PHGY 212    Biomedical Signals Lab
Waveform Aquisition
Waveform Aquisition    I    Artifacts    I    EEG Alpha waves

In all the laboratory sessions concerned with the acquisition of electrophysiological data, we will use a system that acquires, amplifies and transforms the signal into a digital one and sends it to the computer via a special port (USB).

In this experiment, an electrical sine wave generated by a Function Generator. It is then converted by Analogue to Digital Conversion using PowerLab unit. Then processed further by the hardware and software (LabChart) and displayed on computer screen, in order to demonstrate some key issues in data acquisition and A/D conversion. This way one wave (signal) can be split into multiple channels in order to analise it in many different ways.

Procedure

Tasks 1:

  1. Collect data from a 2 Hz, 12 Volt peak-to peak sine wave.
  2. Adjust the amplitude on the function generator (see figure 1.2) to 12 V peak-to-peak by previewing the signal.
  3. Acquire this sinusoidal wave on Channel 1 with a sample rate of 2 Hz, and on Channel 2 with a sample rate of 10 Hz. View the dominant frequencies on both channels. 
  4. Make measurements.
 



Tasks 2:

  1. Collect data from a 2 Hz, 12 Volt peak-to peak sine wave. 
  2. Acquire this sinusoidal wave on Channel 1 with a sample rate of 10 Hz.
  3. Acquire the sinusoidal wave on Channel 2 with a sample rate of 20 Hz.  
  4. View and record the dominant frequencies on both channels. 
 

Tasks 3:

  1. Change the sample rate of Channel 1 to 20 Hz.
  2. Leave the sample rate of Channel 2 at 20 Hz. 
  3. Apply a gain of 3 to the data collected on Channel 2 only.
  4. Observe the display change on Channel 2.
 

Tasks 4:

  1. Remove the gain from Channel 2.
  2. Change the sample range to 2V for Channel 2 only.
  3. On Chart view window, set the vertical display: top= 5 V, bottom = -5 V (figure 1.11). 
  4. Record for 10 seconds.
  5. Observe the shape of the sine wave on Channel 2.
 



Tasks 5:

Study the effect of adding a low-pass hardware filter to a 10 Hz sinusoidal wave on Channel 1 as opposed to keeping the filter “off” for Channel 2.  





© Department of Physiology
McGill University 2020
References