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Waveform with nothing attached to 2205

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Waveform with nothing attached to 2205

Postby phunfoto » Sun Nov 01, 2009 6:17 am

I recently received the education kit and hooked up my 2205. There was a wave form showing up in PicoScope 6 with no input. Is this normal? I haven't set all of the parameters yet, but thought it odd that with no input there is a wave with lots of what looks like interfernce in it.
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Re: Waveform with nothing attached to 2205

Postby ziko » Mon Nov 02, 2009 1:46 pm

Hi and thank you for your post. It could be mains hum? Are you using a laptop? If so try disconnecting the power supply and leave it running on the battery. If the problem does not occur any more then it will be mains hum.

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Re: Waveform with nothing attached to 2205

Postby phunfoto » Tue Nov 03, 2009 2:51 am

ziko wrote:Hi and thank you for your post. It could be mains hum? Are you using a laptop? If so try disconnecting the power supply and leave it running on the battery. If the problem does not occur any more then it will be mains hum.

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I removed the mains and a lot of the movement went away, but there is still some wave form with the battery only. Is is a Sony Laptop. Is there some way to filter the mains power? The battery life is about 45 minutes for the laptop, despite the claim from Sony that it is good for about 2.5 hours.
Thank you for your quick reply.
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Re: Waveform with nothing attached to 2205

Postby gruntman » Tue Nov 03, 2009 8:26 pm

Phunfoto,

If a good portion of the noise disappeared after you disconnected the AC power from the laptop, I would suspected that the power supply that you are using is injecting a good amount of noise into the laptops power system.

With nothing connected to the scope input there will be some noise injected into the scope due to RF, electrical lines in the building etc. To see the noise floor on the scope itself connect a probe to the channel and connect the ground lead to the probe tip. After you do this there should be ~<1mV noise displayed. If you still see large amounts I would try the scope on another computer.
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Re: Waveform with nothing attached to 2205

Postby ziko » Thu Nov 05, 2009 10:25 am

Hi what I would add is if you can send us a screenshot of what you are seeing.

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Re: Waveform with nothing attached to 2205

Postby phunfoto » Sun Nov 08, 2009 6:22 am

Here are PDFs of screen shots. I tried pluuging the computer into a different outlet and using the PcoScope on my desktop. Results for both are included.
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PIco Scope readings smaller minus pages.pdf
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Re: Waveform with nothing attached to 2205

Postby phunfoto » Sun Nov 08, 2009 4:41 pm

Here are enlarged screen shots of desktop computer with nothing attached.
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Desktop Zoomed.pdf
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Re: Waveform with nothing attached to 2205

Postby Picoscopian » Wed Nov 11, 2009 4:26 pm

Hi there.

I have the same with my brandnew 2205.

In addition:
Just measured a calibration curve (square wave from our 16bit precision Calibrator) of 10V and it has all along little spikes of around 180 mV.
Changed the leads, but issue stays the same. Will check further ....
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Re: Waveform with nothing attached to 2205

Postby ziko » Tue Nov 17, 2009 1:50 pm

Hi this is normal it is the frequency of switching of the switch mode power supply.

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Re: Waveform with nothing attached to 2205

Postby Picoscopian » Wed Nov 18, 2009 11:12 am

Hi Ziko
Do I understand it correctly: If I use the 2205 with a Notebook (with battery as power-source) there is still a switch mode power supply involved (?)
From the "irregularity" of these spikes I had assumed it is pure "Noise".
I just measured the power supply outlet to the Notebook - a perfectly straight line of 19VDC, however with triangular spikes of +182 mV, which show no regular pattern.
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Re: Waveform with nothing attached to 2205

Postby PeterF » Mon Nov 23, 2009 8:35 am

Hi,
Please be aware that this is an 8 bit scope. There are only 256 steps of voltage resolution from top to bottom of the screen. On the +/-10V range this means that each LSB of resolution is 78mV so only 2 Least Significant Bits of noise will give you about the noise you see.
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