How to set threshold to trigger for start and stop finding max value?

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Chen Kevin 2020-4-17

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此问题的直接链接

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评论： Chen Kevin 2020-4-19

Hi all,

I am measuring flowing particles with a system. The particle will start to induce a pulse signal once it just enters the sensing zone, and the max amplitude can be obtained around the center of the zone.

What I have considered method by used for and if function is :

Set a threshold for switch on and switch off record the data
Once the amplitude (y>threshold) which means the cell just enter the sensing zone, start the search
When the amplitude (y<threshold) which means the cell almost leave the zone, stop searching
Find the max value from this recording time interval
Also get the time interval

However, I am quite fresh in MATLAB so don't know how to write down them...

Thanks if someone can help me design this tool!

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Answer 1

Image Analyst 2020-4-17

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/518778-how-to-set-threshold-to-trigger-for-start-and-stop-finding-max-value#answer_426699

在 MATLAB Online 中打开

Can you post a diagram, plot, image, data or anything to help illustrate your situation?

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

Otherwise, just try find:

indexEnters = find(y > threshold, 1, 'first'); % Index when particle enters and signa becomes big enough.
indexLeaves = find(y > threshold, 1, 'last'); % Index when particle leaves and signa becomes small again.

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Image Analyst 2020-4-18

在 MATLAB Online 中打开

Try this:

clc;    % Clear the command window.
fprintf('Beginning to run %s.m.\n', mfilename);
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
clear global;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
%Simulation signal generated
fs = 1e9;
tc = gauspuls('cutoff',10e3,0.5,[],-40); 
t = -tc:1/fs:tc; 
x = gauspuls(t,10e3,0.5); 
ts = 0:1/50e3:0.025;
d = [0:1/1e3:0.025;sin(2*pi*0.1*(0:25))]';
y = pulstran(ts,d,x,fs);
hFig = figure
subplot(3, 1, 1);
plot(ts,y, 'b-', 'LineWidth', 2)
grid on;
xlim([0 0.01])
hFig.WindowState = 'maximized';
binarySignal = y < 0.0001;
% Plot signal
subplot(3, 1, 2);
plot(ts,binarySignal, 'b-', 'LineWidth', 2)
grid on;
xlim([0 0.01])
title('Signal where y < 0.0001', 'FontSize', 18);
% Find the length of the small inter-wave gaps.
props = regionprops(binarySignal, 'Area');
allLengths = sort([props.Area], 'descend')
% Get rid of pulses less than 15 elements
binarySignal = ~bwareaopen(binarySignal, 15);
% Plot signal
subplot(3, 1, 3);
plot(ts,binarySignal, 'b-', 'LineWidth', 2)
grid on;
xlim([0 0.01])
ylim([0, 1.2]);
title('Signal where there is a pulse', 'FontSize', 18);
subplot(3, 1, 1);
% Now get the start and stop of each pulse
props = regionprops(binarySignal, 'PixelIdxList');
% Print them out
for k = 1 : length(props)
	starts(k) = props(k).PixelIdxList(1);
	stops(k) = props(k).PixelIdxList(end);
	fprintf('Pulse #%d starts at element %d (ts = %f) and stops at element %d (ts = %f).\n', k, starts(k), ts(starts(k)), stops(k), ts(stops(k)));
	xline(ts(starts(k)), 'Color', 'g', 'LineWidth', 2);
	xline(ts(stops(k)), 'Color', 'r', 'LineWidth', 2);
end
title('Signal with starts and stops indicated', 'FontSize', 18);

In the command window, you'll see:

Pulse #1 starts at element 52 (ts = 0.001020) and stops at element 73 (ts = 0.001440).

Pulse #2 starts at element 102 (ts = 0.002020) and stops at element 123 (ts = 0.002440).

Pulse #3 starts at element 152 (ts = 0.003020) and stops at element 173 (ts = 0.003440).

Pulse #4 starts at element 202 (ts = 0.004020) and stops at element 223 (ts = 0.004440).

Pulse #5 starts at element 301 (ts = 0.006000) and stops at element 321 (ts = 0.006400).

Pulse #6 starts at element 351 (ts = 0.007000) and stops at element 371 (ts = 0.007400).

Pulse #7 starts at element 401 (ts = 0.008000) and stops at element 421 (ts = 0.008400).

Pulse #8 starts at element 451 (ts = 0.009000) and stops at element 471 (ts = 0.009400).

Pulse #9 starts at element 552 (ts = 0.011020) and stops at element 573 (ts = 0.011440).

Pulse #10 starts at element 602 (ts = 0.012020) and stops at element 623 (ts = 0.012440).

Pulse #11 starts at element 652 (ts = 0.013020) and stops at element 673 (ts = 0.013440).

Pulse #12 starts at element 702 (ts = 0.014020) and stops at element 723 (ts = 0.014440).

Pulse #13 starts at element 801 (ts = 0.016000) and stops at element 821 (ts = 0.016400).

Pulse #14 starts at element 851 (ts = 0.017000) and stops at element 871 (ts = 0.017400).

Pulse #15 starts at element 901 (ts = 0.018000) and stops at element 921 (ts = 0.018400).

Pulse #16 starts at element 951 (ts = 0.019000) and stops at element 971 (ts = 0.019400).

Pulse #17 starts at element 1052 (ts = 0.021020) and stops at element 1073 (ts = 0.021440).

Pulse #18 starts at element 1102 (ts = 0.022020) and stops at element 1123 (ts = 0.022440).

Pulse #19 starts at element 1152 (ts = 0.023020) and stops at element 1173 (ts = 0.023440).

Pulse #20 starts at element 1202 (ts = 0.024020) and stops at element 1223 (ts = 0.024440).

Image Analyst 2020-4-19

编辑：Image Analyst 2020-4-19

在 MATLAB Online 中打开

xline() was introduced in r2018b. You can replace it with line():

line([ts(starts(k)), ts(starts(k))], ylim, 'Color', 'g', 'LineWidth', 2);

If anymore happen, just delete the line that threw an error. Most of them are just for making fancy graphics anyway.

I'll edit your post to add your Product on the right hand side of this page.

Chen Kevin 2020-4-19

Thanks! Closer now, but how about get the max amplitude at each wave sets?

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