Query related to debounce time when using ST safety library

[SaikumarBaddireddy]

We are developing a safety-related application based on an STM32 microcontroller and aligning our design with IEC 60730 Class B requirements.

In our application, we implement fault detection mechanisms for analog and digital signals (e.g., sensor inputs, voltage monitoring, heater control). Due to noise and transient conditions, we are considering adding a software debounce/filtering time before declaring a fault.

We would like clarification on the following points:

1. Does IEC 60730 Class B explicitly require or prohibit the use of debounce time for fault detection?
2. Is it acceptable to introduce a software debounce (e.g., 100 MSto a few seconds) to avoid false fault triggering?
3. Are there any recommended guidelines from ST for implementing debounce while still complying with Class B requirements?
4. Does the STM32 IEC 60730 Class B self-test library include any reference implementation or best practices for handling such debounce scenarios? 

[Petr Sladecek]

Hello,

above all, note that efficiency of any software self-test method (like those applied by STL) to detect short life transient errors is very pure. You need to apply HW diagnostic instead (e.g. like ECC on RAM  & FLASH, HW comparators of the signals etc.). Concerning any definition of the process safety time (PST - see ST family safety manuals) comes from definition of the safety task (~application), it cannot be defined by any standard. I guess your requirements comes rather from motor control application where (so far I know)  effect of debouncing is suppressed by selection of proper slots to apply the ADC measurement to be pretty out of the switching time of the shunts (middle of the symmetrical PWM pulses) where the measured values are settled down (I suggest checking AN6179, too, describing problematic of the STL run at time critical control systems). 

Best regards,

Petr