When I change the sensitivity from the “5” column to the “2” column, I get a significant amount of noise regardless the coupling selection or the presence of a signal on channel 2.
If I then select a sensitivity from the “1” column and move back to the “2” column, the noise disappears.
I know the solution is to not go directly to the “2” column from the “5” column, but I am interested to know what is happening. Is it a noisy relay? Can I replace it? Which one is bad and where do I get new one?
What you describe sounds very similar to what I see on my own PCSU1000. Actually it is not noise, it is an oscillation. Same for me - going to some other sensitivity setting and then moving back to the original one can make it disappear. So you can manually work around it, but it does not help e.g. when doing an automated Bode plot with the PCGU signal generator.
I’m glad somebody else (you) observed that behavior, too - this means that I’m not crazy It seems to be a problem in the scope’s design (my guess is some stage in the input amplifier does not have enough phase margin and thus becomes unstable). I actually see it more frequently on channel 1 but also on channel 2.
At this time, we are trying to reproduce this behaviour on two of our scopes in the lab, without any results.
Does it show this behaviour every time or just on random occasions ?
Is there any other important info you can supply which could help us investigate the problem ?
Keep us informed.
thank you. It happens every time, never random. It happens after re-booting and a re-install of software/drivers. It only happens on channel 2.
I don’t understand the circut specifics, but it seems like a noisy relay, however, I don’t know why it would only do it when changing from the one sensitivity. I’ve visually inspected the PCB and didn’t see anything that looked bad. Is there a way I can send you a screen grab showing the “smooth” and “noisy” traces? Would that help?
The fact someone else on the list sees the same problem makes me think this isn’t necessarily a random error on my particular scope.
My scope is out of warranty, but would it be possible to swap the circut board for a reasonable fee?
Note: In re-reading the original posts, what I have observed and described below may not be the same issue. The oscillations I have observed are transient “settling” events, NOT persistant noise/oscillations.
—my original posting—
Mine does the same thing–on both channels, though with lesser amplitude and less consistency on CH 1. It can be captured easily with triggered sweeps. It does this when switching from “2” to “5” or from “5” to “2”. There is a distinctly characteristic pattern depending on the “direction” of the switch…
This is the CH 2 “2V” to “0.5V” characteristic pattern:
No, that’s not the same problem. What I see is not a one-time glitch when switching (I wouldn’t be worried about that); instead, I see an ongoing oscillation that does not go away unless I switch vertical sensitivities. I posted that issue when I first observed it - April 2007. (if you want to see the full thread, search for posts with my user name (womai).
Quote:
On CH1 when I set the resolution to first to 50mV and then to 20mV/div (or from 0.5V to 0.2V), about one time out of four the signal on the screen oscillates, even though nothing is attached to CH1. Setting a different sensitivity and then setting it back to 20mV/div fixes the problem. I did not observe this when coming from any other resolution (e.g. 10mV/div) either, it’s specific to the 50mV/div -> 20mV/div and 0.5V/div -> 0.2V/div change. The oscillation shows a peak at around 18 MHz (although I can’t tell if it really is a higher frequency that got aliased by the 50 MHz sampling rate). Amplitude is about 0.5units (i.e. 10mV) peak-to-peak. No other vertical setting shows this behavior. CH2 has a similar issue but has much smaller oscillation amplitude. Also there is no influence of the trigger setting (on or off).
At this time, we are still looking into this issue.
Our lab instruments do not show this behaviour.
More info will be posted as soon asap.
You cannot attach a picture. You can provide a link to a picture, which is hosted by e.g. your provider or a free picture base.
I suspect that it is not a general behavior problem and that it is due to a noisy relay or something. I think it is isolated to just a few units or there would have been a lot of others complaining.
Now a modified software is available. I hope it fixes this problem.
You can download the updated files from: vel255.diinoweb.com/files/PCSU1000_fix.zip
Just extract the files to the \Program Files\Velleman\PC-Lab2000SE folder. (Replace the existing files.)
You may see a minor trace jump when you change the sensitivity from the “5” column to the “2” column.
Nice that this software patch seems to fix the problem.
This is just a very simple workaround: It just avoids direct jump from the column “5” to column “2”. The voltage setting ‘visits’ in column “1” for about 50ms in between.
This patch doesn’t remove the original source of the problem but it prevents it from appearing anyhow…
BTW: In this version of software there is a new “Logic Analyzer” check box added. You may use this new feature to capture a large amount of digital data to the acquisition memory of the scope.
For more info on this function please see the thread: Compress values
It seems to be a problem in the scope’s design (my guess is some stage in the input amplifier does not have enough phase margin and thus becomes unstable). I actually see it more frequently on channel 1 but also on channel 2.
