Thermocouples are often the go-to device for temperature measurement. They’re fast, simple to use, and accurate — everything you look for in a piece of measurement equipment. However, thermocouples are only able to operate due to the Seebeck effect, the phenomenon in which a temperature difference between two points creates a voltage.

This article will explain the Seebeck effect, its history, and how Seebeck coefficients affect thermocouples.
Seebeck Effect Definition
The Seebeck effect is a thermoelectric effect in which the temperature difference between two materials creates a voltage. It is most commonly seen in thermocouples.
As the temperature at the hot junction changes, a voltage runs between the hot and cold junction that is proportional to the difference in temperature. This is how thermocouples can measure temperature so accurately. It is important to note, however, that the effect only occurs between conductors or semiconductors made of different materials. If a thermocouple only uses one type of metal wire, the effect does not happen.
As a current passes through a thermocouple, it will generate heat at one of its junctions and absorb it at the other. This phenomenon has a name: the Peltier effect. It goes hand-in-hand with the Seebeck effect, and you will often see the two discussed in tandem.
Similarly, you will hear about the Thomson effect when discussing thermoelectricity as well – it is the principle that a material will gain or lose heat in a temperature gradient when a current flows through it. This is why it’s important to know what metals a thermocouple is made of in order to make proper calculations, such as Seebeck coefficients.
Thermoelectric phenomena like the Seebeck, Peltier, and Thomson effects happen because electrons are responsive to temperature changes. Heat naturally causes electrons to increase their kinetic energy and move. Electrons in a thermocouple’s hot junction naturally travel towards the cold junction, carrying heat and negative charge with them. This is, at a basic level, what creates the voltage observed between the junctions. There are also certain situations where the transferred atoms are positively charged, instead of the negatively charged, as is normally the case with electrons.
History of the Seebeck Effect
The Seebeck effect was discovered in 1821 by German physicist Thomas Seebeck. He observed that it was possible to create voltage by combining two wires of copper and bismuth in a loop with a different temperature at each meeting point. He proved this by utilizing a magnetic compass, which was deflected by the loop’s electric current.
Initially, Seebeck could only observe the magnetic field, so the effect was called a thermomagnetic effect, not thermoelectrical. Around the same time, Danish physicist Hans Christian Oersted discovered that the magnetic field was indeed created by an electrical current, defining the Seebeck effect as we understand it today.
Incidentally, this thermoelectric effect was actually discovered decades earlier by Italian scientist Alessandro Volta in 1794 while he was investigating Luigi Galvani’s “animal electricity.” It would be refined and better observed by Seebeck and Oersted nearly 30 years later.
What Is the Seebeck Coefficient?
The Seebeck coefficient is the thermoelectric voltage a particular material will have in response to a difference in temperature. It is the key to knowing how certain metals will respond when under the Seebeck effect. It is measured in voltage per kelvin (V/K).
A metal with a high Seebeck coefficient will create far more thermoelectric energy than one with a low coefficient. While that may not matter as often in a thermocouple, using a metal with a high coefficient can be crucial in other thermoelectric applications. In a thermocouple, a material that is able to better resist the Thomson effect is more desirable than a high or low initial coefficient. Metals that have variable coefficients depending on the temperature can inflict a lot of uncertainty on measurement calculations.
To calculate a Seebeck coefficient, determine the ratio of voltage running between the junctions in regards to the temperature gradient. The simple equation for a material’s Seebeck coefficient is:
S = ΔV/ΔT
- ΔV = Voltage difference between two junctions
- ΔT = Temperature difference between two junctions
Using this formula would net a Seebeck coefficient, but it would not be an absolute Seebeck coefficient. It is not easy to directly measure the voltage created by the Seebeck effect with certainty, as the temperature is not one consistent value and any measurement equipment would undergo its own Seebeck effect. This is why pre-calculated Seebeck coefficients are so important, as they allow for more precise measurement.
Every metal's Seebeck coefficient is calculated at room temperature relative to platinum. Platinum’s actual coefficient is −5 microvolts per Kelvin (μV/K) so that must be compensated for in any final measurements.
The Seebeck coefficients of some common metals in μV/K are:
- Silicon: 440
- Iron: 19
- Tungsten: 7.5
- Gold: 6.5
- Silver: 6.5
- Copper: 6.5
- Lead: 4.0
- Aluminium: 3.5
- Carbon: 3.0
- Mercury: 0.6
- Platinum: 0 (technically -5)
- Sodium: -2.0
- Potassium: -9.0
- Nickel: -15
- Bismuth: -72
Some materials have positive and some have negative coefficients. Materials with negative coefficients are moving electrons from the hot to the cold junction while those with positive coefficients are moving positively charged electron holes. Basically, the coefficient indicates what type of charge the material carries.
The Seebeck Effect and Thermocouples
As we discussed at the start, thermocouples and the Seebeck effect are inextricably linked to one another. The fact that a change in temperature between two materials creates a voltage is how thermocouples are able to approximate temperatures. It allows for consistent measurement even under variable situations such as longer wires or different metals.
Thermocouples are crucial in a multitude of applications, such as controlling the temperature in furnaces, engines, or medical devices. Experts use them across industries to ensure accurate temperature measurements, from calibration labs to manufacturing lines.
Other Applications of the Seebeck Effect
Thermocouples are not the only useful application of the Seebeck effect. It turns out that being able to create voltage via heat (or heat via voltage) is pretty convenient for other reasons, too. Some common applications of the Seebeck effect are:
Thermopiles
Thermopiles are connections of thermocouples in a series, utilizing the Seebeck effect to increase voltage output. They are generally used within different temperature measurement devices, like infrared thermometers. The larger output allows for a more specialized range of uses than a single thermocouple provides.
Thermoelectric Generators
A thermoelectric generator is exactly what its name implies: it uses heat to generate electrical power. It uses the Seebeck effect to do so, and while inefficient, it is great at converting wasted heat into extra power. Unlike thermocouples, which value stability, generators will be built out of high-conductivity materials to maximize the amount of power they create. The best materials will have high electrical conductivity, but low thermal conductivity.
Automobiles
The Seebeck effect helps cars increase fuel efficiency. Using an automotive thermoelectric generator, the extra heat created from the engine can be converted back into electricity to keep the car running longer. Similar to larger thermoelectric generators, the efficiency of these devices may be lacking, but they still help reclaim some of the enormous amounts of heat lost during engine operation.
Keep Your Thermocouples Properly Calibrated
Ultimately, the Seebeck effect is fairly simple when it comes down to it: a proportional link between heat and electricity. Yet even 200 years after its discovery, research into its applications has not slowed down. As researchers discover better thermoelectric materials, there is real promise for thermoelectric power in fields like advanced aerospace technology.
However, for the sake of calibration, we’ll continue to utilize the Seebeck effect in its most common form: when we want to know the temperature of something. Fluke Calibration can help ensure that your equipment is regularly calibrated to guarantee accurate, reliable temperature calculations every time.
Explore our calibration baths to keep your thermocouples measuring as accurately as possible.