a system for sensing and controlling the level of fluent material in a reservoir or other receptacle . in electrically conducting materials levels are sensed by low voltage direct current conduction between electrode pairs placed at desired &# 34 ; high &# 34 ; and &# 34 ; low &# 34 ; control levels which send d . c . digital logic sensing signals over connecting wires to very high resistance &# 34 ; high &# 34 ; and &# 34 ; low &# 34 ; inputs of a digital logic signal processing circuit , while nonconducting material levels are sensed by suitable transducers which upon immersion can send d . c . digital logic signals . the digital signal processing circuit receives the sensor signals and provides a digital output signal or absence thereof , depending on the relative state and sequence of the sensing signals and transmits a digital output signal to a solid state relay which controls the power of flow control means to maintain desired levels of the fluent material .