INTERFACE APPARATUS FOR TWO-WIRE COMMUNICATION IN PROCESS CONTROL LOOPS

摘要

A process control system includes a process controller that develops a controller output signal having at least a desired DC component and an undesired AC component and a device having an adjustable parameter. An interface apparatus is coupled to the process controller and to the device via a two-wire loop, and means are provided for coupling a communication signal onto the two-wire loop between the interface apparatus and the device. The interface apparatus includes means for substantially attenuating the undesired AC component and means electrically coupled to the attenuating means for substantially preventing the communication signal from electrically affecting the process controller. The device is responsive to the DC component of the controller output signal, and the adjustable parameter of the device is responsive to the communication signal.