How to see micro pulsations of dc power supply using oscilloscope rigol dho 900 - Page 1
Forum section: electronics / testgear

author: VP 777
author_rank: Newbie
timestamp: May 22, 2025, 10:59:33 pm
content: How to see micro pulsations of dc power supply 38v using oscilloscope rigol dho 800-900.Everyone praises this oscilloscope, but I find more serious problems in it. I came across the fact that I need to look at the output of the power supplies for micro pulsations. I could not find how to do this. That is, if I need to check, say, 25 volts of voltage, look at the width of 10 millivolts, then the oscilloscope does not provide such an opportunity. When choosing the voltage width, it always takes the diagram readings to the top. What is wrong with this, I do.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 22, 2025, 11:17:34 pm
content: Nothing is wrong, you just have to learn how to use the oscilloscope.Set your input channel for "AC coupling" instead of "DC coupling".That will eliminate the DC component, and the oscilloscope will show you only the variations around those 38V DC.

author: Smokey
author_rank: Super Contributor
timestamp: May 22, 2025, 11:24:34 pm
content: what RoGeorge said..Next step would be a power rail probe:Code:https://www.youtube.com/watch?v=q9GOP8umScUhttps://github.com/blinken/power-rail-probe/https://www.eevblog.com/forum/oshw/open-hardware-power-rail-(dc-offset)-oscilloscope-probe/https://www.eevblog.com/forum/testgear/prp1-low-cost-2ghz-power-rail-probe/?allhttps://www.eevblog.com/forum/testgear/probe-to-use-for-5v-dc-power-supply-ripple-measurement/?all

author: VP 777
author_rank: Newbie
timestamp: May 23, 2025, 12:34:03 am
content: I have been using it for 1 year and would not buy it now. Model dho914. Everyone praises this oscilloscope, but I find more serious problems with it. I came across the fact that I need to look at the output of the power supplies for micro pulsations. I could not find how to do this. That is, if I need to check, say, 25 volts of voltage, look at the width of 10 millivolts, then the oscilloscope does not provide this opportunity. When choosing the voltage width, it always takes the diagram readings to the top. What am I doing wrong with this. You will not be able to increase 30 volts to a channel width of 10 millivolts. And when measuring voltages, it very often shows with an error of up to 20 percent. I compared it with an accurate tester. It is a mystery to me why this is so. Try to see the pulsation of the output voltage of 12 volts or higher, and at least up to 50 millivolts per cell. You will not succeed. Rigol has a limitation. QUESTION, why? What do you think?

author: JDubU
author_rank: Frequent Contributor
timestamp: May 23, 2025, 12:46:19 am
content: Look in the users manual of the Rigol DHO900:https://beyondmeasure.rigoltech.com/acton/attachment/1579/f-b9a4918d-da06-49ff-8226-0de6d3866ebb/0/-/-/-/-/DHO900_UserGuide_EN.pdfAs described on page 42 in section 5.4, set the channel coupling to "AC".Every oscilloscope ever made has this feature.

author: temperance
author_rank: Super Contributor
timestamp: May 23, 2025, 01:36:43 am
content: QuoteThat's not a problem with the scope. As stated by others: use AC coupling so the scope only sees the AC signal and not the DC and AC signal.I didn't read the manual of the scope you've got. But the manual will probably not guide you step by step on how to this. It is something you should know. To get you going you can read this primer written by Tektronix. It guides you trough the basics of taking measurements with an oscilloscope.https://download.tek.com/document/XYZs-of-Oscilloscopes_Primer_03W-8605-8.pdfWhat you are after is on page 20: Input Coupling

author: Someone
author_rank: Super Contributor
timestamp: May 23, 2025, 01:37:41 am
content: Quote from: VP 777 on May 23, 2025, 12:34:03 amWhich oscilloscope does do this?When all products of a category fail to do your task, sounds like that is not a problem of the specific model.

author: temperance
author_rank: Super Contributor
timestamp: May 23, 2025, 01:31:50 pm
content: The OP is using "micro pulsations" to refer to noise. This probably explains the problems he has with the oscilloscope.

author: JDubU
author_rank: Frequent Contributor
timestamp: May 23, 2025, 02:02:49 pm
content: The OP is testing power supply output quality.I interpreted "micro pulsations" as AC ripple/switching artifacts originating from the DUT.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 23, 2025, 02:04:13 pm
content: About "micro pulsation", the proper term is either "ripple" or "noise".

author: Aldo22
author_rank: Super Contributor
timestamp: May 23, 2025, 03:06:27 pm
content: Well, by “ripple” I understand something periodic of at least 50/60Hz. By "noise" I understand high-frequency spikes.But there are other forms.My DPS-150, for example, shows a small approx. 2Hz pulse.Is that ripple? Is that noise?Maybe that's what he means?I have no idea.

author: Fungus
author_rank: Super Contributor
timestamp: May 23, 2025, 03:48:08 pm
content: Quote from: Aldo22 on May 23, 2025, 03:06:27 pmRipple is what you get in switching power supplies from turning the voltage on/off to keep the capacitor at the output charged to the correct voltage.The ripple's frequency will be whatever the supplies switching frequency is, usually in the kHz range (and hopefully above the audible frequency range).Quote from: Aldo22 on May 23, 2025, 03:06:27 pmThat's a crappy power supply.(although it probably doesn't impact anything in real life)Is that with a load applied to it or is it just there all the time?Ripple should be zero when there's no load (because there's nothing discharging the capacitor).

author: Aldo22
author_rank: Super Contributor
timestamp: May 23, 2025, 04:13:00 pm
content: Quote from: Fungus on May 23, 2025, 03:48:08 pmI think I had measured that against a 50 ohm load resistor so it has something to do.But yes, it's not really a problem (<1mVrms) and that's not the point here.I just wanted to show that such pulses can exist.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: May 23, 2025, 04:34:14 pm
content: The complete name for PARD; periodic and random disturbances. It includes everything that deviates from pure DC.Back on topic, to the TS: if you’re unfamiliar with an instrument’s operation, you did the right thing and asked. What is not kosher is to automatically blame the instrument when the issue is that you ignore how to use it.