Update analysis of slip-ring noise

index.org

@@ -36,10 +36,14 @@ Control loop influence:
 - [[file:2018-10-15%20-%20Marc/index.org][Perturbation due to the control loop of each stage]]
 - [[file:disturbance-control-system/index.org][Disturbance induced by the control system of each stage]]
 
+* Measurement Noise
+Noise coming from the Slip-Ring:
+- [[file:slip-ring-electrical-noise/index.org][Slip Ring - Noise measurement when using geophones]
+- [[file:slip-ring-noise-turning/index.org][Slip Ring - Noise measurement when turning]
+
 * Other
 - [[file:huddle-test-geophones/index.org][Huddle Test - Geophones]]
 - [[file:instrumentation/index.org][Measurement on the instrumentation]]
-- [[file:slip-ring-electrical-noise/index.org][Slip Ring - Noise measurement]]
 - [[file:actuators-sensors/index.org][Actuators and Sensors]]
 - [[file:equipment/index.org][Equipment used for the measurements]]
 - [[file:src/index.org][Matlab functions used for the data analysis]]

slip-ring-electrical-noise/index.org

@@ -615,23 +615,45 @@ We load the data of the z axis of two geophones.
   sr_lpf_1khz_on = load('mat/data_036.mat', 'data'); sr_lpf_1khz_on = sr_lpf_1khz_on.data;
 #+end_src
 
+*** Pre-processing
+There is a sign difference between the signal going directly to the ADC and the signal going through the slip-ring. We add a minus sign on the signal going through the slip-ring.
+
+We also subtract the mean value as the voltage amplifiers were on the DC option.
+
+#+begin_src matlab
+  sr_lpf_1khz_of(:, 1) =   sr_lpf_1khz_of(:, 1)-mean(sr_lpf_1khz_of(:, 1));
+  sr_lpf_1khz_of(:, 2) = -(sr_lpf_1khz_of(:, 2)-mean(sr_lpf_1khz_of(:, 2)));
+
+  sr_lpf_1khz_on(:, 1) =   sr_lpf_1khz_on(:, 1)-mean(sr_lpf_1khz_on(:, 1));
+  sr_lpf_1khz_on(:, 2) = -(sr_lpf_1khz_on(:, 2)-mean(sr_lpf_1khz_on(:, 2)));
+#+end_src
+
 *** Time Domain
 We compare the signal when the Slip-Ring is OFF (figure [[fig:sr_lpf_1khz_geophone_time_off]]) and when it is ON (figure [[fig:sr_lpf_1khz_geophone_time_on]]).
 
-#+begin_src matlab :results none :exports none
+#+begin_src matlab :exports none
   figure;
+  subplot(1, 2, 1)
   hold on;
-  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 1)-mean(sr_lpf_1khz_of(:, 1)), 'DisplayName', 'Direct');
+  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 1), 'DisplayName', 'Direct');
-  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 2)-mean(sr_lpf_1khz_of(:, 2)), 'DisplayName', 'Slip-Ring');
+  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 2), 'DisplayName', 'Slip-Ring');
   hold off;
   xlim([0, 100]); ylim([-1, 1]);
   legend('Location', 'northeast');
   xlabel('Time [s]'); ylabel('Voltage [V]');
+  subplot(1, 2, 2)
+  hold on;
+  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 1), 'DisplayName', 'Direct');
+  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 2), 'DisplayName', 'Slip-Ring');
+  hold off;
+  xlim([0, 1]); ylim([-1, 1]);
+  legend('Location', 'northeast');
+  xlabel('Time [s]'); ylabel('Voltage [V]');
 #+end_src
 
 #+NAME: fig:sr_lpf_1khz_geophone_time_off
 #+HEADER: :tangle no :exports results :results value raw replace :noweb yes
-#+begin_src matlab :var filepath="figs/sr_lpf_1khz_geophone_time_off.pdf" :var figsize="wide-normal" :post pdf2svg(file=*this*, ext="png")
+#+begin_src matlab :var filepath="figs/sr_lpf_1khz_geophone_time_off.pdf" :var figsize="full-tall" :post pdf2svg(file=*this*, ext="png")
   <<plt-matlab>>
 #+end_src
 
@@ -640,20 +662,29 @@ We compare the signal when the Slip-Ring is OFF (figure [[fig:sr_lpf_1khz_geopho
 #+RESULTS: fig:sr_lpf_1khz_geophone_time_off
 [[file:figs/sr_lpf_1khz_geophone_time_off.png]]
 
