188720 ⎘
Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems; Regulating voltage or current wherein the variable actually regulated by the final control device is dc using discharge tubes in series with the load as final control devices additionally controlled by the unregulated supply