Resistance Temperature Detectors or RTDs are contact sensors that operate under the principal that the resistance of a metal changes directly with temperature. RTDs use pure elements like platinum for which the resistance has been well documented by a multitude of international standards institutes. The metal has a predictable change in resistance as the temperature varies; it is this change that is used to determine temperature. Here is more information on RTDs.
Thermocouples are also contact temperature measuring devices, consisting of two different metals joined together at one end. When the junction of the two metals is cooled or heated a voltage is produced that can be correlated back to a temperature. There are a number of different types of thermocouples, more information on the various types can be found here.
There are a number of applications where contact temperature devices are not appropriate and a non-contact device is required. Infrared pyrometers provide non-contact temperature measurements. This is achieved by measuring infrared energy; the higher the temperature the more infrared energy emitted. The amount of emitted infrared energy is directly proportional to the temperature of the object; this is what allows pyrometers to be used as a non-contact temperature measurement devices. Since all objects emit infrared energy, this gives pyrometers an advantage whereas other temperature measuring devices like RTDs and thermocouples must make direct contact with the intended energy source. Similar to thermocouples, pyrometers come in many different forms and sizes. More information on the six Williamson pyrometer technologies and how they overcome the limitations of traditional infrared sensors can be found here.
Below is a comparison of the characteristics of thermocouples, RTDs, and infrared pyrometers in relation to how they may behave in industrial conditions. The next table provides an overview of the advantages and disadvantages of each technology in an industrial setting.
If you are wondering if an infrared pyrometer would be suitable for your application, please click below for a free consultation with one of our temperature measurement experts.