Cut Sinusoidal signal in a integer number of periods

조회 수: 9(최근 30일)
s0ter48
s0ter48 2019년 7월 9일
댓글: s0ter48 2019년 7월 9일
Hey guys,
I have an measurement of three sinusoidal signals.
But it is enough to only work with one in this case.
The measurement doesn´t have an int number of periods and i need to cut for my further work.
To make it more clear here is an picutre:
In this case we have 4 periods.
2019-07-09_09-41-27.png
So i have to find the first negative to positive zero corssing and the last negative to positive zero crossing.
I found this code in the forum but it don´t work with my files but maby it can help u ?!
t = linspace(0,10*pi,200);
x = sin(t);
mcs = x .* circshift(x, [0 -1]);
zxix = find(mcs <= 0);
for k1 = 1:2:size(zxix,2)-1
zx(k1) = interp1(x(zxix(k1):zxix(k1)+1), t(zxix(k1):zxix(k1)+1), 0);
end
figure(1)
plot(t, x)
hold on
plot(zx, zeros(size(zx)), '+r', 'MarkerSize',10)
hold off
grid
I hope u can help me.
Thanks in advance
  댓글 수: 2
s0ter48
s0ter48 2019년 7월 9일
With this:
index1 = find(y > 0, 1, 'first');
index2 = find(y > 0, 971, 'last');
yCropped = y(index1:index2);
xCropped = x(index1:index2);
I get what i want but how can i find this 971 automtically?

댓글을 달려면 로그인하십시오.

채택된 답변

David Sanchez
David Sanchez 2019년 7월 9일
Hi,
bear in mind that the sampling of your curve might play an important role in the game.
The code below might help you out:
t = linspace(0,10*pi,200);
x = sin(t);
zero_crossings_pos = [];
for kind = 1:length(t)-1
if (x(kind) <= 0) && (x(kind+1) > 0)
zero_crossings_pos = [zero_crossings_pos kind];
end
end
figure,
plot(t,x,t,x,'o')
hold on
plot(t(zero_crossings_pos),x(zero_crossings_pos),'r*')
hold off
xlabel('x')
ylabel('sin(x)')
title('sin')
t_crop = t(zero_crossings_pos(2):zero_crossings_pos(5));
x_crop = x(zero_crossings_pos(2):zero_crossings_pos(5));
figure,
plot(t_crop,x_crop)
xlabel('x')
ylabel('sin(x)')
title('Cropped sin')
  댓글 수: 1
s0ter48
s0ter48 2019년 7월 9일
Thanks for your answer.
I tried the code and had to change a small thing but now it works:
t_crop = t(zero_crossings_pos(1,1):zero_crossings_pos(1,end));
x_crop = x(zero_crossings_pos(1,1):zero_crossings_pos(1,end));
Thank you very much.

댓글을 달려면 로그인하십시오.

추가 답변(0개)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by