Zero up crossing frequency in a random signal

Hi everyone,

I already asked a related question in this old thread.

For a random (vibration) signal there are two important statistical values: the peak rate and the zero up crossing frequency.  The first one I was able to compute using a the function localmax provided in the "Data Analysis Extension Pack".  Now I would also need the zero up crossing frequency, that is the number of time the signal crosses the X-axis going up. To clarify here is an image from Wirsching, Random Vibration.  The zero up crossing in the example are highlighted in yellow.

Before I start writing a simple iterative program like

for i=0 to npoints

  if x(i) <0 and x(i+1) >0 then

     zup=zup+1

  endif

next i

... I just wanted to ask if someone in the community knows some elegant and straightforward way, similar to the "localmax" function.  That function has the advantage of providing the ability to give a window width (for noisy signals).

Thanks a lot

Regards

Claudio

PS: the other thread about localmax/localmin contains sample data and sample Mathcad worksheet to read them