A portable, isolation-guarding measuring instrument that may be easily carried by electronic technicians, television service repairmen, etc. The instrument comprises a suitable meter movement of the voltmeter-type for providing an indication of the magnitude of an electrical signal and having first and second input measurement terminal leads for coupling the opposite terminals of an in-circuit component to be measured to the meter movement and to an excitation signal. A third isolation-guarding terminal lead maintained at essentially the same potential as the potential of one of the first and second input measurement terminal leads, is provided for connection to nodal points of other circuit components connected in parallel circuit relationship with the in-circuit component to be measured. As a result, measurement of the actual value of the in-circuit component can be obtained without requiring that the in-circuit component be disconnected even partially from the other components with which it is in circuit relationship.
This application is a continuation of application U.S. Ser. No. 713,436, filed Mar. 5, 1968 entitled "Isolation Guarding Measuring Instrument For In-Circuit Component Testing," Melvin E. Stanford, inventor, and assigned to Systomation, Inc.
An ohmmeter and circuit therefor which does not require an internal battery or a continuing coupling to an external voltage source during normal use, with the necessary operating electrical power supplied through a high capacity capacitor which, after initial energization by a temporary connection to an external voltage source, develops a stored source of operating power. As the operating current is constant, there is no necessity for scale adjustment prior to each use of the ohmmeter.
