Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Patent
1995-03-31
1997-05-06
Arana, Louis M.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
324549, G01R 3106
Patent
active
056274750
ABSTRACT:
A metal detector comprises a detection coil disposed in a magnetic field, the ends of the coil being connected through a balanced resistor network to the inputs of a differential amplifier. A test signal is injected into the metal detector at a point such that the coil is effectively in series with one branch of the balanced resistor network. The injected signal produces a potential difference at the inputs of the differential amplifier, the magnitude of the potential difference being dependent on the resistance of the detection coil. The test signal is generated by a circuit including a microcomputer which successively feeds digital values corresponding to the sine function to a digital-to-analog converter, so that the converter generates the test signal in the form of a sine wave. The output signal from the differential amplifier is applied to an analog-to-digital converter. The microcomputer controls the analog-to-digital converter to repetitively sample the output signal from the amplifier and convert each sample to a digital value. The digital values are compared with two threshold values corresponding to the maximum and minimum values the amplifier output signal may have when the coil resistance is within an acceptable range and when the amplifier output signal exceeds the maximum or is less than the minimum value an error indication is produced.
REFERENCES:
patent: 4746869 (1988-05-01), Schrag et al.
patent: 4829234 (1989-05-01), Gretsch
patent: 5111149 (1992-05-01), Lebesch
Arana Louis M.
New Holland North America Inc.
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