Instrumentation data highway

The distributed control system (DCS) hardware areas are often referred to as "process computer rooms." I/O Rooms contain the incoming and outgoing wiring, cables and data highway links, and often small transformers and other related electrical equipment. Often, additional space is needed for a master process engineering computer terminal/work station for process control system changes and for critical safety instrumented systems (SIS) for interlocks and emergency shutdowns. 

Microprocessor-based equipment, such as smart instruments and single-loop controllers with digital communications capability, are now used extensively in process plants. A field bus, which is a low-cost protocol, is necessary to perform efficient communication between the DCS and devices that may be obtained from different vendors. Figure 8-65 illustrates a LAN-based DCS with field buses and smart devices connected to a data highway. 

Instrumentation philosophy (local/remote control, hardwired/data highway, failure mode(s), analog/digital, emergency alarms, etc.). 

Another major development of modern control systems is the data highway. Field information going to and received from devices such as thermocouples, transmitters, controllers, and other instruments are converted into digital numbers. The reason for the digital highway, which conveys all of this information to and from the field instruments and the control room, is to reduce the amount of wiring required. For example, some of the most advanced computer control systems for process plants can convey 150,000 bits of information per second using a coaxial cable. 

The use of a data highway eliminates large quantities of instrumentation and control system hardware, cabling, cable trays, cable spreading areas, containment penetrations and other equipment. 

APC, MPC and RTO require modem instrumentation, which includes actuator valves, distributed control systems (DCS), high-flux data highways, analyzers, and dedicated computers. They also require trained support staff, which at this writing is in short supply. 

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