Difference Between Thermocouple and RTD

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DIFFERENCE BETWEEN THERMOCOUPLE AND RTD



The most notable difference between a thermocouple and an RTD (Resistance Temperature Detector) is the principle of operation.
  •  A thermocouple operates on the principle that two dissimilar metals joined together will produce a voltage related to a temperature difference. An RTD operates on the principle that electrical resistance of certain metals changes in a predictable way depending on the rise or fall in temperature.
  • Advantages of the thermocouple include a wide temperature measuring range (depending on the thermocouple type the range can be as much as from -300°F to 2300°F), fast response time (under a second in some cases), low initial cost, and durability. Overall, thermocouples are able to withstand rugged applications.  
  • Advantages for RTDs include stable output over a long period of time, ease of recalibration, and accurate readings over narrow temperature spans. Disadvantages, when compared to the thermocouples, are: smaller overall temperature range (-330°F to 930°F), higher initial cost and they are more fragile in rugged, industrial environments.
  • Thermocouples are inexpensive, rugged, and have a fast response time but are less accurate and the least stable and sensitive.  Thermocouples also read only relative temperature difference between the tip and the leads while RTD's and Thermistors read absolute temperature. RTD's are the best choice for repeatability, and are the most stable and accurate.  However they have a slow response time and because they require a current source they do have a low amount of self heating.  Thermistors have a fast output and are relatively inexpensive but are fragile and have a limited range.  They also require a current source and do experience more self heating than an RTD and are nonlinear.
Criteria
Thermocouple
RTD
Thermistor
Temp Range
-267°C to 2316°C
-240°C to 649°C
-100°C to 500°C
Accuracy
Good
Best
Good
Linearity
Better
Best
Good
Sensitivity
Good
Better
Best
Cost
Best
Good
Better  

Comments

  1. Unknown21 September 2014 at 16:30

    Thank you for sharing this interesting article on thermocouples and RTDs. I am sure that this info that you provided will help many people, as it did me. Furthermore, it will help people decide on which one, a thermocouple or RTD, fit their needs the best. Now, as far as actually buying a thermocouple or RTD goes, a great place to purchase thermocouples, RTDs, and even thermometers from is Thermo/Probes, Incorporated. Their company has over 40 years of engineering experience, and is dedicated to providing customer satisfaction.

    For more information on Thermo/Probes, Inc.,
    Please visit:
    www.thermo-probes.com

    ReplyDelete

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