nass-micro-station-measurements/disturbance-sr-rz/index.org

Vibrations induced by the Slip-Ring and the Spindle

• Experimental Setup
• Data Analysis
  • ZIP file containing the data and matlab files
  • Load data
  • Voltage to Velocity
  • Time domain plots
  • Frequency Domain
  • Conclusion

Experimental Setup

Setup: All the stages are OFF.

Two geophone are use:

• One on the marble (corresponding to the first column in the data)
• One at the sample location (corresponding to the second column in the data)

Two voltage amplifiers are used, their setup is:

• gain of 60dB
• AC/DC switch on AC
• Low pass filter at 1kHz

A first order low pass filter is also added at the input of the voltage amplifiers.

Goal:

• Identify the vibrations induced by the rotation of the Slip-Ring and Spindle

Measurements: Three measurements are done:

Measurement File	Description
mat/data_024.mat	All the stages are OFF
mat/data_025.mat	The slip-ring is ON and rotates at 6rpm. The spindle is OFF
mat/data_026.mat	The slip-ring and spindle are both ON. They are both turning at 6rpm

Each of the measurement mat file contains one data array with 3 columns:

Column number	Description
1	Geophone - Marble
2	Geophone - Sample
3	Time

A movie showing the experiment is shown on figure fig:exp_sl_sp_gif.

Movie of the experiment, rotation speed is 6rpm

Data Analysis

<<sec:spindle_slip_ring_vibrations>>

ZIP file containing the data and matlab files   ignore

All the files (data and Matlab scripts) are accessible here.

Load data

  of = load('mat/data_024.mat', 'data'); of = of.data;
  sr = load('mat/data_025.mat', 'data'); sr = sr.data;
  sp = load('mat/data_026.mat', 'data'); sp = sp.data;

Voltage to Velocity

We convert the measured voltage to velocity using the function voltageToVelocityL22 (accessible here).

  gain = 60; % [dB]

  of(:, 1) = voltageToVelocityL22(of(:, 1), of(:, 3), gain);
  sr(:, 1) = voltageToVelocityL22(sr(:, 1), sr(:, 3), gain);
  sp(:, 1) = voltageToVelocityL22(sp(:, 1), sp(:, 3), gain);

  of(:, 2) = voltageToVelocityL22(of(:, 2), of(:, 3), gain);
  sr(:, 2) = voltageToVelocityL22(sr(:, 2), sr(:, 3), gain);
  sp(:, 2) = voltageToVelocityL22(sp(:, 2), sp(:, 3), gain);

Time domain plots

  figure;
  hold on;
  plot(sp(:, 3), sp(:, 1), 'DisplayName', 'Spindle - 6rpm');
  plot(sr(:, 3), sr(:, 1), 'DisplayName', 'Slip-Ring - 6rpm');
  plot(of(:, 3), of(:, 1), 'DisplayName', 'OFF');
  hold off;
  xlabel('Time [s]'); ylabel('Velocity [m/s]');
  xlim([0, 100]);
  legend('Location', 'northeast');

  <<plt-matlab>>

Velocity as measured by the geophone located on the marble - Time domain

  figure;
  hold on;
  plot(sp(:, 3), sp(:, 2), 'DisplayName', 'Spindle and Slip-Ring');
  plot(sr(:, 3), sr(:, 2), 'DisplayName', 'Only Slip-Ring');
  plot(of(:, 3), of(:, 2), 'DisplayName', 'OFF');
  hold off;
  xlabel('Time [s]'); ylabel('Velocity [m/s]');
  xlim([0, 100]);
  legend('Location', 'northeast');

  <<plt-matlab>>

Velocity as measured by the geophone at the sample location - Time domain

  <<plt-matlab>>

Velocity as measured by the geophone at the sample location - Time domain

Frequency Domain

We first compute some parameters that will be used for the PSD computation.

  dt = of(2, 3)-of(1, 3);

  Fs = 1/dt; % [Hz]

  win = hanning(ceil(10*Fs));

Then we compute the Power Spectral Density using pwelch function.

