Thermocouples are widely used in industry to measure temperatures. They are manufactured from different metals and to different calibrations depending on the type of application they are to be used in.
What Is a Thermocouple?
A thermocouple is an instrument made from two different types of metal connected at one end. When the thermocouple is heated or cooled, the end where the metals join makes a voltage. The voltage can then be referenced to the temperature of the application it is measuring.
This is then collated and used in various calculations to determine the efficiency of the application being measured. The data can be inputted and stored in a number of different ways, with direct connections to PC systems and networks for ease of use.
What Are the Different Types of Thermocouples?
Thermocouples use different mixtures of metals depending on their intended use. Type K is the most widely used thermocouple, largely due to its low cost and large temperature range. This is manufactured from nickel-chromium and nickel-aluminium conductors.
Some types of thermocouples can be used in temperatures up to 2320 degrees C. In order to remain efficient at such high temperatures, they are made from precious metals, including platinum-rhodium and tungsten-rhenium, which makes them considerably more expensive.
Thermocouples of the same metal combinations can still be calibrated to suit different temperatures and applications. The diameter of the wire will also affect the maximum temperature that can be reached; an extremely thin thermocouple won’t be able to reach the highest temperature for its combination.
Thermocouples, such as those available here http://uk.rs online.com/web/c/automation control gear/sensors transducers/thermocouples/, use different junctions which will be affected by their intended use. These are grounded, insulated and exposed.
With a grounded junction, the wires are connected to the interior wall of the probe. This ensures an excellent level of heat transfer. In an insulated thermocouple the wires are not attached to the wall. This causes it to react more slowly to temperature changes, but provides electrical isolation. An exposed junction reacts quickest to changes in temperature, but it also has its limitations. As the junction comes out of the top it’s exposed and so can only be used in dry, non-corrosive and non-pressurised environments.
What to Consider When Specifying Thermocouples
Thermocouples are used in a number of different industries and therefore are manufactured and calibrated to suit individual applications. It is crucial to decide exactly how the thermocouple will be utilised in order to make the correct choice.
– What temperature range will the thermocouple be measuring?
– Is it necessary to have any chemical-resistance properties?
– Will the thermocouple need to be resistant to abrasion or vibration?
– Are there any installation issues and does the thermocouple need to be compatible with any existing equipment?
All elements of the thermocouple need to be taken into consideration. Areas such as the diameter of the wire and the combination of metals will have an effect on the temperatures that it can be used to measure.
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