Differential delay intrusion detection sensory system

摘要

An electromagnetic intrusion sensor including a sensing element, a first phase shifter circuit for phase shifting an input or oscillation signal in accordance with a capacitance of the sensing element, a second phase shifter circuit for outputting a reference signal having a fixed delay relative to the input or oscillation signal, a phase detector circuit for providing a detector signal having a duty cycle representing the phase differential between the outputs of the first and second phase shifter circuits, and an oscillator circuit for outputting a signal having a frequency which changes according to the duty cycle of the detector signal.