The 5V isolated feature of the circuit is achieved by a power isolation transformer in the DC-to-DC Conversion Circuit. Because of the power isolation transformer, the signal output terminals will have no DC reference to the excitation terminals. No common frame of reference exists between the excitation and the signal. No DC voltage will be present if a voltmeter is connected between either excitation terminal, or if it is connected between either signal terminal. Yet a voltage will exist between both excitation terminals and both signal terminals.

This isolation allows the user to arbitrarily tie either signal terminal to either excitation terminal to create a “three wire system” if so desired. The output signal at the untied signal terminal will be either positive or negative to the node at the tied terminals. If the “+” signal terminal is tied, the “-” signal terminal will be negative to the tied node. If the “-” signal line is tied, the “+” signal terminal will be positive to the tied node. The use of the three-wire system is purely arbitrary; a four-wire system will work just fine. The excitation and signal can be left isolated if desired.

The outputs of the circuit are differential with respect to each other’s noted polarity. What this means is the “+” terminal is positive with respect to the “-” terminal, with the “-” terminal acting as the return line for the signal current flow (using the conventional current flow model). These are the only two points that the output signal can be measured across, and they are truly differential in nature.