Permanent magnets and other magnetic elements can be tested by passing the elements or components through a coil and integrating the resulting voltage induced in the coil. This is a well-known and tried method which, however, has some disadvantages. Customarily used integrators have a comparatively high drift. Thus, if quiescent or remainder signals are applied to the integrator, or noise signals reach the integrator, it will also integrate such signals and thus not provide appropriately controlled output signals. Integrators, of course, are polarity sensitive. If magnetic elements are passed through a coil and then removed, the time integral of the induced voltage will be zero since first a positive, and then a negative voltage will be induced in the coil, resulting in an overall integral of zero, so that no remaining measurable output can be sensed. To prevent such zero output, additional circuitry may be needed which, usually, is quite complex and introduces additional errors, and particularly drift errors.
USPTO Backgrounds
USPTO Backgrounds