REVIEW OF RTD AND THERMOCOUPLE BASICS ( Temperature Sensor )
RTD'S contain a sensing element which is an electrical resistor that changes resistance with temperature. This change in resistance is well understood and is repeatable. The sensing element in an RTD usually contains either a coil of wire, or a grid of conductive film which has a conductor pattern cut into it. Extension wires are attached to the sensing element so it's electrical resistance can be measured from some distance away. The sensing element is then packaged so it can be placed into a position in the process where it will reach the same temperature that exists in the process.
Thermocouples, on the other hand, contain two electrical conductors made of different materials which are connected at one end. The end of the conductors which will be exposed to the process temperature is called the measurement junction. The point at which the thermocouple conductors end (usually where the conductors connect to the measurement device) is called the reference junction When the measurement and reference junctions of a thermocouple are at different temperatures, a millivolt potential is formed within the conductors.
Knowing the type of thermocouple used, the magnitude of the millivolt potential within the thermocouple, and the temperature of the reference junction allows the user to determine the temperature at the measurement junction.
The millivolt potential that is created in the thermocouple conductors differs depending on the materials used. Some materials make better thermocouples than other because the millivolt potentials created by these materials are more repeatable and well established. These thermocouples have been given specific type designations such as Type E, J, K, N, T, B, R and S.
Very informative article on Thermocouples and RTDs. Thank you Rajdeep for sharing it! I prefer using thermocouples than RTDs, because thermocouples have a fast response time than RTDs do. Also, thermocouples do not self heat, and RTDs do. Now, that isn't to say RTDs are less useful than thermocouples. They have their own benefits over thermocouples. For instance, RTDs have a better interchangeability, long-term stability, and a higher accuracy than thermocouples. What it ultimately comes down to for me is cost. I use thermocouples, because they are less expensive than RTDs. However, that doesn't necessarily mean that thermocouples are better than RTDs. This is merely one person's preference. Transitionally, I really enjoyed reading your article, and I look forward to reading more articles from you.
ReplyDeleteThanks again! :-)
Germaine K. | Thermo/Probes Inc.