hello
see code below for midline and signal oscillation frequency computation (cycle to cycle "zero" crossing detection)
a PID tuning problem ?
data = extract_data_from_figures('2.fig');
VN = data.names;
data = data.Y;
% {'X' }
% {'midline'}
% {'target' }
% {'y vs x' }
x = data(:,1);
y_target = data(:,3);
y = data(:,4);
idx = (x>=1); % valid data for t > 1 s
midline = mean(y(idx));
%%find frequency of this signal
threshold = midline; %
t0_pos1 = find_zc(x,y,threshold);
period = diff(t0_pos1); % delta time of crossing points
freq = 1./period; % signal frequency
figure(1)
subplot(2,1,1),plot(x,y,'b',x,y_target,'g',x(idx),midline*ones(size(x(idx))),'k--',t0_pos1,midline*ones(size(t0_pos1)),'dr','Linewidth',2);
legend('signal','target','midline','crossing points');
xlabel('Time(s)')
subplot(2,1,2),plot(t0_pos1(2:end),freq,'b.-','linewidth',2,'markersize',12);grid on
xlim([min(x) max(x)]);
legend('signal rate (frequency)');
xlabel('Time(s)')
ylabel('Freq(Hz)')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [Zx] = find_zc(x,y,threshold)
% positive slope "zero" crossing detection, using linear interpolation
y = y - threshold;
zci = @(data) find(diff(sign(data))>0); %define function: returns indices of +ZCs
ix=zci(y); %find indices of + zero crossings of x
ZeroX = @(x0,y0,x1,y1) x0 - (y0.*(x0 - x1))./(y0 - y1); % Interpolated x value for Zero-Crossing
Zx = ZeroX(x(ix),y(ix),x(ix+1),y(ix+1));
end
function data = extract_data_from_figures(filename)
%%
%
% Input : File name <filename.fig>
% with multiple plots in a single file
% Output : struct data
% : data.names contains names of the display object Yvalues
% : data.Y contains the actual plot values withthe first column
% containing the x-values
%
% Written by Chetanya Puri, 2019
% Last Modified: Nov 6, 2019
%
fig = openfig(filename); % Open figure and assign it to fig object
dataObjs = findobj(fig,'-property','YData'); % Find all graphic objects with YData, in our case line values
xval = dataObjs(1).XData; % Find the X-axis value
Ymat = [xval(:)]; % Create a matrix with first column of x values
for i=1:length(dataObjs)
legend_name{i,1} = dataObjs(i).DisplayName;
yval = dataObjs(i).YData;
Ymat = [Ymat yval(:)]; % Keep appending column vectors
end
close(fig); % close the figure
data.names = ['X';legend_name];
data.Y = Ymat;
end
