Apparatus for capacitive measurement of coating thickness utilizing a square wave source and galvanometer responsive to unidirectional discharge current

Claim 1

A BALLISTIC GALVANOMETER CIRCUIT FOR MEASURING CAPACITANCE TO DETERMINE THE THICKNESS OF INSULATING COATINGS COMPRISING A SQUARE WAVE PULSATING D.C. GENERATOR, A RANGE CAPACITOR CIRCUIT AND A GALVANOMETER CONNECTED IN SERIES WITH AN UNKNOWN CAPACITOR FORMED FROM AN ELECTRODE PAIR ON EITHER SIDE OF SAID INSULATING COATING, SAID RANGE CAPACITOR CIRCUIT ENABLING SAID GALVANOMETER TO OPERATE WITHIN A PREDETERMINED RANGE AND INCLUDING AT LEAST ONE VARIABLE CAPACITOR CONNECTED IN PARALLEL WITH AT LEAST ONE FIXED CAPACITOR, A DIODE CONNECTED IN PARALLEL WITH SAID GALVANOMETER, AND BEING CIRCUIT ORIENTED THAT DURING THE ON STATE OF THE GENERATOR THE CURRENT OF THE GENERATOR WILL FLOW THROUGH THE DIODE AND SUBSTANTIALLY NO CURRENT WILL FLOW THROUGH THE GALVANOMETER, SAID GALVANOMETER HAVING A SERIALLY CONNECTED INPUT RESISTANCE SUFFICIENT TO CAUSE NON-FLOW OF SUBSTANTIALLY THE ENTIRE CURRENT APPLIED IN THE FORWARD DIRECTION OF SAID DIODE, ONE OF SAID ELECTRODES HAVING A PROBE OF RESILIENT CONDUCTING MATERIAL FIXEDLY MOUNTED IN A MOVABLE HEAD TO BEAR UPON SAID INSULATING COATINGS TO BE MEASURED, SAID GALVANOMETER PROVIDING SUBSTANTIALLY EXCLUSIVELY THE SOLE PATH FOR CURRENT FLOW IN THE OTHER DIRECTION THROUGH SAID CIRCUIT IN RESPONSE TO SUCCESSIVE CHARGING AND DISCHARGEING OF THE UNKNOWN CAPACITOR, THE CURRENT OF SAID SOLE PATH THEREBY INDICATING A VALUE ON SAID GALVANOMETER IN ACCORDANCE WITH THE VALUE OF SAID UNKNOWN CAPACITOR.