Abstract: To prevent hunting in an automatic vehicle speed maintenance circuit having a closed control loop, the control element is so arranged that the controller has not only proportional, but additionally derivative control characteristics to increase the response speed while permitting loop amplification which is necessary in view of the response delay characteristic of the controlled element, namely the vehicle itself.

Abstract: To improve the reliability of systems which, upon operation of the brake, must be disconnected but otherwise operate reliably, and to reduce the number of components required, a memory and control circuit is provided which includes an amplifier having a self-holding feedback connection. Upon receiving a "disconnect" signal, for example due to operation of the brake of the vehicle, control operation of the circuit is inhibited; upon operation of a "resume" switch, connected to the feedback junction, the self-holding feature of the amplifier in the "disconnect" mode is inhibited so that the circuit can again resume its control function.