Connect 2 transmitter to single thermocouple

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parinya_naraj

Is there any technical concern, like a cold junction problem, if I connect 2 temperature transmitters with 1 thermocouple?
 
Once upon a time, thermocouple devices (xmtrs/recorders/indicators/controller/DSC/PLC/RTU/AI) did a continuity check of the sensor by sending a tiny pulse of current out one thermocouple terminal and looking for its return on the other terminal. The absence of a return current indicated an open circuit, which would trigger a "thermocouple break" response.

Commercial thermocouple devices are smart enough to not take a measurement at the moment the device is also checking the continuity of the thermocouple.

When you have two T/C devices that use that continuity check technique sharing one thermocouple, you risk getting measurement errors when one device is reading the current pulse the other device is sending for a T/C break check. The error appears as noise spikes.

Sharing a thermocouple is considered heresy in the 'temperature transmitter' world (be prepared to see words a thesaurus lists for 'heretic' for merely proposing the idea), but has been done for decades in the thermocouple extension wire world, heat treat in particular.

You should be aware that dual element probes, whether MgO or industrial protection tube style are routinely available and using such provides a separate and dedicated element for each T/C device. For the minimal added cost of a 2nd element, why not?
 
B

bob peterson

I have never liked doing so but it is a pretty common practice. Since you can get dual T/C elements for only a little more than single T/C elements I see no reason to do it.

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Bob
 
Either use dual thermo couples which in most probability are nothing but two T/C extension wires connected directly to single thermocouples as this has been done internally we presume that this is dual. Otherwise hook up two transmitters at thermocouple terminal head. This will solve the purpose. But why don't you use dual output thermocouple barrier??
 
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