Thermocouple junction style selector
Choose between an exposed, grounded and ungrounded junction from the two things that actually decide it: how fast the reading has to move, and whether the loop needs electrical isolation.
Recommendation
Answer both questions to see which junction style matches your requirement.
The three options side by side
Exposed junction
Fastest
None, the junction is in direct contact with the process
Where you must track a fast transient and the process is benign enough to expose the junction to, or where the junction is protected by the process itself.
Grounded junction
Fast
None, the junction is electrically common with the sheath
The common industrial default: fast response with a rugged sheath, wherever the loop does not have to be electrically isolated from the process.
Ungrounded junction
Slowest
Full, the junction is electrically isolated from the sheath
Where isolation matters: to break a ground loop or where a conductive sheath would otherwise inject interference into the millivolt signal.
Frequently Asked Questions (FAQ)
Which junction style is the industrial default?
Grounded. It balances a fast response with a rugged sheath and keeps the junction electrically common with the sheath, which suits the majority of process loops. It is the wrong choice only where the loop has to stay electrically isolated.
What do I give up by choosing an ungrounded junction?
Response speed. The isolation barrier the junction sits behind is also a thermal barrier, so an ungrounded probe reacts more slowly. You are trading milliseconds or seconds of response for a clean signal, and that trade is only worth making when the isolation is genuinely needed.
Can a junction choice fix a noisy reading?
It can, if the noise is arriving through the sheath. Where a conductive path to the process is injecting interference or creating a ground loop, an ungrounded junction breaks it. If the noise is on the signal path instead, the answer is shielding and routing rather than the junction.
When should this decision be revisited?
Whenever the process or the earthing scheme changes. The choice is always speed versus isolation, and both sides of that trade move when the installation does, which is why it belongs in a design review rather than a one-off purchase decision.
Need the probe built to that decision?
Tell us the junction style, sheath and gauge, we supply matched assemblies and conductor wire for the same loop.