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Accurately measuring temperature of various components in an SMPS?

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Flyback

Well-Known Member
Hello,

Please can you evaluate this method of ensuring that the reading of infra red temperature monitors is correct? (it relates to accurately reading the temperature of components in an smps).

Infrared thermometer:
http://www.maplin.co.uk/handheld-non-contact-thermometer-590711

When testing an SMPS, it is essential to do thermal tests on the various components, eg the diode, the FET, the transformer (or inductor) ferrite, the current sense resistors, etc etc.

The fastest way to test for temperature of any of these components is to use an infra-red temperature monitor, because it simply involves pointing the infra-red monitor at the component surface and reading off the temperature.

However the problem with all of these devices is that the temperature reading is affected by the type and color of the component’s surface material. (eg shiny metal heatsink surfaces may often read lower temprature than they actually are)
We cannot know whether the particular infra red monitor is calibrated to accurately read the temperature of the particular material that its being pointed at.

Therefore, we must make up a “calibration SMPS”. This comprises an SMPS with thermocouples glued to each of its components.
It should be ensured that this “calibration smps” comprises both shiny as well as anodised heat sinks etc etc. One simply then points the infra red monitor at the various components of this “calibration SMPS” and checks to see if the reading of the infra red monitor corresponds to the readings on the thermocouple reader for each type of component.

Then one can confidently use this infra red monitor on the SMPS under test.

Why do no companies do this?
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

I dont know if they do or not, but some IR temperature guns include a calibration setting for surfaces of different emissivity. So you can change the setting depending on what surface you are looking at.
It might also work to paint part of the surface black with some high temperature paint and take readings on that black spot.

I have used one for measuring power resistors and i get reasonable readings although i dont expect it to be super super accurate.
 

Flyback

Well-Known Member
thanks, that's good advice, i do see what you mean....but I am going to struggle to calculate the emissivity of various surfaces. Also, it seems like a nuisance to have to paint every surface you want to measure....the whole idea of infrared thermometers is the speed of just point and click.
 

Flyback

Well-Known Member
and easy enough to do that with contact methods.
[email protected] Nigel Goodwin...looks like we posted simultaneously last time
....yes but I might want to rewind the transformer say and get another temperature reading, redo the snubber resistor and do another temperature reading, change the FET to a much cheaper one and do a subsequent reading etc etc etc......so I don't want to waste time with always gluing thermocouples.
 

ChrisP58

Well-Known Member
Most Helpful Member
My experience with those is that the measurement target area is fairly large. You probably won't be able to see the temperature of a single component unless they are spaced wide apart. What you will see is the heat of all the parts in a ~2" diameter area.
 

Flyback

Well-Known Member
Well, yes, id really like to buy the RS6654694 thermal imaging camera but it costs £1495.

I used to work at a huge lighting multinational, and a huge TV multinational, and both places had one like this, but due to price, they only had the one, and it was always in use by somebody somewhere, and I reckon a lot of cheap ones that do a satisfactory job, are just as good as an expensive one that you can never get hold of.

At the lighting company, The expensive thermal camera was often set up on a tripod over an smps, and left there for ages, monitoring temperature and recording it into a data logger, absolutely wonderful, unless youre stood there waiting to use it.
Incidentally, I worked at a huge telecoms place, and they didn't have any thermal cameras or thermometers anywhere.....all temperature readings were done with glued on thermocouples.....presumably because of the problem of the user accidentally not properly setting the emissivity.


I reckon the RS7600385 FLUKE 62 is going to be fine at a 'relaxing' £89......its got 10:1 distance to spot, so if I hold the thing 50mm away from a DPAK FET then my measurement spot is 5mm radius, which is just right for the DPAK......I just hope I can see the laser pointers when i'm that close to the dpak, as the actual body of the thermometer may stop me from seeing if i'm properly aimed at the blessed dpak.......the datasheets and user manuals just don't help you with this kind of practical user knowledge

RS7600385 £89
http://uk.rs-online.com/web/p/ir-thermometers/7600385/


RS665 4694 £1485
http://uk.rs-online.com/web/p/thermal-imaging-cameras/6654694/
 

MrAl

Well-Known Member
Most Helpful Member
My experience with those is that the measurement target area is fairly large. You probably won't be able to see the temperature of a single component unless they are spaced wide apart. What you will see is the heat of all the parts in a ~2" diameter area.
Hi Chris,

It depends on how far away the gun is from the work piece. Very close up like 2 inches mine reads within less than a 1/2 inch diameter area, but farther back it could be as big as 6 inch diameter (several feet away).

Flyback:
Sometimes you have to do your own experimenting to find the right answers. Run some comparative tests see what you get.
 

Flyback

Well-Known Member
Thanks , but im surprised these infra red thermometer companies simply don't supply basic information which can help them sell their product....

[email protected] just replied me and quoted the listed spec which I already knew........what is important is the "minimum measurable area" when you have the lens virtually touching the thing being measured.....they must know this, after all, they made the product.
 

ronv

Well-Known Member
Most Helpful Member
Hello,



Therefore, we must make up a “calibration SMPS”. This comprises an SMPS with thermocouples glued to each of its components.
It should be ensured that this “calibration smps” comprises both shiny as well as anodised heat sinks etc etc. One simply then points the infra red monitor at the various components of this “calibration SMPS” and checks to see if the reading of the infra red monitor corresponds to the readings on the thermocouple reader for each type of component.

Then one can confidently use this infra red monitor on the SMPS under test.
You don't really believe this do you? :confused:
 

Flyback

Well-Known Member
yes, lets face it, if you don't have the calibration smps, then how do you know if your infra red thermometer is reading accurately? I have got no way of working out the emissivity of ferrite or dpak plastic etc, so I need this 'calibration' step.
 
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