Temperature measurement is an integral part of many industrial applications, whether it’s used for essential aircraft components or automotive engines. Simply put, various types of sensors and probes can help you identify the rise or fall in temperature. However, the two most common devices in today’s market include Resistance Temperature Detectors (RTDs) and thermocouples. Each sensor has its own set of advantages that make it suitable for specific environments. This article offers a comparative analysis between RTDs and thermocouples, along with how to pick the best one based on your needs.
RTDs
An RTD is a sensor that changes its resistance as heat increases and decreases. They are used to measure temperature in industrial settings and have established a known reputation for accuracy, repeatability, and stability. Most RTD elements contain thin metal wiring wrapped around a ceramic or glass base. In order to achieve accurate readings, the metals used in RTDs must have a stable electrical resistance and be recorded for accessible reference. For example, modern aircraft systems use platinum because of its corrosion resistance, lasting strength, and vast temperature measurement capabilities. Although nickel and copper have also been used in the construction of RTDs, these materials have lower temperature capabilities and are not as stable or repeatable as platinum.
Thermocouples
Instead of using a single metal element like RTDs, thermocouples are made with two different materials. This temperature sensor consists of varied metal wiring on one end, followed by a thermocouple thermometer or another corresponding thermocouple device at the other end. There are dozens of metal combinations that can be used when making thermocouples to provide a diverse range of calibrations. But the most popular design, especially in modern aerospace applications, is Type K Thermocouples that have Nickel-Chromium and Nickel-Alumel alloys.
Comparing RTDs and Thermocouples
Since RTDs and thermocouples were designed under a broad scope of industry demands, it is nearly impractical to determine whether one is the superior choice over the other for all applications. You can, however, compare the performance of these temperature measurement devices by using additional factors, such as their price and measuring scope to facilitate an appropriate decision based on your specific needs. Check out the table below to learn more about the key advantages and disadvantages of each sensor type.
| Sensor Category | RTD | Thermocouple |
|---|---|---|
| Temperature Range | –200°C to +600°C | −200°C to +1370°C |
| Cost | Cost is relatively high, however, installation and maintenance are cheaper than most thermocouples. | Cost up to two times less than RTDs. |
| Accuracy | RTDs are typically more accurate than thermocouples because of their readings and repeatability. This means that users reading the same temperatures produce the same consistent results. RTDs can also be purchased by their required accuracy, with the highest being AA and lowest at C. That said, the more accurate an RTD is, the more it costs to procure and integrate into a system. | Accuracy can range between 0.5 and 5°C. Despite this, some thermocouples can match RTD accuracy depending on the material and sensor features. |
| Stability | RTD readings are more stable and their design ensures that it continues to produce stable readings longer than thermocouples. | Thermocouple readings are known to drift because of chemical shifts in the sensor, such as oxidation or corrosion. |
| Sensitivity | While RTDs respond quickly to temperature changes, it can still be much slower than the average thermocouple. | In terms of build, thermocouples are more sensitive to RTDs and have a faster response time. |
| Linearity | RTDs present fair linearity. | Non-linear, containing an ‘S’ type plot. |
Overall, the main difference between thermocouples and RTDs is their selection of metal and material. Thermocouples are more affordable than RTDs due to their low-end manufacturing process. Depending on the number of sensors that you need for your application or business, the cost can be an important factor to consider. RTDs, on the other hand, provide more reliable outputs. At CCS, we offer RTD Temperature Sensors for air and fluid temperature measurement. Our innovative designs are based on platinum sensing elements, resistance outputs, and quality IEC60751 standards. For more information about CCS RTD sensors and how they operate in your routine operations, take a look at our product page or contact us directly.