I'm using field junction boxes to gather individual sensor and valve signals from/to the plant area. From the field junction boxes I would like to use 12-pair Belden 9776 (details below) to transmit all device signals to the PLC IO. My discrete signals are 24VDC and the analog are 4-20mA; but I would like to generalize the discussion for all common IO signals.

What do you think?
THANKS

Details of Belden 9776
18 AWG stranded (19x30) tinned copper conductors, polyethylene insulation, twisted pairs, individually shielded with 100% Beldfoil®, 20
AWG stranded tinned copper drain wire, PVC jacket.

 

You should have no problems with your proposal.

In 1996 we installed a reasonably large DCS (3000 I/O) and did exactly what you propose. We used an Australian/New Zealand cable that had 24 unshielded twisted pairs with an overall screen. All the signals to and from the field boxes were either 4-20 mA for the analogs or 0-24 volt for the digitals. If we required anything else we converted in the field boxes.

To my knowledge there have been no problems at all with this arrangement.

Good luck

Peter Green

 

Of course you must use different pairs for analog and digital signals and right connection of all screens to chassis.

Leonid

 

Not a problem since all thje signals are low voltage, keep all of the digital commons seperate from the analog commons.

Would be like using a lot of 14awg or 16awg wire instead of 18awg multi-conductor. YOu may want to check the NEC, interconnection wires are typically 14awg for all ac adn dc control siganls, analog signals can be in a properly sized shielded cable (18awg.) Wire size will depend upon length of the run, voltage of the signal and the current involved.

MJH