nass-micro-station-measurements/slip-ring-test/index.org

Measurements

• Effect of the rotation of the Slip-Ring
  • Measurement Description
  • Load data
  • Analysis
  • Conclusion
• Measure of the noise of the Voltage Amplifier
  • Measurement Description
  • Load data
  • Time Domain
  • Frequency Domain
  • Conclusion
• Measure of the noise induced by the Slip-Ring
  • Measurement Description
  • Load data
  • Time Domain
  • Frequency Domain
  • Conclusion
• Measure of the noise induced by the slip ring when using a geophone
  • Measurement Description
  • Load data
  • Time Domain
  • Frequency Domain
  • Conclusion
• Measure of the influence of the AC/DC option on the voltage amplifiers
  • Measurement Description
  • Load data
  • Time Domain
  • Frequency Domain
  • Conclusion

Effect of the rotation of the Slip-Ring

The data and matlab files are accessible here.

Measurement Description

Random Signal is generated by one DAC of the SpeedGoat.

The signal going out of the DAC is split into two:

• one BNC cable is directly connected to one ADC of the SpeedGoat
• one BNC cable goes two times in the Slip-Ring (from bottom to top and then from top to bottom) and then is connected to one ADC of the SpeedGoat

Two measurements are done.

Data File	Description
mat/data_001.mat	Slip-ring not turning
mat/data_002.mat	Slip-ring turning

For each measurement, the measured signals are:

Data File	Description
t	Time vector
x1	Direct signal
x2	Signal going through the Slip-Ring

The goal is to determine is the signal is altered when the spindle is rotating.

Here, the rotation speed of the Slip-Ring is set to 1rpm.

Load data

We load the data of the z axis of two geophones.

  sr_off = load('mat/data_001.mat', 't', 'x1', 'x2');
  sr_on  = load('mat/data_002.mat', 't', 'x1', 'x2');

Analysis

Let's first look at the signal produced by the DAC (figure fig:random_signal).

  figure;
  hold on;
  plot(sr_on.t,  sr_on.x1);
  hold off;
  xlabel('Time [s]'); ylabel('Voltage [V]');
  xlim([0 10]);

  <<plt-matlab>>

Random signal produced by the DAC

We now look at the difference between the signal directly measured by the ADC and the signal that goes through the slip-ring (figure fig:slipring_comp_signals).

  figure;
  hold on;
  plot(sr_on.t,  sr_on.x1  -  sr_on.x2,  'DisplayName', 'Slip-Ring - $\omega = 1rpm$');
  plot(sr_off.t, sr_off.x1 - sr_off.x2,'DisplayName', 'Slip-Ring off');
  hold off;
  xlabel('Time [s]'); ylabel('Voltage [V]');
  xlim([0 10]);
  legend('Location', 'northeast');

  <<plt-matlab>>

Alteration of the signal when the slip-ring is turning

  dt = sr_on.t(2) - sr_on.t(1);
  Fs = 1/dt; % [Hz]

  win = hanning(ceil(1*Fs));

  [pxx_on,  f] = pwelch(sr_on.x1  - sr_on.x2,  win, [], [], Fs);
  [pxx_off, ~] = pwelch(sr_off.x1 - sr_off.x2, win, [], [], Fs);

  <<plt-matlab>>

ASD of the measured noise

Conclusion

Remaining questions:

• Should the measurement be redone using voltage amplifiers?
• Use higher rotation speed and measure for longer periods (to have multiple revolutions) ?

Measure of the noise of the Voltage Amplifier

The data and matlab files are accessible here.

Measurement Description

Goal:

• Determine the Voltage Amplifier noise

Setup:

• The two inputs (differential) of the voltage amplifier are shunted with 50Ohms
• The AC/DC option of the Voltage amplifier is on AC
• The low pass filter is set to 1hHz
• We measure the output of the voltage amplifier with a 16bits ADC of the Speedgoat

Measurements:

• data_003: Ampli OFF
• data_004: Ampli ON set to 20dB
• data_005: Ampli ON set to 40dB
• data_006: Ampli ON set to 60dB

Load data

  amp_off = load('mat/data_003.mat', 'data'); amp_off = amp_off.data(:, [1,3]);
  amp_20d = load('mat/data_004.mat', 'data'); amp_20d = amp_20d.data(:, [1,3]);
  amp_40d = load('mat/data_005.mat', 'data'); amp_40d = amp_40d.data(:, [1,3]);
  amp_60d = load('mat/data_006.mat', 'data'); amp_60d = amp_60d.data(:, [1,3]);

Time Domain

The time domain signals are shown on figure fig:ampli_noise_time.

