Home > Knowledge > Content
How do thermocouples work?
Jan 29, 2020

What exactly are thermocouples? How do thermocouples work?

Before choosing thermocouples, we need to answer the following questions.

1) What is the temperature range you want to measure and the upper and lower temperature limits?

2) What is the temperature of the object to be measured? The first question will help you categorize applications.

3) How does the measurement environment affect the type of thermocouple I use? Before installing the selected thermocouple, ensure that it meets the following conditions:

a) Proper temperature range

b) Thermocouple or sheath material (for probe with sheath) resistant to chemical corrosion

c) Correct grounding if necessary (many instruments have grounding loop problems when used with grounded jacketed probes)

D) wear resistance

E) anti vibration

F) immersion

What are exposed, grounded, and ungrounded contacts?

The connection point type is another classification of thermocouples. Thermocouples with exposed contacts are widely used for gas temperature measurement requiring extremely fast response time. If the response time of several seconds is acceptable, the ground contact probe with small diameter sheath can meet the requirements. In addition to the above environmental limits, the exposed contact probe must also meet the lower limit of the rated temperature of the exposed small diameter thermocouple wire.

Non grounded thermocouple probe or thermocouple probe with non grounded contact refers to the probe with electrical insulation between measuring end and sheath (usually stainless steel or inconel). In the presence of electrical noise, this probe has great advantages. The sheath may be electrically grounded, which provides a low impedance path for the transmission of electrical noise and keeps the measurement results reliable and accurate. The response time of ungrounded probes may be slightly longer, but the difference is small compared with exposed and grounded contact probes with small diameter sheath (such as 1.6 mm (1 ⁄ 16 ")). The grounded probe allows the thermocouple connection point to contact the end of the sheath, which has the double advantages of short response time and sealed sheath protection.