EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: jared555 on November 22, 2016, 02:08:54 pm
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I just got the Rigol DS1054Z. Sorry for what is probably a dumb question, but is this likely noise being picked up from the environment (multiple computers, online battery backups, audio amplifiers, tvs etc. within a few feet of the scope) or something internal or that I need to fix with adjustments?
Channels 1/2 have probes in 1x mode (configured that way in the scope too) with the probe connected to the ground lead and Channel 3 is not connected
http://imgur.com/a/hgfii (http://imgur.com/a/hgfii)
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I also noticed a bit of an offset on the 500 uV range across all inputs (can see that in the image with just channel 3)
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The first thing to do is to measure the frequencies and intervals, and see if they can be correlated to anything you would expect to find in the environment. Don't implicitly trust a scope's measured values; double check them manually. The correlation for the middle image is pretty obvious! I suspect that the other pictures are a consequence of what's shown in the middle picture.
Then start moving things (probe, hand, etc) and seeing what changes. That can give you clues as to the source.
Finally, do be aware that a traditional "high" impedance *10 probe with a 6" ground lead will resonate at around 100MHz.
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I definitely know not to trust a single instrument. Pretty much all I have at the moment is an extech ex330 and the scope to compare.
The changes on the waveforms definitely gave me the feel that the probes are just acting as antennas. I have a feeling my battery backups are not being helpful in that regard because they are only FCC rated for business/industrial use.
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I have a fluorescent desk lamp that I must turn off whenever doing low level captures. Times past i have placed everything including the scope on a sheet of metal and grounded the scope to the metal to minimize pickup.
Take your scope into the living room away from the lectronics and see if it improves. I would expect it is external to the scope.
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Select GROUND coupling instead of AC or DC and what is left on the screen is internal noise. Some is to be expected. What you have is up around 200 MHz on a 100 MHz scope. There will always be some noise in the ADC and front end. A few hundred microvolts isn't a big deal in most cases.
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Rigol DS1054Z has no working 500 uV/div range. You hacked it to pretend it has, but it has no hardware to support that, so forget that this mode even exists.
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Select GROUND coupling instead of AC or DC and what is left on the screen is internal noise. Some is to be expected. What you have is up around 200 MHz on a 100 MHz scope. There will always be some noise in the ADC and front end. A few hundred microvolts isn't a big deal in most cases.
This is not true on the Rigol DS1000Z series (and DS2000A series?) which have no ground input coupling hardware; instead they alter the gain of the amplifier which drives the digitizer. To see the input noise, short out the BNC connector.