Resistance Temperature Device - RTD

Resistance Temperature Devices (RTD’s) are more accurate than traditional thermocouples.  An RTD also registers temperatures in less time than it takes for a thermocouple.  RTD’s can be used at lower temperatures but are not available for temperatures higher than 600° C/1112° F.  RTD elements are made from pure material like platinum, nickel or copper, it is this material that has a predictable change in resistance when temperature changes, this predictable change is how temperature is determined.  Whenever possible an RTD should be used instead of thermocouples due to its higher accuracy and repeatability.  At Will Webb Associates, Inc. we can assist you in determining whether an RTD is the right choice for your temperature measurement needs.

-    Resistance Temperature Device – RTD
    These are devices whose material resistance changes along with the temperature change, which is why they are resistant to temperature devices.
-    Type B
    A platinum/rhodium base thermocouple, is extremely stable, but has a very low sensitivity level.  The Type B thermocouple is similar to the S&R types, but has a lower output, and is less susceptible to grain growth and drift.
-    Type C
    This is a platinum/rhodium base thermocouple with tungsten and rhenium that is good for vacuum furnaces, although must never be used in environments with oxygen at temperatures above 260 degrees Celsius.  The Type C thermocouple has no oxidation resistance and in thus limited to functioning in inert atmospheres.
-    Type E
    Has a high output making it ideal for cryogenic uses, and is not magnetic.  This thermocouple is recommended for continuously oxidizing or inert atmospheres.  Out of the thermocouples with common calibration, Type E has the highest thermoelectric output.
-    Type J
    Serves a similar purpose as the Type K thermocouple with a smaller range, but greater sensitivity in that range.  These thermocouples have a shorter lifespan in oxidizing atmospheres, and should not be used in sulfurous atmospheres above 1000 degrees F.
-    Type K
    Is a nickel and chromium wire, and is the most commonly used thermocouple for general purposes.  This is one of the most functional thermocouples, although it is subject to malfunction when exposed to sulfur.
-    Type N
    These thermocouples are ideal for high heat environment and having a high resistance to oxidation.  These thermocouples also have a higher resistance to temperature and life through application in sulfurous environments.
-    Type R
    These are thermocouples with 13%Rhodium and 87% pure platinum.  Is almost exactly the same as Type S thermocouples in use.
-    Type S
    Type S thermocouples are used made with both a Positive and Negative wire charge and are the standard for measuring the melting point of gold.  These are the thermocouples used in the highest density of heat environments, although non-metallic protection tube and ceramic insulators are needed to protect them.  While they are useful in high heat environments, you must watch for grain accumulation as that will cause the thermocouple to malfunction.
-    Type T
    Type T thermocouples cover the low ranges the scale and are used in differential measurements, as they have no magnetic link, and is one of the few thermocouples that is not subject to corrosion in moist atmospheres.