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

• Measurement Description
• Load data
• Analysis
• Conclusion

#+TITLE:Effect of the rotation of the Slip-Ring

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) ?