Taking Temperatures at a Distance with Infrared Thermometers

Handheld digital thermometers can determine surface heat without touching what's being measured. While you won't need this style thermometer to check how cold it is outside or take your child's temperature, they're extremely useful if you need to know the surface temperature of something that is in motion, too hot to touch, or too far away to get a temperature reading using other means.

Increasing Safety Measures
For many industrial operations, elevated temperatures are one of the first signs that something is wrong, including lubrication failure and excessive bearing wear. Infrared thermometers are an essential safety tool that can help identify potential problems early on without risking the safety of crew members. These thermometers reduce the potential of burn or injury when working with unfamiliar equipment. They're also vital to safe protocol in the event of a fire or other emergency — employees can use them to check the surface temperatures of doors and walls to safely exit the job site.

How They Work
These devices measure the infrared radiation (IR) given off by any object compared to the ambient temperature that surrounds the object. Let's use the example of an incandescent light bulb, which gives off heat when it's turned on. The amount of heat the bulb gives off can be determined in many ways. The IR thermometer calculates the difference in temperature between the bulb and its surroundings and converts this to a digital temperature value on a screen located on the back side of the tool.

Typical readouts happen in less than a second, and accuracy claims for the less expensive models are about plus or minus 3 degrees Fahrenheit on a measurement range between 0 and 600 degrees Fahrenheit. To use the tool, point it toward the surface you want to evaluate, center the red dot it emits on that area, then check the digital readout for the temperature result.

Understanding Distance-to-Spot Ratios
These tools are also rated in terms of their distance-to-spot relationship, known as the D/S ratio. When evaluating an object, the distance at which the tool can be used varies depending on the size of the area being measured.

For example, if you need to check the temperature of a spot with an approximate diameter of 2 inches and your thermometer has a D/S rating of 8:1, then accurate readings are possible up to 16 inches away. If your spot is 4 inches in diameter and you have a thermometer with a D/S rating of 12:1, an accurate reading can be taken up to 48 inches away. Because the distance goes up in a direct proportion to the spot size, the farther away you make the evaluation, the larger the spot being read must be. If you need to check a smaller spot from a greater distance away, you'll need a higher D/S rating, such as 12:1 or higher.

Additional Considerations
There are some limitations to these devices. They measure surface temperatures, so they can't deliver readings through material, even transparent ones such as glass, water, and acrylic plastics. They can also be thrown off by airborne pollutants such as smoke, dust, and moisture.

Fortunately, these tools are relatively affordable. Many models are available for $50 or less, but there are also units that cost nearly $200. As the number of features, accuracy, and D/S ratios increase, the price does, too. Think carefully about what you need the tool to do. Professional users will normally need very specific capabilities to match the requirements of their work. For this reason, careful comparison-shopping is required.

A Welcome Addition to a Well-Rounded Toolbox
Safety, reliability and convenience are important factors on any job site. By adding this important tool to your arsenal, you’ll be able to offer improved safety measures and ensure your next project runs smoothly.


Steve Willson began his career as an owner-operator of a carpentry contracting business. He joined Popular Mechanics magazine as their home improvement editor, a position he held for 22 years. He has written three books about home improvement and using tools. To see a wide selection of tools, including infrared thermometers like the ones Steve describes, please visit The Home Depot website.
This article is editorial content that has been contributed to our site at our request and is published for the benefit of our readers. We have not been compensated for its placement.

Posted on Dec 11, 2017


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