Two-wire transmission system for remote indication

Claim 1

A remote indicating system comprising: a dual conductor transmission means for connecting a remote position to a local position; a source of AC energizing power at said local position coupled through said dual conductor transmission system to said remote position; clipping means at said remote position coupled to said dual conductor transmission system for clipping said AC energizing power applied supplied to said remote position to a substantially square wave form having a regulated amplitude, said clipping means including a pair of back-to-back serially connected zener diodes shunting said conductors, differential transformer means having its coupling varied by a movable slug coupled to a desired variable and being energized by said clipped energizing power to yield an output determined by said slug position; means for converting said square wave form of said transformer output into a DC level varying with the desired of a device to be monitored at said remote position; and impedance means for coupling said DC level from said means for converting to said dual conductor transmission system so that said DC level is coupled back therethrough to said local position over the same dual conductors employed for furnishing AC energizing power to said remote position whereby effects caused by fluctuations in the level of said AC energizing power supplied to said remote position are minimized.