Process control systems, like those used in chemical, petroleum, pharmaceutical, pulp and paper, or other manufacturing processes, typically include one or more process controllers communicatively coupled to at least one host including at least one operator workstation and to one or more field devices configured to communicate via analog, digital or combined analog/digital communication protocols. The field devices, which may be, for example, device controllers, valves, valve actuators, valve positioners, switches and transmitters (e.g., temperature, pressure, flow rate, and chemical composition sensors) or combinations thereof, perform functions within the process control system such as opening or closing valves and measuring or inferring process parameters. A process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine, and generates control signals that are sent over the buses or other communication lines to the field devices to control the operation of the process control system.
A process control system can include a plurality of field devices that provide several different functional capabilities and that are often communicatively coupled to process controllers using two-wire interfaces in a point-to-point (e.g., one field device communicatively coupled to a field device bus) or a multi-drop (e.g., a plurality of field device communicatively coupled to a field device bus) wiring connection arrangements or with wireless communications. Some field devices are configured to operate using relatively simple commands and/or communications (e.g., an ON command and an OFF command). Other field devices are more complex requiring more commands and/or more communication information, which may or may not include simple commands. For example, more complex field devices may communicate analog values with digital communications superimposed on the analog value using, for example, a Highway Addressable Remote Transducer (“HART”) communication protocol. Other field devices can use entirely digital communications (e.g., a FOUNDATION Fieldbus communication protocol).
In a process control system, each field device is typically coupled to a process controller via one or more I/O cards and a respective communication path (e.g., a two-wire cable, a wireless link, or an optical fiber). Thus, a plurality of communication paths are required to communicatively couple a plurality of field devices to a process controller. Often the plurality of communication media coupled to the field devices are routed through one or more field junction boxes, at which point, the plurality of communication media are coupled to respective communication media (e.g., respective two-wire conductors) of a multi-conductor cable used to communicatively couple the field devices to the process controller via one or more I/O cards.