Mixed DC supply

That sounds OK - but I'm not sure where this 120Vac comes in. If it's just the supply to a unit which produces a 0 - 10V signal, then procede as you've suggested. Sensor device 0V to PLC 0V (BTW - what's a PLR?), & signal to PLC input.

Hello JohnDG, and thank you for your reply. The 120 V AC supplies a thermostat that has a set of dry contacts, a temperature display, and a 0 to 10 V DC output to feed a building automation system. In this case a PLR (programmable logic really) basically a cheap PLC missing some of the features that I now wish I had, it would've been worth $150 price difference or so. This PLR can only read 0 to 10 V for analog inputs, a 4 to 20 milliamps analog input would've made life much simpler. Again thank you for your reply I was pretty sure this would work however I have been wrong before.

All sounds fine - for Safety, just make sure that every point with an Earth symbol or letter E (on the PLR, thermostat unit etc.) is solidly tied to a PE (protective earth) point.

If the PLR is DC-only supplied, then it could float (though a functional earth (black wire in UK, depends on your regs) could be tied to the PE and will probably make fault-finding easier). The thermostat body may well be earthed through the pipework (which you should also check for earth connection!).

Sorry to harp on about the safety aspects, but better safe ...

No harping perceived here, truthfully I hadn't yet consider the safety of the system, I had been focused on not damaging the PLR. Most custom controls that I am involved with, I'm also the only one working with, in this instance I will be turning it over to the end-user's maintenance personnel, so safety is well worth considering. I've already specified that there will be no unshielded high-voltage in my panel, quite to the electrician's dismay, But it is certainly worth reviewing all safety aspects of the system. I do not know if you're acquainted with him in the UK , we have this guy called Murphy here in the US. The last time I thought I had everything figured, and that nothing could possibly go wrong I had one part of an AC circuit get out of phase with the other, fortunately the only damage was the egg on my face as the circuit breakers tripped.

mixit said it. Wish you well.

We know Murphy very well...