Temperature probe including thermocouples, require an accurate internal temperature to function properly. Unfortunately, this can be difficult to obtain in areas not protected by a controlled environment. According to Process Parameters, one solution is to take advantage of the fact that many electronic components have a temperature coefficient of resistance.
For those components, a thermistor can be used to measure the temperature of the circuit in question.
Temperature probe including thermocouples and thermowells can be used to measure temperatures in these environments.
We’ll look at the different types of thermocouples and thermowells, and how they can be applied in the laboratory.
What is a Thermocouple?
It refers to a temperature measuring sensor designed with two varied metal wires that link at a thermal junction. When gauging temperature, this thermal junction can be applied at any point.
The sensor works by heating or cooling at the junction, creating a voltage in the circuit, which reads as the temperature. It covers a broad temperature spectrum, with some types measuring up to 2000°C.
Thermocouples are available in many forms, allowing them to serve a wide range of applications. A thermocouple can also be designed to match specific requirements. Some application fields for these temperature probes are power generation, biotech, pharmaceutical, oil & gas and cement.
A thermocouple differs from a resistant temperature detector in that it has a higher measuring range. At low temperatures, an RTD is more accurate than a thermocouple.
Types of Thermocouples
The two dissimilar metals make the thermocouple itself, but a thermocouple probe refers to the construction that houses the sensor. These configurations can be different, which is why not all products are alike.
However, the type of thermocouple depends on the metals used. Some metal combinations were standardised over time, creating a range of common thermocouples. A few of them are more popular than others, and this section looks at them.
Type K is the most used because it is highly accurate, cost-efficient and reliable. It compromises Nickel-Chromium and Nickel-Alumel. This thermocouple has an expansive temperate spectrum – between 95 and 1260°C – allowing it to serve an array of applications.
Another widely popular thermocouple is the type J, with iron and constantan (copper-nickel) as its two dissimilar metals. It measures temperatures between 0 and 760°C, meaning it doesn’t last long in high temperatures. A J type thermocouple is suitable in inert and vacuum environments. It’s commonly used in the plastics industry during injection molding.
T types thermocouples are the best options for food production and cryogenics applications due to their low-temperature spectrums. The sensor contains copper and constantan, and measures temperatures between -200 to 370°C. T types have a high tolerance for decomposition, even in moist settings.
A type B thermocouple is made up of Platinum-Rhodium (6%) and Platinum-Rhodium (30%), with a temperature spectrum of 1370 – 1700°C. The sensor is appropriate for applications requiring extremely high temperatures, like glass production.
Other thermocouple configurations are type E (0 – 870°C), type N (650 – 1260°C), type R (870 – 1450°C) and type S (980 – 1450°C).
What is a Thermowell?
It’s a cylindrical tube with closed ends used to encase a temperature sensor. Thermowells protect temperature probes, such as thermocouples, thermistors and bimetal thermometers by attaching tightly to vessels.
Temperature sensors are necessary components in an extensive category of applications. Therefore, they have to put up with significant punishment, including corrosive environments, high pressure and material velocity.
Constant exposure to some of these elements causes wear and tear, compromising the sensors’ integrity. Thermowells safeguard probes by acting as barriers between the component and the measurement setting. So, they are suitable in any process involving abrasion, corrosion or pressure.
Types of Thermowells
One thermowell differs from another depending on the stem construction and process connection. The common alternatives are;
Threaded – The thermowell has to be threaded into the connection
Weld-in – The connection requires the thermowell to be welded into the piping and is suitable in applications where thread contamination is a threat.
When choosing a thermowell, the material is critical because it determines performance and durability. A wide variety of materials are used to make the components. Stainless steel is one of the most popular metals. Titanium, carbon steels, chromium/molybdenum steels and socket weld are other examples.
When buying a temperature probe including thermocouples, it’s important to remember that they can be used to measure temperatures in specific environments. Make sure you get the right part for a specific job. Learn about the various kinds and how reliable they are for different applications.
