In general application, the instrumentation and automation architecture is consist of field instruments, individual & multicore cable, junction boxes, marshalling cabinet, and system cabinet.
Each of them is combined together so that the control loop application can be performed correctly.
Architecture of Instrumentation
The field instruments are any of the instrument equipment used to measure and control the process variables. Such type of instruments is pressure transmitter, temperature transmitter, flow transmitter, level transmitter, control valves, solenoid valves etc. This device is acting as a front liner in the instrumentation control loop.
The cables, both individual and multicore, are used to connect the field instruments with the controller. This cable is used as a signal or power transmission.
First of all, the individual field instruments are connected by and individual cables to a junction box. This junction box is used to re-connect the individual cables with the respective multicore cables.
So, instead of laid up the individual cables for each instrument to the control room, we laid up the multicore cables (usually comes in big size) to the control room.
Junction Box Connections
The marshalling cabinet is used as a place to do a cross-wiring of the multicore cables with the respective terminal block allocations. The arrangements of the multicore cables that come from the field usually didn’t come in the control loop point of view.
And usually, the ICS vendors have their own arrangement regarding their I/O module and the respective controller. So they do a cross-wiring in this marshalling and the incoming multicore cables adapt the arrangement of the I/O and controller make by ICS vendors.
The system cabinet is used to place all the I/O card/module and also the controller itself. All the wire that has already arranged in the marshalling goes to this cabinet directly without any more difficult arrangement.
The incoming cables come to this cabinet has already tidy and match with their respective I/O channels. In this controller, the signal comes in and comes out from and to the field to establish complete control loops.
Typical Instrumentation Layout
Below is the typical instrumentation architecture illustration that widely used in any oil & gas projects.