# How do I count the number of times zero is being crossed by a signal?

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Rajesh Siraskar on 8 Jan 2020
Edited: hossein on 2 Feb 2022
Hi,
I am trying to build a control system and I want to count the oscillations in a time-span of say 100 seconds.
Can I count the number of times a signal crosses zero (probably using MATLAB's zer-crossing detection algo.) to count the oscillations?
I want it to happen within Simulink - is there any other better way? I just want a count say 10, that tells me there were 10 oscillations.

Fangjun Jiang on 8 Jan 2020
If you have the DSP toolbox, there is a Zero-Crossing counter block. If not, you can compare the signal with zero, which creates a square wave signal. Use the rising and falling edge to trig an triggered subsystem, inside which adding a Counter block.
Rajesh Siraskar on 10 Jan 2020
Make sense - will try. Thanks a lot for your guidance.

### More Answers (1)

hossein on 2 Feb 2022
Edited: hossein on 2 Feb 2022
You can count the number of times the product of the signal and the shifted signal becomse negative. The below formula gives the number of crossings I guess. I am not sure if this is bug free.
"Sig" is your signal data vector here.
sum(sign((Sig.*[Sig(2:end),Sig(end)]))<0)

R2019a

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