How deos a DCS works?


#1

DCS (Distributed Control System) is a control system where each individual controller communicating to a central computers acting as workstations.

Such a system has the advantage that failure of a single component will not cause system failure, shutdown; sometimes called graceful degradation. And a hardware or software failure will not go undetected.

The working of DCS system is based on both hardware and software working.

Working of DCS:

Working of DCS can be divided into two parts: 1 Hardware flow 2. Software flow.

Hardware flow:

In all processes, sensor unit or transmitters measure process variable from the process, through which the status of the process is known. The flow of the signal starts from the transmitter, the signal from the transmitter passes to the Field JB(Junction Box), where a number of wires come from different other sensors.

From field junction box through multicore cable, it goes to the main junction box. From it comes to Marshalling cabinet, where wires enter into control panel from the junction.

In control panel, controller and I/O cards are placed. After signal entering the control panel, the signal wire is connected to the I/O card of the controller with or without Relay card. Controller thereby processes the data according to the logic created and gives output to the Final Control Element through output cards, following the same route.

Software Flow:

The basic purpose of the software is to scan. There is a scan cycle that must be completed for the execution of a necessary instruction to control the process. The user establishes the scan period while configuring DCS and the following steps are performed for each scan period:

  • Initially the software scans or checks the input from the process through the input cards are checked.

  • Then, the values are updated in the program and according to the logic prepared by the programmer, the output values are decided.

  • These outputs then go to the field through output cards.

  • In addition, the status is updated in the SCADA and the changes are stored for future reference in the historian. Any alarm, that is, the deviations in the process are there, then they are also recorded and stored.

Software consists:

  • To view and control the process using mimic, same as the real process (SCADA).
  • Programming environment wherein logic can be created.
  • A hierarchical view of the whole system
  • Advance Control Strategy Schemes
  • Configuration Suite to configure the hardware attached.
  • Diagnostic Suite
  • Alarm Module
  • History Module
  • Trends Module
  • Database management module