What are insulated thermocouples, grounded thermocouples, and exposed thermocouples?

The type of connection point is another way to classify thermocouples. Thermocouples with exposed connections are widely used for gas temperature measurement that requires extremely fast response time. Because the temperature measuring wire is exposed, its life is short and it is not resistant to high temperatures. Generally speaking, the test temperature cannot exceed 150°C and cannot be used in liquid temperature measurement.

Insulated thermocouples refer to probes with insulation between the measuring end and the sheath (usually stainless steel or Inconel). This probe has the greatest advantage in test environments with interference.

Ungrounded probes may have a slightly longer response time, but the difference is minimal when compared to exposed junction and grounded junction probes with small diameter sheaths (e.g., 1.6 mm (1⁄16")).

Grounded thermocouples allow the thermocouple junction to contact the end of the sheath, offering the dual advantages of fast response time and sealed sheath protection.

In a nutshell:

Exposed types have faster response, lower temperatures, shorter life, and weaker interference resistance

Insulated types have slower response, higher temperatures, longer life, and better interference resistance

Grounded types have faster response, higher temperatures, longer life, and weaker interference resistance