What are the applications of thermocouples?
Application of thermocouples: Thermocouples are the widest device for measuring temperature (type S thermocouples).
Application of various types of thermocouples
Thermocouples are either available as bare wire thermocouples that have a short and fast response time or are built into probes. A wide variety of probes are available, suitable for various measurement applications (industrial, scientific, food temperature, medical research, etc.). A word of warning: When choosing a probe, make sure it has the correct type of connector. The two types of connectors are “standard” with round pins and “miniature” with flat pins. This causes some confusion because “miniature” fittings are more popular than “standard” fittings.
When choosing a thermocouple, the type of thermocouple, insulation and construction of the probe should be considered. All of this will affect the temperature measurement range, accuracy and reliability of the readings. The following is a (somewhat subjective) guide to different types of thermocouples.
Thermocouple type K
Type K thermocouple is the “general purpose”. It is cheap and because of its popularity, it is available in a variety of probes. Thermocouples are available in the range of -200 ° C to 1200 ° C. The sensitivity is about 41 μV / ° C. Use type K unless you have a good reason.
Thermocouple type E.
Type E has a high output (68 microvolts per degree Celsius) which makes it well suited for low temperature (cryogenic). It is also non-magnetic.
Thermocouple Type J
The limited range (-40 to +750 ° C) makes type J less popular than type K. The main application is with old equipment that can not accept modern thermocouples. J types should not be used above 760 ° C because a sudden magnetic change will cause permanent deformation.
Thermocouple type N
High stability and high temperature oxidation resistance make type N suitable for measuring high temperatures without the cost of platinum types (B, R, S). With the “K” design of the “improved” type, it becomes more popular.
Types of thermocouples B, R and S All metal thermocouples are “noble” and show similar characteristics. They are the most stable of all thermocouples, but due to their low sensitivity (approximately 10 microvolts per degree Celsius) they are usually only used to measure high temperatures (> 300 ° C).
Thermocouple type B
Suitable for measuring high temperatures up to 1800 ° C. Unusually, type B thermocouples (due to the shape of their temperature / voltage curve) give the same output at 0 ° C and 42 ° C. This makes them useless below 50 ° C.
Thermocouple type R
Suitable for measuring high temperatures up to 1600 ° C. Low sensitivity (10 microvolts per degree Celsius) and high cost make them suitable for general use.
Thermocouple type S
Application of Type S thermocouple suitable for measuring high temperatures up to 1600 ° C. Low sensitivity (10 microvolts per temperature) and high cost make them unsuitable for general use. Due to its high stability, the S type is used as the calibration standard for the melting point of gold (4/10644 ° C).
Advantages of thermocouples
- Low costs
- small size
- Wide range of operations
- Reasonable table
- quick answer
Disadvantages of thermocouples
- Poor output, mV
- Limited accuracy for small changes in temperature.
- Sensitive to electrical noise
- Complex conversion from emf to temp.
- Small temperature changes mean very small voltage changes
- Prone to noise
- Calibration changes over time
- They can not be used in bare conductive liquids
Summary of thermocouple performance
- Thermocouples are the most cost-effective elements for measuring temperature and also provide the highest amplitudes.
- The emf produced is independent of the length and diameter of the wire, however noise can be a factor.
- Thermocouples are not recommended for narrow openings or for measuring small temperature differences.
- To measure the critical temperature, the exact reference connection temperature must be measured and compensated.
- T / C is low cost but should only be used if the other element is no longer viable.
Detection of thermocouple errors
- Short format wires may not be detected
- Measure resistance continuously to record changes
Thermocouple voltage curves
Rose Calibration Company in Melbourne, Australia with over ten years of experience provides all calibration, maintenance, and repair services throughout Australia. If you live in Sydney, Melbourne, Adelaide, Perth, Geelong, and Brisbane, you can receive your quote in less than two hours by fill-up the form via the “Booking” link.