Both RTD and Thermocouple are sensor devices that are used to measure temperature. You can find these devices in use in a broad range of applications and are often customized to work in very particular settings. Due to the fact that they function, in a broad sense, the same way, there is often a lot of confusion when it comes to distinguishing between the two. The choice between which of the two devices one is going to use depends largely on what they intend to do with them. Each of the devices comes with different characteristics, advantages, and disadvantages. Let us look at these two temperature-measuring sensors and tell you about RTDs vs. thermocouple devices and how you can apply each one of them.
Resistance Thermometer Detectors
RTD sensors or Resistance Thermometer Detectors use the electrical resistance of metals in order to measure heat. When a metal is heated up, the electrical resistance of that metal increases. The opposite happens when the metal cools. As it grows colder, the electrical resistance of the metal decreases. RTD sensors use this principle to calculate the temperature of any metal. They measure the electrical resistance of metal and by doing this, are able to determine the temperature. However, this means that, for RTD to work, there must be a baseline electrical resistance of the said metal, against which increases or reduction in electrical resistance is measured. For this reason, common metals are largely used in the construction of these devices. Such metals include nickel, copper, and platinum.
Thermocouples
Thermocouples on the other hand are temperature-measuring devices that use a charge between two metals to produce a voltage. This voltage can then be used to determine the local temperature. For this reason, engineers have since learned that by varying the type of metals used in a thermocouple, they can vary the range of temperature that these devices can measure and even sensor characteristics.
Which Is Better?
It is a difficult question to answer as the suitability of each device depends on the use that it is being put under. In general terms, thermocouples work better than RTDs in situations that require ruggedness as they are a lot tougher than RTDs. They also are able to produce results a lot faster than thermocouples which means that for applications where temperature measurements are required quickly, you are probably better off using thermocouples. Another reason why thermocouples are popular and this could be what tips the balance in their favor is the fact that they have a significantly wider range of temperature measurement than RTDs.
One advantage that RTDs have over thermocouples is the fact that they are easier to install. Even though the cost savings between the two devices is not that significant, it can make a difference depending on the scale in which these devices are being deployed. Another advantage of RTDs is that they tend to have a far more accurate reading than thermocouples. This means that if accuracy is a critical factor and speed/ruggedness is not, then you are better off working with an RTD device.