Glossary of Thermocouples

Cold Junction or Reference Junction

The junction generally at the measuring device that is held at a relatively constant temperature.

Cold Junction Compensation

Measures the ambient temperature at the connection of the thermocouple wire to the measuring device. This allows for accurate computation of the temperature at the hot junction by the measuring device.

Dual Element

Two thermocouple elements housed within one thermocouple hardware assembly.

Extension Wire

Wires which connect the thermocouple itself to a reference junction, i.e.
controller, receiver, recorder, etc. Extension wire must be of the same type as the
thermocouple. Special plugs and jacks made of the same alloys as the thermocouple
should be used if a quick disconnect is required for the application.

Grounded Junction

The internal conductors of this thermocouple are welded directly to
the surrounding sheath material, forming a completely sealed integral junction.

Ungrounded Junction

Although the internal thermocouple conductors are welded together they are electrically insulated from the external sheath material and are not connected to the sheath in any way.

Ungrounded junction thermocouples are ideal for use in conductive solutions or wherever circuit isolation is required. Ungrounded junctions are required where the measuring instrumentation does not provide channel to channel isolation.

Exposed Junction

The thermocouple junction or measuring point is exposed without any protection assembly or tube. Exposed junction thermocouples due to their design, offer the user the fastest response time.

Hot Junction

The measuring junction.

Immersion Length

The portion of the thermocouple which is subject to the temperature which is being measured.

Measuring Junction

The junction in a thermocouple which actually measures the temperature of the object. Often referred to as the Hot Junction.

Protection Tube

A tube like assembly in which the thermocouple is installed in order to protect the element from harsh environments.


Abbreviation for Resistance Temperature Detector. It is a sensor which operates on
the principle that the resistance increases with an increase in temperature at a specific
rate. Commonly manufactured using a platinum resistance element. More accurate and
more linear than most thermocouples and generally much more costly and slower


A temperature sensor based on the principle that a voltage is produced
when two dissimilar metals. The junction produces a voltage in proportion to the difference
in temperature between the measuring junction and the reference junction.


A threaded or flanged closed end tube which is mounted directly to the
process or vessel, designed to protect the thermocouple from the process surroundings.