APPARATUS FOR USE WITH CAPACITIVE PRESENCE DETECTION SYSTEMS

摘要

A capacitance presence sensing apparatus ( 10 ) having a fail-safe circuit ( 13 ) and modular units ( 100 ). The fail-safe circuit ( 13 ) includes delivering a low voltage (FIG. 5 ) to a sensor and connecting voltage through a resistor to an oscillator ( 18 ). An opener ground in the circuit changes frequency of the oscillator ( 18 ) to indicate a problem With the fail-safe circuit ( 13 ). The apparatus also contains a number of inductance coils ( 28 ) which may be selected to tune the frequency of the system. Circuitry is provided in cards which may be combined together with receiver transmitter cards ( 106 ) and to easily facilitate the use of the system for desired applications.