A versatile and sensitive balanced magnetic comparator

A magnetic circuit is described wherein a pair of matched square-loop magnetic cores are connected in a balanced manner to act as a sensitive null-detector called a balanced magnetic comparator. A material characteristic and a mode of operation that significantly increase the sensitivity over that of the basic circuit are also described. The sensitivity of the balanced magnetic comparator is such that low-level transducers/sensors can be directly connected to the input winding and produce an unbalanced condition. Thus, by means of successive approximation, the measurand signal from a sensor can be converted to digital form without interposing semiconductor amplifiers. Comparator circuits have been operated over a temperature range of 100°C with a resolution of 10 μA, and a 7-bit accuracy. In this use as an A-D converter the balanced magnetic comparator is unbalanced by the current output from a transducer, and balance is restored by precision weight currents. These weight currents can be generated in pulse form by transistorized circuits that use additional comparators operating in a dynamic mode. In this dynamic mode the time function of the output waveform is used, rather than polarity, as in the A-D converter. These comparators provide feedback control to the transistors in order to achieve the necessary precision in the weight-current pulses. Using a balanced comparator rather than a single square-loop core has a major advantage in that the offset contributed by the threshold of a single core is eliminated.