Abstract: A universal input-output apparatus has: a controllable source of electrical energy including at least one drive source having an output terminal and a return terminal; an electrical energy measuring device including at least one energy sensor having an input terminal connected to the output terminal of the controllable source of electrical energy; a twin leaded line having the first ends thereof connected to the output and return terminals of the drive source, respectively; and an integrity tester in the form of a zener diode connected across the second ends of the first and second leads, respectively, a first terminal connected to one of the second ends, a second terminal connected via a unidirectional conductor to the one second end and a third terminal connected via a resistive device to the one second end.