What Is A Thermocouple?

You may be wondering, exactly what is a thermocouple? Well in short, a thermocouple is a device that allows you to measure temperature at a precise point in a process. 

It’s used in temperature-sensing applications for various industries, including food processing and medical diagnostics, to name a few. 

Thermocouples are available in analog and digital forms, but the key to using one is to choose one that’s best for your application. Here’s how you can use thermocouples to measure temperature at your facility.

 

What Does A Thermocouple Look Like?

A thermocouple looks like a tube of metal that is smaller than a regular straw. It has a wire coming out one end with a connector for different applications. It can vary in appearance depending on the type and its purpose. It’s generally about the size of your palm – could be a little smaller or bigger. 

 

What Is A Thermocouple Used For?

They are widely known for being very versatile temperature sensors. They are used across various applications and scales. Thermocouples are often used for home appliances and industrial processes such as food prep, furnace monitoring, power generation, beverage processes, etc. you could also use them for aircraft engines, automotive sensors, satellites, rockets or spacecraft.

If you are looking to use a thermocouple for any specific purpose, you need to understand a list of things first. Thermocouples come in a big range of specifications and models, so you need to know how they work, their temperature ranges and their basic structure.

Once you get the hang of the basics, you can better determine the correct thermocouple type and which materials are right for your applications. 

 

How Does A Thermocouple Work?

It comprises two wires of different types of metals that are joined at the ends. When one end is heated or cooled, it sends a continuous current flow through the thermoelectric circuit. If the circuit is broken in the center, the open-circuit voltage results from the metal compositions and junction temperature. 

The wires are connected to a thermocouple thermometer or any other compatible devices at one end. When a thermocouple is properly configured, it can give you a very wide range of temperature readings.

 

What Is A Thermocouple Junction?

The measuring point of the thermocouple sensor is called the junction. The negative and positive thermocouple wire legs are welded together. You can find three types of junctions for thermocouples. There are exposed, ungrounded or grounded junctions. 

 

What Is A Thermocouple Probe?

The thermocouple part gets exposed to various temperatures so the wire can receive a current and provide a reading. The long, solid and thin section of the top of a thermocouple protects the wires without affecting the temperature measurements. 

 

What Is A Thermocouple Wire?

A thermocouple wire is the two dissimilar metallic wires used to generate current and receive or respond to readings. When temperature changes occur, current flowing through the wires will generate a certain voltage or EMF. The voltage generated is then used to determine the temperature the sensor detected. 

 

How To Choose A Thermocouple Type For Your Application

Thermocouples can suit nearly any type of purpose and application. You can choose to make them robust and quick to respond and measure any temperature range. 

To choose the right thermocouple type for your application, you need to keep a handful of things in mind. Starting with determining how you aim to use the thermocouple and for what. Secondly, you need to know the exact temperature ranges to which you will expose the thermocouple probe. Once you determine the range, you can use a thermocouple range chart that will help you decide which type you need.

You can find a thermocouple in different metal combinations and calibrations. The most common types are N, T, E, J, and K thermocouples, also known as Base Metal thermocouples. If you are looking for higher calibration, you can use a Noble Metal Thermocouple (R, S, C, and GB types).

Thirdly, you must determine the importance of the thermocouple response time for your application. Depending on the junction type, you can decide how fast the response time of your thermocouple will be. For example, an exposed junction can give you the quickest response time compared to other types. However, you cannot use it if your probe is exposed to high pressures and corrosive gasses. In this case, you need to ensure that the thermocouple is shielded by a sheath and isolated electronically. 

You also need to consider chemicals, vibration resistance and abrasion around your thermocouple. So, an ungrounded or exposed thermocouple will be limited to applications that do not risk corrosion. However, you can use grounded and ungrounded thermocouples in high pressure or corrosive applications if they are appropriately shielded. 

Lastly, you have to consider the installation requirements of the thermocouple you want to choose. It needs to be compatible with your equipment and appliances. 

 

What Is The Difference Between A Thermocouple And RTD?

As discussed, a thermocouple is a sensor utilizing thermoelectricity and voltage changes to read temperature changes. However, an RTD utilizes changes in metal resistance to predict temperature changes. An RTD usually operates between the -200˚C and 600˚C range, whereas you can calibrate a thermocouple to suit various temperature ranges. 

It is hard to declare which one’s superior, but you can compare them in terms of costs and specifications based on intended purposes and applications. Thermocouples cost a good deal lesser than RTDs, whereas RTDs are cheap to install. Regardless, thermocouples are designed to react faster and be more durable. The best part about thermocouples is their temperature ranges.

On the contrary, RTDs can repetitively provide you with very accurate readings and measurements. Hence, if you are looking for a very stable thermal sensor, an RTD would be perfect if you are not worried about the response time. However, the thermocouple is still a winner in terms of response timings. 

 

What is a Thermocouple Summed Up

There are various thermal sensors, but we hope you got all the information you needed on thermocouples. You now know what it is, what it does and how to choose the right one for your application. Now you are one step closer to getting started with your home or industrial-scale projects!