Multiple signals on one input channel with analog input block

Hi,

I'm using the data acquisition toolbox to read in an analog signal using Simulink.

The problem I seem to be having is when I read in an analog voltage, Simulink seems to read in the signal, but another signal that is slightly offset.

You can see this happens in the example posted on the matlab website: when they read in two channels, left and right, there are two main signals (green and red) but also some smaller signals (blue and yellow). (Look at the graph in step 8.)

http://www.mathworks.com/help/toolbox/daq/bqufzkc.html

Does anyone know where those smaller ghost signals come from or how to get rid of them?

thanks

Answer 1

[Guy Rouleau]

This is very likely due to the "block size" property that you set to 5. This means that the scope displays the last 5 samples for each channels.

You can confirm that by going in the Fornat menu of the model, Port and Signals, and enable Signals Dimensiion. the dimensions of the signal should be proportionnal to the block size and the number of channels.

I am not expert with Data Acquisition, but setting the block size to 1 should result in only 2 lines on the scope, one per channel.