×

Walk-through metal detector

  • US 4,821,023 A
  • Filed: 01/07/1988
  • Issued: 04/11/1989
  • Est. Priority Date: 01/07/1988
  • Status: Expired due to Fees
First Claim
Patent Images

1. A pulsed-field metal detector system comprising a transmitting coil for transmitting pulses and a receive coil for receiving signals derived from said transmitted pulses, means for driving the transmitting coil responsive to current pulses recurring in cyclically alternating polarity, timing means coupled to synchronize measurement cycles at an odd half-multiple of an AC power main frequency, means for amplifying received signals derived from said transmitting pulses, means for subtracting from the amplified signals those components of said received signals which are due to periodic noise signals and static metal, means responsive to the subtracting means for limiting the absolute amplitude of residual signals remaining after said subtraction, means for demodulating and averaging the residual signals, means for detecting excursions of the averaged signal above or below preset threshold values, and means responsive to detection of said signals beyond said preset threshold values for giving an alarm when said threshold is exceeded for a majority of several successive process intervals.

View all claims
  • 2 Assignments
Timeline View
Assignment View
    ×
    ×