[time-nuts] thoughts on IR thermometers??

Arnold Tibus Arnold.Tibus at gmx.de
Wed May 28 09:15:39 EDT 2008

Hello Patrick,
you got already a lot of good comments.
I am using since years a IR temp measurement tool from Snap-on,
mod. RTEMP2PB, with a resolution of 0.1 deg. showing in deg. C
and F. The distance to spot size is 8:1,  a more narrow range would 
be sometimes preferable but for most cases it is ok. 
I do not want to miss this device anymore.
Of course, that device never measures the core temperature of 
a body/ mass but just the radiation via its surface and they are not 
not very good on the absolute values (precision). 

At room temp the measurement value is conform within a few tenth 
to the real values, but the device seem to not have a tempcoeff. 
compensation. Outside in winter or at higher temperatures in summer 
the reading starts to wander up to around 1 or 2 deg. C away.

I got with this device a sheet with a list of radiation coefficients for 
the most practical masses like concrete, dry wood, metals etc. 
but I do not apply it normally.

I use this radiation thermometer for fast and quick look on
black radiators of oscillators and other devices quite successful 
and can easily watch even fast changes. 
E.g my PRS10 with the standard radiator (a bit too small) does show 
around 45 deg. C at 22 deg. C room temperature. 
I am thinking to bring it down by a bigger cooler size and somewhen 
finally stabilizing the coretemp by a regulated peltier element.

It is also wise watching power supplies and other big consumers ;-) 
and looking for thermal leaks on cold winter days. E.g. I measured the 
temperature gradient on my (32mm triple glass) windows and found some 
weak points in the design of the already very thick frames.The 
fixation of the glass may still to be improved.

When measuring I do always look to find the center point of radiation 
by scanning and observing the max.(or min.) reading. The precise amount 
is not that important I believe, but one can easily find the hot
elements and define the value reproducible. 
I do countercheck always with the reading from a concrete inner wall 
which is very stable due to a very good insulated house :-) 

Unfortunately there is no interface to transfer the readings, but 
there is a hold for the actual reading and the max. value during 
the on time.

Do you know how one can know without looking if the sky is clear or 
Day or night, a bright sky does show temperatures below -33 deg.C
(readout limit) and clouds do reflect the earth (re)radiation and 
show then -3deg C to +3 deg C, depending the density of the clouds. 

I never found a practical circuit or schematic for such a meter. 
It would perhaps be interesting to build such a meter personally. 

Arnold Tibus

On Mon, 26 May 2008 20:21:02 -0400, Patrick wrote:

>Hey Everybody

>I tried to use a cheap IR thermometer to do some quick, pre-circuit 
>analysis tests, a couple of years ago on a particular job.

>It went bad, the laser did not even line up with the area being 
>measured, I missed a burning hot capacitor and wasted a lot of time.

>I was thinking about buying a better one this time. Does anyone have any 
>suggestions? Do you think they are useless for PCB tests? Caps should 
>not be hot and power resistors and transistors should not be cold right? 
>but the spot size to laser ratio on most of these are not good, are they 
>still useful?

>I had a hell of a time trying to read my Son's temperature last night 
>when he had a fever, anyone tried one of these out on their children?

>Thanks in advance-Patrick

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