A Comprehensive Guide to Thermocouples: Types, Uses & Installation

Posted: October 05, 2023

Thermocouples play a crucial role in ensuring safety, efficiency, and precision in commercial kitchen appliances. What does a thermocouple do? From ovens and grills to deep fryers and steamers, these temperature-sensing devices are indispensable in maintaining the ideal cooking conditions. However, understanding the various thermocouple types, their uses, and proper installation techniques can be overwhelming. 

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Let us explore what is a thermocouple, delve into different types, and provide expert insights on the correct installation methods. Also, we will find out What does a thermocouple do? in ovens, fryers, grills etc.

Table of Contents:

What is a thermocouple?
How does a thermocouple work?
How many types of thermocouples are there?
Is a thermocouple safe for your restaurant equipment?
How to tell if thermocouple is bad?
How to replace a thermocouple?
Cost of replacing thermocouple in commercial kitchen appliances 
How to clean thermocouple?
Top thermocouple manufacturers in the USA
FAQs on Thermocouples

What is a thermocouple?

A thermocouple is a temperature sensor that operates on the principle of thermoelectric effect. Typically composed of two dissimilar metal wires joined together, it produces a voltage proportional to the temperature difference between its ends. 

What does a thermocouple do? In commercial kitchen appliances, the thermocouple is often utilized as a safety device. It serves to detect the presence of a pilot flame in gas-powered equipment, such as ovens and grills. If the pilot flame goes out, the oven thermocouple detects the drop in temperature and sends a signal to shut off the gas valve, preventing potential hazards.

How does a thermocouple work?

As we know, a thermocouple is a device used to measure temperature. When two different types of metals are put in contact with each other, an electric current will form and flow between them, also known as a circuit. In order to measure this current, a thermocouple has two different tips that are connected to the measuring device with a thin wire. There is one end that is connected to the hot junction and the other end that is connected to the cold junction. 

A thermocouple will conduct an electric current when it reaches an equilibrium temperature, which means that it will stop changing and flowing until it loses heat or gains heat. In order to measure this current, the thermocouple has a temperature sensing end and an electrical output end. The wire of the thermocouple can be twisted around so that it is pushed under the surface of the appliance, and then it will give an easy way to connect the wire from inside. 

How many types of thermocouples are there?

There are several types of thermocouples available, each with its own unique characteristics and temperature range capabilities. Let's explore some of the commonly used thermocouple types.

K Type Thermocouple

The K type thermocouple is composed of a positive Chromel (nickel-chromium alloy) wire and a negative Alumel (nickel-aluminum alloy) wire. K type thermocouples can measure temperatures ranging from -200°C to 1,372°C (-328°F to 2,502°F) and are commonly used in various industries such as heating, cooling, and food processing.

J Type Thermocouple

The J type thermocouple consists of a positive Iron wire and a negative Constantan (copper-nickel alloy) wire. It has a temperature range from -210°C to 1,200°C (-346°F to 2,192°F). J type thermocouples are known for their low cost, good accuracy, and are often used in applications such as ovens, furnaces, and power plants.

T Type Thermocouple

The T type thermocouple is composed of a positive Copper wire and a negative Constantan wire. It has a temperature range from -200°C to 350°C (-328°F to 662°F). T type thermocouples are highly stable and resistant to corrosion, making them suitable for applications involving cryogenic temperatures, HVAC systems, and temperature measurement in chemical processes.

B Type Thermocouple

The B type thermocouple is made up of a positive Platinum-Rhodium alloy (PtRh30-PtRh6) wire and a negative Platinum-Rhodium alloy (PtRh30-PtRh6) wire. It has a high-temperature range from 0°C to 1,820°C (32°F to 3,308°F). B type thermocouples are commonly used in industries such as glass manufacturing, ceramics, and certain high-temperature applications in the aerospace industry.

E Type Thermocouple

The E type thermocouple consists of a positive Chromel wire and a negative Constantan wire. It has a temperature range from -200°C to 900°C (-328°F to 1,652°F). E type thermocouples are known for their excellent accuracy and stability, making them suitable for applications in the petrochemical industry, food processing, and gas turbine exhaust monitoring.

N Type Thermocouple

The N type thermocouple is composed of a positive Nicrosil (nickel-chromium-silicon alloy) wire and a negative Nisil (nickel-silicon alloy) wire. It has a temperature range from -200°C to 1,300°C (-328°F to 2,372°F). N type thermocouples are often used in high-temperature applications, particularly in the aerospace industry and heat treatment processes.

