Sensor having two-wire connection to load

Claim 1

In the combination of a speed sensing circuit for connection with a load circuit, the sensing circuit having one or more active elements requiring a regulated operating potential and a reference potential and output circuit means for providing an output signal to the load circuit, the output signal being representative of the phenomenon being sensed, and wherein said load circuit is adapted to receive said output signal and is the relative source of a source potential and the reference potential, the improvement comprising: said load circuit including first and second terminals, impedance means and signal processing means, said impedance means and said signal processing means each being operatively connected to said load circuit first terminal, said impedance means being adapted to be connected to a supply voltage for providing the source potential, unregulated, at said load circuit first terminal and said signal processing means being adapted to receive said output signal from said sensing circuit; said sensing circuit including first and second terminals for conductive connection with said first and said second terminals respectively of said load circuit to provide said source potential and said reference potential respectively thereat; said output circuit means being operatively connected to said sensing circuit first terminal for providing said output signal at said first terminal for connection to said load circuit; said sensing circuit including regulated voltage supply means operatively connected to said first and said second terminals for receiving said source potential and said reference potential and for providing said regulated operating potential; and said output circuit means including a power buffer, said buffer comprising a bipolar transistor operatively connected to said reference potential and to said source potential at said first terminal and having a base electrode for receiving a control signal from said sensing circuitry for said transistor to provide said output signal at said first terminal, and further including current shunting means operatively connected with said transistor for preventing lock-up conduction by said transistor during powering-up of the sensing circuitry with the unregulated source potential and until said regulated operating potential is substantially at steady state.