First for the geophone located on the marble

  [pxof_m, f] = pwelch(of(:, 1), win, [], [], Fs);
  [pxsr_m, ~] = pwelch(sr(:, 1), win, [], [], Fs);
  [pxsp_m, ~] = pwelch(sp(:, 1), win, [], [], Fs);

And for the geophone located at the sample position.

  [pxof_s, ~] = pwelch(of(:, 2), win, [], [], Fs);
  [pxsr_s, ~] = pwelch(sr(:, 2), win, [], [], Fs);
  [pxsp_s, ~] = pwelch(sp(:, 2), win, [], [], Fs);

And finally for the relative velocity between the sample and the marble.

  [pxof_r, ~] = pwelch(of(:, 2)-of(:, 1), win, [], [], Fs);
  [pxsr_r, ~] = pwelch(sr(:, 2)-sr(:, 1), win, [], [], Fs);
  [pxsp_r, ~] = pwelch(sp(:, 2)-sp(:, 1), win, [], [], Fs);

And we plot the ASD of the measured velocities:

• figure fig:sr_sp_psd_marble_compare for the geophone located on the marble
• figure fig:sr_sp_psd_sample_compare for the geophone at the sample position

  figure;
  hold on;
  plot(f, sqrt(pxsp_m), 'DisplayName', 'Spindle - 6rpm');
  plot(f, sqrt(pxsr_m), 'DisplayName', 'Slip-Ring - 6rpm');
  plot(f, sqrt(pxof_m), 'DisplayName', 'OFF');
  hold off;
  set(gca, 'xscale', 'log');
  set(gca, 'yscale', 'log');
  xlabel('Frequency [Hz]'); ylabel('ASD of the measured velocity $\left[\frac{m/s}{\sqrt{Hz}}\right]$')
  legend('Location', 'southwest');
  xlim([2, 500]);

  <<plt-matlab>>

Comparison of the ASD of the measured velocities from the Geophone on the marble

  figure;
  hold on;
  plot(f, sqrt(pxsp_s), 'DisplayName', 'Spindle - 6rpm');
  plot(f, sqrt(pxsr_s), 'DisplayName', 'Slip-Ring - 6rpm');
  plot(f, sqrt(pxof_s), 'DisplayName', 'OFF');
  hold off;
  set(gca, 'xscale', 'log');
  set(gca, 'yscale', 'log');
  xlabel('Frequency [Hz]'); ylabel('ASD of the measured velocity $\left[\frac{m/s}{\sqrt{Hz}}\right]$')
  legend('Location', 'southwest');
  xlim([2, 500]);

  <<plt-matlab>>

Comparison of the ASD of the measured velocities from the Geophone at the sample location

  figure;
  hold on;
  plot(f, sqrt(pxsp_r), 'DisplayName', 'Spindle - 6rpm');
  plot(f, sqrt(pxsr_r), 'DisplayName', 'Slip-Ring - 6rpm');
  plot(f, sqrt(pxof_r), 'DisplayName', 'OFF');
  hold off;
  set(gca, 'xscale', 'log');
  set(gca, 'yscale', 'log');
  xlabel('Frequency [Hz]'); ylabel('ASD of the relative velocity $\left[\frac{m/s}{\sqrt{Hz}}\right]$')
  legend('Location', 'southwest');
  xlim([2, 500]);

  <<plt-matlab>>

Comparison of the ASD of the relative velocity

Conclusion

• The slip-ring rotation induces almost no vibrations on the marble, and only a little vibrations on the sample above 100Hz.
• The spindle rotation induces a lot of vibrations of the sample as well as on the granite.

• There is a huge peak at 24Hz on the sample vibration but not on the granite vibration

  • The peak is really sharp, could this be due to magnetic effect?
  • Should redo the measurement with piezo accelerometers.