Preliminary development of a magnettor current standard

In the wartime development of the air-borne magnetometer, a method of detecting extremely small changes in magnitudes of magnetic fields was developed. The principle involved was the use of a second-harmonic type of magnetic modulator now known as a magnettor. This instrument can detect changes in magnetic fields in the order of 10¿5 oersted. A study was made at Rutgers University under the sponsorship of Bell Telephone Laboratories to determine the feasibility of obtaining a standard of current using the magnettor principle. In this case, the magnettor was placed in a stable permanent-magnet field of a few oersteds and the field nulled by means of a solenoid carrying the current to be stabilized. This current was supplied by an electronic self-balancing system, which maintained a null condition. If a field of 1 oersted is used, an ultimate accuracy of one part in 105, or 0.001 per cent, might be expected.