Thomas N Crouch

US Patent:

39744450, Aug 10, 1976

Filed:

Oct 31, 1974

Appl. No.:

5/519426

Inventors:

Thomas J. Crouch - Leonard MI
Larry G. Hait - Roseville MI

Assignee:

Merc-O-Tronic Instruments Corporation - Almont MI

International Classification:

G01R 130
G01R 1504

US Classification:

324123R

Abstract:

A portable kilovoltmeter especially suited for measuring the secondary voltage of an ignition coil includes an operational amplifier whose input is connected via an input circuit to the ignition coil secondary winding and whose output is connected via an output circuit to a galvanometer on which the secondary voltage is read. The input circuit to the operational amplifier includes a probe which forms a portion of a capacitive voltage-dividing network via which the secondary voltage is reduced in amplitude before it is supplied to the operational amplifier input. The probe includes a capacitive probe element which makes contact with the hot terminal of the ignition coil secondary and a length of high-tension, high-resistance conductor which leads from the probe element to the console containing the galvanometer and the kilovoltmeter circuitry. The input circuit further includes filters and dropping resistors to filter and further drop the secondary voltage before it is supplied to the operational amplifier input. A switch means in the input circuit selects either positive or negative polarity portions of the secondary voltage for input to the kilovoltmeter.