As discussed in link below you can apply FFT to your data set.

For simplicity regarding your data set,

Just load your data to Matlab environment using import tab or by "dlmread".

The first requirement for FFT is that there is no data gap (missing data).

Now load your volts value in e.g. X variable considering time intervals are equal.

Then follow the link mentioned below to perform FFT using  Y = fft(X).

or

simply use  [pxx,w] = periodogram(X);

                      plot(w,10*log10(pxx));

to see any periodicity is present in your data set or not.

Thanks

http://in.mathworks.com/help/matlab/ref/fft.html?requestedDomain=in.mathworks.com

I would edit your text file to make your headers on a single line without spaces. As a general rule, things are easier that way. 

e.g., 

     Time  ==> time_s

       (s)         

Then I would import your .txt file into Matlab directly using the 'importadata' function: 

filename = 'vibrational signal data.txt';

delimiterIn = ' ';

headerlinesIn = 1;

A = importdata(filename,delimiterIn,headerlinesIn);

Then I would apply a FFT to your function on 'channel_a', as stated above. 

https://www.mathworks.com/help/matlab/ref/importdata.html