  <<plt-matlab>>

Output of the amplifier

Frequency Domain

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

  dt = amp_off(2, 2)-amp_off(1, 2);

  Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function.

  [pxoff, f] = pwelch(amp_off(:,1), win, [], [], Fs);
  [px20d, ~] = pwelch(amp_20d(:,1), win, [], [], Fs);
  [px40d, ~] = pwelch(amp_40d(:,1), win, [], [], Fs);
  [px60d, ~] = pwelch(amp_60d(:,1), win, [], [], Fs);

We compute the theoretical ADC noise.

  q = 20/2^16; % quantization
  Sq = q^2/12/1000; % PSD of the ADC noise

Finally, the ASD is shown on figure fig:ampli_noise_psd.

  <<plt-matlab>>

Amplitude Spectral Density of the measured voltage at the output of the voltage amplifier

Conclusion

Noise induced by the voltage amplifiers is not a limiting factor.

Measure of the noise induced by the Slip-Ring

The data and matlab files are accessible here.

Measurement Description

Goal:

• Determine the noise induced by the slip-ring

Setup:

• 0V is generated by the DAC of the Speedgoat
• Using a T, one part goes directly to the ADC
• The other part goes to the slip-ring 2 times and then to the ADC
• The parameters of the Voltage Amplifier are: 80dB, AC, 1kHz
• Every stage of the station is OFF

First column: Direct measure Second column: Slip-ring measure

Measurements:

• data_008: Slip-Ring OFF
• data_009: Slip-Ring ON
• data_010: Slip-Ring ON and omega=6rpm
• data_011: Slip-Ring ON and omega=60rpm

Slip-Ring rotating at 6rpm

Slip-Ring rotating at 60rpm

Load data

We load the data of the z axis of two geophones.

  sr_off = load('mat/data_008.mat', 'data'); sr_off = sr_off.data;
  sr_on  = load('mat/data_009.mat', 'data'); sr_on  = sr_on.data;
  sr_6r  = load('mat/data_010.mat', 'data'); sr_6r  = sr_6r.data;
  sr_60r = load('mat/data_011.mat', 'data'); sr_60r = sr_60r.data;

Time Domain

We plot the time domain data for the direct measurement (figure fig:sr_direct_time) and for the signal going through the slip-ring (figure fig:sr_slipring_time);

  <<plt-matlab>>

Direct measurement

  <<plt-matlab>>

Measurement of the signal going through the Slip-Ring

Frequency Domain

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

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

  Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function.

  [pxdir, f] = pwelch(sr_off(:, 1), win, [], [], Fs);
  [pxoff, ~] = pwelch(sr_off(:, 2), win, [], [], Fs);
  [pxon,  ~] = pwelch(sr_on(:, 2),  win, [], [], Fs);
  [px6r,  ~] = pwelch(sr_6r(:, 2),  win, [], [], Fs);
  [px60r, ~] = pwelch(sr_60r(:, 2), win, [], [], Fs);

And we plot the ASD of the measured signals (figure fig:sr_psd_compare);

  figure;
  hold on;
  plot(f, sqrt(pxoff), 'DisplayName', 'OFF');
  plot(f, sqrt(pxon),  'DisplayName', 'ON');
  plot(f, sqrt(px6r),  'DisplayName', '6rpm');
  plot(f, sqrt(px60r), 'DisplayName', '60rpm');
  plot(f, sqrt(pxdir), 'k-', 'DisplayName', 'Direct');
  hold off;
  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', 'northeast');
  xlim([0.1, 500]);

  <<plt-matlab>>

Comparison of the ASD of the measured signals when the slip-ring is ON, OFF and turning

Conclusion

Measure of the noise induced by the slip ring when using a geophone

The data and matlab files are accessible here.

