[SystemSafety] Units for Functional Safety variables ? - A Friday afternoon question on a Wednesday.

[Jon Hind]

I posted this (only partially) frivolous question on out internal
system, without any reply.

So trying here for some erudition...

What dimension and or units does Hardware Fault Tolerance (HFT) have ?
- A Friday Poser on Functional Safety Terminology (FST).

I remember being taught at university in the last century that
everything has a dimension in terms of Length (L) , Mass (M) and or
Time (T), or is a ratio (factor). A good check of the validity of an
equation is that it must balance dimensionally.

Availability Common Cause Factor (β, CCF) and Safe Failure Fractions
(SFF) are dimensionless ratios, failures rates (λ) are T^-1, Proof
Test intervals are T etc.

And HFT ? HFT is an integer - In our (oil & gas process) world, 0 1 or
2 ; is it part of a case statement, or heaven forbid a pointer like in
the C language ?

I don't want to call it a factor as we already have that in CCF and SFF.

Answers on a postcard please....

Jon Hind
jon at jonhind.co.uk