SIGNAL HANDLING APPARATUS

Signal-processing apparatus for use with industrial instrumentation systems and the like, and comprising memory means to maintain a signal level for long time periods without drift. An input signal level is translated into the positioning of a movable member, through the use of an actuator motor controlled by the input signal and a position feedback signal. A friction device is coupled to the movable member to hold it in any given position, thereby to serve as a memory for the input signal level. The friction device comprises a thin vane-like element which is secured to the movable member and disposed in the air-gap of a permanent magnet. The air-gap also includes a mass of tiny magnetizable particles which, under the influence of the magnetic field, engage the surfaces of the vane-like element to develop a frictional restraining force. This frictional restraint has the characteristic of being relatively low upon initial movement away from a start point, and thereafter increasing progressively to a plateau level, thereby providing superior dynamic performance particularly in a servo positioning system. Various applications are disclosed including process controllers and chart recorder systems.