit whenever a change in the resistive path between said contacts occurs, said device operating to produce said output signal when the level of liquid in the tank falls below said predetermined level.

Claim 2

A device for sensing the presence of a dielectric liquid at a predetermined level in a tank, comprising first and second bimetallic strips having substantially identical thermal characteristics, each of said strips bearing an electric contact, said contacts forming a low resistance electrical path when said contacts are closed and a high resistance electrical path when said contacts are opened, said strips being adapted to be disposed in said tank in contact with the dielectric fluid at a level equal to said predetermined level; a source of electric current; a resistor connected between a switching element and one of said contacts and disposed in heat exchange proximity for heating said second strip; a timer circuit for periodically operating said switching element to provide current flow through said resistor; and a memory circuit having a signal input connected to the other of said contacts and an enabling input responsive to said timer circuit, said memory circuit providing an electrical output signal only when enabled by said timing circuit whenever a change in the resistive path between said contacts occurs, said device operating to produce said output signal when the level of liquid in the tank falls below said predetermined level.