Patents Assigned to Allied Security Devices, Inc.
  • Patent number: 5148149
    Abstract: 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.
    Type: Grant
    Filed: January 31, 1991
    Date of Patent: September 15, 1992
    Assignee: Allied Security Devices, Inc.
    Inventors: David J. Campbell, Kenneth I. DeWitt