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I am confused that some of my digital meters will go crazy, when I try to read the noises in my switching mode power supply. I thought the reading sud be near zero.
i am not sure if it applies only to smps. It happened often but usually I just ignore it, because the ps is working just find with no noise.
Any kind advise please? Thanks!
William
Follow Ups:
Ordinary digital or analog meters have a limited bandwidth and are essentially designed to read steady, not impulsive signals.
What you are experiencing is the inability to capture fast lf or hf transients generated by a computer's demand for current as requirements kick in.
To see real voltage rail noise in a computer and to measure pulses, you need a high bandwidth scope, ideally an analog one with a good trigger. When you do, you will see low frequency pulses as well as high frequency ones that are orders of magnitude above the common 'mV' noise quoted in PC magazines or websites. These numbers mean nothing by way of real life performance.
What meter and what do you mean by go crazy?
While a multimeter is fine for measuring ripple on a linear power supply (where ripple would be 60Hz or 120Hz) it is the wrong tool for measuring ripple on a switching power supply.
Most switching power supplies switch in the megahertz range and their ripple would be at or twice the switching frequency.
You need to use an oscilloscope to measure this.
Its just the cheap 30 dlr digital meter. The reading swing like crazy when using AC to measure DC.
I just want to see if there any residual AC left. I hv osciloscope though hv not used yhem for years. The Fluke hand held has been in storage for yrs that the battery need to be changed 7 yrs ago...
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