Abstract: The disclosure is directed to a transformer circuit apparatus which receives an input signal and generates an output signal representative of the input signal. For example, the input signal may be an AC current, and the output signal to be generated may be a voltage that is proportional to the current. A transformer is provided, and has a core, a primary winding for receiving the input signal, a sense winding, and a feedback winding. A first circuit is coupled to the sense winding, and is responsive to the magnetic flux sensed by the sensed winding, for applying a signal to the feedback winding that tends to reduce the flux sensed by the sense winding. A feedback circuit is provided, and includes a low-pass filter, for feeding back a signal that depends on the output signal to the first circuit means. A circuit is provided for determining the presence of input signal offsets, and for generating offset indication signals in response thereto.

Abstract: Electrical equipment which is configurable to operate in a number of modes includes an enclosure, a transparent window in the enclosure through which may be viewed a connector which configures the equipment in a selected mode so enabling a user to determine the mode.