-#+begin_src matlab :results none :exports none
+#+begin_src matlab :exports none
   figure;
+  subplot(1, 2, 1);
   hold on;
-  plot(sr_lpf_1khz_on(:, 3),  sr_lpf_1khz_on(:, 1)-mean(sr_lpf_1khz_on(:, 1)),  'DisplayName', 'Direct');
+  plot(sr_lpf_1khz_on(:, 3),  sr_lpf_1khz_on(:, 1),  'DisplayName', 'Direct');
-  plot(sr_lpf_1khz_on(:, 3),  sr_lpf_1khz_on(:, 2)-mean(sr_lpf_1khz_on(:, 2)),  'DisplayName', 'Slip-Ring');
+  plot(sr_lpf_1khz_on(:, 3),  sr_lpf_1khz_on(:, 2),  'DisplayName', 'Slip-Ring');
   hold off;
   xlim([0, 100]); ylim([-1, 1]);
   legend('Location', 'northeast');
   xlabel('Time [s]'); ylabel('Voltage [V]');
+  subplot(1, 2, 2);
+  hold on;
+  plot(sr_lpf_1khz_on(:, 3),  sr_lpf_1khz_on(:, 1),  'DisplayName', 'Direct');
+  plot(sr_lpf_1khz_on(:, 3),  sr_lpf_1khz_on(:, 2),  'DisplayName', 'Slip-Ring');
+  hold off;
+  xlim([0, 1]); ylim([-1, 1]);
+  legend('Location', 'northeast');
+  xlabel('Time [s]'); ylabel('Voltage [V]');
 #+end_src
 
 #+NAME: fig:sr_lpf_1khz_geophone_time_on
 #+HEADER: :tangle no :exports results :results value raw replace :noweb yes
-#+begin_src matlab :var filepath="figs/sr_lpf_1khz_geophone_time_on.pdf" :var figsize="wide-normal" :post pdf2svg(file=*this*, ext="png")
+#+begin_src matlab :var filepath="figs/sr_lpf_1khz_geophone_time_on.pdf" :var figsize="full-tall" :post pdf2svg(file=*this*, ext="png")
   <<plt-matlab>>
 #+end_src
 
@@ -664,7 +695,7 @@ We compare the signal when the Slip-Ring is OFF (figure [[fig:sr_lpf_1khz_geopho
 
 *** Frequency Domain
 We first compute some parameters that will be used for the PSD computation.
-#+begin_src matlab :results none
+#+begin_src matlab
   dt = sr_lpf_1khz_of(2, 3)-sr_lpf_1khz_of(1, 3);
 
   Fs = 1/dt; % [Hz]
@@ -673,7 +704,7 @@ We first compute some parameters that will be used for the PSD computation.
 #+end_src
 
 Then we compute the Power Spectral Density using =pwelch= function.
-#+begin_src matlab :results none
+#+begin_src matlab
   % Direct measure
   [pxdi_lpf_1khz_of, f] = pwelch(sr_lpf_1khz_of(:, 1), win, [], [], Fs);
   [pxdi_lpf_1khz_on, ~] = pwelch(sr_lpf_1khz_on(:, 1), win, [], [], Fs);
@@ -685,7 +716,7 @@ Then we compute the Power Spectral Density using =pwelch= function.
 
 Finally, we compare the Amplitude Spectral Density of the signals (figure [[fig:sr_lpf_1khz_geophone_asd]]);
 
-#+begin_src matlab :results none
+#+begin_src matlab
   figure;
   hold on;
   plot(f, sqrt(pxdi_lpf_1khz_of), 'DisplayName', 'Direct - OFF');
@@ -693,7 +724,7 @@ Finally, we compare the Amplitude Spectral Density of the signals (figure [[fig:
   plot(f, sqrt(pxdi_lpf_1khz_on), 'DisplayName', 'Direct - ON');
   plot(f, sqrt(pxsr_lpf_1khz_on), 'DisplayName', 'Slip-Ring - ON');
   hold off;
-  xlim([0.1, 500]);
+  xlim([1, 500]);
   set(gca, 'xscale', 'log'); set(gca, 'yscale', 'log');
   xlabel('Frequency [Hz]'); ylabel('ASD of the measured Voltage $\left[\frac{V}{\sqrt{Hz}}\right]$')
   legend('Location', 'southwest');
@@ -710,8 +741,72 @@ Finally, we compare the Amplitude Spectral Density of the signals (figure [[fig:
 #+RESULTS: fig:sr_lpf_1khz_geophone_asd
 [[file:figs/sr_lpf_1khz_geophone_asd.png]]
 
