PLC/DCS - I/O Cables.

[rajant2001]

I would request the Forum Members to suggest the type of cables to be used for connecting following I/Os to DCS/PLC based on their experience.

1 Analog inputs 4-20mA (from transmitters & VFD feedbacks)
2 Analog inputs Thermocouples
3 Analog inputs RTDs
4 Analog outputs 4-20mA (to I/P converters & VFD reference)
5 Digital inputs - voltage 24v DC (from field swithches & aux. potetial free contacts in MCC/VFD)
6 Digital outputs voltage 240/110 v AC (commands for start/stop, open/close to MCC/Solenoid coils)

Normally these I/Os are grouped (typewise)in Field Junction/Marshalling boxes so that Multicore/pair cable can be run from field to PLC/DCS panel in the control room.

Can we use Multicore armoured (0.8sq.mm for AI/AOs, 1.5sq.mm for DI/DOs & 1.32sq.mm for thermocouples)?

Or we have to use multipair screened cables for the above applications.

R.Thiyagarajan.

 

[ScottyUK]

4-20mA inputs: use individually screened twisted pairs, in an overall screened multicore if you wish.
Thermocouples: use thermocouple compensating cable which is invariably screened,in an overall screened multicore if you wish.
RTDs: use an individually screened 3-core (triad) cable for a typical industrial RTD, in an overall screened multicore if you wish.
4-20mA outputs: use individually screened twisted pairs, in an overall screened multicore if you wish.
Digital inputs: use standard multicore control cable.
Digital outptus: use standard multicore control cable.

Sizes look ok subject to volt-drop around the loops, except the thermocouples - comp cable is usually much thinner than that.


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