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Message ID: 680     Entry time: Wed Jul 24 22:10:08 2013
Author: Giorgos 
Type: DailyProgress 
Category: SUS 
Subject: Adjusting DC motors resistors, Bode Plots in Matlab and Test Components 

DC motors - Tuning Adjustable Resistors

I first tuned the resistors of our DC motors circuits, such that the voltage meters read close to 0V when the strain gauge sensors are not stretched by the plate. A zero voltage reading would later help us know when the plate is at equilibrium. The equilibrium is unstable and so the plate moves either up or down. I tuned the resistors for the bottom sensors while the plate was stuck against the top ones and vice versa. The BE adjustable resistor (R2 in the picture) was very sensitive and acting strangely; the voltage reading would change as long as the screw driver touched the resistor, making it impossible to know whether we are close to 0V while adjusting. The resistances also drifted away from their values throughout the day. Whereas the initial offset was set within 5-10mV, at the end of the day it had grown much larger as is evident in the following image:IMG_4502.JPG     IMG_4507.JPG

Bode Plots in Matlab

I developed a code in Matlab to read .dat files and create Body plots. For future reference, Matlab files should not include a "." in their name, since Matlab recognized whatever comes after the period as the extension of the file. Following is the code for the phase plot and the results:Low_Pass.pdf

>> cd('C:\Users\Γιώργος\Dropbox\maglev\SURF\progress_report\Transfer Functios of Coils')
>> load 008ASC.dat
>> G = semilogx(X008ASC(:,1), X008ASC(:,2))
>> axis ([0.5 1000 -160 0])
colorss = {[0.5  0.5  0.5],
           [0.8  0.3  0.7],
           [0.0  0.0  1.0],
           [0.97  0.1  0.0],
           [0.1  0.9  1.0],
           [0.2  0.8  0.1],
           [0.4  0.4  1.0]};
for k = 1:length(G)
    set(G(k), 'Color', colorss{k});
end
grid
grid minor
%axis tight
hXLabel = xlabel('Frequency [Hz]');
hYLabel = ylabel('Phase [degrees]');
title('Phase of the Low-Pass filter', 'FontWeight', 'bold', 'FontSize',12)
set( gca                       , ...
    'FontName'   , 'Times'     , ...
    'FontSize'   , 15          );
set([hXLabel, hYLabel], ...
    'FontName'   , 'Times',...
    'FontSize'   , 15          );
set([Legend, gca]             , ...
    'FontSize'   , 15          );
%set( hTitle                    , ...
%    'FontSize'   , 12          , ...
%    'FontWeight' , 'bold'      );

set(gca, ...
  'Box'         , 'on'     , ...
  'TickDir'     , 'in'     , ...
  'TickLength'  , [.02 .0] , ...
  'XMinorTick'  , 'on'      , ...
  'YMinorTick'  , 'on'      , ...
  'YGrid'       , 'on'      , ...
  'XColor'      , .1*[.3 .3 .3], ...
  'YColor'      , .1*[.3 .3 .3], ...
  'FontSize'    , 25, ...
  'LineWidth'   , 1.5        );

 HE boards and coils test

I also measured the output of the HE sensors to see whether there were working fine:

AC1=105mv, AC2=128mV, AC3=137mV, S1=1.73V, S2=82mV, N=16mV, W=7mV. In the same way, I measured the resistances of the coils (since we have not yet created a signal with the computer) and they worked fine, too (same values as before, slightly higher resistances, possibly because of the long ribon wires attached).

Tomorrow, I will start working on Simulink and learn how to use the computer to provide the feedback filter.

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