Part 2- Thermocouple Thermistor or RTD?

 
CLEVELAND - Aug. 25, 2022 - PRLog -- As you remember from Part One, temperature is the most common parameter measured by those who use data loggers. I also outlined the basic principles of temperature sensors—detailing the specifics of how thermocouples, thermistors, and RTDs function. In Part Two, I will talk about tips for selecting which temperature sensor is best for your needs, as well as some examples of how these temperature sensors are used in real-world applications.

Selection Criteria

Picking which type of sensor to use for a particular application requires consideration of 3 important factors related to the measurement, along with the cost:
  • Temperature Measurement Range
  • Required Measurement Accuracy
  • Sensor Wire Length, Noise, and Accuracy

One of the most important things is the expected temperature measurement range. Of the three types of sensors, thermocouples have the widest measurement range, from well below -200°C to over 1700°C depending on the thermocouple type. RTDs are more limited spanning -200C to around 500°C although specialized models can go somewhat higher. Thermistors have the most limited measurement range of the 3 types because of both their composition and their non-linear characteristics.

Of course, any consideration of which type of sensor to use has to include the cost. Of the 3 types, thermocouples are probably the least expensive. Standard thermocouple wire can be purchased for less than $1.00/foot.

Typical Examples

Here are a few common applications along with the sensor type that was used:

We have provided data loggers and sensors for several applications for skin temperature measurement. This is an ideal application for a thermistor sensor; the temperature measurement range is small typically only ± a few degrees and right in the sweet spot for thermistors measurements around 30°C and accuracy is very important, a few tenths of a degree can make a big difference. Fortunately, there are a few vendors that provide medically rated thermistor stick-on surface probes just for this application.

The last example is one of our biggest applications, monitoring the temperature in a medical refrigerator or freezer, for example, a refrigerator in a clinic used to hold vaccines. As dictated in the guidelines from the CDC for vaccine storage and the Vaccines For Children (VFC) program they recommend a digital data logger (DDL) with an uncertainty of ± 0.5°C (±1.0°F). This is a perfect application for a class A RTD probe which has an accuracy at least 2x better than the recommendation.

Summary

Well, there you are. Selecting between a thermocouple, thermistor, or an RTD comes down to what temperature you will be measuring, the accuracy that you need, where you will be using the sensor, and how important the cost is vs. the performance.

Call us today (800) 956-4437 or visit us at https://www.dataloggerinc.com.

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CAS DataLoggers
Elizabethe Zala
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