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Dual thermocouple wiring

Dual thermocouple wiring

Dual thermocouple wiring

(OP)
I was wondering if there is a way to wire two thermocouples so that they send the highest of the two signals to the signal processor.  I have a single temp reader but there are two things that I need to measure the temperature that should remain about the same temperature all of the time.  I need to know if I can simply wire them in series or paralell in order to get the signal from one of them without halfing or doubling the signal or have any other undesired effects.

RE: Dual thermocouple wiring

Each thermocouple needs a cold junction and a subtracting
amplifier. A thistd amplifier may be connected to output
the highest of the two.

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

RE: Dual thermocouple wiring

(OP)
Im a Mechanical engineer so I dont really know what a thistd amplifier is I googled it but it came up with nothing if you could elaborate on what that is that wousl help maybe its just a spelling error but I dont know.  

RE: Dual thermocouple wiring

cooleyjo I've never heard of that either... methinks maybe a typo?

  You can always hook two T/Cs in parallel which will give you the average. Never in series!

  Generally instead of the hassle you are heading for, you would just acquire a T/C scanner and see both. Some scanners would probably let you select for "highest".

RE: Dual thermocouple wiring

(OP)
so if you hook them up in paralell it will give you the average of the two TCs?

RE: Dual thermocouple wiring

it depends on the internal resistance of the two TC-s.
If they are the same: yes  else : no.

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

RE: Dual thermocouple wiring

   cooleyjo nbucska is correct you would want to use the same style T/Cs when paralleing.

   We often hooked up to 12 in parallel for large sterilization chambers. In other cases we would hook up three sets of three.

RE: Dual thermocouple wiring

(OP)
Well I wired the two thermocouples in paralell and it seems that the tepmerature is wayyyy too hot for what its supposed to be I would say around twice as hot as it should be any suggestions about why this is acting up like this??

RE: Dual thermocouple wiring

Are you sure you have the correct polarity of the wires?

TTFN



RE: Dual thermocouple wiring

Double?!?

It sounds like you hooked them in SERIES!

RE: Dual thermocouple wiring

(OP)
no I definately hooked them up in paralell I thought that would be the problem too. but just to make sure I hooked 2 T/C + to + on plug and 2 T/C - to - on plug is there only one way to hook up a thermocouple isnt it just two disimilar metals? I will try to hook reverse polarities on the two TCs tonight Hope it works anyone have any other suggestions

RE: Dual thermocouple wiring

This is wierd. What are you using to monitor the T/Cs?

RE: Dual thermocouple wiring

I suggest the following:

Measure each T/C individually with a multimeter on mV DC setting, convert to Temperature using the tables for your type T/C (ie. J, K or whatever).  Don't forget to add on ambient temperature of the location where your multimeter is.  Calculate the average of the 2 measurements.

Then parallel the T/Cs and do it again.  You should get the same result.  Otherwise you are doing something wrong.

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