Author Topic: DS1054Z input voltage and strange double image  (Read 1907 times)

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Offline thatguyyouknow

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DS1054Z input voltage and strange double image
« on: November 04, 2016, 08:46:26 AM »
I just upgraded from a basic picoscope to a DS1054Z and I have some questions.
For starters, I need to know if I broke the damn thing  :-[
I wanted to measure the ripple on a huge 250v LC filter I have because my DMM was showing 5V AC ripple on the output and I scoured the manual and the internet and the manual says nothing about DC voltage while a post I found did say that the the 300v RMS input maximum is good for about 400v DC.

I couldn't get the offset to stay still in AC coupling for some reason, it kept shifting downward so I DC coupled it and slowly ramped up the voltage of the LC filter to 250v and above 130 volts or something it would not allow me to see the voltage offset, the line was crammed up against the top of the screen. So I unplugged the thing and used AC coupling instead until I managed to somehow get the offset to stay still, then the osciloscope randomly rebooted for no reason and after rebooting I measured the LC filter again and it was showing about 2mv of a frequency that seemed to be far above the capabilities of the scope to display with strange visual artifacts that looked like lightning flickering across the horizontal line. I don't have a screenshot of this because the LC filter is far from my PC and I don't have a thumb drive on me.

So to make sure I didn't break it I hooked up my picoscope signal generator to the rigol  with a square wave and the higher the frequency goes the more I see a double image like this
https://i.imgur.com/NXrGgLv.png

Did I break it?  :(

« Last Edit: November 04, 2016, 09:16:13 AM by thatguyyouknow »
 

Offline danadak

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Re: DS1054Z input voltage and strange double image
« Reply #1 on: November 04, 2016, 09:44:11 AM »
I assume (hope) you were using 10x probe....Look at manual for AC and DC
input limits.

Double image means from one sweep to the next its triggering at different point
on waveform. Use trigger level adjust to get a stable display. Or the timebase
is jittering, possible scope firmware revision needed.

Chan 4 is showing a lot of noise.

Also check the firmware revision of your scope, it may need an update as
there have been some bug fixes.


Regards, Dana.
« Last Edit: November 04, 2016, 09:47:57 AM by danadak »
 

Offline thatguyyouknow

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Re: DS1054Z input voltage and strange double image
« Reply #2 on: November 04, 2016, 09:51:41 AM »
I was using X1 probe. I've already updated firmware.
The manual says nothing about DC input limit. The only statistic listed is the RMS limit.
Adjusting trigger level doesn't help.
 

Offline rs20

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Re: DS1054Z input voltage and strange double image
« Reply #3 on: November 04, 2016, 09:55:57 AM »
Your horizontal trigger point is a mile off to the left (scope is configured to 2us/div, but the horizontal offset is 50.27us), so jitter in the signal will indeed appear as you see it here. Depress the horizontal position button to return it to zero.
 

Offline thatguyyouknow

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Re: DS1054Z input voltage and strange double image
« Reply #4 on: November 04, 2016, 10:04:36 AM »
Doesn't help. The "Auto" button resets all that anyway.
 

Offline rs20

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Re: DS1054Z input voltage and strange double image
« Reply #5 on: November 04, 2016, 10:12:48 AM »
Can I see an updated screenshot then? My eyes cannot look past the horizontal offset.
 

Offline thatguyyouknow

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Re: DS1054Z input voltage and strange double image
« Reply #6 on: November 04, 2016, 10:24:48 AM »
 

Offline rs20

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Re: DS1054Z input voltage and strange double image
« Reply #7 on: November 04, 2016, 11:15:54 AM »
See how the curve is not doubled up on the rising edge at the trigger point? This confirms that you are seeing real jitter/"sampling quantisation" on the input signal.

Your picoscope signal generator is basically a sound card with a certain sampling rate. Let's pretend that sampling rate is 150 kHz. If the frequency that you request from the sig gen does not divide cleanly int 150 kHz, e.g. 11 kHz (which corresponds to 13.63 samples per cycle), the gen has no choice but to alternate between two surrounding integer values (in this case, 13 and 14 samples). So, you end up with a train of 13-and-14 sample wide pulses, and the oscilloscope overlays all those permutations.

Press the "single" button repeatedly to see each captured waveform separately, you will soon see that the display you're seeing right now is just the superposition of all the single-shot waveforms.
 

Offline thatguyyouknow

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Re: DS1054Z input voltage and strange double image
« Reply #8 on: November 04, 2016, 11:39:42 AM »
Oh okay, I was afraid I broke it. That would really suck because I just got it.

Danadak is right though, any channel that isn't channel 1 is showing increased noise. I wonder what that is about?
 

Offline rs20

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Re: DS1054Z input voltage and strange double image
« Reply #9 on: November 04, 2016, 11:50:08 AM »
Have you got Channel 1 set with a 20 MHz bandwidth limit?
 

Offline rstofer

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Re: DS1054Z input voltage and strange double image
« Reply #10 on: November 04, 2016, 12:06:45 PM »
Read the manual re: Single Shot Mode

Press Mode button until Single LED is lit
After first trigger, Run/Stop will be red
Press Single button to get a single event

You can practice using the calibrator output.

Obviously, you have to have the proper Trigger Source, Edge and level.  You already have that, all you need to do is get down to single shot mode.

I would strongly encourage you to use x10 probe settings.  Actually, x100 would be better.  Working up against the limits is not a good idea.
« Last Edit: November 04, 2016, 12:08:44 PM by rstofer »
 

Offline alsetalokin4017

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Re: DS1054Z input voltage and strange double image
« Reply #11 on: November 04, 2016, 01:12:17 PM »
1. Use the 10x probe and channel settings for almost all purposes unless you have a really good reason to use 1x. In this case you don't have any good reason to use 1x.

2. The screenshots indicate that you are seeing a real jitter in your signal source.

3. The "random rebooting" is something to worry about, I've never seen or heard of that before. Do you have a stable power source for the scope? Are you perhaps creating a groundloop in your scope connections by connecting the probe ground reference to some point in your circuit that is not truly at ground potential? All the BNC shields of the scope probes, the ground reference clips, are all connected together at the scope chassis and are connected to the mains cord ground pin and thus to your mains ground itself so you need to make _damn sure_ that your probe ground clips are not connected to some "live" point in your circuit that is not at ground potential.

4. The different levels of noise on different channels is normal for this scope, as long as the difference isn't too bad. Your screenshots are normal in this respect.
The easiest person to fool is yourself. -- Richard Feynman
 


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