What is a thermocouple? How it works? What is its purpose or use? (2023)

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What is a thermocouple? How it works? What is its purpose or use? (1)

Measuring the temperature is an essential process for many activities that happen around us. Think of the air conditioning that makes your room comfortable, the cars driving down the street, the planes flying by, or even the power plant that produces the electricity you use. These activities can be very different, but they have at least one thing in common: thermocouple temperature measurement. What exactly is a thermocouple? How it works? What is your use? Let's explore the question: what is a thermocouple?

What is a thermocouple? How it works? What is its purpose or use? (2)

Illustration 1:A real thermocouple!

What is a thermocouple?

A thermocouple measures temperature, so technically a thermocouple is a type of thermometer. Of course, not all thermometers are created equal. Two dissimilar metals form a thermocouple. Usually in the form of two twisted wires, soldered or crimped together. Temperature is detected by measuring voltage. Heating a metal wire causes the electrons inside the wire to become excited and want to move. We can measure this potential for electrons to move with a multimeter. With this measurement we can calculate the temperature.

In short, a thermocouple converts thermal energy into an electrical signal. If necessary, a person controlling the thermocouple can act directly on this signal. But it's more likely an automated system that observes, records, or uses the data to perform an action. Let's take a look at a thermocouple diagram to get an idea of ​​how this instrument works.

What is a thermocouple? How it works? What is its purpose or use? (3)

Figure 2:single thermocouple

As you can see in Figure 2, a thermocouple is a relatively simple instrument. When the temperature is to be measured, two wires made of different metals are connected. This connection is called a measurement point. The other ends of the wires are also connected. But this time in an area where the temperature is known. This area is called the reference junction. Let's do a little experiment by heating one end of the thermocouple and adding a way to measure what happens.

What is a thermocouple? How it works? What is its purpose or use? (4)

Figure 3: heating a thermocouple

By applying heat to the measurement point, we can excite the electrons in the metal wire and cause them to flow, creating a current. Since we want to measure the voltage of this current, we connect the reference junction to a multimeter with copper wire. The current detected by our multimeter gives us a reading in millivolts (mV). Let's turn up the temperature on our meter and see what happens to the multimeter reading.

What is a thermocouple? How it works? What is its purpose or use? (5)

Figure 4: Application of more heat

If the measurement point becomes warmer, the measured value of our multimeter at the comparison point increases proportionally. The important part of the multimeter reading is that it is a function of the temperature difference between the two junctions. We can represent this relationship between the two variables. So if we know the temperature of the controlled reference junction and can measure the change in voltage when the measuring junction is heated. Then we can determine the temperature at the measurement point.

What is a thermocouple? How it works? What is its purpose or use? (6)

Figure 5: Graph of temperature vs. voltage

Although a thermocouple does not directly tell us the temperature of the measuring point, it does provide us with a voltage. This voltage is a readable electrical signal that depends on the temperature difference between the measurement and the reference junction. You can graph or tabulate this correlation between stress and temperature. And we can reference the voltage signal to determine the associated temperature. Some aspects, such as the type of cables used and the reference junction temperature, must remain constant. But ultimately, we have a repeatable process for measuring temperature, which is infinitely repeatable.

The science behind a thermocouple

Let's examine the science behind a thermocouple in a little more detail. We start with two different metal wires, one is iron (Faith) and the other of constantan (an alloy of copper and nickel,CuNi). The combination of these wires creates a voltage potential. A voltage potential is a current flow capacity that varies according to the properties of the metals that make up the connected wires.

Have in mind; Nothing really happens just by connecting two wires together, just the possibility of something happening. In this case, potential current flows. A simple way to visualize this stress potential is to imagine a stationary rock on top of a hill. If you apply a force to it, it will smash a bunch of rocks down the hill. Until you push the rock though, there's only potential.

What is a thermocouple? How it works? What is its purpose or use? (7)

Figure 6: two wires connected, creating a voltage potential

Since our wires are only connected at one point, no current can flow. However, when we connect the other end of the wires, we create a circuit or path for the current to follow. As we reconnect two wires, we also create another voltage potential. Remember that this is just the potential for current flow. Since the two junctions are nickel-iron wires connected together, these two voltages are identical; there is no measurable difference between them.

What is a thermocouple? How it works? What is its purpose or use? (8)

Figure 7: two wires connected in a circuit with two voltage potentials

In the previous diagram we have a circuit formed by two different metallic wires with two voltages. The final ingredient needed to complete this thermocouple tutorial is temperature, or more specifically, a temperature differential. Let's heat up one of the wire connections. The temperature difference at one end creates a different voltage. We finally have something we can measure. If we keep heating one end and create a larger and more significant temperature difference, we can measure an increasing voltage difference. take a look belowFigure 8Isn't this starting to look like our simple thermocouple?

What is a thermocouple? How it works? What is its purpose or use? (9)

Figure 8: circuit, heating one end causes voltage difference

Well, a complete thermocouple is more than just a few wires; this is the most basic form they can take. For example, modern thermocouples are usually constructed with some type of outer coating and insulation to protect them from corrosion and wear.

Also, they are usually not connected to multimeters as in our previous examples. That's not to say you can't have a worker read voltage readings and compare them to a temperature chart. However, thermocouples are usually connected to a centralized computer system. A type of automation that can receive thermocouple readings and act on that data. Finally, the measured voltage does not correlate with a straight-line temperature reading. Thermocouple outputs are not linear, so our plot is inFigure 5it is very simplified.

There are many little details about this temperature sensor that are easy to miss, but the important thing is to understand the basics behind this instrument. For a more in-depth discussion, visitwhere you can find answers to help you fill in some of the blanks.

Did we pique your interest in thermocouples? If you want to see the real variety and availability of different thermocouples. upside downON HEREand see thermocouples manufactured by Enercorp.

What are the differences between thermocouples?

Thermocouples come in many shapes, sizes and materials. The different properties of different metals are the key to how thermocouples work. In fact, we measure how two different cables react in the same environment and calculate these small differences against a standard temperature reference. Typical metals used in thermocouples are iron (Fe), copper (Cu), nickel (Ni), constantan (a Cu/Ni alloy), nichrome (an alloy of nickel and chromium (Cr)), and platinum (Pt). . Each metal has advantages and disadvantages when measuring thermocouple temperature.

Certain combinations of metals may work well for colder temperatures, but not for warmer temperatures. Other combinations may provide more accurate readings within a certain temperature range. Also, a different combination may be more resistant to the corrosive environment in which it is used and extend the life of the thermocouple before it needs to be replaced.

There are so many differences between thermocouples. Take a look at our blogthermocouple differencesdedicated to examining the wide range of different types of thermocouples and the specific areas in which they excel.

Where are thermocouples used?

With the large number of different types of thermocouples, there are many possible uses. Of course, a thermocouple can only do one thing, and that's read temperature, but it can cover such a wide measurement range and is so versatile that it can be a useful tool for many different industries and environments.

Product manufacturing requires accurate measurement of all types of gases and liquids. HVAC systems require data to be routed to a centralized, automated system to create a comfortable living and working environment. Transportation, petrochemicals and power generation are areas where thermocouples are used. The possibilities are endless as today many different processes require some type of temperature sensing capability.To see the true size of the thermocouple world, check out our blog"What are thermocouples for?".

So now you know a little more about thermocouples. Here at Enercorp we stock and manufacture Thermocouples for every need. Our customers range from energy producers to food processing companies, industries such as steel production and much more. This may be a diverse group of customers, but they all share the same universal need: thermocouple temperature sensing.

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