Electronics > Metrology

Power supply calibration procedure

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tszaboo:
Hi. I just got a task to calibrate all our power supplies, because one of our visiting customer wasn't happy with the "NOT CALIBRATED" stickers on them. Sending them out for cal would be quite pricey, probably scrapping them would be cheaper. So I'll attempt to calibrate it in-house.
The DUT is nothing fancy, U8001A power supply for example, 30V 3A, linear. And a bunch of similar supplies.

My plan was to place 2x 34465A parallel + series with the output, route it into a DC load (Keithley 2380) and verify DC ranges, CC and CV.
However when I checked the user manual of the power supply, there are extra steps to verify CV, CC noise. And step response.
https://www.keysight.com/nl/en/assets/9018-02142/user-manuals/9018-02142.pdf?success=true
They also use a 100MHz differential amplifier, which is about 6KEUR, and the only reason to use it is to AC couple the signal and a gain of 10? And an RMS voltmeter... Seems a bit excessive to just measure the 1mV noise specification.

How would you do a basic check for a power supply noise specification? Am I thinking about this too much, just place a MSO on it and measure the RMS?

penfold:
You could always try the flippant approach and use "FOR INDICATION ONLY" if they're unhappy with the negative connotations of "NOT CALIBRATED".

In all pragmatism, if you're just interested in knowing whether or not the ripple is just ridiculously out of spec (i.e. not re-verifying manufacturer's spec's and instead just indicating broken/not-broken... on a PSU that you would normally not calibrate), I see no harm in just checking it with a scope+traditional-probe... (if you have a 1mV/div input range) it'll show you whether or not its ~1mV or ~2mV etc. But of course, indicate such uncertainty in your calibration cert. Especially on something like a bench PSU which would be used to power a circuit which itself should have some tolerance to ripple/noise/transients etc.


BradC:
Just cover the sticker with a “QC Passed” sticker. Seems to work everywhere else.

MiDi:

--- Quote from: BradC on May 11, 2021, 01:07:05 pm ---Just cover the sticker with a “QC Passed” sticker. Seems to work everywhere else.

--- End quote ---

 :-DD

Customer should be grateful that the psus have a sticker...

thermistor-guy:

--- Quote from: BradC on May 11, 2021, 01:07:05 pm ---Just cover the sticker with a “QC Passed” sticker. Seems to work everywhere else.

--- End quote ---

Seems to me that the OP is performing a functional test, and possible adjustment and repair, rather than a calibration.

"Calibration" to me means (a) measurement using equipment traceable to primary standards, using (b) an audited measurement procedure, plus (c) an uncertainty calculation.

Since it is a functional test, yeah, add a sticker with "Pass/Fail: ______________ Tested on:  ________________ Next test due:  _________________ "

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