Point and shoot IR thermometers


They are supposed to give instant temperature readings of the surface they are pointed at. But when I point it at the shiny copper pipe out of my water heater, it reads just a degree or two above the cold water input pipe (also shiny copper), even though the output pipe is so hot I can barely touch it.
What's happening?
Ray
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Are you using it within the specs? Different IR thermometers have different fields of vision. If you're trying to take a reading from too far away it might be picking up too much of the background. The curved surface and reflectiveness of the material might have something to do with it as well.
http://www.omega.com/prodinfo/infraredthermometer.html
R
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RicodJour wrote:

Even before my original post, I had been holding the thermometer within one-half inch of the pipe, just to eliminate background readings from being averaged in.
Here's how the plumbing is: the output of the heater is a threaded nipple (can't tell if it's copper or steel). Screwed into the nipple is a 2" long copper coupling. The output of the coupling is soldered to the copper pipe that supplies the house. (Same arrangement on the supply side.)
At the nipple, I'll measure about 98F. At the middle of the coupling, about 78F. Just above the coupling, about 73F. Still seems far to low, considering how it feels to my hand.
At the laundry sink nearest the heater (about six feet), water measures 50F out the cold faucet, and 110F out of the hot faucet. Ambient is about 69F.
I figured out why I there was such a small difference between the hot and cold pipes: No hot water was being drawn. So the water in the supply pipe was being heated, by conduction, from the water in the tank. When I felt the supply pipe at least three feet ahead of the heater, it definitely felt much colder. But the IR thermometer still read about 68F, a much smaller difference that I would expect based on the touch test.
I dare not "rough up" the pipe, because I worked too hard to polish it. But I darkened a section with a black Magic Marker; that section read about 3 degrees higher than 1/4 inch away directly off copper.
Ray
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Ray K wrote: ...

You really need to know what the focus angle is to have any clue at all as well as what the instrument is designed for regarding surface emissivities. Some of the less expensive are pretty basic and quite flawed for anything but large flat surfaces (again, based on our evaluation of competitors' products when designing one as noted previously).
Also, as I presume this is 1/2 or 3/4" pipe you may well be seeing geometry effects from the curvature as well; there's almost certainly no firmware compensation for that effect.
As somebody else noted, if knew which particular instrument, just _might_ have significantly more specific information on how it works internally. ( :) )
--
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It's an Extech IR250. Got it at Sears just before Christmas for $20.
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Ray K wrote:

Below our target market so no direct help, sorry.
Did look at the users' guide for the device however...
Note particularly the following note 3 --

Also note this isn't claimed to be a very accurate device and it does use a fixed emissivity as I suspected. That makes a big difference.
I'd also suspect you're having a difficult time in ensuring that the spot of sensitivity is actually only on the pipe and that the curvature is an issue as well since as you move the device closer to the pipe probably you're occluding your view of the laser and the parallax problem of where it's aiming as opposed to the "sweet spot" gets larger as you get nearer to a small object.
The actual accuracy claimed is only the larger of 3% or reading or 5F for room temperature ambient anyway in the calibration--that's not very good and when taken to random object it's almost nothing.
To make one that worked well under a wide range of conditions was a real trick when we were designing one; it wasn't at all hard to find ways to fool almost all we bought/tested as benchmarks nor was it easy to eliminate such problems from our product. In some areas we did quite a bit better, others were hard enough that "not so much"...
My overall conclusion would be likely it's just as good as the particular instrument will/can do; you're expecting to much of an inexpensive tool for the conditions.
--
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dpb wrote:

of emissivity, does this mean that the accuracy figures in the specifications apply only to surfaces with 0.95 emissivity?

My intended uses are very simple and do not require accuracy:
1. To locate insulation gaps in the envelope of my house (by scanning the walls and ceiling and areas around the electrical outlets)and looking for temperature changes.
2. To locate leaks in the hvac ducts in the attic. The ducts are above the insulation in the attic's floor and are made of insulated fiberboard (shiny, silvery exterior, fiberglass insulation on the inside). I'm particularly concerned with losses at the junctions.
So this inexpensive thermometer seems suited for these uses.
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Ray K wrote:

Only the manufacturer knows for sure; there's insufficient detail to know what their calibration/specification are in reference to but that would be the logical surmise, yes. They claim a reference back to NIST; however all that necessarily would imply would be a fixed target and that it passed under those specific conditions. One would presume that target would have an emissivity of 0.95.
...

For those applications where only a differential is needed absolute accuracy isn't particularly important, true.
For the exterior house it'll probably work fine; for the location of air leaks in the attic it may not be so good as you may not have a good target. The basis for the differential being of value is that the surface is consistent; if that isn't so you may not be so able to find the hot spots particularly if it is simply an air path.
--
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dpb wrote:

When it warms up a few degrees here in central New Jersey, I'll venture into the distant bowels of the attic. Near its entrance (via pull-down ceiling stairs), the duct temperatures were about what I'd expect (mid 50 degrees). Right at the pickoff points to the individual rooms, at the fittings with the damper doors, temperatures were about 95F around the circumference (attic ambient, 38F). But the square inches of all these pickoffs are trivial - probably less than 1 percent - compared to the overall surface areas of all supply and return ducts. There may be much greater losses at questionable joints further into the attic.
Thanks, again, to all who responded.
Ray
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How did you measure the 110F at the laundry???
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With a quick-reading, dial-type meat thermometer held under running water. Same way with the cold water reading.
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RTFM, especially the part where it talks about shiny metal.
--
Christopher A. Young
Learn more about Jesus
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What make of thermometer is it
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ransley wrote:

Extech IR250.
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It may be the unit, a Ray Tech works well. Cheaper units are not accurate 3-5 degree + or - is common so you cant even test a room accurately. Better units will have 1 degree + - accuracy and measure metal, its the only safe and quick way to do it.
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Spray the pipe/tubing with some flat black paint and get reading as close as you can to the surface!
wrote:

What make of thermometer is it
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Ray K wrote:

I have a copper/stainless pan like that. Some surfaces don't emit waves very well. Your readings could be affected by cooler waves from another surface being reflected off the metal.
I think I'd wrap it in a thin layer of tape and let the tape generate the waves.
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Ray K wrote the following:

I just bought a Ryobi IR/Sonic Measurer. I noticed the same problem with pipes. Like others have said, it may be that it can't read accurately on small round items due to reflection or some such. The IR gets scrambled, much like radar on a stealth plane. I also noticed that the Sonic Measurer doesn't work when aiming through a narrow opening, or when there is a closer item to the path of the sonic signal.
--

Bill
In Hamptonburgh, NY
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Ray K wrote:

2 cheap IR thermomemeters are useless on surfaces with emissivity other than 0.95. 3 most shiny metal is not anywhere near 0.95 4 rtfm has already been suggested.
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Thanks, everyone, for your replies. They have been very informative.
I put a piece of black electrician's tape around the hot water pipe closest to the heater's outlet; the temperature reading on the tape now jumped to what I would expect, about 110F. I ignored the red laser pointer and just held the reading portion of the meter about 1/4" from the tape. On the shiny copper just above the tape, the reading was about 25F lower.
Someone asked how I measured the cold and how water temperatures. I used a dial-type, quick-reading meat thermometer under running water from the laundry faucet. I found, however, that if I point the IR thermometer where the water hits the laundry tub, the two readings matched.
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