There are different types of thermocouples and their applications may vary. An exposed thermocouple will work best when high response times are required, but an ungrounded thermocouple is better in corrosive environments. To help you determine the best thermocouple for your purposes, here are five considerations:
- Determine the application where you will use the thermocouple sensor
Thermocouples can be used across industries and applications, so selecting the right one for your purposes starts with knowing exactly how and where you want to use it
- Determine the temperature ranges the probe will be exposed to
Once you know the thermocouple temperature range that you need, you can refer to our thermocouple range chart to help you determine which thermocouple is best for the temperature ranges you need.
A type K thermocouple offers a wide temperature range and is one of the most often used thermocouples. However, if your thermocouple probe will be exposed to extreme temperatures, a type N thermocouple is more stable in high temperatures and a type T thermocouple is best for extremely low temperatures
- Determine how important a fast response time is
There are three types of thermocouple junctions: exposed, grounded or ungrounded. An exposed junction will provide the fastest response times. However, if the probe will be exposed to corrosive gas or high pressure, an exposed junction should not be used. An ungrounded thermocouple offers the slowest response time but can still be the best choice if it is also desirable to have the thermocouple electronically isolated from and shielded by the sheath.
- Consider any chemical, abrasion or vibration resistance
An exposed thermocouple is limited in use to noncorrosive applications. Both a grounded or ungrounded thermocouple can be used in corrosive or high-pressure environments, but an ungrounded probe is best if there is a need to have the thermocouple electronically isolated from and shielded by the sheath. If faster response times takes priority in a corrosive environment, then a grounded thermocouple is best
- Consider any installation requirements
The thermocouple may need to be compatible with existing equipment. For example, existing holes may determine the probe diameter
Should I use a grounded or ungrounded probe?It depends on the instrumentation. If there is any chance that there may be a reference to ground (common in controllers with nonisolated inputs), then an ungrounded probe is required. If the instrument is a handheld meter, then a grounded probe can almost always be used
Sheathed thermocouple probes are available with one of three junction types: grounded, ungrounded or exposed. At the tip of a grounded junction probe, the thermocouple wires are physically attached to the inside of the probe wall. This results in good heat transfer from the outside, through the probe wall to the thermocouple junction.
In an ungrounded probe, the thermocouple junction is detached from the probe wall. Response time is slower than the grounded style, but the ungrounded offers electrical isolation.