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Measurements On the Slip-Ring

Table of Contents

First, the noise induced by the slip-ring is measured when using geophones:

Then, we determine is the slip-ring add some noise to the signal when it is turning:

1 Effect of the Slip-Ring on the signal when turned ON - Geophone measurement

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

1.1 Experimental Setup

Goal: The goal is to determine if some noise is added to a signal passing through the slip-ring.

Setup: Two measurements are made with the control systems of all the stages turned OFF.

One geophone is located on the marble while the other is located at the sample location (figure 1).

The two signals from the geophones are amplified with voltage amplifiers with the following settings:

  • Gain: 60dB
  • AC/DC switch: AC
  • Low pass filter at the output set at 1kHz

IMG_20190430_112615.jpg

Figure 1: Experimental Setup

Measurements: Two measurements are done:

Measurement File Description
mat/meas_018.mat Signal goes through the Slip-ring (as shown on the figure above)
mat/meas_019.mat Signal from the top geophone does not goes through the Slip-ring

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

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

1.2 Load data

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

meas_sr = load('mat/data_018.mat', 'data'); meas_sr = meas_sr.data;
meas_di = load('mat/data_019.mat', 'data'); meas_di = meas_di.data;

1.3 Analysis - Time Domain

First, we compare the time domain signals for the two experiments (figure 2). 

figure;
hold on;
plot(meas_di(:, 3), meas_di(:, 2), 'DisplayName', 'Geophone - Direct');
plot(meas_sr(:, 3), meas_sr(:, 2), 'DisplayName', 'Geophone - Slip-Ring');
hold off;
xlabel('Time [s]'); ylabel('Voltage [V]');
xlim([0, 50]);
legend('location', 'northeast');

slipring_time.png

Figure 2: Effect of the Slip-Ring on the measured signal of the geophone at the sample location - Time domain

1.4 Analysis - Frequency Domain

We then compute the Power Spectral Density of the two signals and we compare them (figure 3). 

dt = meas_di(2, 3) - meas_di(1, 3);
Fs = 1/dt;

win = hanning(ceil(5*Fs));

[px_di, f] = pwelch(meas_di(:, 2), win, [], [], Fs);
[px_sr, ~] = pwelch(meas_sr(:, 2), win, [], [], Fs);

figure;
hold on;
plot(f, sqrt(px_sr), 'DisplayName', 'Slip-Ring');
plot(f, sqrt(px_di), 'DisplayName', 'Wire');
hold off;
set(gca, 'xscale', 'log');
set(gca, 'yscale', 'log');
xlabel('Frequency [Hz]'); ylabel('Amplitude Spectral Density $\left[\frac{V}{\sqrt{Hz}}\right]$')
xlim([1, 500]);
legend('Location', 'southwest');

slipring_asd.png

Figure 3: Effect of the Slip-Ring on the measured signal of the geophone at the sample location - Frequency domain

1.5 Conclusion

  • The voltage amplifiers are saturating during the measurements (as shown by the LED on figure 1)
  • This saturation is mainly due to high frequency noise => a LPF will be added at the input of the voltage amplifiers in the further measurements
  • The measurements will be redone

2 Measure of the noise induced by the Slip-Ring using voltage amplifiers - Geophone

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

2.1 First Measurement without LPF

2.1.1 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 same following settings:
    • Gain: 60dB
    • AC/DC option: AC
    • Low pass filter at the output set to 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

Measurements: Two measurements are done:

Measurement File Description
data_012 Slip-Ring OFF
data_013 Slip-Ring ON

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

Column number Description
1 Measure of the geophone at the sample position with a direct wire
2 Measure of the geophone at the sample position going through the slip-ring
3 Time

2.1.2 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;

2.1.3 Time Domain

We compare the signal when the Slip-Ring is OFF (figure 4) and when it is ON (figure 5).

sr_geophone_time_off.png

Figure 4: Comparison of the time domain signals when the slip-ring is OFF

sr_geophone_time_on.png

Figure 5: Comparison of the time domain signals when the slip-ring is ON

2.1.4 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 6); 

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]);

sr_geophone_asd.png

Figure 6: Comparison of the Amplitude Spectral Sensity

sr_geophone_asd_zoom.png

Figure 7: Comparison of the Amplitude Spectral Sensity - Zoom

2.1.5 Conclusion

  • The fact that the Slip-Ring is turned ON adds some noise to the signals
  • The signal going through the Slip-Ring is less noisy than the one going directly to the ADC
  • This could be due to better electromagnetic isolation in the slip-ring

Questions:

  • Can the sharp peak on figure 7 be due to the Aliasing?

