hello, I'm walrus.

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walrus
Posts: 6
Joined: Tue Jan 03, 2006 6:46 pm

hello, I'm walrus.

Post by walrus »

As an animal, I've nothing to introduce myself. I just begin to learn BioSemi.

By the way, does anybody know why we calculate

(1) [PhysMax-PhysMin]/[DigMax-DigMin] (let's name it Ratio) and multiply it with our recorded data?

(2) and how do we get the offset formula: PhysMin-DigMin*Ratio?

Sorry, I cannot find suitable Forum to post these fundamental questions.

Coen
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Post by Coen »

It is just a scaling issue. The 24-bit analog-to-digital converters have an output range from -8388608 (-2^23) to + 8388607 (2^23-1). The signal range of the electrode inputs is - 262144 uV to +262144 uV. The formula above converts the ADC output words in the BDF file into values in microVolt. It is another way of defining an LSB value of 31.25 nV. Please note that the scaling for some sensor channels differs from the scaling of the electrode channels.

The offset value is the DC value of the signals, see viewtopic.php?t=56&highlight=offset (use the search function !)

Best regards, Coen (BioSemi)

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