j type thermocouples

The J-type thermocouple is a temperature-sensing device commonly used to measure smaller temperature ranges, generally 32 degrees Fahrenheit to 1,382 degrees Fahrenheit or 0 degrees Celsius to 750 degrees Celsius. Its accuracy is +/ 2.2 degrees or +/- 0.75% with special limits of error: +/- 1.1 Celsius or 4%.

Thermocouple TypeTemperature Range:
Temperature Range:
J32°F – 1,382°F0°C – 750°C+/- .75%
+/- 2.2C
+/- 1.1C

Common Applications

Thermocouples are well-suited for industrial uses, but there are many different types. Most general industrial applications fall within type J’s temperature range, 0°C to 750°. Hi-Watt also custom-configures J-types to meet space limitations, response requirements, and insulation specifications. 

Industrial and manufacturing applications:

  • industrial kilns
  • boilers
  • furnaces
  • flues
  • ovens

Thermocouple Composition

Two wires are used, and one side of the device has the wires spread apart or “open,” while the other side has the wires connected. Each thermocouple wire is made of a different material, which is what allows for a detectable voltage difference between the two wires.

By keeping the open end of the thermocouple at a constant reference temperature and using a microprocessor reading device, you can see the temperature of whatever material the connected end is submerged in by reading the voltage created at different temperatures.

While some thermocouples are more specialized to specific temperature ranges and thus tend to be more expensive, a J-type thermocouple occupies the middle of the potential temperature ranges.

Understanding Thermocouple Temperature Ranges

thermocouple sensors

A key part of what makes the different types of thermocouples differ so much in the temperature ranges they can effectively read and in their costs is the material that the wires are made from. For example, a type B thermocouple is made of platinum and rhodium and can measure temperatures ranging from 871 to 1704°C due to the incredible heat resistance of these materials.

A type T thermocouple is made of copper and constantan, and while it has a much lower range, coming in at 0 to 350°C, it also provides very stable readings. You are more likely to see a type B used for work with metals, while a type T is typically used in cryogenics.

A J-type thermocouple range falls between these two extremes. As mentioned above, it can read temperatures from 0 to 750°C, and this is due to its composition of iron and constantan. The Curie point of iron is 770°C, at which point the magnetic field of the iron wire begins to change its behavior, causing any voltage readings to be unreliable.

Even though the structure of the thermocouple will remain intact at temperatures up to 1200°C, it should not be used at temperatures above 750°C. You are more likely to see J types being used in electric furnaces, as well as in the production of resins and plastics.

Hi-Watt Offers Thermocouples Customized to Your Needs

Based in Michigan, Hi-Watt is a leading regional distributor of high-quality thermocouple sensors from leading brands like Watlow®, Tempco, and Pyromation®. We carry a variety of J-types with different termination options, including cables, pot seals, and connectors. 

We can also custom-design J-type thermocouples to meet your industrial or environmental applications.

Contact us today to learn more about our products and capabilities or request a quote.