Condition for Specific Data collection
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Hi everyone
I am facing a problem i have different Excel files in which there is a lot of data. i want to find some common condition for all these file to get the specific data (e.g i circle some example in the graph). I also attach 3 excel file as an example. I want to find some condition according to current or volatge column in the excel file. there is 3 column time, voltage and current. you can use any columnn for finding the condition to get some specific data and discard the remaining data. waiting for your kind help.
Thank you.
2 个评论
Mathieu NOE
2020-11-17
hello
reading the excel files is no problem but how to select the portion of data of interest (as you described) is not evident
what are the crietria / condition to select this or this particular portion of data ?
that's the main issue and you need to provide a methodology for that.
tx
Adil Sardar
2020-11-17
采纳的回答
Mathieu NOE
2020-11-17
hello
see example below
this could be interesting for data 1 example
but the two other data it's not feasible unless someone come's with a clever condtion equation to select such fraction of data
[num,txt,raw] = xlsread('Data 1.xlsx') ;
time = num(:,1); % s
current = num(:,2); % A
voltage = num(:,3); % V
samples = length(time);
dt = (time(end)-time(1))/(samples-1);
Fs = 1/dt;
% main loop : extract min max vales for every 5 min data %
[dvoltage, ddvoltage] = firstsecondderivatives(time,voltage);
figure(1);
subplot(2,1,1),plot(time,voltage,'-b');grid
subplot(2,1,2),plot(time,dvoltage,'-b');grid
% selected buffer is defined between the two positive peaks of dvoltage
dvoltage_max = max(dvoltage(dvoltage>0));
threshold = dvoltage_max/2;
ind = find(dvoltage > threshold);
ind_start = ind(1)-100;
ind_stop = ind(end)-100;
% plot selected portion of data
figure(2);
plot(time,voltage,'-b',time(ind_start:ind_stop),voltage(ind_start:ind_stop),'or');grid
function [dy, ddy] = firstsecondderivatives(x,y)
% The function calculates the first & second derivative of a function that is given by a set
% of points. The first derivatives at the first and last points are calculated by
% the 3 point forward and 3 point backward finite difference scheme respectively.
% The first derivatives at all the other points are calculated by the 2 point
% central approach.
% The second derivatives at the first and last points are calculated by
% the 4 point forward and 4 point backward finite difference scheme respectively.
% The second derivatives at all the other points are calculated by the 3 point
% central approach.
n = length (x);
dy = zeros;
ddy = zeros;
% Input variables:
% x: vector with the x the data points.
% y: vector with the f(x) data points.
% Output variable:
% dy: Vector with first derivative at each point.
% ddy: Vector with second derivative at each point.
dy(1) = (-3*y(1) + 4*y(2) - y(3)) / 2*(x(2) - x(1)); % First derivative
ddy(1) = (2*y(1) - 5*y(2) + 4*y(3) - y(4)) / (x(2) - x(1))^2; % Second derivative
for i = 2:n-1
dy(i) = (y(i+1) - y(i-1)) / 2*(x(i+1) - x(i-1));
ddy(i) = (y(i-1) - 2*y(i) + y(i+1)) / (x(i-1) - x(i))^2;
end
dy(n) = (y(n-2) - 4*y(n-1) + 3*y(n)) / 2*(x(n) - x(n-1));
ddy(n) = (-y(n-3) + 4*y(n-2) - 5*y(n-1) + 2*y(n)) / (x(n) - x(n-1))^2;
end
8 个评论
Adil Sardar
2020-11-18
Mathieu NOE
2020-11-18
hello
this is an improved code
please try it
tx
[num,txt,raw] = xlsread('Data 1 updated.xlsx') ;
time = num(:,1); % s
current = num(:,2); % A
voltage = num(:,3); % V
samples = length(time);
dt = (time(end)-time(1))/(samples-1);
Fs = 1/dt;
% first and second derivative
[dvoltage, ddvoltage] = firstsecondderivatives(time,voltage);
% some smoothing ?
N = 100;
dvoltage = myslidingavg(dvoltage, N);
figure(1);
subplot(2,1,1),plot(time,voltage,'-b');grid
subplot(2,1,2),plot(time,dvoltage,'-b');grid
% selected buffer is defined between the two positive peaks of dvoltage
dvoltage_max = max(dvoltage(dvoltage>0));
threshold = dvoltage_max/2;
% zero crossing detection of the dvoltage signal
[ind_pos,t0_pos,s0_pos,ind_neg,t0_neg,s0_neg] = crossing_V6(dvoltage,time,threshold,'linear');
figure(1);
subplot(2,1,1),plot(time,voltage,'-b',t0_pos,voltage(ind_pos),'+r');grid
subplot(2,1,2),plot(time,dvoltage,'-b',t0_pos,s0_pos,'+r');grid
% % plot selected portion of data
ind_start = ind_pos(1);
ind_stop = ind_pos(2);
figure(2);
plot(time,voltage,'-b',time(ind_start:ind_stop),voltage(ind_start:ind_stop),'or');grid
Adil Sardar
2020-11-18
I am really sorry but there is 2 errors in the code i am attaching the screenshot of the error. one is unrecognized function or variable "myslidingavg".. and the other is in crossing_v6.m (line 38) which show not enough arguments. kindly check it
Mathieu NOE
2020-11-18
ok
I send you back all files . I have no error on my side (R2020b)
Adil Sardar
2020-11-18
Mathieu NOE
2020-11-18
ok
it's not so simple because each case is very specific
I have a hard time finding a criteria that works in all situations
Mathieu NOE
2020-11-18
hello again
probably my last contribution here
I could more or less find a way for data 1 and 3 , but data 2 is so fuzzy, I doubt someone will find one day a criteria to select the appropriate time slots
hope this was helping a bit somehow
good luck for the future ; I'm stopping here now;
Adil Sardar
2020-11-18
更多回答（1 个）
Peter Perkins
2020-11-19
0 个投票
Unless you are using a fairly old version of MATLAB, I strognly recommend that you stay away from xlsread, and use readtable or readtimetable instead.
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