How to measure voltage ripple with an osciloscope - Page 1
Forum section: electronics / beginners

author: Jane
author_rank: Frequent Contributor
timestamp: May 21, 2015, 06:04:25 pm
content: 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)

author: wraper
author_rank: Unknown
timestamp: May 21, 2015, 06:18:26 pm
content: Set input to AC coupling, profit.

author: Asmyldof
author_rank: Regular Contributor
timestamp: May 21, 2015, 06:21:00 pm
content: 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)

author: Jane
author_rank: Frequent Contributor
timestamp: May 22, 2015, 08:04:34 pm
content: Thanks for the replies.Yes, in my Hantek too, there are possibilities:AC couplingDC couplingGroundSo, if need to measure a ripple of DC , I just choose AC coupling?And where is useful to chose DC coupling and Ground option?

author: Asmyldof
author_rank: Regular Contributor
timestamp: May 22, 2015, 08:58:33 pm
content: 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)

author: John_ITIC
author_rank: Frequent Contributor
timestamp: May 22, 2015, 09:08:03 pm
content: Quote from: Jane on May 21, 2015, 06:04:25 pmWhat 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.

author: tautech
author_rank: Super Contributor
timestamp: May 22, 2015, 09:30:42 pm
content: @JaneIn 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.

author: Shock
author_rank: Super Contributor
timestamp: May 23, 2015, 12:19:53 am
content: Here is a video someone made on youtube