Guide to Watlow® Thermocouples

A thermocouple is a specific type of sensor that’s used to read a wide range of temperatures in many industrial environments. The type of thermocouple you’ll need largely depends on your application, equipment, and environment.

Whether you need a sensor that can withstand extreme temperatures or one with exceptional chemical resistance, Hi-Watt has everything you need. We’re proud to offer a full line of temperature sensor products from brands like Watlow®, a leading manufacturer for over a century. Since their founding, they’ve been committed to producing innovative products for manufacturers around the world.

Keep reading this guide to learn more about the different types of Watlow® thermocouples available through Hi-Watt and how to select the best one for your application.

J Thermocouples

The first type of thermocouple we offer is Type J. The J-type thermocouple typically consists of a (positive) iron wire and (negative) constantan, or copper-nickel) alloy wire. 

Compared to some of the other types of thermocouples, it does have a shorter temperature range (between 0 and 750 degrees Celsius), so it’s not suitable for high-temperature applications. Although J-types will not be damaged at higher temperatures, it’s not recommended because the magnetic field of the iron wire will change at 770 degrees Celsius. Additionally, J-type thermocouples may also be prone to rusting in humid conditions or extremely low temperatures.

J-type thermocouples are most frequently used for temperature monitoring in vacuum applications or to measure temperatures of inert materials.

K Thermocouples

Next, Type K thermocouples are capable of accurately reading temperatures between -270 degrees and 1260 degrees Celsius, making them great for many applications. They’re usually composed of Chromel (positive) and Alumel (negative) conductors, and provide exceptional corrosion resistance. Unlike J-types, they are not suitable for vacuum or reducing applications. Common applications include measuring temperatures in boilers, oil heaters, and engines.

T Thermocouples

Type T thermocouples are composed of two non-magnetic copper (positive) and constantan/copper-nickel alloy (negative) wires. They can typically read temperatures between 0 and 350 degrees Celsius, making them a better option for low-temperature applications, including cryogenics.

They also have great rust and corrosion resistance, and can be used in both oxidizing and reducing atmospheres.


Finally, mineral-insulated thermocouples are great for many industrial applications, including measuring temperatures in nuclear reactors, furnaces and kilns, jet engines, and food processing equipment.

Watlow’s® mineral-insulated thermocouples can handle temperatures up to 1,200 degrees Celsius and are available in many diameters (.25 millimeters to 13 millimeters). They also are insulated with special XACTPAK® material, which allows the sensor to quickly transfer heat to its measuring junction. The outer metal sheath also protects the sensor from oxidation.

Selecting the Right Watlow® Thermocouple

When it comes to choosing the right Watlow® thermocouple, there are a few important factors to keep in mind: the temperature range of your application, the environment the thermocouple will be in, measuring response time, and your mounting capabilities.


As previously mentioned, each thermocouple type has its limitations. Type-T thermocouples are great for low-temperature applications while mineral-insulated and type K are better suited for high-temperature applications.


If you have a humid or harsh operating environment, you’ll want to avoid a type J thermocouple as it’s prone to oxidation. Most other thermocouple types can withstand humid or extreme environments. It’s also important to note that an ungrounded thermocouple is better for corrosive environments or electrically active environments.

Response Time

Watlow’s® mineral-insulated thermocouple is the best option for manufacturers who are looking for incredibly fast read times, even in corrosive environments.

Mounting Capabilities

Lastly, there are many different styles of thermocouples, including surface mount and direct immersion. It’s important that you choose a style that works best for your existing setup. Because thermocouples are only capable of measuring their own temperature, you want to be sure that your thermocouple comes into contact with the equipment or component that you need measured.

Why Choose Watlow®?

Founded over 90 years ago, Watlow® is a world-class provider of innovative temperature sensing solutions for all types of industries. Since their founding, they’ve been committed to not only improving their processes and products, but also minimizing their environmental impact. All products are patented, manufactured in closed-loop systems, and maintain compliance with ISO 14001 standards. When you need quality and reliability, you need Watlow®.

Looking for Watlow® Thermocouples? Contact Hi-Watt Today!

Find your solution with help from Hi-Watt. Founded in 1979 and serving clients throughout Michigan, we’re a manufacturer’s representative and leading distributor of Watlow® products. If you have general questions about Watlow’s® line of thermocouples, or need help selecting the right one for your application, please contact us today, and one of our experts will be in touch with you shortly.