The McGill Physiology Virtual Lab

Biomedical Signals Acquisition

Gain settings
  To be able to better resolve the signal, one can adjust the gain after acquiring the signal


A 10 V peak-to peak sine wave is acquired. The A/D board is configured to acquire signals of +/- 10V.

If one wants to better display the signal by enlarging the signal, the following can be done:
A given channel can be multiplied by the gain one wants to achieve. In this case, a gain of 4 is applied, with the results below. The amplitude (+/- 5V) of the signal becomes (+/- 20V).

If the A/D board is configured to acquire a signal from +/-2 V, then the situation below occurs:
To the left of the display, the sine shows a gain of 4 while being acquired with a sampling range of +/-10V (gain of 4: +/-20V). When the acquisition range is changed to 2 V (right of the display), the Powerlab recording system is only able to digitize signals with original amplitude of 4V (+/-2V); the sine wave shows clipping of the signal at the hardware limits of the recording instrument (at +/- 8V of the amplified signal). This is saturation.

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