+*** Difference between the direct signal and the signal going through the slip-ring
+We subtract the signal coming from the direct wire to the signal going through the slip-ring when the slip-ring is ON and when it is OFF (figure [[fig:diff_sr_direct]]).
+
+#+begin_src matlab :exports none
+  figure;
+  subplot(1, 2, 1);
+  hold on;
+  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 1)-sr_lpf_1khz_of(:, 2));
+  plot(sr_lpf_1khz_on(:, 3), sr_lpf_1khz_on(:, 1)-sr_lpf_1khz_on(:, 2));
+  hold off;
+  xlim([0, 100]); ylim([-0.3, 0.3]);
+  xlabel('Time [s]'); ylabel('Voltage [V]');
+
+  subplot(1, 2, 2);
+  hold on;
+  plot(sr_lpf_1khz_of(:, 3), sr_lpf_1khz_of(:, 1)-sr_lpf_1khz_of(:, 2), 'DisplayName', 'OFF');
+  plot(sr_lpf_1khz_on(:, 3), sr_lpf_1khz_on(:, 1)-sr_lpf_1khz_on(:, 2), 'DisplayName', 'ON');
+  hold off;
+  xlim([0, 0.1]); ylim([-0.3, 0.3]);
+  legend('Location', 'northeast');
+  xlabel('Time [s]'); ylabel('Voltage [V]');
+#+end_src
+
+#+NAME: fig:diff_sr_direct
+#+HEADER: :tangle no :exports results :results value raw replace :noweb yes
+#+begin_src matlab :var filepath="figs/diff_sr_direct.pdf" :var figsize="full-tall" :post pdf2svg(file=*this*, ext="png")
+  <<plt-matlab>>
+#+end_src
+
+#+NAME: fig:diff_sr_direct
+#+CAPTION: Difference between the signal going directly to the ADC and the signal going through the slip-ring before the ADC
+#+RESULTS: fig:diff_sr_direct
+[[file:figs/diff_sr_direct.png]]
+
+Then we compute the Power Spectral Density using =pwelch= function (figure [[fig:diff_sr_direct_psd]]).
+#+begin_src matlab
+  % Direct measure
+  [px_diff_lpf_1khz_of, f] = pwelch(sr_lpf_1khz_of(:, 1)-sr_lpf_1khz_of(:, 2), win, [], [], Fs);
+  [px_diff_lpf_1khz_on, ~] = pwelch(sr_lpf_1khz_on(:, 1)-sr_lpf_1khz_on(:, 2), win, [], [], Fs);
+#+end_src
+
+#+begin_src matlab :exports none
+  figure;
+  hold on;
+  plot(f, sqrt(px_diff_lpf_1khz_of), 'DisplayName', 'OFF');
+  plot(f, sqrt(px_diff_lpf_1khz_on), 'DisplayName', 'ON');
+  hold off;
+  xlim([1, 500]);
+  set(gca, 'xscale', 'log'); set(gca, 'yscale', 'log');
+  xlabel('Frequency [Hz]'); ylabel('ASD of the measured Voltage $\left[\frac{V}{\sqrt{Hz}}\right]$')
+  legend('Location', 'southwest');
+#+end_src
+
+#+NAME: fig:diff_sr_direct_psd
+#+HEADER: :tangle no :exports results :results value raw replace :noweb yes
+#+begin_src matlab :var filepath="figs/diff_sr_direct_psd.pdf" :var figsize="full-tall" :post pdf2svg(file=*this*, ext="png")
+  <<plt-matlab>>
+#+end_src
+
+#+NAME: fig:diff_sr_direct_psd
+#+CAPTION: Amplitude Spectral Density of the difference between the signal going directly to the ADC and the signal going through the slip-ring before the ADC
+#+RESULTS: fig:diff_sr_direct_psd
+[[file:figs/diff_sr_direct_psd.png]]
+
 *** Conclusion
 #+begin_important
   - Using the LPF, we don't see any additional noise coming from the slip-ring when it is turned ON
-  - We here observe a signal at $50Hz$ and its harmonics
+  - The signal going through the slip-ring only differs from the direct signal by some 50Hz and its harmonics
 #+end_important