Okay, you must know the sample time of your data in the text file. Let's assume your sample time is 0.1 second. Your data in the text file contains a 100x3 matrix, representing the x, y and z displacement from 0 to 10 seconds.
First, import your text data into workspace use importdata(), uiimport() or textscan. Once you have the data, for example, x=rand(100,1), you need to create a time vector t=(0:0.1:9.9)', the reason for 9.9 is because it starts at 0 so the vector t also has exactly 100 samples of data.
Then drag a "From Workspace" block, double click, put in [t,x] for 'data' in the dialog window. You've got the time varying signal for x.
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