There are many different types of thermocouple available today. So how do you know which one to use?
The type of thermocouple you need depends on the application and the temperature range you need to measure. Here are a few of the most common thermocouple types.
Common Types of Thermocouple
Each type of thermocouple has its unique characteristics that differ in durability, chemical resistance, application compatibility and vibration resistance.
We have type R, S and B thermocouples which are noble metal thermocouples used in high-temperature applications. We also have type K thermocouple, J, T and E, the most common ones, base metals.
Thermocouples are usually protected in a special wrapper that isolates them from the normal atmosphere. The sheath ensures that when in use, the thermocouple will give the correct temperature readings. It also offers protection against corrosion.
Each type of thermocouple is classified by an alloy. When two metals join together at two junctions, they create an emf.
An ASTM e230 is an example of a thermocouple standard and you can get it from an ANSI web store.
1. Type R Thermocouple
This type of thermocouple is used to measure high temperatures in different applications. It is costly because it has a higher percentage of Rhodium. When you compare it to type S, their performance is similar, but what distinguishes them is the amount of Rhodium they both contain.
You can use this appliance in lower temperature applications since it is stable and very accurate. Its output is slightly higher and it is also more stable if you compare it to type S.
Temperature Range of Type R Thermocouple
The thermocouple grade wire has a temperature range from -58 to 2700F. The extension wire ranges from 35 to 392F.
2. Type S Thermocouple
This thermocouple type contains high thermoelectric voltages; therefore, it is used in high-temperature appliances. This characteristic gives it the advantage of being used in medical fields, for example, in pharmaceutical industries. It will create a voltage when the temperatures on either side are different.
3. Type B Thermocouple
What distinguishes type B from all the other thermocouple types is that it has the highest temperature limit. It works well in extremely high-temperature applications. Even at extremely high temperatures, it still maintains accuracy and stability.
4. Type J Thermocouple
Of all types of thermocouple, type J has a short lifespan; it is common and has a smaller temperature range. You can compare it to type K in terms of expense and reliability.
5. Type K Thermocouple
This type of application is commonly used since it’s affordable, reliable, and offers accurate temperature readings. Type K is mostly used in nuclear applications due to its radiation hardness. The see beck coefficients of this thermocouple range between 0- 1000 degrees Celsius.
6. Type T Thermocouple
It used mainly in deficient temperature application due to its stability. It is used in low freezers or laboratories.
7. Type E Thermocouple
When you compare type J and type K to type E, type E is accurate, stable and has a higher signal than the two.
8. Type N Thermocouple
It is similar to type K as they share the same accuracy and temperature limits. However, type N is more expensive and offers better readability.
All these factors give it more accuracy.
Why Use a Thermocouple
You may be wondering whether you should use a thermocouple to measure temperature or not. There are certain advantages that you will experience when using a thermocouple. Here are some of them.
Everyone loves using an appliance that has good speed. It saves on time and energy that you would spend on a rather slower one. What usually determines the speed of a thermocouple is its size and mass.
If the application is big, the temperature readings will be slower. Thermocouples have thermistors, which are larger in most cases, but due to improvements in technology, they can now be made small to fit.
There are thermocouple wires attached to a bead of carbon and coated with glass. Both the cold junction points and the hot junction points play a vital role in the operation of a thermocouple.
If you want your thermocouple to be fast and efficient, choose one small size or get one with a small thermistor.
What determines the accuracy of a thermocouple is the materials used in manufacturing it. If a manufacturer uses wires of a poor grade, manufacturers can improve the accuracy by permanently attaching the thermocouple probe assembly to the electronic circuit.
In most cases, thermocouples are considered to be quite affordable if you compare them to most scientific probes. Of course, the price is relative depending on the type of appliance.
However, thermocouples are more costly than thermistors. This is because the probe materials used to make the thermocouples are durable and of a higher grade.
If a manufacturer substitutes the materials and uses low-grade ones, the efficiency and accuracy of the thermocouple become compromised.
The different types of thermocouple will tell you the most appropriate one to use.