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What is a Visual IR Thermometer?

March 2013

By Chuck Newcombe

Dog now in focus

Dog -FAR setting

I touch base with the Fluke thermography group from time to time to see what new tricks they have up their sleeves. This last month, I discovered something called a Visual IR Thermometer. They loaned me one so I could check it out.

At first glance, you could easily mistake the Fluke VT02 for a conventional IR (infrared) thermometer, such as the Fluke 62 MAX. But, when I turned it on, I discovered the difference. Instead of the digital-only display of temperature values, this unit displays a low-resolution thermal image combined with a visual image - similar to the more expensive thermal imagers.

I pointed the VT02 at a warm object in my living room. It happened to be my dog, happily gnawing away on her favorite bone toy. There appeared to be something wrong - the hot spot displayed (75.4) was in a cloud above the dog. A closer look at the keypad of the VT02 gave me a clue.

It turns out Fluke has provided a NEAR-FAR focus setting, and since the dog was not within 9 inches of the VT02, I was seeing the effect of parallax - the two cameras were not centered on the same spot.

Dog across room

Dog -NEAR setting

Selecting the FAR setting fixed the problem. By the way, the thermometer isn’t reading a wrong value at about 75 degrees. While the dog’s normal temperature is about 100°F, my Airedale's curly hair acts as a pretty good insulator. Remember, we’re reading the radiation from the surface we’re looking at - her hair.

In any case, now that I had some familiarity with this new tool, it was time to explore its features (and those of the companion Fluke SmartView® software) in more detail.

Classic Fluke non-contact thermometry

Fluke has produced non-contact infra

Fluke has produced non-contact infrared thermometers for many years. Non-contact thermometers measure infrared radiation from an area in front of the device that varies with distance. The meter then interprets the result as surface temperature.

Visualize a cone ending in a circle, the diameter of which varies as the distance between the thermometer and the surface. A 10:1 Optical Resolution specification for an IR thermometer describes a one-foot circle at a distance of ten feet. The temperature reported is the average of the temperatures within the circle. While laser spots help locate the center of the area being evaluated, it takes some practice to figure out just how big an area is being averaged, and it might not be immediately apparent which part of the measured scene is the hottest. Moving closer helps, but sometimes it’s just not possible to do so safely.

Thermal imagery and Fluke IR-Fusion® Technology

Dog across room

Infrared image of power supply board

Fluke introduced thermal imaging products several years ago. These products are high-resolution IR cameras that show display temperature variation across the displayed field. With one of these you can quickly identify hot spots. They become even more helpful with Fluke’s recently introduced innovative feature called IR-Fusion®. Using a conventional camera in addition to the IR unit, you can blend a visual image with the less distinct thermal image, allowing quick and easy identification of a hot bearing, electrical circuit breaker, or leaking exhaust manifold gasket.

A visual IR thermometer adds IR-Fusion visual image technology to the relatively inexpensive lower resolution IR sensor array in the thermometer.

A real-life example

As it happens, I’ve been working recently to ensure that emergency exit lighting units in a museum will function correctly when the facility loses power. And while I had the Fluke VT02 a regional power failure helped me with my task.

Dog across room

Visual image of power supply board

When the building went dark, most of the emergency and exit lights worked as they should. The problem was that several of them dimmed and went out just a minute or two later. I suspected that we needed to replace the batteries.

One EXIT light was not operating properly before the power failure, so after replacing the fixture, I decided to see if I could determine the nature of the failure. After removing the covers, I applied power to the fixture and focused my attention on the power supply board. I used the NEAR setting for the Fluke VT02, since I was within a few inches of the board.

As you can see in the infrared image of the power supply board, the red area highlighted in the center of the image was at a temperature of about 82 degrees, but the real hotspot was in the bottom of the image. A look at the saved image on my computer, using Fluke SmartView software, provided more detail.

Further investigation revealed that the battery in this unit had a shorted cell, which led to higher current in the power supply and a voltage too low to operate the lighting circuits. Replacing the battery solved the problem.

With the introduction of the Fluke VT02, I think Fluke has added one more easy-to-use tool to its already impressive collection.