Apparatus for detecting faults in magnet wire insulation without thermally damaging the insulation and which does not respond to impedance indications above a predetermined threshold value

Claim 1

Apparatus for continuously testing continuity of the insulation coating on a moving insulated wire conductor, said apparatus comprising: a. contact means for applying one of a plurality of D-C high voltage test potentials between the exterior surface of the insulation coating and the interior conductor; b. first switching means for selecting any one of the test potentials to be applied; c. a current limiting impedance connected in circuit with the contact means for limiting the current through a fault to a value such that the product of the D-C high voltage and the fault current does not exceed about 150 milliwatts; d. current sensing impedance means connected in circuit with the contact means, the current sensing impedance means including a plurality of different values of impedance each of which corresponds to one of the test potentials in a predetermined chosen relationship; e. second switching means ganged to the first switching means for connecting in the circuit one of the values of impedance as determined by the test potential selected, the value of impedance connected in the circuit being chosen predeterminedly in accordance with the test potential such that the apparatus responds to the highest resistance pin-hole fault desired to be detected for the particular thickness of insulation coating under test, each of which resistance pin-hole faults are different for different thicknesses of insulation coating; f. threshold amplifying means for amplifying pulses of current flowing through said current sensing impedance means and passing only pulses above a predetermined threshold level; and, g. fault-rate counter means for counting the number of fault current pulses for each successive predetermined incremental length of insulated wire.