Abstract: An operator interface for a programmable controller is disclosed. The programmable controller has a plurality of discrete input terminals, a discrete input switch coupled to one of the input terminals, a plurality of discrete output terminals, a processor and a memory. The memory stores operating system software processed by the processor and comprises relay logic. The processor controls states of the output terminals in response to states of the input terminals and the relay logic. The operator interface selectively operatively coupled the input switch to a desired one of the output terminals and comprises an operator actuable control switch coupled to another one of the input terminals and an element responsive to actuation of the control switch for selectively coupling the input switch to the selected one of the output terminals, the coupling element comprising the operating system software processed by the processor.

Abstract: A voltmeter for selectively indicating the polarity and magnitude of a peak value of voltage. The voltmeter comprises an ammeter, a diode bridge including positive and negative terminals and first and second probe terminals, a capacitor connected to the positive and negative terminals, and variable resistance switching means connected in series between one of the positive and negative terminals and the ammeter for selectively coupling the ammeter across the positive and negative terminals. Filter switching means are provided for selectively coupling the probe terminals to a single polarity of the voltage whereby the voltmeter affords charging of the capacitor so that the magnitude of the positive voltage differential between the positive and negative terminals is substantially equal to the magnitude of the peak value of the single polarity of voltage coupled to the probe terminals.