Analog input wiring?

Hello- I'm wondering if this would be an issue:

Main PLC panel with 24VDC supply and inputs. the + side of the 24VDC is being feed to a equipment skid junction box 80' away. It will feed one side of input switches and one side of 2 wire 4-20mA transmitters. All the returns will come back to the PLC panel. Would you run a shielded twisted pair and clip one of the wires for the return side of the transmitters? Technically you would only need 1 analog return wire since the +feed is common to all. Would there be trouble since the 24+ common is being shared with other dry contact closures?

You need two wires for each transmitter - the plus to power it and the minus for the analog signal. You need a wore for each discrete signal. You can use a single wire for the +24 for the analog and discrete. The discrete don't need to be shielded twisted pair.

please use a twisted shielded pair, as any spikes or disturbance will be eliminated by the twist and the shield.
best is to use separate power supplies to have no spikes on the line a switch is no problem, but a solenoid or coil is a big issue

I agree on the shielding, even tho I have never had trouble while using 4..20 mA signals.
I have never had trouble with solenoids or coils causing spikes either. As long as your supply and cable specs are good you should be fine right?

So, in the attached drawing the power rail on the left is the + 24DC coming from the remote PLC panel. I guess the consensus is to remove jumpers on 22,24,26,28 , 30 and run twisted pair per analog device back to main PLC panel? I guess that would be typical so the analog is not sharing the common +24vdc wire to the discrete devices.

Then why would you have the analog signals go through the box at all?

?? Customer wants all signals pulled to 1 junction box on the skid so he can make field terminations there.

Aye, those pesky costumers!

Again, if it were up to me, I wouldn't worry about the 24 VDC being shared. I would use a separate cable for valves, with own conductor for 24 VDC. And separate cable for all analog, with own conductor for 24 VDC. And I would use a screened cable.

Hope to be of help, not trying to be difficult .

No problem- I welcome any replies! There are no solenoids, coils, etc on the 24vdc supply so I don't see any problems. I'll probably just suggest they have all analog returns come back in a shielded multiconductor cable. There's 6 separate skids with 5 analog devices on each- all returning to main PLC panel.