R Type Thermocouple

The R type thermocouple consists of a positive Platinum wire and a negative Platinum-Rhodium alloy (PtRh13-Pt) wire. It has a temperature range from -50°C to 1,768°C (-58°F to 3,214°F). R type thermocouples are commonly used in applications such as metal refining, combustion control, and laboratory research.

Is a thermocouple safe for your restaurant equipment?

Here is how a thermocouple enhances the safety of your restaurant equipment:

Oven: In an oven, the thermocouple acts as a safety feature to prevent gas leaks. It is typically located near the oven's burner and is responsible for sensing the flame's presence. If the oven thermocouple detects that the flame is extinguished, it automatically shuts off the gas supply, preventing the accumulation of unburned gas that could lead to a dangerous situation. This feature ensures the safety of your staff and customers by reducing the risk of fire or gas-related accidents.

Grill: Grills, especially those powered by gas, also rely on thermocouples for safety. The gas thermocouple in a grill performs a similar function as in an oven, monitoring the presence of the flame. If the thermocouple senses that the flame has gone out, it immediately shuts off the gas supply to prevent the release of gas without ignition. This safety mechanism provides peace of mind, as it minimizes the risk of gas leaks and potential fire hazards that can occur during grilling operations.

Fryer: Thermocouples are commonly found in commercial fryers as well. They ensure the safety of fryers by monitoring the pilot flame. If the gas thermocouple detects that the flame has gone out, it quickly shuts off the gas flow, preventing the accumulation of gas and potential explosions. This safety feature is essential in a fast-paced kitchen environment where fryers are frequently used, as it significantly reduces the risk of accidents and ensures the well-being of your kitchen staff.

How to tell if thermocouple is bad? 

Here are the signs of a bad thermocouple in commercial cooking appliances:

Pilot Light Issues: One of the common signs of a faulty thermocouple is a pilot light that won't stay lit. If the pilot light keeps going out despite repeated attempts to relight it, there's a possibility that the thermocouple is not functioning properly.

Inconsistent Flame: Another indicator of a bad thermocouple is when the flame on the burner is weak or flickering. The thermocouple is responsible for sensing the heat from the pilot light and generating a small electric current. If it's malfunctioning, it may not produce a consistent flame.

Difficulty in Ignition: A faulty thermocouple can make it difficult to ignite the burner. When you turn the knob to start the appliance, the gas valve relies on the thermocouple to send a signal to allow the gas flow. If the thermocouple is defective, it may fail to send the signal, resulting in ignition issues.

Sudden Appliance Shutdown: A malfunctioning thermocouple can cause the appliance to shut down unexpectedly. If the thermocouple fails to sense the heat from the pilot light, it will send a signal to the gas valve to shut off the gas supply as a safety measure. This sudden shutdown can indicate a problem with the thermocouple.

Faulty Safety Features: Thermocouples are designed to provide a safety feature by shutting off the gas supply if the pilot light goes out. If the thermocouple is not working correctly, this safety feature may be compromised, posing a potential hazard.

Testing with a Multimeter: To confirm whether a thermocouple is bad, you can use a multimeter to measure the voltage generated by the thermocouple. A functioning thermocouple should produce a specific voltage when heated. If the reading on the multimeter is significantly lower or inconsistent, it may indicate a faulty thermocouple.

Age and Wear: Thermocouples can degrade over time due to constant exposure to heat. If your commercial cooking appliance has an old thermocouple that has been in use for several years, it may be more prone to failure. Consider replacing it if you notice any of the above signs.

How to replace a thermocouple?

Read on this step-by-step process and learn how to replace thermocouple yourself to ensure the safety and efficient operation of your equipment.

Step 1: Ensure Safety Precautions

Before replacing thermocouple, make sure the appliance is turned off and disconnected from the power source. Wear safety goggles and protective gloves to protect yourself from any potential hazards.

Step 2: Locate the Thermocouple

Identify the thermocouple's location within the appliance. In most cases, it is located near the burner, usually positioned next to the pilot light assembly. Refer to the appliance's user manual or consult a professional if you're unsure about its location.

