What is the difference between a Thermocouple and RTD?

Instrumentation Temperature
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Difference between a Thermocouple and RTD

Temperature Range

First, consider the difference in temperature ranges. Noble Metal Thermocouples can reach 3,100 F, while standard RTDs have a limit of 600 F and extended range RTDs have a limit of 1,100 F.

Cost

A plain stem thermocouple is 2 to 3 times less expensive than a plain stem RTD. A thermocouple head assembly is roughly 50% less expensive than an equivalent RTD head assembly.

Accuracy, Linearity, & Stability

As a general rule, RTDs are more accurate than thermocouples. This is especially true at lower temperature ranges. RTDs are also more stable and have better linearity than thermocouples. If accuracy, linearity, and stability are your primary concerns and your application is within an RTD’s temperature limits, go with the RTD.

Durability

In the sensors industry, RTDs are widely regarded as a less durable sensor when compared to thermocouples. However, REOTEMP has developed manufacturing techniques that have greatly improved the durability of our RTD sensors. These techniques make REOTEMP’s RTDs nearly equivalent to thermocouples in terms of durability.

Response Time

RTDs cannot be grounded. For this reason, they have a slower response time than grounded thermocouples. Also, thermocouples can be placed inside a smaller diameter sheath than RTDs. A smaller sheath diameter will increase response time. For example, a grounded thermocouple inside a 1/16” dia. sheath will have a faster response time than a RTD inside a ¼” dia. sheath

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Dear sir
We have encountered a problem in Turbine bearing RTD which shows hunting in its value during running condition.

After we have checked during shutdown time values shown normal in both pairs and had steady values .
What might be the problem in RTD or is that the problem arised due to aging .

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As RTD works fine, It may due to terminations / Terminal blocks.

Check all the loop connections again, check all junction terminations.

Turbine vibrations may cause this issue. even if you find the continuity with the cable, re-tight all terminations again.

or there may be really issue with the turbine ? check remaining RTD response at the same time.

Also I suggest to start a New Topic in respective category for easy discussions instead of discussing in unrelated posts, if applies.

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We checked the terminations and all are normal.
Turbine vibrations are also normal and finally we mounted a new one .

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Sometimes terminations may get disconnected momentarily due to turbine vibrations. so even if we check continuity it will look fine at some cases.

Also How was the RTD response at that time ? is it a spike or some type of exponential rise ?

what is the other RTD response ? Trend wise ? any change or normal…

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