types of thermocouple with range and sensitivity

 Thermocouples are temperature sensors that work based on the principle of the Seebeck effect. They consist of two different metal wires joined at one end to form a junction. When this junction is exposed to a temperature gradient, it generates a voltage that is proportional to the temperature difference between the two ends. This voltage can then be measured and converted into temperature readings.

There are various types of thermocouples, each made from different combinations of metals or alloys. The type of thermocouple used depends on factors such as the temperature range to be measured, the required accuracy, and the environmental conditions. Here are some common types of thermocouples:

1. Type K (Chromel-Alumel): This is one of the most widely used thermocouple types. It operates in a wide temperature range (-200°C to 1350°C) and is suitable for general-purpose applications.
   
   
   
2. Type J (Iron-Constantan): Type J thermocouples are suitable for a range of -40°C to 750°C. They are often used in applications involving vacuum or inert atmospheres.
3. Type T (Copper-Constantan): These thermocouples can operate in the range of -200°C to 350°C. They are often used in cryogenic applications.
4. Type E (Chromel-Constantan): Type E thermocouples are commonly used in the range of -200°C to 900°C. They are known for their high accuracy and stability.
5. Type N (Nicrosil-Nisil): Type N thermocouples can operate in the range of -270°C to 1300°C. They offer good accuracy and stability, making them suitable for many industrial applications.
6. Type R (Platinum-Rhodium): Type R thermocouples are designed for high-temperature applications, operating in the range of 0°C to 1600°C. They are often used in the steel industry and other high-temperature processes.
7. Type S (Platinum-Rhodium): Similar to Type R, Type S thermocouples are also designed for high-temperature measurements, covering the range of 0°C to 1600°C. They are commonly used in the same applications as Type R.
8. Type B (Platinum-Rhodium): Type B thermocouples are suitable for ultra-high-temperature measurements, operating in the range of 0°C to 1820°C. They are often used in specialized industrial processes.

It's important to note that each type of thermocouple has its own unique characteristics, including sensitivity, accuracy, and temperature range. When selecting a thermocouple for a specific application, factors such as the desired temperature range, accuracy requirements, environmental conditions, and potential chemical interactions should be considered to ensure accurate and reliable temperature measurements.

The grounded thermocouple junction is an integral part of the thermocouple sheath tip.

Advantages:

• fast response time in relation to ungrounded and isolated junctions. 

• protects the wires from environmental chemicals and corrosives. 

• prolongs the operational life of the thermocouple. Longer lifespan than the exposed junction thermocouple. 

• it is recommended for high pressure applications. 

• it is the least expensive construction. 

Disadvantages: 

• thermal expansion of sheath material may differ from element to cause mechanical stress and work hardening of metals. 

• ground loops may cause interference with instruments. 

• faults in insulation are more difficult to detect.

The ungrounded thermocouple junction is electrically insulated and electrically isolated from the outer sheath material. In a dual ungrounded thermocouple, one common junction is electrically insulated from the outside sheath.

Advantages:

•the thermocouple junction is isolated from the ground. 

• defects in the MgO insulation can be detected by measuring resistance from loop to sheath. 

• long term drift under cycling conditions is minimized. 

Disadvantages: 

• response time is usually slower than grounded thermocouples. 

• more expensive than grounded thermocouples. The exposed thermocouple junction extends beyond the protective metallic sheath.