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Electronics => Beginners => Topic started by: Jane on May 22, 2015, 04:04:25 am

Title: How to measure voltage ripple with an osciloscope
Post by: Jane on May 22, 2015, 04:04:25 am
Is it possible to use Hantek 200Mhz scope and  measure 50mV (5%) ripple of a voltage from the  reference value?
(That ripple can last for a very short time)
Title: Re: How to measure voltage ripple with an osciloscope
Post by: wraper on May 22, 2015, 04:18:26 am
Set input to AC coupling, profit.
Title: Re: How to measure voltage ripple with an osciloscope
Post by: Asmyldof on May 22, 2015, 04:21:00 am
I think you are looking for the "AC coupling" setting.

I'm too lazy to look up the device, but Hantek and 200MHz make me believe it should have "AC/DC" or "AC coupling" written on the case next to a button.

Basically you are telling the scope to either measure everything (DC coupling) by applying "a straight wire" from input to measurement system (whether analogue deflection or ADC), or measure only the AC content (AC coupling) by effectively putting a galvanic separation between input and measurement system. Much like the decoupling caps on analogue amplifiers and such, only with a more rigidly controlled impedance matching, I'd expect.

(paraphrasing of course)
Title: Re: How to measure voltage ripple with an osciloscope
Post by: Jane on May 23, 2015, 06:04:34 am
Thanks for the replies.
Yes, in my Hantek too, there are possibilities:
AC coupling
DC coupling
Ground

So, if need to measure a ripple of DC , I just choose  AC coupling?
And where is useful to chose DC coupling and Ground option?
Title: Re: How to measure voltage ripple with an osciloscope
Post by: Asmyldof on May 23, 2015, 06:58:33 am
As I pointed out, the DC option shows you all of the signal. It is very useful to compare an AC ripple to the DC, or if you are actually interested in DC or very low frequency waves.

The AC coupling doesn't work well for things below a couple of Herz.

Ground is to show you the baseline, if the device connects the signal to ground internally it will be the most noise free ground there is, so you can see and adjust the origin of your signal.
(And possibly debug input stage problems if it still shows distinguishable signals)
Title: Re: How to measure voltage ripple with an osciloscope
Post by: John_ITIC on May 23, 2015, 07:08:03 am
Is it possible to use Hantek 200Mhz scope and  measure 50mV (5%) ripple of a voltage from the  reference value?
(That ripple can last for a very short time)

What you'll do is to set the input to AC mode such that only the ripple will be displayed, not your DC base voltage. Then set the trigger to trigger on negative going pulses. Finally, adjust the trigger level down from 0V. As the ripple causes the voltage to deviate from the base-line, the AC voltage will dip causing the scope to trigger. At some point it will be harder and harder to trigger. At that point, you have your maximum negative ripple. Do the same for positive going ripple, if you are interested in it.

With a 200 MHz bandwidth scope, you may not see the ripple caused by fast switching circuitry. It may show a lower ripple than what is actually there.

/John.
Title: Re: How to measure voltage ripple with an osciloscope
Post by: tautech on May 23, 2015, 07:30:42 am
@Jane
In your OP you mention ripple for a short duration.
After setting your scope to AC coupling and channel attenuation (v/div) for expected ripple levels, in order to see or capture fast events you'll need to use Single shot. The Trigger level setting then determines when the capture is made. The Trigger suite available makes a DSO a powerful tool and more so the operators ability to use that suite.  ;)
Title: Re: How to measure voltage ripple with an osciloscope
Post by: Shock on May 23, 2015, 10:19:53 am
Here is a video someone made on youtube

http://www.youtube.com/watch?v=Edel3eduRj4 (http://www.youtube.com/watch?v=Edel3eduRj4)