Double condition to find index

I have force data from force plate and I try to determine the impact time/index.

For that, I need two conditions:

1) Data exceeds 20 newtons (>20)

2) Data exceeds 20 newtons for more than 50 milliseconds

I tried with for + if and with for using find fonction.

Do you have some idea to resolve that ?

Thank you so much.

[Torsten]

Is the time interval in which the force data are reported constant ? If yes: how long is it ?

[James Tursa]

What is the sampling rate of your recorded data?

[Jeanne Dury]

The sample rate is 2000Hz

Answer 1

[Walter Roberson]

freq = 2000;  %hz
threshold = 20; %newtons
significant_time = 50;  %milliseconds

significant_samples = ceil(significant_time/1000 * freq);
mask = ForceData(:).' > threshold;
streak = repmat(1, 1, significant_samples);
starts = strfind([false mask], [0 streak]);
stops = strfind([mask false], [streak 0]);

At this point, starts and stops will be vectors the same length, in which ForceData(starts(K):stops(K)) is a run of samples that exceed the threshold for at least as long as you require.

[Jeanne Dury]

Thank you very much for your answer. It works perfectly!

Answer 2

[Jonas]

myData=...;
fs=2000;
minLength=ceil(fs*0.05);
highVals=myData>20;

searchFor=conv(highVals,ones(1,minLength),'same');

% areas in which the condition is fullfilled are greater than your minLength

plot(searchFor);

findpeaks(searchFor>=minLength)