Solid state scale expanding circuit for electrical indicator devices

Abstract

A scale modifying circuit for providing either expanded or compressed scale readings on a conventional electrical indicating instrument. The device includes a pair of input terminals adapted to be connected to a source of voltage to be monitored or measured, a voltage responsive network connected with one of said input terminals for supplying output voltage to output terminals of the device, and amplifier means driven from the input terminals and having an output connected to supply a driving voltage to at least one of the output terminals. Expanded scales (or compressed scales) can be provided at the lower, middle, or high end of a particular range of voltages being monitored, or at intermediate points. This results in higher resolution over the expanded scale portion, together with improved accuracy. An illustrated embodiment of the invention embraces a voltage-limiting diode, to effect a cut-off of an ascending applied voltage. Some embodiments involve cascaded and summing amplifiers, negative feedback circuits, and multi-coil instrument movements where the coils are involved with the feedback.