Strange values at recording.

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priack
Posts: 3
Joined: Thu May 28, 2015 7:47 am

Strange values at recording.

Post by priack »

Hi everyone
thank you in advance for your replies. I created a program to record data from the amplifier but there are some values that intrigues me.

Just to clarify, I record 16 channels downsampled to 1024 and each value is divided by 8192 to transform to uV.
This was done following the webpage were they state:
"The receiver converts every 24-bit word from the AD-box into a 32-bit Signed Integer, by adding an extra zero Least Significant Byte to the ADC data. The 24-bit ADC output has an LSB value of 1/32th uV. The 32-bit Integer received for the USB interface has an LSB value of 1/32*1/256 = 1/8192th uV"

Once I start to record I receive in every channel 256 for several seconds (between 5 and 10). That is my first question. Why? Also I didn't found any information regarding that.

After that every channel start to record correctly, but there is a huge offset in every electrode. I attach a picture so you can see it. Basically each electrode has an offset between -1000 and 1000 uV and each of them is different. Why is that? I am recording incorrectly the data?

Thank you,

Jacobo
Attachments
electrode offset.jpg
electrode offset.jpg (151.84 KiB) Viewed 14429 times

Coen
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Joined: Fri Mar 26, 2004 7:00 pm
Location: Amsterdam, Netherlands
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Re: Strange values at recording.

Post by Coen »

Data should start immediately, compare with acquisition with ActiView. The initial stream of 256 values must be caused by a bug in your acquisition program probably displaying the wrong (empty) channels for the first seconds.

The offsets are normal, it is a DC amplifier, see viewtopic.php?f=4&t=58 see and viewtopic.php?f=2&t=347 and viewtopic.php?t=56

Best regards, Coen (BioSemi)

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