infrared thermometers

[oly]

I have been using a raytek infrared thermometer for the last 4 years, but I have lost faith in the readings. I have crossed checked it and seems to be off by about 5-10 degrees. I have been looking for a new infrared, I like the fluke but having a hard time choking down a couple bills. Any suggestions on what to buy and feel satisfied with the results?

[NedFlanders]

I don't use the infa-red's for very much , except quick reference.

Like pointing up to supply/return air grates on ceilings.

Quick temp readings on compressers.

Fuses/breakers ect.

They seem to do better reading warmer temps then cold temps.
I have both a Raytek and a 3M IR therms.
Again I don't lean on them too much , my opinion they're only good for getting quick info.

[rocket]

supply/return air OK

copper tends to reflect causing incorrect readings
wet copper & dry copper have different readings

for quick ball bark checks OK
for superheat NO NO

[smilies]

Originally posted by NedFlanders
Like pointing up to supply/return air grates on ceilings.

Quick temp readings on compressers.

Fuses/breakers ect.

All I use them for. Health dept. here is using the Raytek guns and always have concerns on cases. I have showed them what their guns say versus my Fluke laser, Fluke thermometers, Fieldpiece thermometer, and my Wavetek.

Guess what. The lasers are high. They don't care though.

[oly]

This is what I am talking about. Health Dept., manufact., owner, salesperson, and so on down the line. Trusting the equipment or satisfying ones own JOB.

[frozenhead]

i use it for a yes or no answer. condensing unit running or not running? other than that it just bull****ting.

[sonc]

good for radiant tubes

[midhvac]

I've got a $350 sh & subcooling test setup, so no I ain't using the IR unit to do that with, but having said that, I must say a little in defense of the IR units. I've been studying the technology and it does have some applications which it excels at. Taking the temp of a moving object, or the temp of an object far away from you or taking quick readings of multiple areas are some applications, to name a few.

If you understand how the technology works and have a good quality IR unit, your readings will be much more accurate.

The cheap IR units have only a 6-1 or 8-1 distance to spot ratio. The high quality units have 30-1 and 50-1 ratios. The object you're checking the temp of must be larger than the spot or you're measuring the temp of things outside of the spot area. So if you're using a 6-1 d-s ratio IR gun and you're taking the temp of something 6" away, the spot size is 1" which may be larger than the object you're trying to take the temp of, so you're seeing the temp of the object and what's around it. Conversely, if you have a 50-1 d-s unit, at 6" the spot size is going to be 1/8".

The other often misunderstood part of IR technology is how the emissivity of the object affects the temp reading. The cheaper IR units have a fixed .95 emissivity sensor, while the more expensive units have an adjustable emissivity sensor. A piece of shiny metal may have an emissivity of .2 to .5, whereas as painted object will be .95, so if you have the cheap unit you'll have to interpolate the temp readings with the emissivity of the object, for example, if you're shooting an object with a .50 emissivity with a gun with a fixed .95 emissivity setting, you'll have to do the math to convert the .50 emissivity reading to .95. But with the adjustable emissivity units you can set the emissivity of the IR gun to that of the object and get a direct temp reading.

Also, the better units have better +/- degrees of accuracy.


[Edited by midhvac on 08-07-2004 at 10:27 PM]

[oly]

Thank you Midhvac, that was answer I was looking for. The following info. helps me on making a new purchase of a infared thermometer.