Arthur Vincent Pohm

High Sensitivity Ballistic Fluxmeter

The sensitivity of a ballistic galvanometer, used as a fluxmeter, can be considerably increased when it is employed for measuring flux changes which occur in a time which is much less than the damping time, in the case of a highly damped galvanometer, or the period of oscillation for a slightly damped one. This is accomplished by mechanically opening a switch in the galvanometer test coil circuit a short time after the flux change is completed thereby leaving the galvanometer either critically or lightly damped as desired. By use of this method gain in flux sensitivity of 56 has been obtained with a critically damped Leeds and Northrup Type 2290 galvanometer. With the critical damping resistance removed, the gain is 152. Such a ballistic fluxmeter is well suited for measuring the ferromagnetic properties of very small toroidal cores frequently employed in computers, etc.