2.2 Measurement using an oscilloscope

2.2.1 Measurement Setup

We are now measuring the same signals than in the previous section, but with an oscilloscope instead of with the Speedgoat ADC.

2.2.2 Observations

Then the Slip-Ring is ON (figure 8), we observe a signal at 40kHz with a peak-to-peak amplitude of 200mV for the direct measure and 100mV for the signal going through the Slip-Ring.

Then the Slip-Ring is OFF, we don't observe this noise at 40kHz anymore (figure 9).

IMG_20190506_160420.jpg

Figure 8: Signals measured by the oscilloscope - Slip-Ring ON - Yellow: Direct measure - Blue: Through Slip-Ring

IMG_20190506_160438.jpg

Figure 9: Signals measured by the oscilloscope - Slip-Ring OFF - Yellow: Direct measure - Blue: Through Slip-Ring

2.2.3 Conclusion

  • By looking at the signals using an oscilloscope, there is a lot of high frequency noise when turning on the Slip-Ring
  • This can eventually saturate the voltage amplifiers (seen by a led indicating saturation)
  • The choice is to add a Low pass filter before the voltage amplifiers to not saturate them and filter the noise.

2.3 New measurements with a LPF before the Voltage Amplifiers

2.3.1 Setup description

Goal: The goal is to see if we can remove high frequency noise from the signals before the voltage amplifiers in order to not saturate them.

Setup: We are measuring the signal from a geophone put at the sample position. Using a BNC slitter, one part is going directly to the Low pass filter, voltage amplifier and ADC (first column), the other part is going through the slip ring before the low pass filter and the voltage amplifier (second column).

The two voltage amplifiers have the same following settings:

  • Gain: 60dB
  • AC/DC option: DC
  • Low pass filter at the output set to 1kHz

The low pass filter is a first order low pass filter RC circuit. It is added before the Voltage Amplifiers and has the following values:

\begin{aligned} R &= 1k\Omega \\ C &= 1\mu F \end{aligned}

And the cut-off frequency is \(f_c = \frac{1}{RC} = 160Hz\).

Measurements: Two measurements are done:

Measurement File Description
mat/data_016.mat Signal from the geophone at the sample location - Slip-Ring OFF
mat/data_017.mat Signal from the geophone at the sample location - Slip-Ring ON

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

Column number Description
1 Direct measurement
2 Signal going through the slip-ring
3 Time

2.3.2 Load data

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

sr_lpf_off = load('mat/data_016.mat', 'data'); sr_lpf_off = sr_lpf_off.data;
sr_lpf_on  = load('mat/data_017.mat', 'data'); sr_lpf_on  = sr_lpf_on.data;

2.3.3 Time Domain

We compare the signal when the Slip-Ring is OFF (figure 10) and when it is ON (figure 11).

sr_lpf_geophone_time_off.png

Figure 10: Comparison of the time domain signals when the slip-ring is OFF

sr_lpf_geophone_time_on.png

Figure 11: Comparison of the time domain signals when the slip-ring is ON

2.3.4 Frequency Domain

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

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

Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function. 

% Direct measure
[pxd_lpf_off, ~] = pwelch(sr_lpf_off(:, 1), win, [], [], Fs);
[pxd_lpf_on,  ~] = pwelch(sr_lpf_on(:, 1),  win, [], [], Fs);

% Slip-Ring measure
[pxsr_lpf_off, f] = pwelch(sr_lpf_off(:, 2), win, [], [], Fs);
[pxsr_lpf_on,  ~] = pwelch(sr_lpf_on(:, 2),  win, [], [], Fs);

Finally, we compare the Amplitude Spectral Density of the signals (figure 12); 

figure;
hold on;
plot(f, sqrt(pxd_lpf_off),  'DisplayName', 'Direct - OFF');
plot(f, sqrt(pxsr_lpf_off), 'DisplayName', 'Slip-Ring - OFF');
plot(f, sqrt(pxd_lpf_on),   'DisplayName', 'Direct - ON');
plot(f, sqrt(pxsr_lpf_on),  'DisplayName', 'Slip-Ring - ON');
hold off;
xlim([0.1, 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');

sr_lpf_geophone_asd.png

Figure 12: Comparison of the Amplitude Spectral Sensity

sr_lpf_geophone_asd_zoom.png

Figure 13: Comparison of the Amplitude Spectral Sensity - Zoom

2.3.5 Conclusion

  • Using the LPF, we don't see any additional noise coming from the slip-ring when it is turned ON
  • However, we should use a smaller value of the capacitor to have a cut-off frequency at \(1kHz\)
  • We here observe a signal at \(50Hz\) and its harmonics