Measurement Description

Goal:

• Determine if the noise induced by the slip-ring is a limiting factor when measuring the signal coming from a geophone

Setup:

• The geophone is located at the sample location

• The two Voltage amplifiers have the following settings:

  • AC
  • 60dB
  • 1kHz

• The signal from the geophone is split into two using a T-BNC:

  • One part goes directly to the voltage amplifier and then to the ADC.
  • The other part goes to the slip-ring=>voltage amplifier=>ADC.

First column: Direct measure Second column: Slip-ring measure

Measurements:

• data_012: Slip-Ring OFF
• data_013: Slip-Ring ON

Load data

We load the data of the z axis of two geophones.

  sr_off = load('mat/data_012.mat', 'data'); sr_off = sr_off.data;
  sr_on  = load('mat/data_013.mat', 'data'); sr_on  = sr_on.data;

Time Domain

We compare the signal when the Slip-Ring is OFF (figure fig:sr_geophone_time_off) and when it is ON (figure fig:sr_geophone_time_on).

  <<plt-matlab>>

Comparison of the time domain signals when the slip-ring is OFF

  <<plt-matlab>>

Comparison of the time domain signals when the slip-ring is ON

Frequency Domain

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

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

  Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function.

  % Direct measure
  [pxdoff, ~] = pwelch(sr_off(:, 1), win, [], [], Fs);
  [pxdon,  ~] = pwelch(sr_on(:, 1),  win, [], [], Fs);

  % Slip-Ring measure
  [pxsroff, f] = pwelch(sr_off(:, 2), win, [], [], Fs);
  [pxsron,  ~] = pwelch(sr_on(:, 2),  win, [], [], Fs);

Finally, we compare the Amplitude Spectral Density of the signals (figure /tdehaeze/nass-micro-station-measurements/src/commit/d39efd8afe12f3edeef22a1aa0a8c35a42756432/slip-ring-test/);

  figure;
  hold on;
  plot(f, sqrt(pxdoff), 'DisplayName', 'Direct - OFF');
  plot(f, sqrt(pxsroff), 'DisplayName', 'Slip-Ring - OFF');
  plot(f, sqrt(pxdon),  'DisplayName', 'Direct - ON');
  plot(f, sqrt(pxsron),  'DisplayName', 'Slip-Ring - ON');
  hold off;
  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', 'northeast');
  xlim([0.1, 500]);

  <<plt-matlab>>

Comparison of the Amplitude Spectral Sensity

  <<plt-matlab>>

Comparison of the Amplitude Spectral Sensity - Zoom

Conclusion

• When the slip-ring is OFF, it does not add any noise to the measurement
• When the slip-ring is ON, it adds significant noise to the signal

Measure of the influence of the AC/DC option on the voltage amplifiers

The data and matlab files are accessible here.

Measurement Description

Goal:

• Measure the influence of the high-pass filter option of the voltage amplifiers

Setup:

• One geophone is located on the marble.
• It's signal goes to two voltage amplifiers with a gain of 60dB.
• One voltage amplifier is on the AC option, the other is on the DC option.

Measurements: First measurement (mat/data_014.mat file):

Column	Signal
1	Amplifier 1 with AC option
2	Amplifier 2 with DC option
3	Time

Second measurement (mat/data_015.mat file):

Column	Signal
1	Amplifier 1 with DC option
2	Amplifier 2 with AC option
3	Time

Picture of the two voltages amplifiers

Load data

We load the data of the z axis of two geophones.

  meas14 = load('mat/data_014.mat', 'data'); meas14 = meas14.data;
  meas15 = load('mat/data_015.mat', 'data'); meas15 = meas15.data;

Time Domain

The signals are shown on figure fig:ac_dc_option_time.

  <<plt-matlab>>

Comparison of the signals going through the Voltage amplifiers

Frequency Domain

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

  dt = meas14(2, 3)-meas14(1, 3);

  Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function.

  [pxamp1ac, f] = pwelch(meas14(:, 1), win, [], [], Fs);
  [pxamp2dc, ~] = pwelch(meas14(:, 2), win, [], [], Fs);

  [pxamp1dc, ~] = pwelch(meas15(:, 1), win, [], [], Fs);
  [pxamp2ac, ~] = pwelch(meas15(:, 2), win, [], [], Fs);

The ASD of the signals are compare on figure fig:ac_dc_option_asd.

  <<plt-matlab>>

Amplitude Spectral Density of the measured signals

Conclusion