Step 3: Remove the Old Thermocouple

Using a wrench or adjustable pliers, loosen the nut that connects the thermocouple to the gas valve. Carefully disconnect the thermocouple from the gas valve, making sure not to damage any surrounding components. If necessary, use a screwdriver to remove any screws holding the thermocouple in place.

Step 4: Install the Replacement Thermocouple

Take the new thermocouple and insert it into the same position as the old one. Ensure that the thermocouple is properly aligned and secured. If there were any screws, tighten them securely. Reconnect the other end of the thermocouple to the gas valve and tighten the nut using a wrench or adjustable pliers. Be cautious not to overtighten the nut.

Step 5: Test the New Thermocouple

Once the replacement thermocouple is installed, it is important to test its functionality. How to check the thermocouple? Turn on the gas supply and reignite the pilot light. Hold down the pilot button until the flame remains lit. Verify that the appliance remains operational and that the flame doesn't extinguish when you release the button. This indicates that the new thermocouple is functioning correctly.

Step 6: Reassemble and Clean

If you had to disassemble any components to access the thermocouple, reassemble them following the reverse order of removal. Take a moment to clean any dirt or debris from the appliance and ensure all connections are secure.

Cost of replacing thermocouple in commercial kitchen appliances

The cost to replace a thermocouple in commercial kitchen appliances can vary depending on several factors, such as the type of appliance, the brand, and the service provider. On average, the cost of a replacing thermocouple ranges from $10 to $50. However, additional charges may apply if you hire a professional technician to install it. Labor cost to replace a thermocouple can vary, but you can expect an average hourly rate of $50 to $100 for appliance repair services. It's recommended to contact local service providers for accurate pricing information tailored to your specific needs.

How to clean thermocouple?

Due to a buildup of soot and carbon on the thermocouple, a pilot light may not ignite. The problem can be resolved and the device's lifespan increased by cleaning the garland thermocouple parts. 

Here are the steps to clean thermocouple:

  • Find the pilot and thermocouple assembly. The thermocouple's tip often makes contact with the pilot light.
  • The thermocouple should be removed from the gas valve using an adjustable wrench if necessary.
  • The thermocouple must be separated from the pilot assembly. Some thermocouples can be removed by pulling them, while others need to have their screws removed using a screwdriver.
  • To remove the soot, gently clean thermocouple with the abrasive side of a sponge or scouring pad. 
  • Take additional care to prevent scratching the coating if you use steel wool.
  • The thermocouple assembly, gas valve, and thermocouple should all be reconnected.
  • Restart the appliance and check to see if the pilot continues to burn.

Top thermocouple manufacturers in the USA

When it comes to thermocouples, there are several top manufacturers in the USA known for producing high-quality and reliable products. Here are five well-established thermocouple manufacturers in the USA:

Top Thermocouple ManufacturersBenefits
Garland thermocouplesKnown for their accuracy, durability, and compatibility
Vulcan thermocouplesWell-named for their precision, reliability, and compatibility
Blodgett thermocouplesDesigned to withstand high temperatures, ensuring accurate temperature readings
Bakers Pride thermocouples Provides precise temperature control, ensuring consistent baking results.
Imperial thermocouplesWithstand in harsh operating conditions and provide accurate temperature measurements

Thermocouples are versatile temperature sensors widely used in various industries and applications. This comprehensive guide has explored the different types of thermocouples, their uses, and the proper installation techniques. From their ability to withstand extreme temperatures to their simplicity and accuracy, thermocouples provide valuable data for temperature monitoring and control systems.

FAQ’s

How long does a thermocouple last?

The lifespan of a thermocouple varies depending on usage, but typically lasts between one to five years.

What does thermocouple look like?

A thermocouple typically looks like a thin, metallic probe with a wire extending from it, often with a sensor at the tip for temperature measurement.

Are all thermocouples the same?

No, not all thermocouples are the same; they come in various types and configurations, each suited for specific temperature ranges and applications.

How to remove thermocouple?

To remove a thermocouple, first, turn off the gas supply, then carefully disconnect it from the gas valve and burner assembly, usually with a wrench.

How to identify thermocouple type?

You can identify the thermocouple type by checking its color-coded wires or markings on the probe itself, or refer to the manufacturer's documentation.

How much should a plumber charge to replace a thermocouple?

The cost for a plumber to replace a thermocouple can vary by location and complexity but is generally in the range of $100 to $200, including parts and labor.