Temp probe for troubleshooting

[Russ]

I read somewhere that when a IC develops a short it will start to heat up.
So I was thinking that maybe one of the new laser type of Temp probes might
help in troubleshooting. Are they sensitive enough? Can they isolate a
small 1 inch square area without picking up things close by? I talked to
one company and they said a large 12:1 or higher ration between the distance
and spot being measured is what to look for. Any particular model or ideas
a long this line?

Thanks

 

[Sam Goldwasser]

I read somewhere that when a IC develops a short it will start to heat up.
So I was thinking that maybe one of the new laser type of Temp probes might
help in troubleshooting. Are they sensitive enough? Can they isolate a
small 1 inch square area without picking up things close by? I talked to
one company and they said a large 12:1 or higher ration between the distance
and spot being measured is what to look for. Any particular model or ideas
a long this line?

This doesn't seem to be particulalry useful unless you have a reverence
thermal map of a working unit. Some parts run hotter than others under
normal conditions. And, what is going on in the electronics will also
affect the heat generated.

Any significant overheating will be obvious to a reasonably well calibrated
finger.

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[mike]

This doesn't seem to be particulalry useful unless you have a reverence
thermal map of a working unit. Some parts run hotter than others under
normal conditions. And, what is going on in the electronics will also
affect the heat generated.

Any significant overheating will be obvious to a reasonably well calibrated
finger.

Might wanna be careful about sticking that well calibrated finger into
an off-line switching power supply...or Horizontal Output Transistor.
I'll use my IR probe, thank you.

You might find other uses for an IR probe. I use mine to find heat
leaks in the house, in cooking, auto repair etc. Handy little gadgets.
mike

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Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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[Russ]

Mike,

Do you think any model will work or should I buy one of the expensive ones?
They have them from around $40.00 and up. It would be cool when working on
a pinball if I could point my thermal laser probe at all of the transistors
and find the one that isn't working.

Thanks
Russ

 

[Seafarer]

I read somewhere that when a IC develops a short it will start to heat up.
So I was thinking that maybe one of the new laser type of Temp probes might
help in troubleshooting. Are they sensitive enough? Can they isolate a
small 1 inch square area without picking up things close by? I talked to
one company and they said a large 12:1 or higher ration between the distance
and spot being measured is what to look for. Any particular model or ideas
a long this line?

Thanks

I use the finger test and have for thirty years,if you want to be more
precise you can buy small square temp strips that you stick on top of
the IC.Readout is the same as a medical digi.thermometer.Got some five
years ago as they are cheap,but never used them.Use your finger tip
away from the hot chassis.To hot to touch,it's bad!

 

[sofie]

If the IC gets too hot it may be a problem or fault with the associated
circuitry..... the IC is not the only suspect here when it gets too hot.

 

[mike]

Mike,

Do you think any model will work or should I buy one of the expensive ones?
They have them from around $40.00 and up. It would be cool when working on
a pinball if I could point my thermal laser probe at all of the transistors
and find the one that isn't working.

Thanks
Russ

There are a bunch of issues.
The spot/distance ratio is critical. At the distance of measurement,
the spot size has to be small enough to measure just the thing you want.
But as it gets smaller, you have trouble aiming it. Even with a laser,
there's an offset that causes parallex error. The sense spot can't be
in the same place as the laser spot at all distances.

Emissivity relates to how well a particular material and surface
treatment radiates relative to a black body. Most cheapo units are
fixed at .95. More expensive ones have a calibration adjustment, but
that won't help if you don't know what to set it at.
Point it at a shiny aluminum heat sink and your reading won't be
anywhere near accurate. It's a relative measurement for similar
materials only.

In most cases, you have no idea what 'normal' temperature is.
You can't tell if the problem is the device, a loose mounting bolt,
something else causing the overheat.

"back in the day" story alert....

Once tried to measure the temperature of a circuit board with an early
IR video scanner. Result was dismal because of the widly varying
emissivities.
Sprayed the whole board with spray-on foot powder.
Worked great cause it normalized emissivity.
Problem was that I couldn't wash the stuff of when I was done.
Ended up scrapping the board...very expensive temperature test.

Bottom line,
I use mine more to check the temperature of my coffee when I nuke it
prior to pouring it into the thermos. Fun toy, but relatively little
used in electronic diagnostics.
mike




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[Russ]

Mike,

Thanks for the feedback. Another idea of mine that doesn't seem to be
working out. I did order the Fluke temp probe, but not the IR one. I
almost ordered the IR one but after reading your post I am glad I didn't. I
guess I will just use the probe for coffee and tea also.

Thanks
Russ

 

[Russ]

A few times the finger thing worked real well for me. One was a pinball
transistor It was so hot it burned my finger. I guess I was wondering if
something more sensitive would be helpfull.
Thanks for input
Russ

 

[Russ]

Good point. Thank you.

 

[RonKZ650]

If you get one, get a good one. Most IR guns with 12/1 ratio will not
work. It depends on the focal point size. Generally 12/1 guns have a
focal point of about 3" meaning you are measuring the average
temperature over a 3" area, plus many the laser beam is offset somewhat
from the actual point you are measuring. Raytek makes some nice guns.
Two that work real nice are the ST80 with 50/1, and the ST25 Autopro. I
use the ST80 sometimes when I suspect something heating on a board but
can't quite pinpoint it. Works nice and easy.

 

[Asimov]

"Russ" bravely wrote to "All" (22 Apr 05 06:56:36)
--- on the heady topic of "Re: Temp probe for troubleshooting"

Ru> From: "Russ" <[email protected]>
Ru> Xref: aeinews sci.electronics.repair:46218

Ru> A few times the finger thing worked real well for me. One was a
Ru> pinball transistor It was so hot it burned my finger. I guess I was
Ru> wondering if something more sensitive would be helpfull.

A wax crayon... Wax melts just under the boiling point of water around
180-200'F. IIRC there are even special wax mixtures calibrated for
specific temperatures. These are used to calibrate furnaces, ovens,
etc.

Many ceramic capacitors are highly sensitive to radiant heat and their
capacitance value will drift according to temperature. When used in a
bridge or a counter even the heat from a hand can be readily detected.

IR diodes are also sensitive to radiant heat but have to be compared
to a known temperature.

A*s*i*m*o*v

.... 'Keep the smoke inside.' -- 1st Rule of Electronics.