[time-nuts] Thoughts on IR thermometers?
didier at cox.net
Wed May 28 00:01:00 EDT 2008
I found a cheap IR sensor (not a spot meter) useful to identify the one IC
that's warmer than the others in a fully populated PWB. That has been useful
to isolate the one bad part, but a contact thermometer would have been
almost as useful. While the IR sensor reading depends on emissivity, the
contact thermometer depends on ... contact. Not easily reproduced. The IR
sensor may be off, but readings on a given part are more reproducible, in my
Another useful application for an IR sensor is to spot the area in the
ceiling where you need more insulation. I found out that way that squirrels
had a party in my attic and moved the insulation on one side of the house...
I also used it to verify that the reflective film applied against the window
reduced the temperature of the sun shades by a couple of degrees F in the
summer. That would have been much harder to do with a contact thermometer
(sun shades are thin plastic, with little thermal mass and even less
So, in my experience, an IR sensor is useful around the house, more so than
around the shack.
I agree that absolute temperature measurements are in most cases out of the
question because of the unknown emissivity and the broad pattern, but for
relative measurements, they have their use.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Brooke Clarke
> Sent: Tuesday, May 27, 2008 10:46 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Thoughts on IR thermometers?
> 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
> http://www.prc68.com/Alpha.shtml All my web pages listed
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> http://www.prc68.com/I/WebCam2.shtml 24/7
> Sky-Weather-Astronomy Web Cam
> 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
> > Thanks in advance-Patrick
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