T.C. and PID Question

[lwknight]

Can a single TC be wired to operate 2 PID controllers ,or will it mess with the reading if another load is paralleled?
I'm going to figure out a reasonable way to use PIDs on a gas smelting pot. It will have 2 gas valves so I can have low, med, and high burner.
I think the low temp alarm will work for low-medium relay.
What I have in mind is splitting the output from a single regulator to two gas valves with needle valves to adjust the settings. I'm not sure about the low fire. Maybe a 3rd split will do for low/pilot mode.

Next hurdle is to find solenoid gas valves that are not ginormous with a built in differential. I need something simple like the water valves on a washing machine.

[OS OK]

Good question...depends on how the PID references the signal, how it's coupled to the circuit within the PID.

It's worth a try...you could temp one together and see if the PID's follow the temp.
We used to use one speed reference signal to get multiple DC motors to track the same speed, worth a try.

[dikman]

Yep, the only way to be sure is to try it. Theoretically if the input impedance of the PID is high enough it should work, but these TC's are working on pretty miniscule voltages, so it's likely that anything else across the TC wiring will have some effect.

[OS OK]

Couldn't sleep tonight so I found myself looking for your answer.
One engineer says try it, one says no and another says they have been doing it for years in the heat treating business.

The best answer a couple of fellas suggested was using a dual element thermocouple...one sheath two thermocouples within. They said they are readily available and that they are cheap.

Here's the conversation in another forum where the 'brains' hang out...
http://www.eng-tips.com/viewthread.cfm?qid=196705

[lwknight]

I guess it would be easy enough to just wire tie two TCs together just so they stay out of the way. I was just thinking that two separate TCs would get in a tangle or something.
Even better like OS OK said, two in one well would work too.