Thermocouples are the planet’s most widely used temperature sensors due to their comprehensive temperature capabilities, ruggedness, and affordability. They are used in various applications, from home appliances to industrial processes, electric power generation, furnace monitoring and control, food and beverage processing, automotive sensors, aircraft engines, rockets, satellites, and spacecraft.
When precision, speed, or extreme conditions are needed, thermocouples are the go-to for accurate temperature measurements. With their ability to withstand high temperatures, small size, fast response, high vibration, and shock, thermocouples provide reliable solutions for countless temperature-sensing applications.
What are Thermocouples?
Thermocouples are sensors that measure temperature by utilizing two different types of metals together at one end. When the junction of the two metals is heated or cooled, a voltage is created, which can be correlated back to the temperature. Thermocouples are simple, robust, and cost-effective temperature sensors used in various temperature measurement processes.
Thermocouples are available in different styles, such as thermocouple probes, thermocouple probes with connectors, transition joint thermocouple probes, infrared thermocouples, bare wire thermocouples, or even just thermocouple wire. These are used in a wide range of applications, and it’s essential to understand the basic structure, functionality, and ranges of different thermocouple types to determine the best type and material for a particular application.
Advantages of a Thermocouple
- Thermocouples can withstand extremely high temperatures, making them ideal for demanding environments.
- With high reproducibility and accuracy at a wide operating range, you can rely on consistent readings.
- The fast response time of thermocouples means that you get results quickly.
- Thermocouples are extraordinarily durable and self-powered, so they don’t require a separate current or voltage source.
- They can also withstand high vibrations, making them a reliable and robust choice.
Limitations of a Thermocouple
Thermocouples are popular for temperature sensing due to their low cost and broad temperature range. However, they are with their limitations.
- Thermocouples are less accurate than RTDs in a specific temperature range, meaning they may be less precise in particular applications.
- They can suffer from drift over time, affecting the readings’ accuracy.
- Poor insulation can also make them vulnerable to corrosion, further impacting their accuracy.
- Thermocouple signals are not perfectly linear, meaning there may be some deviation between the expected and actual readings.
For these reasons, it is crucial to consider the limitations of thermocouples when choosing a temperature-sensing device.
Most Common Application of Thermocouple
1. Thermocouples for Food Applications
Thermocouples are essential tools for food and beverage production. They offer a range of applications that help you maintain the highest food safety and quality standards. From Clean-In-Place sensors that help minimize contamination to Penetration Probes for temperature monitoring to Oven Control and Hotplate Control for precise cooking, Thermocouples provide a reliable and accurate way to monitor, control, and adjust temperatures in food production. Additionally, they can be used to monitor food chain temperatures and steam kettle temperature control. With the help of thermocouples, you can ensure that all food products are processed and stored at the correct temperature for the safety and quality of your customers.
2. Thermocouples for Extruders
Thermocouples are an excellent choice for monitoring the temperature of extruders. Their unique threaded adapter allows you to position the sensor tip directly in the molten plastic under high-pressure conditions, ensuring accurate readings. They can handle temperatures as high as 400°C and pressures up to 10 bar, making them ideal for extrusion applications. Thermocouples’ reliable performance can help you monitor the temperatures in your extruder and ensure your process is working at its best.
3. Thermocouples for Low Temperature
Type E, K, T, and N thermocouples can measure temperatures down to -200°C. However, for accurate readings, the alloys used in these thermocouples must be explicitly selected for temperatures at or below -200°C. Most thermocouple manufacturers purchase their thermocouple alloys calibrated from 0°C and above. While these alloys can still measure temperatures down to -200°C, the accuracy may not be as precise. You can purchase individual calibrations to determine offset values if you require accurate readings.
4. Thermocouples for Furnaces
For furnaces, selecting a suitable thermocouple is essential for successful and safe operation. When choosing the best thermocouple for your application, it is vital to consider the environment, temperature range, and mounting configuration. The thermocouple wires must be able to withstand the temperature of the furnace. The protective covering, either metal or ceramic, must also withstand the stove’s temperature. The atmosphere in which the thermocouple will operate should also be considered. This includes air, reducing, oxidizing, or inert atmospheres. Finally, the mounting configuration should be determined based on the application. Considering all these factors, you can select the proper thermocouple for your furnace and ensure that it operates safely and efficiently.
5. Thermocouples for Molten Metal
Measuring the temperature of molten metal is a challenging task. Thermocouples are the best choice for contact measurements in this environment. Withstanding temperatures up to 2,500°F (1,371°C), Type K and N Base Metal, and Types R, S, and B Platinum thermocouples are the only options for taking accurate temperature readings of molten metal. In addition, these thermocouples provide reliable and repeatable measurements to ensure your molten metal processes are safe and efficient.
When base metal thermocouples are used, Type K and Type N thermocouples are designed with large diameter #8 or #14 AWG solid wires with ceramic insulators and ceramic and metal protection tubes to provide superior protection in high-temperature environments. In addition, the thick wire ensures that measurements can be taken before the extreme heat begins to degrade the wires. The Platinum Thermocouple Wires are ideal for applications requiring accurate and reliable temperature measurement over long periods.
These wires are available in sizes #20 to #30 AWG Solid (as part of the RAT/SAT/BAT series). Unlike base metal Type K and N wires, Platinum Wires are resistant to oxidation and corrosion and have the added benefit of being immune to long-term annealing, meaning they will not fail due to grain growth.