Thermocouples are sophisticated devices used to measure the temperature in various applications, from kilns, to cold storage, to diesel engines. The critical nature of these devices means they require high-quality wiring inside. Otherwise, the readings could be incorrect, leading to varying problems.

California Fine Wire offers the best thermocouple wires for any industry or application, no matter how big or small. This page will outline how thermocouple wire works and what makes it so valuable.

How Does a Thermocouple Wire Work?

A thermocouple consists of two dissimilar metal wires coming together to create a temperature measurement junction. Heating the connection point of both metals creates a thermoelectric current known as a Seebeck current. As the heat transfers from the hot end to the cooler end, the electrons within the metals create electricity.

For a thermocouple to function correctly, one metal must be positively charged and the other negatively charged. An example would be positively charged copper on one wire and negatively charged nickel on the other.

Thermoelectric currents are minuscule, typically measuring in microvolts. That voltage then gets translated into temperature readings. Thermocouple readouts can be quite precise, which is why these devices hold value in so many unique applications.

A Guide to Thermocouple Wire Parts

A thermocouple is made up of multiple components. Here is a breakdown of each piece.

Measuring Junctions

A measuring junction is the “hot” end of the thermocouple. This junction is where the two wires meet, and where temperature is measured. There are three kinds of measuring junctions:

  • Exposed junction – Nothing protects the wire ends, meaning that they can rust or get damaged over time.
  • Grounded junction – A metal sheath covers the wires (usually stainless steel). This design is much more stable and long-lasting.
  • Ungrounded junction – In this case, the sheath is not connected electrically to the wires. An ungrounded junction is less susceptible to electromagnetic interference.

Reference Junctions

The reference junction is the other side of the thermocouple, or the “cold” connection. To get an accurate thermocouple readout, you need to know the wires’ temperature at rest—hence the term “reference.” The reference junction is often built into the display instrument, so the user won’t even see it.

Extension Wire

Since thermocouples are often placed in conditions not suitable for people, such as extreme cold or heat, the temperature reader often gets placed a significant distance away from the measuring junction. To ensure the accuracy of the readout, these systems use extension wires. These wires are insulated and protected so that the voltage isn’t affected by other environmental factors. The wires are never calibrated above 204°C to ensure stability.

Thermocouple Types

Since thermocouples may use multiple metals for wiring, these devices are classified into different types. Here is a breakdown of the most commonly used options.

  • Type K – This thermocouple uses chromel (80% nickel and 20% aluminum) and alumel (95% nickel, 2% aluminum, 2% manganese, 1% silicone) for its wiring. A Type K thermocouple can measure temperatures between -200°C and 1260°C.
  • Type J – This option uses iron and constantan (45% nickel and 55% copper). Type J is quite common and ideal for vacuum environments due to the iron wiring. Its features a temperature range of -210°C to 760°C.
  • Type T – A Type T thermocouple uses copper and constantan and works well for sub-freezing temperatures. Its range is -270°C to 370°C.
  • Type E – This thermocouple features better stability than Type K or J thanks to its composition of nickel-chromium and constantan. It’s also more accurate at temperatures below 538°C. Its maximum range is -270°C to 870°C.

Beyond these four primary thermocouple types, there are four others, including B, N, R, and S types. Each class is used for specific applications based on its wiring composition, stability, accuracy, and temperature range.

Get the Best Thermocouple Wire From California Fine Wire

Accuracy, stability, and precision are all critical for a thermocouple, so you need to make sure you’re using the best wires possible. California Fine Wire produces high-quality materials for all applications, both big and small. Contact us today to see what we can do for your business.