A New Digtal Method for DC-Current Measurement with Floating Input

This paper describes a new method for direct-current measurement without direct connection to the circuit under test, producing a time-coded indication. A magnetizable ring core with three separate windings is driven to positive and negative saturation by a triangular alternating current. The voltage induced in the detector winding is differentiated. The time interval between two zero-axis crossings of the differentiated voltage is a measure of the current in the measuring winding. Investigations on an experimental setup showed that high resolution and sensitivity and small error of linearity can be achieved. Furthermore the internal resistance can be kept small.