FIT Rate & Chi-square distribution & more

Guest

Hello someone,

This is Rel boy-new rel engineer with following questions:

1) Why chi-square distribution is used for FITs calcualtion? In some cases I saw using Poisson distribution. Why I use one vs. other?

2) Why DOF, degrees of freedom is used? Do we have to use it in calculation? If we have to then why distribution value for "0" is given in the table? I mean to say is that it will never be zero if DOF is used since it is 2n+1.

3) Why FIT rate is just for HTOL/HTRB and THB? Let say you are calcualting FIT rate for HTOL and THB. What would be the cumulative FIT rate for both stresses? You just add the individual FIT rate or add the device hours and calculate the FIT rate? Should FIT rate be combined let's say in a qual that has both HTOL and THB stresses? Please explain. Sorry for asking too many questions.

That's all for now.

Thanks,
Rel boy