TEL 281-272-5333   :   FAX 281-272-5332  

Thermocouple Theory
Specifying Thermocouples
Specifying RTDs
Improving Temperature Measurements
Specifying Temperature Sensors in Hazardous Areas
Thermowells - Why They Fail
Thermowell Selection Guide
Choosing the Right Temperature Sensor

Choosing the Right Temperature Sensor

Criteria Thermocouples vs RTDs TC RTD

Although new and improved manufacturing techniques have increased the range of RTDs, this category belongs to Thermocouples. Better than 95% of RTDs are used in temperatures below 1000 F. Thermocouples can be used up to 2700 F.


Grounded Thermocouples are inheritantly tip sensitive; while RTD elements are isolated from their sheaths. A grounded Thermocouple will respond to a 63% step change in temperature nearly 3 times faster than a RTD counterpart.


Comparing a 12 inch, SS sheath .25'', Type J grounded Thermocouple, with a 100 Ohm platinum RTD.00385 Alpha, prices the thermocouple at 2.5 to 3 times less than an RTD. Installed cost make up some of this difference since RTDs use inexpensive copper lead wire to transmit the signal back to the DCS.


There are many factors to determine accuracy; linearity, stability, and repeatability to name a few that can affect accuracy. While a Thermocouple's stand alone accuracy can approach that of an RTD, the superior advantages in these other areas make the RTD the choice.


Temperature vs. resistance nearly plot a straight line for an RTD, while a Thermocouple shows an almost "S" like curve.


Thermocouples can essentially be one piece. RTD elements both thin film and wire wound must be connected to copper wire.


Due to their linearity and virtually drift free output, RTDs are more stable than Thermocouples.

 Copyright 2002 Smart Sensors Inc . All Rights Reserved. Site Map      Web Master