What are Thermocouples used for?
If you’ve read through our blog, “What is a Thermocouple?” then you have an idea of what they are and how they work. But what are there, usages? And, why would someone choose to use a thermocouple over one of the other types of temperature sensors out there? We’ll examine some of the characteristics that make them such an important sensor. Let’s start by looking at some examples of how one can use these devices throughout the real world.
Figure 1: Testing a thermocouple in boiling water
Where are Thermocouples used?
You can find them within your home; think of a safety switch for your water heater or furnace. How about cooking? Your oven may regulate temperature with a thermocouple. The car parked in your garage will require the measurement of exhaust gases to compute optimal engine performance.
Industries, such as steel and iron, need to measure the temperature of molten metals; a terrifically uninviting environment but a perfect place for a thermocouple. Apartment, office, or industrial building air conditioning systems employ them too. They require vast amounts of heated or cooled air to circulate to provide for comfortable living and working conditions. This is an ideal situation for the use of an automated system where thermocouples can provide the temperature data.
Processes like power generation, chemical production, and other types of manufacturing rely on thermocouples to measure temperature. The instruments typically provide passive temperature data, however, they can be used actively too. The incredibly small voltage generated by a thermocouple could power something directly, like the opening of a valve. The need for temperature sensing is widespread and the possibilities for using a thermocouple to perform that task are endless.
For a specific example of a thermocouple look no further than one of Enercorp’s very own custom designs, the TS-MP-T-J-240. This J-type thermocouple measures the temperature within different types of manufactured products within the food industry. The protective sheath has a pointed sheath tip, therefore it can pierce through a tough membrane. It is comprised of stainless steel and Teflon. These materials make the sensor easy to clean and sanitize.
Figure 2: One of Enercorp’s custom thermocouples, the TS-MP-T-J-240
Why use a thermocouple?
Temperature can be sensed by many different methods and types of instruments. Performance, cost, and durability are all factors that can be considered. What positive characteristics merit the use of a thermocouple over other sensors?
Most thermocouples are accurate to within two or three degrees of the actual temperature. Some are naturally more accurate than others because of the characteristics of the metals used. For example, platinum and rhodium thermocouples are able to sense temperature within accuracies of 0.5°C. Other metals and alloys may not be as precise. However, a few degrees of error are negligible because of the broad measurement ranges.
As mentioned throughout this discussion, thermocouples are simple instruments. There are just two differing metal wires that make up the entire sensor. Some are physically short, just a couple of inches long. Some can be many feet long. Therefore, the amount of material will affect the actual cost.
Thermocouples will also differ in price because they are made from a variety of different materials. For example, platinum has some ideal properties but is a much more expensive metal than nickel. Also, additional features can enhance the sensor, allowing for a unique and specialized way to measure temperature. A stainless steel sheath with magnesium oxide insulation, for example, can be incorporated into the design. These measures are used because they keep the thermocouple wire from being exposed to a hostile environment. This customized protection helps it from wearing out at a faster pace and gives it a longer life. Allowing for fewer replacement purchases, but that comes with a bigger initial price tag.
Figure 3: Cross-section of a sheathed and insulated thermocouple.
Since there are no moving parts and nothing fragile a thermocouple is pretty hard to break or damage. Now keep in mind, some conditions that they measure can be pretty inhospitable, so this is all relative. However, all thermocouples will eventually degrade. The metal wires will oxidize or corrode, therefore, the readings will become less accurate. There are steps that can be taken to prolong their lifespan. Housing the sensor inside a vacuum or surrounding it with an inert gas to avoid oxidization will ensure longevity. Check out our blog “Do Thermocouples Wear Out?” for more specifics on the factors that affect the lifespan of this instrument.
Thermocouples can sense a wide range of temperatures. Towards cooler temperatures, type T thermocouples can measure down to -200ºC. At the other end of the spectrum are type B thermocouples. They can measure temperatures up to 1700ºC. Aside from temperature range, you can also customize them by length, component material, and degree of protective measures. You can tailor them to fit as specific a job and purpose as necessary. Check out our blog on “What are the Different Thermocouple Types” for a closer look at the wide range of available sensors.
Figure 4: The range of some common thermocouples
Thermocouples are an ideal option for temperature measurement because of their immense range, low cost, and simple construction. They sense temperatures for an incredible variety of processes and are found across all sorts of industries. In this discussion, we’ve only addressed a small portion of the topic. If you still have questions, then the best place to look is our “Question and Answer Guide: Thermocouples.” You can also follow the other links within this article to keep learning about this remarkable instrument that has helped shaped the processes of our modern world.