Metal detector circuit having selectable exclusion range for unwanted

Abstract

A metal detector circuit of the balanced induction type is utilized to detect hidden metal objects. A receive signal is provided with two fixed concurrent phase shifts relative to the transmit signals. Each of the phase shifted receive signals is synchronously demodulated to produce first and second vector signals. The vector signals are combined in a summation circuit to produce a third vector signal. The first and third vector signals are then selectively combined by an operator to produce a fourth vector signal having a desired vector range between minimum and maximum vector angles. The metal detector circuit of the present invention provides a response for objects having a phase response signal outside the selected phase range. The first and fourth vector signals are each differentiated twice then level detected. The outputs from the level detection process are logic signals which are input to an AND gate. The output of the AND gate is a control signal for selectively gating the second differential signal of the fourth vector signal. The output from the circuit provides a response when an object produces a receive signal which is outside the selected exclusion phase angle range.