2.4 Measurement of the noise induced by the slip-ring with additional LPF at 1kHz

2.4.1 Measurement description

Setup: Voltage amplifier:

  • 60db
  • AC
  • 1kHz

Additionnal LPF at 1kHz

geophone at the sample location slit into 2 BNC:

  • first one (column one): direct wire
  • second one (second column): slip-ring wire

Additionnal LPF is added before the voltage amplifiers

Goal:

Measurements:

Three measurements are done:

Measurement File Description
mat/data_035.mat All off
mat/data_036.mat Slip-Ring ON

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

Column number Description
1 Direct Wire
2 Slip-Ring Wire
3 Time

2.4.2 Load data

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

sr_lpf_1khz_of = load('mat/data_035.mat', 'data'); sr_lpf_1khz_of = sr_lpf_1khz_of.data;
sr_lpf_1khz_on = load('mat/data_036.mat', 'data'); sr_lpf_1khz_on = sr_lpf_1khz_on.data;

2.4.3 Time Domain

We compare the signal when the Slip-Ring is OFF (figure 14) and when it is ON (figure 15).

sr_lpf_1khz_geophone_time_off.png

Figure 14: Comparison of the time domain signals when the slip-ring is OFF

sr_lpf_1khz_geophone_time_on.png

Figure 15: Comparison of the time domain signals when the slip-ring is ON

2.4.4 Frequency Domain

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

dt = sr_lpf_1khz_of(2, 3)-sr_lpf_1khz_of(1, 3);

Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function. 

% 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);

% Slip-Ring measure
[pxsr_lpf_1khz_of, ~] = pwelch(sr_lpf_1khz_of(:, 2), win, [], [], Fs);
[pxsr_lpf_1khz_on, ~] = pwelch(sr_lpf_1khz_on(:, 2), win, [], [], Fs);

Finally, we compare the Amplitude Spectral Density of the signals (figure 16); 

figure;
hold on;
plot(f, sqrt(pxdi_lpf_1khz_of), 'DisplayName', 'Direct - OFF');
plot(f, sqrt(pxsr_lpf_1khz_of), 'DisplayName', 'Slip-Ring - OFF');
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]);
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');

sr_lpf_1khz_geophone_asd.png

Figure 16: Comparison of the Amplitude Spectral Sensity

2.4.5 Conclusion

  • 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

3 Effect of the rotation of the Slip-Ring - Noise

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

3.1 Measurement Description

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

Setup: Random Signal is generated by one SpeedGoat DAC.

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

All the stages are turned OFF except the Slip-Ring.

Measurements:

Data File Description
mat/data_001.mat Slip-ring not turning but ON
mat/data_002.mat Slip-ring turning at 1rpm

For each measurement, the measured signals are:

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

3.2 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');

3.3 Analysis

Let's first look at the signal produced by the DAC (figure 17). 

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

random_signal.png

Figure 17: 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 18). 

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');

slipring_comp_signals.png

Figure 18: 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);

psd_noise.png

Figure 19: ASD of the measured noise

3.4 Conclusion

  • The measurement is mostly limited by the resolution of the Speedgoat DAC (16bits over \(\pm 10 V\))
  • In section 4, the same measurement is done but voltage amplifiers are added to amplify the noise

4 Measure of the noise induced by the Slip-Ring using voltage amplifiers - Noise

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

4.1 Measurement Description

Goal:

  • Determine the noise induced by the slip-ring when turned ON and when rotating

Setup:

  • 0V is generated by one Speedgoat DAC
  • Using a T, one part goes directly to one Speedgoat ADC
  • The other part goes to the slip-ring 2 times and then to one voltage amplifier before going to the ADC
  • The parameters of the Voltage Amplifier are:
    • gain of 80dB
    • AC/DC option to AC (it adds an high pass filter at 1.5Hz at the input of the voltage amplifier)
    • Output Low pass filter set at 1kHz
  • Every stage of the station is OFF

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

Measurements:

Data File Description
mat/data_008.mat Slip-Ring OFF
mat/data_009.mat Slip-Ring ON
mat/data_010.mat Slip-Ring ON and omega=6rpm
mat/data_011.mat Slip-Ring ON and omega=60rpm

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

Column number Description
1 Signal going directly to the ADC
2 Signal going through the Slip-Ring
3 Time

VID_20190503_160831.gif

Figure 20: Slip-Ring rotating at 6rpm

VID_20190503_161401.gif

Figure 21: Slip-Ring rotating at 60rpm

4.2 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;

4.3 Time Domain

We plot the time domain data for the direct measurement (figure 22) and for the signal going through the slip-ring (figure 23);

sr_direct_time.png

Figure 22: Direct measurement

sr_slipring_time.png

Figure 23: Measurement of the signal going through the Slip-Ring

4.4 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 24); 

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]);

sr_psd_compare.png

Figure 24: Comparison of the ASD of the measured signals when the slip-ring is ON, OFF and turning

Questions:

  • Why is there some sharp peaks? Can this be due to aliasing?
  • It is possible that the amplifiers were saturating during the measurements. This saturation could be due to high frequency noise.

