Abstract: Thickness of an electrically insulative metal oxide film deposited on an electrically conductive metal substrate is determined by electrolytically reducing the metal oxide in an electrochemical cell while continuously measuring the cell voltage. A mathematical relationship between the cell voltage change and elapsed time of electrolytic reduction serves as a means for determining thickness of said oxide coating. This method and apparatus is particularly suitable for measurement of the oxide coating thickness on a metal wire substrate.

Abstract: Electronic protective circuitry for protecting an electrical circuit, such as a constant current source circuit, from damage due to an overvoltage applied to the circuit. The protective circuit employs circuitry for limiting the magnitude of the voltage across a first portion of the circuit, such as an amplifier output circuit, so that the voltage thereacross is limited to a given maximum voltage level. A current limiter is connected in series between the first portion and second portion for limiting the magnitude of current flowing through the circuitry to a given maximum current level. Essentially all of the overvoltage is applied across the current limiter. The protective circuit is particularly applicable for protecting an amplifier from damage due to an overvoltage applied to its output circuit, as well as for protecting a resistor connected in series with the output circuit of the amplifier.