DCS wiring connection from field to control room

now we can discuss about DCS connections
We have thousands of field transmitters installed in a process plant. So it is practically difficult to lay straight individual cables from each field transmitter to control room for displaying the process variables on the workstation.
As per design standards, particular number of field devices or transmitters are wired and terminated in a Field Junction box.
Cable used for connecting the field device to Junction box are called as Branch cables or field cables. Generally we use one pair cables for branch cables.
five field devices are connected to a Junction Box using individual Branch cables.
for carrying out these five signals to control room we need minimum five pair cable means one cable have 5 pairs and also we have to consider spare cable requirement for future purpose.
so at least six pair cable or better a 12 pair cable best suitable for our requirement.
So we choose 12 pair cable and is nothing but a Main Cable or Home run cable as it interfaces the field junction box and marshalling cabinet in the control room.
so finally one big main cable is required and serves our purpose.
next we discuss about Field Instruments to Junction Box
In a Process plant, we have so many Junction boxes installed and connected with number of field devices.
Say we have hundred number of Junction boxes installed, that means we have hundred number of main cables are coming from field to control room.
so practically it not possible to directly wire these main cables to analog input or output cards. To avoid these problems we use Marshalling cabinet for terminating these hundred number of main cables.
Marshalling cabinet main purpose is to provide main cables termination and then redistribute the field devices to respective Analog Input or Output card using internal wiring.
Internal wiring will be used to connect from Marshalling cabinet to system cabinet.
and next we discuss about Wiring between Marshalling and System Cabinets
System cabinet consists of Processor card CPU, Analog Input Cards, Analog Output Cards, Communication cards etc.
Once Main cables are terminated in Marshalling cabinet, we have to take these field devices to the respective Analog input card channel.
so we use internal wiring to route these main cables or field devices from marshalling to system cabinet.
Once the main cables are connected to the Analog Input card via internal wiring and it converts the 4 to 20 milliamps which is coming from field devices into equivalent Digital signal, in Binary codes and the same will be communicated to Processor card.
The processor card performs as per the predefined or programmed instructions. The processor card may have inbuilt or separate Ethernet communication link which is used to display the measured process variables on the workstation.

[@Shadowwand]

Now we have IOT devices that live in the Junction Box, and use a single PoE to control and report the field devices.

[@humanbeing4097]

Very useful,but it should have more details after Marshalling cabinet to System.

[@INSTRUMENTATION27]

Yes, you are right

[@sharifhossain8830]

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