How to Measure a Thermocouple with a Multimeter

This site contains affiliate links to products. We may receive a commission for purchases made through these links.

Have you ever thought about how important thermocouples are? Thermocouples are essential devices with different applications in regulating and tracking temperatures and chemical conditions in areas such as steelmaking. Nonetheless, their use in applications that need more accurate and complicated temperature monitoring and corrections, like where a variance of 0.1 degrees is required, is much limited. 

Introducing The Durable and Practical Thermocouple

A thermocouple is a basic but highly efficient temperature sensor that utilizes the joining of wires made from two different alloys or metals to create a voltage measure. Hence, it recognizes the heat range that is present in a specific region.

It’s particularly helpful for gauging temperature in applications where other modes of heat measurement might be complex. A wide array of industries utilize thermocouples as part of their regular operations. Here’s a quick peek at how it works and its different uses.

How Does a Thermocouple Functions? 

You will find two different metal wires attached at one by the thermocouple while the other ends (outputs) are connected to the measured object. The principle driving that sensor is referred to as the Seebeck effect, where two metals attached will create electric voltage.

In short, the higher the heat temperature entering into the output, the higher the produced voltage would be. A technician, engineer, or scientist uses the voltage measure to gauge whether the ambient temperature they’re using remains in acceptable parameters for that specific application.

Various types of metals attached by a thermocouple will create different voltage levels. Hence, the material types and thermocouples required vary on the temperature range within the area being tested or measured.

Such various types of thermocouples are normally created with their corresponding letters and suitable for only particular temperature ranges. 

Where Can You Use Thermocouples?

Any substantial alteration in voltage is a sign that the heat parameters in the tested environment are not met. That serves as a warning indication to electricians or technicians in many various industries such as HVAC, food, pharmaceuticals, industrials, and more.

  • Gas Appliances – A thermocouple alerts the gas valve that the pilot is lit so it will stay open. The thermocouple is located in the center of the pilot flame. It senses the flame’s heat and produces the voltage keeping the gas flowing. When the flame goes out, the thermocouple voltage vanishes and closes the gas valve. 
  • High Pressure Broiler – The perfect instrumentation for high pressure uses is very challenging due to heavy vibrations and high temperatures. Thermocouples and RTDs have typically utilized temperature sensors for high pressure industrial uses. Thermocouples have been seen to be the better option. 
  • Food – Thermocouples are ideal for the food industry as they present exact readings in just a few seconds. Food products could be checked in any production phase. These thermocouples are a 2-piece unit with a handheld readout unit and a removable probe. Two wires are attached at the top of the probe. 
  • Molten metal – A molten metal thermocouple could be utilized in a non-ferrous metal setting to measure temperatures at least 1250 degrees Celsius. They regulate and track the temperature of liquid metals during the melt preparation stage, holding, degassing, and casting operations. 
  • Furnace – A pilot light is in charge of starting the furnace burner. The thermocouple closes the gas supply if it does not detect a flame and stops the furnace from getting gas every time the pilot is out. On top of that, it stops gas from accumulating in the furnace and makes the system a lot safer. 

Depending on the application, thermocouples have huge differences in both material construction and appearance. As such, you will find unique devices for applications in various sectors like pharmaceuticals, food, and plastics.

For instance, thermocouples utilized in the plastic industry come with magnesium oxide, not to mention they have a bayonet cap for simple installation. Further, thermocouples utilized in pharmaceutical industries have an annealed metallic sheath for simple bending. 

The efficiency of such components is reliant on alloy combinations it’s made from. The perfect device for a specific application will vary on the needed sensitivity and temperature range conceivable in that specific application. 

However, many applications fit in with either of the three common models: type J, type K, and type T thermocouples. 

Keep in mind that thermocouple utilizes old technology and is quite a basic device. However, it can accurately measure to within one degree of accuracy and is undoubtedly a vital device for today’s modern industries. 

How Should You Test a Thermocouple?

There’s no doubt that thermocouples are durable and dependable, but don’t forget that they can also fail and should be checked. You can test your thermocouple using a digital multimeter. Follow the steps below to learn the process you need to do. 

In this example, let’s use a fireplace thermocouple. 

  1. The best way to determine a bad and malfunctioning thermocouple is to test it with a digital multimeter with alligator clips on the leads. Set your multimeter to read DC millivolts and attach one lead to the thermocouple probe and the other to the tube. 
  1. Turn on the pilot and let it burn for thirty seconds, and keep in mind the reading. Anything that is less than 25 millivolts suggests a bad thermocouple.
  1. The process for testing a thermopile is very much the same, except you connect the leads to the wire connections on the gas valve. The reading on the meter must be approximately 350 millivolts after the pilot flame has been burning for two minutes. Anything that is less indicates the thermopile is bad. 

Final Thoughts

To sum up, a thermocouple is a very practical transducer converting thermal energy into electrical energy and is created by attaching dissimilar semiconductors or metals to create a junction. The principle of the thermocouple is also based on the Seebeck Effect, saying that when dissimilar metals are connected at a point, they will produce a tiny measurable voltage when the point of the connection’s temperature changes.

About The Author