Accurately measuring temperature of various components in an SMPS?

[treez]

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:
**broken link removed**

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?

 

[chuckey]

As most people would design the PSU for the greatest efficiency, there would be very little scope for reducing its power consumption, because it would have been done at the design stage as would have been the placing of major heat dissipating devices on heat sinks and away from temperature sensitive components such as electrolytic capacitors. So the real question is:- "this beast runs at an internal temperature of X over ambient, is X too large?", if it is then more external area/heatsinking/fan cooling will be required, this can be done with temperature sensitive labels.
Frank

 

[schmitt trigger]

Something I've seen done, is to spray paint the whole board and assembly with a light coat of matte-black paint.

Another thing that you should be aware of this low-cost IR thermometers, is that the laser pointer sometimes is not aiming at exactly the surface being actually measured.

What companies do, at least the company I worked for used to do, is use a full fledged FLIR camera. Those however, are expensive.

 

[tpetar]

@Treez

Instead described device in first post FLIR camera (thermal imager) is used to make pictures/videos.

**broken link removed**

Its very very very usefull device which can help in many cases to solve problems, to make diagnostics, to make documentation, for various types of load testing, testing quality of parts, ...



FLIR device is hard to make in DIY, but here you can see simplified version of infrared temperature measuring device (circuit, example code and demo video) :

MLX90614ESF-AAA single zone Infrared (Ir) thermometer module with 17-bit ADC powerful DSP unit and 10-bit PWM.

IrThermo click
https://www.mikroe.com/click/irthermo-5v/
https://www.mikroe.com/click/irthermo-3.3v/




Best regards,
Peter

 

[treez]

Thanks, those flir devices are brilliant, but £850.
The thermoclick device looks good, because you can move the window right up to the object being measured, though it doesn't have the filter lens in front of the thermopile, which is needed to filter out all except the infra red incidenting on it.

Also, the Flir device would still need the "calibration smps" to be made since the flir device still has to have its emissivity set.........its worth realising that the flir device images the temperature of many components on a pcb, and each of these will have slightly different emissivity, and yet the flir is fixed at any given time to a single emissivity setting, so the flir reading is not entirely accurate.

 

[schmitt trigger]

"the flir device still has to have its emissivity set...he temperature of many components on a pcb, and each of these will have slightly different emissivity"

That is correct...But As I said, if one paints with a light coat everything matte black, and one performs an emissivity calibration ONCE, all the following readings are a snap.