If you’re evaluating temperature sensors, you’ve likely come across both thermocouples and resistance temperature detectors (RTDs) during your research. While both devices are practical tools for measuring temperature, there are a number of essential differences that separate them.
In this article, we will take a more in-depth look at thermocouples and how they compare to RTDs. We’ll describe how each one is used and explain the situations in which you might need to use one over the other. Keep reading to understand the key similarities and differences between the two sensors.
Thermocouples (sometimes abbreviated as TCs) are composed of two different metal pieces that are adjoined at one end and then separated at the other end. The thermocouple measures the difference in voltage between the dissimilar metals, and this is then compared to the cold junction voltage and offset using ACJC (Automatic Cold Junction Compensation).
When compared to other types of temperature sensors, thermocouples are more affordable. They’re also designed to be extremely rugged and durable. But their lower cost also means that their degree of accuracy isn’t as good as what you’ll get with RTDs and other temperature sensors.
In addition to their cost-effective price, thermocouples offer another advantage over RTDs: their more expansive range of measurement. Depending on how they’re constructed, thermocouples have the ability to measure temperatures between -200°C and 2500°C. However, they’re susceptible to inhomogeneity errors when taken over 400°C.
Resistance temperature detectors
In contrast, resistance temperature detectors include a fine wire (usually platinum, copper, or nickel). When the wire is heated or cooled, the resistance changes, increasing when hot and decreasing when cool. RTDs measure temperature by tracking these resistance changes and displaying them on a connected piece of control equipment.
So how do they compare to thermocouples? Resistance temperature detectors are known for their high degree of accuracy, typically in the range of 0.1°C. On the other hand, thermocouples are generally accurate to 1°C or worse.
In comparison to thermocouples, they’re also more repeatable, meaning that the devices consistently provide the same temperature readings over multiple uses. Plus, RTDs have minimal drift if they’re looked after properly, whereas thermocouples drift over time due to chemical changes inside. Finally, linearity on RTDs is very good, while thermocouples have more of an S-type trend.
On the downside, RTDs can’t measure the same range of temperatures that thermocouples can. They offer a more limited measurement range of -250°C to 1000°C, so they aren’t a feasible temperature sensor for certain applications. They’re also far more fragile than thermocouples, and they’ll change if they are knocked or bumped.
How to learn more about thermocouples and RTDs
To sum it all up, the most significant differences between thermocouples and RTDs comes down to these key factors: cost, accuracy, repeatability, and range. As such, you should consider each of these differences when you’re trying to determine which type of temperature sensor is right for your business needs. If you have questions or need more guidance, the team at National Weighing & Instruments is happy to help.
Established in 1994, National Weighing & Instruments is a family-owned Australian business that specializes in the sale, repair, and calibration of measuring equipment for laboratories and manufacturing businesses. We operate in major cities across the country, including Sydney, Adelaide, Brisbane, Melbourne, and Perth.
Get in touch with National Weighing & Instruments today to learn about our products and services. Give us a call on 1300 286 584 or visit our website for more information.