Electronics > Beginners
What oscilloscope bandwidth do i need for measuring Vp-p(ripple, noise)?
spford:
### To bob91343
1. The reason to measure a Vp-p value is.....
I think the quality of the power supply or charger can be judged by the Vp-p value.(is it correct?)
i think that i can decide whether i can trust it and whether will keep use it by the Vp-p value.
If the Vp-p value is high, i can not trust it and i do not like to use it and maybe i will throw it into the trash.(various power supply and chargers around me at home)
So i wanted to know a Vp-p value.
2. "curious or trying to learn how to make measurements", You are right.
This measurement is based on curiosity that I want to measure directly and judge whether it is good or bad.
Maybe i have a little engineering character that I want to measure when i look at something. Lol
Thanks for the reply. :)
### To innkeeper
1. I agree. Used oscilloscopes are also a great opportunity for me. but CRT based scope is...i need more searching.
2. Also I want to buy a Siglent SDS1102CML+ or SDS1104X-E or DS1054Z ETC. and I like use advanced features.
But maybe I will only use one or two features(eg, Vp-p and FFT). I do not want overspending.
Of course, if this measurement was my job, I would have invested a good oscilloscope without hesitation recommended by experts.
and if i was very rich....
3. I will remember "500uV/Div and at least 20Mhz". thanks
Thank you for sharing your experience and insight.
it was very helpful for me.
bob91343 and innkeeper,
Thanks for taking the time. :)
spford:
I am searching about OWON VDS1022i. (USB PC OSCILLOSCOPE, about $110, BW 25Mhz, 100MSa/s, 5mV/Div, 5ns/div )
It is a bit inconvenient to use because of PC booting, line connection, etc,
But it seems to be a good compromise for me. :)
innkeeper:
Tips and techniques for power supply noise measurements
spford:
1. Information.
I found that VDS1022i also has limited 5 MHz bandwidth with the 1X probe(5mv/Div).
[VDS1022i's Manual]--------------------------------------------------------------------------------------------------------
"Caution: When the attenuation switch is set to 1X, the probe will limit the bandwidth of the oscilloscope in 5MHz.
To use the full(25Mhz) bandwidth of the oscilloscope, the switch must be set to 10X."
-------------------------------------------------------------------------------------------------------------------------------
2. Question.
innkeeper said "usually noise measures 20MHz bandwidth."
Do I have to measure with 10x prob mode and 50mV / Div sensitivity?
Is it possible to measure the noise properly if the sensitivity is 50mV / Div?
Or Is it possible to measure the noise properly even if the bandwidth is limited 5 Mhz with 1X probe mode?
I would appreciate for your a reply. :)
innkeeper:
as you might suspect, Dave has done videos on both of these topics.
watch them both, you will learn a lot
but to answer your direct questions.
yes, a x1 probe has lower bandwidth then a x10 probe (or for dual x1/x10 probes you will get higher bandwith at x10)
preferably you want to use a x1 probe with 20mhz bandwidth, to get the best fidelity of the noise measured.
various probes are different and you have to look at the specs to see if it will go to 20mhz at x1.
However, the best type of probe for noise measurement is a differential type probe instead of your standard single ended probe. However, those kinds of probes are expensive.
there is a trick to use 2 channels of your scope as a poor man's differential probe - also described in the videos below u using 50 ohm coax and 50 ohm terminations.
yes, you can measure noise and ripple with lower bandwidth then 20mhz, however, it is just the defacto standard used for such measurements and if you don't use it you will not be able to compare your measurements to other documented specifications etc.
No, your likely not going to be able to measure noise at 50mv/div. unless the PS is very bad... you want to be able to measure 1mv/div or better.
lastly... there is a pitfall with probe bandwidth you should be aware of. a probe bandwidth is a frequency in which the signal drops by 3db, or about 30% lower than the real reading. in order to avoid this, you should use a probe with 3x or more bandwidth than the highest frequency your trying to measure. there is a good video from Tektronix on this I will also post below. the reason for 3x bandwidth is that the 3db point is for pure sinewave, whereas you need to account for high rise time signals for non-sinewave elements.
this is all explained in the videos below
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