[time-nuts] Thoughts on IR thermometers?

[Neon John]

On Tue, 27 May 2008 23:31:49 -0400, Patrick <optomatic at rogers.com> 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.

Since the response profile of those cheap lens-less thermometers is a broad
cone, the laser is at best a joke and at worst an outright fraud.

>
>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?

You might want to take a look at Wahl's (recently gobbled up by palmer
instruments) line of instruments.  They're a very old name in the business.
I've been using their stuff since the 70s.  They used to and probably still do
make a unit especially for inspecting PCB components.  It has a tiny focal
spot.

http://www.palmerwahl.com/heat-spy-hand-held-infrared-thermometers.php

I have an older DHS-24 series and a fairly new DHS-215 series private labeled
for Omega Engineering.  Example:

http://www.omega.com/ppt/pptsc.asp?ref=OS532E_OS533E_OS534E&Nav=temj04

The major feature of the Omega version is their patented circular laser
pattern that fairly sharply defines the sensitive area at any distance.  I've
tested my unit with a heated up power resistor.  The laser quite accurately
delineates the sensitive area.

Mine also has a Type T thermocouple input which is very handy because I can
apply the thermocouple to an object of similar emissivity to what I'm going to
inspect and then adjust the emissivity control to make the infrared part read
the same as the thermocouple.  That removes all guesswork with emissivity
coefficients.

Mine is the 50:1 cone size.  With that fairly sharp cone I can, for instance,
stand back at a reasonable distance and survey an air conditioner condenser to
figure out where the liquid line is.

IR thermometers that actually work aren't cheap but then few things are.  I'm
well pleased with the value I received in my unit.

John

--
John De Armond
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Tellico Plains, Occupied TN
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