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Old 06-21-2014, 09:01 PM   #1
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Handheld "laser" temperature measurement guns

Maybe this has been dicussed before, maybe not. At my former job, we had to have special training to clear up a misconception with those handheld temperature measurement devices with a laser. Our employees were assuming that where the red dot of the laser landed was the exact point where the temperature was measured and the laser somehow did the measuring. Since they could easily hold the laser spot on a small target from several feet away they thought their readings were accurate. Not true at all. The red dot is the approximate center of a circular area where all of the differrent temperatures within that area are averaged together to provide a single output temperature reading. The laser is only a pointing device to assist the user. The diameter of that circle is dependant on the distance from the "gun" to the surface and the quality of the instrument. The cheaper guns have a lower "D:S (distance to measurement spot size) ratio such as 8:1. Quality gear such as a FLUKE is 30:1 or 50:1. 30:1 means at 30 inches distance, the measurment circle diameter is 1 inch. So if you have a hot exhaust outlet next to a cooling water hose within that circle, the result is neither the exhaust temp nor the hose temp. its the AVERAGE of everything in that circle. Moving closer to the target makes the circle smaller.
What this means for you is to get an accurate temperature reading every time, you should hold the gun as close to the target point as safely possible.
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Old 06-21-2014, 09:23 PM   #2
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...and the user have a basic understanding of emissivity as well.
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Old 06-21-2014, 09:42 PM   #3
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Quote:
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...and the user have a basic understanding of emissivity as well.
True. And the owners manuals of quality instruments cover this.
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Old 06-22-2014, 12:40 AM   #4
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They make great cat toys!
Damn you smart guys! You made me look up "emissivity".
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Old 06-22-2014, 06:18 AM   #5
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They make great cat toys!
Damn you smart guys! You made me look up "emissivity".
+1
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Old 06-24-2014, 07:42 PM   #6
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Also calibrate it - one of mine (Raytek I think) is +4 compared to my Fluke thermocouples
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Old 06-24-2014, 09:08 PM   #7
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They make great cat toys!
Damn you smart guys! You made me look up "emissivity".
I don't have those anymore.
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Old 06-24-2014, 09:14 PM   #8
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Think of a regular flashlight, tungsten bulb type, and how far the beam would spread at any given distance. And IR spreads even wider than white light.

A good way to judge is to simply measure a particular spot (like the top, middle of the old filter) at different distances and understand at Archie said, that it's the closest one that's correct.
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Old 06-24-2014, 11:21 PM   #9
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Richard bring your IR temp thingy and you can play with Po Kitty anytime you want.
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