What is marshalling cabinet or marshalling panel?
Marshalling panels are used as an interface between the field junction box & DCS control panel. It also isolates the DCS panel from the field control panel.
All I/Os are grouped in the marshalling panel,I/Os like Analog Input, Analog Output, Digital Input, Digital Output and Pulse I/O are done. The I / O signals are conveyed to the CPU / Controllers scheme via insulation/signal conditioners from the marshalling panel.
In the marshalling cabinet, I/Os can be identified easily, inputs comes from the back side of the panel and output to the CPU goes from the front side.
Functions of marshalling cabinet:
cold junction compensation
field device power supplies
Wiring interface in marshalling cabinet:
Interfacing of cables in marshalling is done in cross wiring mode. Cross wiring is necessary because the number of I/O cards and incoming field wires is different.
Each I/O card consists of 16 I/O channels, all the field wires are connected to the card in order, excess wires are connected to the next I/O card.
It is not a good practice from the operation and maintenance point of perspective to have this divided wiring (cross wiring) in the system cabinet. This requires the marshalling cabinet.
The blended I / O signals that come from the field are another cause of the cross wiring. In the same multipair cable, the incoming multipair cable may have mixed AI (Analog Input) and AO (Analog Output) signals. This mixed signal will be divided into the marshalling cabinet so that in the dedicated AI termination board, the AO signal will be terminated.
Cable connection in Marshalling panel:
The multipair field wires pass through the bottom of the cabinet into the marshalling cabinet.
Then in the surge protection systems or surge arrester, each wire of the incoming multipair field cable is terminated. If such surge protection systems are not required, each wire will be terminated in the terminal block.
There will be a cross wiring from the surge protection instruments in the Non IS application that matches the field signal and the termination board I / O address assignment.
The dedicated system cable with a ’ plug and play ’ attachment is then routed to the I / O card in the system cabinet from the termination board.
Some termination boards may involve a specialized DC power supply which in the marshalling cabinet can be removed from the DC power supply.