nass-micro-station-measurements/slip-ring-electrical-noise/matlab/meas_effect_sr.m

%% Clear Workspace and Close figures
clear; close all; clc;

%% Intialize Laplace variable
s = zpk('s');

% 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]);



% #+NAME: fig:random_signal
% #+CAPTION: Random signal produced by the DAC
% #+RESULTS: fig:random_signal
% [[file:figs/random_signal.png]]

% 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');



% #+NAME: fig:slipring_comp_signals
% #+CAPTION: Alteration of the signal when the slip-ring is turning
% #+RESULTS: fig:slipring_comp_signals
% [[file:figs/slipring_comp_signals.png]]


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);

figure;
hold on;
plot(f, sqrt(pxx_on), 'DisplayName', 'Slip-Ring - $\omega = 1rpm$');
plot(f, sqrt(pxx_off),'DisplayName', 'Slip-Ring off');
hold off;
set(gca, 'xscale', 'log'); set(gca, 'yscale', 'log');
xlabel('Frequency [Hz]'); ylabel('PSD $\left[\frac{V}{\sqrt{Hz}}\right]$');
legend('Location', 'northeast');
xlim([1, 500]); ylim([1e-5, 1e-3])