Abstract: A process controller which has at least a derivative control mode includes a comparison amplifier wherein a measured variable signal is compared with a set-point signal to produce an error signal. An auxiliary control circuit including a signal level change detector is connected to detect changes in the set-point signal. During intervals of constant set-point signal, the primary control circuit operates normally. Upon the occurrence of a change in the set-point signal, the change is detected by the auxiliary control circuit and produces an auxiliary control signal which is applied to momentarily inhibit the operation of the derivative control function of the controller.

Abstract: An interface circuit for a transmission line between a remote transmitter and a central control room instrument includes an operational amplifier. The input of the operational amplifier is derived from the current drawn by the remote transmitter. The output signal of the operational amplifier is applied to control the operation of a transistor current controlling amplifier. The current controlled by the transistor amplifier is drawn from the same source as the current drawn by the transmitter. Because of a feedback connection from the transistor amplifier to the input of the operational amplifier, the output current from the transistor amplifier is a mirror image of current drawn by the transmitter. With that arrangement, both the power supply and the remote transmitter may be grounded without loss of accuracy or reliability.