## Wednesday, March 22, 2023

Thermocouples, learn how thermocouples work in this video. We will talk about the types of thermocouples, the different applications of thermocouples, the physics behind thermocouples as well as experiments to show how it works.

Thermocouple: how does it work?

Thermocouples are probes used to measure temperature. Their accuracy, fast response time and ability to withstand strong vibrations, high pressures and extreme temperatures make them ideal for a wide range of applications. But how does a thermocouple work?

What are thermocouples used for?

If you want to measure the temperature of something as hot as a volcano, an ordinary thermometer would be useless. Stick the bulb of a mercury thermometer in 1000°C lava and you'll have a surprise: the mercury inside will instantly boil and the glass itself might even melt. Try measuring the temperature of something very cold like liquid nitrogen with a mercury thermometer and you'll have the opposite problem. At temperatures below −38°C, mercury becomes a solid. So how do you measure extreme temperatures? With a thermocouple!

Thermocouples are used to measure extreme temperatures such as that of a volcano.

These temperature probes are widely used in scientific and industrial applications because they are generally very accurate and can operate over a wide range of very hot or very cold temperatures. Since they generate electrical currents, thermocouples are also useful for making automated measurements. It is much easier to use an electronic circuit or a computer to measure the temperature at regular intervals than to do it yourself with a thermometer.

Thermocouples are inexpensive and interchangeable. They are supplied with standard connectors and can measure a wide range of temperatures. They are found in refrigerators, air conditioners, water heaters and electric stoves. They are sometimes called thermostats. The main limitation of thermocouples is accuracy. Errors below one degree Celsius can be difficult to obtain.

Discovery of thermocouples

Thomas Seebeck, a German physicist, discovered that when metal is heated, electricity is also generated: this is the Seebeck effect or thermoelectric effect. However, it is not possible to create an electrical circuit from this electricity. Once the metal is joined in a loop, its temperature becomes uniform, which stops the production of electricity.

Different metals conduct heat and electricity at different speeds and produce different current from each other when heated to the same temperature. By taking two strips of different metals that are the same size and joining them at each end, a loop is created. By heating one of the joints and cooling the other, an electric current flows through the loop.

The voltage of the current produced depends on the temperature difference between the two ends. Therefore, a formula can be created to convert current to a temperature reading.

Principle of operation of the thermocouple

The basic design of a thermocouple involves two metal wires with different thermal and electrical properties. The two metals in contact are twisted or welded at one end. They form the measuring point. At the other end is the connection point, so called because it connects to the voltage reader. As the temperature changes at the measurement point, the electron density of each metal wire also changes. A voltage occurs, which is measured at the connection point.

Note that thermocouples do not actually measure absolute temperature. Instead, they measure the differential temperature between the measuring point and the connection point. This is why thermocouples also need cold junction compensation so that the ambient temperature at the connection terminals does not affect the measurement result.

Under laboratory conditions, the reference junction would be maintained at a known temperature, typically 0°C. But in normal industrial practice, the junction is left at room temperature and an external sensor is used to compensate for this variation.

Thermocouples, learn how thermocouples work in this video. We will talk about the types of thermocouples, the different applications of thermocouples, the physics behind thermocouples as well as experiments to show how it works.

Thermocouple: how does it work?

Thermocouples are probes used to measure temperature. Their accuracy, fast response time and ability to withstand strong vibrations, high pressures and extreme temperatures make them ideal for a wide range of applications. But how does a thermocouple work?

What are thermocouples used for?

If you want to measure the temperature of something as hot as a volcano, an ordinary thermometer would be useless. Stick the bulb of a mercury thermometer in 1000°C lava and you'll have a surprise: the mercury inside will instantly boil and the glass itself might even melt. Try measuring the temperature of something very cold like liquid nitrogen with a mercury thermometer and you'll have the opposite problem. At temperatures below −38°C, mercury becomes a solid. So how do you measure extreme temperatures? With a thermocouple!

Thermocouples are used to measure extreme temperatures such as that of a volcano.

These temperature probes are widely used in scientific and industrial applications because they are generally very accurate and can operate over a wide range of very hot or very cold temperatures. Since they generate electrical currents, thermocouples are also useful for making automated measurements. It is much easier to use an electronic circuit or a computer to measure the temperature at regular intervals than to do it yourself with a thermometer.

Thermocouples are inexpensive and interchangeable. They are supplied with standard connectors and can measure a wide range of temperatures. They are found in refrigerators, air conditioners, water heaters and electric stoves. They are sometimes called thermostats. The main limitation of thermocouples is accuracy. Errors below one degree Celsius can be difficult to obtain.

Discovery of thermocouples

Thomas Seebeck, a German physicist, discovered that when metal is heated, electricity is also generated: this is the Seebeck effect or thermoelectric effect. However, it is not possible to create an electrical circuit from this electricity. Once the metal is joined in a loop, its temperature becomes uniform, which stops the production of electricity.

Different metals conduct heat and electricity at different speeds and produce different current from each other when heated to the same temperature. By taking two strips of different metals that are the same size and joining them at each end, a loop is created. By heating one of the joints and cooling the other, an electric current flows through the loop.

The voltage of the current produced depends on the temperature difference between the two ends. Therefore, a formula can be created to convert current to a temperature reading.

Principle of operation of the thermocouple

The basic design of a thermocouple involves two metal wires with different thermal and electrical properties. The two metals in contact are twisted or welded at one end. They form the measuring point. At the other end is the connection point, so called because it connects to the voltage reader. As the temperature changes at the measurement point, the electron density of each metal wire also changes. A voltage occurs, which is measured at the connection point.

Note that thermocouples do not actually measure absolute temperature. Instead, they measure the differential temperature between the measuring point and the connection point. This is why thermocouples also need cold junction compensation so that the ambient temperature at the connection terminals does not affect the measurement result.

Under laboratory conditions, the reference junction would be maintained at a known temperature, typically 0°C. But in normal industrial practice, the junction is left at room temperature and an external sensor is used to compensate for this variation.