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DRdaq noise on signal

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DRdaq noise on signal

Postby ACW » Wed Dec 11, 2013 2:43 pm

Hi
using a DrDaq to log voltage data but when setting up the system we get noise on the signal that cannot be removed.
if we try shorting the input connectors i would expect to see zero volts but the noise moves from 0 to 30mv
the signal we are measuring is in the range zero to 0.5 v
any solutions or do we have a faulty Dr Daq

thanks

Andy
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Re: DRdaq noise on signal

Postby ACW » Thu Dec 12, 2013 3:47 pm

Hi
Got a second DrDaq and it shows the same symptoms
Is my laptop that is generating the noise? or the usb power supply from the laptop

Thanks
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Re: DRdaq noise on signal

Postby Martyn » Thu Dec 12, 2013 4:34 pm

Is the laptop running on batteries?
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Re: DRdaq noise on signal

Postby ACW » Thu Dec 12, 2013 4:43 pm

No
Tried it on batteries, but no difference,

Any more advice

Thanks
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Re: DRdaq noise on signal

Postby Martyn » Thu Dec 12, 2013 9:04 pm

Can you post a psdata file showing the noise, we can then look at the settings and data in context.
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Re: DRdaq noise on signal

Postby ACW » Fri Dec 13, 2013 9:47 am

Hi data recording uploaded as file atachment
Test run with noise

voltage input is on the top line and had the input leads shorted together, when using it with the measuring source we get the same level of noise that interferes with the signal we are trying to look at.

Thanks
Attachments
test2.plw
test run with noise
(21.9 KiB) Downloaded 65 times
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Re: DRdaq noise on signal

Postby Martyn » Fri Dec 13, 2013 11:20 am

What voltage range are you using ?
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Re: DRdaq noise on signal

Postby ACW » Fri Dec 13, 2013 12:11 pm

the range is o to 30 mV on the recording. the noise seen is roughly 20mV when you have the scope running, same with the pico log.

the measurement we are looking at is from zero to 0.5v. that relates to the source, a force gauge that reads zero to 5kg.

the noise is almost as large as the changes we are looking at when taking a reading.

Thanks
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Re: DRdaq noise on signal

Postby Martyn » Fri Dec 13, 2013 1:55 pm

But which range of the four for the DrDaq are you using

±1.25 V, ±2.5 V, ±5 V, ±10 V

As the scope is 8 bits you have 255 steps across the specified range, so if you are on the 10V scale this would give a step resolution of 78mV, on the 1.25V range you would get 10mV.
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Re: DRdaq noise on signal

Postby ACW » Fri Dec 13, 2013 2:03 pm

+/- 1.25v but no change when you use the other ranges

Thanks
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Re: DRdaq noise on signal

Postby Martyn » Fri Dec 13, 2013 2:40 pm

The noise looks to be within the ±3% accuracy quoted for the oscilloscope channel of the DrDaq. As this is gaussian noise it can be removed by using a software moving average filter, resolution enhancement in Picoscope software.
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Re: DRdaq noise on signal

Postby ACW » Fri Dec 13, 2013 2:55 pm

Hi
Thanks
looks like a soulution for now, possibly plot the average reading over 10 - 20 samples to smooth out the curve but problen is that i am looking for small transiant changes in the force.

i will keep experimenting see if i can get any better results

possibly have to resort to a more expensive 24 bit model of A to D

Thanks for your help
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