4.5 Conclusion

  • The measurements are re-done using an additional low pass filter at the input of the voltage amplifier

5 Measure of the noise induced by the Slip-Ring rotation - LPF added

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

5.1 Measurement description

Setup: Voltage amplifier:

  • 60db
  • AC
  • 1kHz

Additionnal LPF at 1kHz

Goal:

Measurements:

Three measurements are done:

Measurement File Description
mat/data_030.mat All off
mat/data_031.mat Slip-Ring on
mat/data_032.mat Slip-Ring 6rpm
mat/data_033.mat Slip-Ring 60rpm

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

Column number Description
1 Direct Measure
2 Slip-Ring
3 Time

5.2 Load data

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

sr_of = load('mat/data_030.mat', 'data'); sr_of = sr_of.data;
sr_on = load('mat/data_031.mat', 'data'); sr_on = sr_on.data;
sr_6r = load('mat/data_032.mat', 'data'); sr_6r = sr_6r.data;
sr_60 = load('mat/data_033.mat', 'data'); sr_60 = sr_60.data;

5.3 Time Domain

We plot the time domain data for the direct measurement (figure 25) and for the signal going through the slip-ring (figure 27);

sr_direct_1khz_time.png

Figure 25: Direct measurement

xlim([0, 0.2]); ylim([-2e-3, 2e-3]);

sr_direct_1khz_time_zoom.png

Figure 26: Direct measurement - Zoom

sr_slipring_1khz_time.png

Figure 27: Measurement of the signal going through the Slip-Ring

5.4 Frequency Domain - Direct Signal

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

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

Fs = 1/dt; % [Hz]

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

Then we compute the Power Spectral Density using pwelch function. 

[px_d_of, f] = pwelch(sr_of(:, 1), win, [], [], Fs);
[px_d_on, ~] = pwelch(sr_on(:, 1), win, [], [], Fs);
[px_d_6r, ~] = pwelch(sr_6r(:, 1), win, [], [], Fs);
[px_d_60, ~] = pwelch(sr_60(:, 1), win, [], [], Fs);

figure;
hold on;
plot(f, sqrt(px_d_of), 'DisplayName', 'OFF');
plot(f, sqrt(px_d_on), 'DisplayName', 'ON');
plot(f, sqrt(px_d_6r), 'DisplayName', '6rpm');
plot(f, sqrt(px_d_60), 'DisplayName', '60rpm');
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, 5000]);

sr_psd_1khz_direct.png

Figure 28: Amplitude Spectral Density of the signal going directly to the ADC

5.5 Frequency Domain - Slip-Ring Signal

[px_sr_of, f] = pwelch(sr_of(:, 2), win, [], [], Fs);
[px_sr_on, ~] = pwelch(sr_on(:, 2), win, [], [], Fs);
[px_sr_6r, ~] = pwelch(sr_6r(:, 2), win, [], [], Fs);
[px_sr_60, ~] = pwelch(sr_60(:, 2), win, [], [], Fs);

figure;
hold on;
plot(f, sqrt(px_sr_of), 'DisplayName', 'OFF');
plot(f, sqrt(px_sr_on), 'DisplayName', 'ON');
plot(f, sqrt(px_sr_6r), 'DisplayName', '6rpm');
plot(f, sqrt(px_sr_60), 'DisplayName', '60rpm');
plot(f, sqrt(px_d_of), '-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, 5000]);

sr_psd_1khz_slipring.png

Figure 29: Amplitude Spectral Density of the signal going through the slip-ring

5.6 Conclusion

  • We observe peaks at 12Hz and its harmonics for the signal going through the slip-ring when it is turning at 60rpm.
  • Apart from that, the noise of the signal is the same when the slip-ring is off/on and turning
  • The noise of the signal going through the slip-ring is much higher that the direct signal from the DAC to the ADC
  • A peak is obverse at 11.5Hz on the direct signal as soon as the slip-ring is turned ON. Can this be due to high frequency noise and Aliasing? As there is no LPF to filter the noise on the direct signal, this effect could be more visible on the direct signal.

Author: Dehaeze Thomas

Created: 2019-05-16 jeu. 09:46

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