[time-nuts] Thoughts on IR thermometers?

Brooke Clarke brooke at pacific.net
Tue May 27 23:45:55 EDT 2008

Hi Patrick:

Many decades ago I used a Barnes Engineering spot IR sensor.  It's cost tens of 
thousands of dollars and had a microscope for alignment.  The problem then and 
now is that you need to know the IR emissivity of the thing you're looking at 
in order to get temperatures.  If you try to read a mirror and are seeing a 
clear blue sky reflection in the mirror, even though the mirror is at room 
temperature you will read some large negative temperature like - 60 deg C.

A way around that is to coat everything with a black paint that's also black 
for IR, but that's messy.

A simpler way is to get a temperature probe for your DMM and just touch parts.

For a crude look use a digital camera that has the IR blocking filter removed 
and you can see near IR.  For example a car driving away viewed in near IR 
shows red for LED lights and bright white for filament lights.

Another problem with low cost IR temperature sensors is that the beam angle is 
around 90 degrees.

Have Fun,

Brooke Clarke
http://www.prc68.com/P/Prod.html  Products I make and sell
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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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