Analog signals

[Rson]

I'm looking for some opinions here.

Typically for analog signals, we use a twisted pair wire with a drain shield. However, am I correct in assuming that this would not be required if all of the voltage is DC only? You could just run 16AWG wire in conduit for an analog signal?

 

[Bit_Bucket_07]

Sure it would work, but I wouldn't do it.

Are you talking about "DC only" in the entire facility, or only in the same conduit in which you intend to pull the analog signal wiring?

Even with DC discrete circuits, you can still experience noise from inductive kick whenever a coil is energized or de-energized.

If you're talking about ferrous steel conduit, that would protect the analog signal circuit from outside EMF or RF noise. PVC or aluminum conduit? Not so much.

I just consider it bad engineering practice, and if a problem should crop up, you'd likely be held responsible for it.

 

[rQx]

I would always go for a screened cable but I often use a non twisted version

 

[Saffa]

Do you mean individual single core wires inside the conduit?

Yeah it'll probably work but you lose the added common mode noise rejection provided by twisted pairs.

Also much easier pulling in one multi

 

[Tom Jenkins]

Any savings in wire cos can be chewed up in a big hurry by troubleshooting time if you develop a problem. Cut costs elsewhere.

 

[rootboy]

Ages ago the electricians in our plant installed the sensor leads from a pulse counter in the same conduit as the AC output for out the alarm bell for the gasoline fill at Saturn.

When the operators got behind, the alarm would go off, triggering the input to count the pulses going out to the alarm as tenths of a gallon of gas because of induced voltage. Effectively "filling" the tank with phantom gas.

Problem solved.

So yeah, it wouldn't hurt to use twisted and shielded cable. That and keep it away from other signals.