DCS Control system;plc control system

 The system cabinet is a cabinet that is designed to accommodate the following DCS equipment:

-          The controller

-          The I/O Card

The typical configuration of the controller and the I/O card is as follows:

-         There are a power supply, controller, and I/O card in the same backplane. This part will be located in the topmost part of the cabinet and will be the 'brain' of the automation system.

-         There are an extended or node I/O cards complete with its power supply and extended or node interface card. This part will be located below the controller unit and acting as an extension of the I/O card in the controller unit.

The system cable that comes from marshalling cabinet will be directed into the intended I/O cards address. The field signal will be digitally processed by this I/O cards and then sent to the controller for further digital logic processing.

In the bottom part of the system cabinet, there are a sets of terminal for incoming power cable termination. Most DCS application in oil and gas industries is requiring a redundant power supply that is fed by the Uninterruptable Power Supply (UPS). The incoming UPS power cable is then terminated into the isolation switch and from the isolation switch it is connected to the mini circuit breaker. There are also non UPS power supply that will be used for feeding the system cabinet utilities such as for lighting and fan. The incoming non UPS power cable is then terminated into isolation switch and then connected to the mini circuit breaker just like UPS power cable.

In the system cabinet there are also fan units that will make sure the air circulation is properly maintained so that the operating temperature of the cabinet is still within the limits. The system cabinet is also equipped with some temperature switch that will activate the alarm in case of the temperature inside the cabinet is exceeding the limits. Ground bar for system ground and protective ground is also provided in the system cabinet and usually it is located in the bottom part of the cabinet.

See below DCS system cabinet drawing as an illustration. Please take a note that the DCS configuration may vary from each DCS vendor but basically it will have more or less the same basic configuration as explained above.