THERMOCOUPLES

Thermocouples are resistance temperature sensors used for measuring extreme temperatures, and they find application in many sectors. These sensors have compact dimensions and very rapid measurement times, and due to their high resistance, thermocouples can also be used in critical conditions.

Temperatures measured can reach up to 2500°C, and thanks to their extreme durability and small size, they are among the most commonly used electric resistors for temperature control.

ESAF Ltd offers a wide range of thermocouples and thermocouple cables. You will find a selection of high-quality electrical components, providing excellent performance regardless of the application context, all at competitive prices. Sale of resistors

WHAT ARE THERMOCOUPLES?

Thermocouples are transducers, temperature sensors that operate based on the thermoelectric effect. The main advantages of thermocouples are their small size, rapid measurement times, and their ability to be used even at extreme temperatures (depending on the type of thermocouple, temperatures can reach up to 2500°C).

HOW DOES A THERMOCOUPLE WORK

Thermocouples consist of two conductor wires that, when joined together, create a circuit. The circuit of a thermocouple is made up of two wires composed of different metals.

The junction where the two wires meet is called the hot junction and is in contact with the temperature to be measured. The point where the two wires are free (not joined together) is the cold junction, which is in contact with a body of known temperature.

There is a temperature difference between the two junctions that generates an electric current within the circuit. This is the Seebeck effect and is the basis for the operation of thermocouples.

The current generated by the circuit corresponds to a temperature difference between the two junctions. By measuring the voltage present in the circuit, the thermocouple can determine the temperature to which the hot junction is exposed.

THE SEEBECK EFFECT

The Seebeck effect describes how two metals at different temperatures, when joined together, generate a specific electromotive force. Much depends on the types of metals used in the thermocouple, allowing for more precise measurements or measurements at particular temperatures. For this reason, thermocouples are classified based on the pair of metals used.

TYPES OF THERMOCOUPLES AND COLOUR CODE TABLE

Thermocouples are classified based on the types of metals used in their construction. Depending on the metals used, the maximum temperature they can measure will vary, along with different applications and characteristics.

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TYPE K THERMOCOUPLES

Type K thermocouples are made from nickel-based wires and are the most widely used in production and industrial sectors due to their reliability and cost-effectiveness.
Measurement range: -200/+1370°C
Colour of Type K thermocouples: Green

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TYPE J THERMOCOUPLES

Type J thermocouples have a more limited measurement range compared to Type K. The two conductors are made of iron (positive pole) and a nickel-copper alloy (negative pole).
Measurement range: -40/+750°C
Colour of Type J thermocouples: Black

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TYPE N THERMOCOUPLES

Type N thermocouples are designed for high temperatures, similar to Type K but more stable and less sensitive to oxidation and extreme external temperatures.
Measurement range: -270/+1300°C
Colour of Type N thermocouples: Pink

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TYPE W3 THERMOCOUPLES

Type W3 thermocouples are ideal for very high temperatures, capable of measuring up to 2500°C. They cannot be used in oxidising atmospheres or in contact with air. They are the most advanced and are primarily used in sectors requiring extremely high temperatures.
Measurement range: 0/+2500°C
Colour of Type W3 thermocouples: Green

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TRADITIONAL THERMOCOUPLES OR MINERAL-ISOLATED THERMOCOUPLES?

The type of insulation used for thermocouples defines various performance factors, particularly response time and measurement speed.

Traditional thermocouples use ceramic insulators and protective sheaths made from metal or ceramic.

Mineral-insulated thermocouples use magnesium oxide (MgO) to insulate the metal wires with a highly insulating sheath.

Thermocouples with mineral-insulated cables offer better response speed and improved resistance to pressure and vibrations compared to standard traditional insulated thermocouples.

USES OF THERMOCOUPLES

The use of thermocouples as temperature sensors is widespread, both in industrial and domestic applications.

THERMOCOUPLES FOR BOILERS, OVENS, AND HOBS
In domestic settings, thermocouples are widely used for heating and the operation of cooktops and ovens. In these contexts, the thermocouple acts as a temperature-regulating thermometer, sending an electrical impulse that controls the opening or closing of the gas valve.
The thermocouple here functions as a safety device for gas ovens and cooktops, indicating the closure of the gas valve if the flame goes out. In this way, once the thermocouple detects a drop in temperature due to the absence of a flame, it sends an electrical impulse to stop the gas flow.
INDUSTRIAL THERMOCOUPLE PROBES
For measuring high temperatures or in challenging conditions, thermocouples are a fundamental tool within industrial probes used in production processes. Here, the significant advantage of thermocouples is their durability, which allows them to be used in a wide range of industrial settings.

THERMOCOUPLES OR THERMISTORS: THE DIFFERENCES

Thermocouples and thermistors are among the most commonly used temperature sensors, both in industrial and civil sectors. When choosing between these electrical components, it is essential to consider two factors: precision and the type of temperatures to be measured. Thermocouples are generally less precise than thermistors but are easier to calibrate and more durable. For measurements requiring very high temperatures, above 650°C, thermocouples are the ideal measurement tool due to their wider measurement range.