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Do I need an RTD Sensor or a Thermocouple?

Whether you choose a thermocouple or an RTD Pt100 sensor depends on the application and measurement requirements (accuracy, speed of response, temperature range etc.) of the user. It is not a case of one being better than the other as both thermocouples and RTD Sensors have their own merits and uses.

We can, however, compare the advantages and disadvantages of each sensor to try and determine which sensor would be most suited to a particular application:

Temperature Range: Thermocouples have a wider temperature range than RTD Sensors, with some able to measure temperatures up to 2900ºF and beyond. For most industrial applications RTD Sensors are limited to 1100ºF and more often to 480ºF.

Accuracy: If high accuracy is of most importance, then a Pt100, which is the most common RTD sensor in general use, is the better choice.. Even the least accurate Pt100 (Class B) will usually be more accurate than a thermoocouple. Pt100s are available with very high accuracies, 1/10 DIN elements for example, have an accuracy of ±0.03ºC at 0ºC.

Stability: Thermocouples tend to drift over time due to chemical changes such as oxidation, whereas measurements from RTD Pt100 sensors are stable and repeatable if the sensor is kept within the temperature range of the RTD sensor.

Response Times: Whilst ever smaller diameters have improved RTD response times considerably, thermocouples, especially with a grounded or exposed junction, are still very much faster in response to changes in temperature.

Durability: Because of the more fragile nature of Pt100 elements, thermocouples are considered more rugged and durable especially for high vibration applications where Pt100 sensors are not suitable. In summary, a thermocouple is a simple rugged sensor that can withstand significantly more mechanical abuse than a Pt100.

Cost: Thermocouples are generally less expensive to manufacture and have lower material costs, except for the cabling where thermocouple wires are slightly more expensive than the copper wires used for RTD sensors.

Advantages and Disadvantages of RTD Sensors and Thermocouples

Sensor Type Advantages Disadvantages
RTD Pt100

High Accuracy
High stablility
Highly repeatable

Low vibration resistance
Self heating
Slower response
Thermocouple Wide Temperature Range
Fast response
Very small size
Low cost

Less accurate
Less stable
Long term drift

Click here for information on RTD Sensors
RTD Element Types
Click here for RTD Pt100 Resistance vs Temperature Output Tables

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