Possibly mains flicker. - Page 1
Forum section: electronics / beginners

author: davelectronic
author_rank: Frequent Contributor
timestamp: October 25, 2019, 02:58:59 am
content: Some time ago i purchased a second hand Oscilloscope 60 MHz HM605, HAMEG. Its sat for a few months, in the last few days I've powered it up. It was purchased as fully working, and i think it is. Just a couple of issues I'm unsure about, my first test with the scope was just low voltage AC from a linear transformer. It displays the wave form on both channels, but there is a persistent flicker of the wave form. I've tried to find out if this is normal to flicker when testing, the only reference i could find was on a forum, and the conclusion was its normal as the phosphor used in the crt tube. I'm a noob when it comes to scopes, but did view a few tutorials, and setting up a scope. The second issue is i can not get the built in test function to display a wave form, upon trying to use it.Thanks for reading, and help appreciated.

author: Brumby
author_rank: Unknown
timestamp: October 25, 2019, 09:37:56 am
content: "Flicker" is a somewhat ambiguous term. If your scope is functioning properly, then this is what I think you may be seeing:The first point is to ensure you are getting consistent triggering. This is usually best achieved with simple waveforms - such as steady sine waves - by setting the trigger to "Auto". Assuming the triggering is OK, then read on...When you display a 50Hz sine wave on an analogue scope, you can get a trace that will not be a solid, steady sine wave. This is especially true if you have the sweep running slow. If you can see 2 or 3 full cycles, then you are going to get a display that seems to flicker. If the sweep is slow enough for you to see 6 or more full cycles, you will just about be able to follow the sweep. If you speed the sweep speed up until you only see part of a single cycle, then you will start seeing a trace that is less "flickering".To see the correlation between the signal and the sweep speed, get a hold of a signal generator and try various signals. I'd suggest you play around with sine waves from 1Hz to 1kHz. That will give you a good feel of what you can expect. (Anything slower than 1Hz will put you to sleep and anything faster than 1kHz isn't going to look much different.)

author: davelectronic
author_rank: Frequent Contributor
timestamp: October 26, 2019, 12:11:04 am
content: Your second paragraph is very a accurate description of what I'm seeing, and if i increase or decrease the time base. I can get a full screen 60hz from the secondary of a small mains transformer. If i speed it up, eventually it disappears. To slow and it become a no flicker moving vertical line, speed it back up and its a uniform sine wave again. Maybe it should be this way, as I'm often watching scopes in tutorials or other projects, and these are digital scopes.the full screen wave form just has a rapid flicker, its a full wave form, but not what i would call solid unbroken. Then is some braking to the wave form, but it is a full representation of a 60hz sine wave.Thanks for your help.

author: davelectronic
author_rank: Frequent Contributor
timestamp: October 26, 2019, 01:21:04 pm
content: Watched Dave's EEVblog #502 video, not the same scope, but its close enough. The flicker is in Dave's video, and as he adjusts the time base that's what i thought was flicker. I would prefer to see a slower scrolling wave form or continuous unbeoken sine wave. I've got very little space indoors, so can't have a lab set up, or workshop. I can use the scope, but after use have to store it away. All the functions appear to work ok, but as a newbie i might have missed something.I originally purchased it hoping it would be suitable for looking at ripple current on loaded output of swich mode and linear power supplys. One thing I've noticed is my scope doesn't have storage function, I'm not sure now if its suitable for measuring ripple on output of psu's.Maybe I'd be better off with a newer digital scope for such measuring tasks. As my interests are mostly power supply repurpose, or power supply built from scratch, I'm not 100% sure of what scope would fulfill that task.

author: Brumby
author_rank: Unknown
timestamp: October 27, 2019, 04:37:42 am
content: Quote from: davelectronic on October 26, 2019, 01:21:04 pmThis is a trait of most analogue scopes. Only those with a storage capability can avoid it - but they are not common. Digital scopes don't have that problem, because they are storing samples which are then displayed.

author: james_s
author_rank: Super Contributor
timestamp: October 27, 2019, 05:21:42 am
content: It's a simple matter of physics. An an analog scope draws the signal directly on the CRT, the horizontal sweep moves the beam from left to right and the voltage at the input directly controls the vertical position of the spot, as it moves across the face of the tube this draws the waveform. If you are drawing a low frequency signal it's going to visibly flicker, there is no way around this, phosphors have only a certain amount of persistence and the electron beam can't be in more than one place at a time.A digital oscilloscope stores the entire capture in memory and displays it the same way any computer displays an image on a raster scanned CRT or LCD.This is one of the things I like about analog scopes though, they feel very "real", very direct, you are seeing the incoming signal being drawn directly in real time. The horizontal sweep control directly controls the speed at which the beam sweeps across the screen, the v/div control directly controls the gain of the vertical amplifier. Everything happens in real time, you can see it working, once you have mastered using the analog scope a digital scope will feel almost like cheating.

author: Brumby
author_rank: Unknown
timestamp: October 27, 2019, 06:22:40 am
content: Quote from: james_s on October 27, 2019, 05:21:42 amMy sentiments also.

author: Shock
author_rank: Super Contributor
timestamp: October 27, 2019, 07:54:16 am
content: Quote from: davelectronic on October 25, 2019, 02:58:59 amAre you talking about the internal square wave calibration signal? Have you been able to trigger successfully off signals yet btw? You know about the input switch DC/AC/GD and the different trigger options? Follow the probe compensation instructions in the manual.Or the component tester? Brief instructions are at the back of the manual. But either way let us know exactly what you are doing and then it's easier to provide an answer.Do you have a second oscilloscope or is this the first? Measuring ripple "current" is probably a topic unto itself. Are you aware about accidentally attaching the probe ground lead onto a live part of the circuit (creating a short circuit to ground). You will need to be aware of that if you go try out a current shunt without thinking it through.Quote from: davelectronic on October 26, 2019, 01:21:04 pmCare to point out what exact time in the video you are referring to here?

author: davelectronic
author_rank: Frequent Contributor
timestamp: October 27, 2019, 11:55:54 pm
content: I'd have to go back into the video again, no doubt i will watch Dave's tutorial again. And James on the low frequency signal, and the phosphor so its perceived as flicker. I'm mainly interested in power supply DC output, and how clean is the delivery to power HF radio transceivers and associated equipment. A lot of my interest is in repurposed psu units, either as a stand alone psu, or a higher voltage, then drop this with a buck converter. Or boost converter if 12 Volts or just under. The picture below shows a repurposed 90 watt hp power adaptor, and the small unit can deliver 12 Volts at around. 7 Amps. Although that would need a larger power psu adapter.The load is halogen lamp off to the right pf the image.