Sorry that i bother you again but i have questions which is killing me!!!
-FM (FMD-93 Normalized):
1. Opens without stimuli 0,51
2. Does not open 0,49
-DC = 100%
Opens without stimuli – Critical (no current – no cooling – mission loss)
Does not open – Critical (electrical damage of PLC – no cooling – mission loss)
– Cm=λp x α x β x t
ad 1. Opens without stimuli: 0,05 x 0,51 x 1 x 100%
Beta here is equal 1 because when circuit is opened there is always the same effect.
ad 2. Does not open 0,05 x 0,49 x [beta] x 100%
What beta it should be?
Due to the RIAC (FMEA 1993 page 21) document we can assume:
Failure Effect | beta Value
Actual loss – 1
Probable Loss – >0.10 to < 1 Possible Loss >0 to 0.10
No effect 0
I Have changed it a little bit:
Actual loss – 1
Probable Loss – 0,1
Possible Loss- 0,01
No effect- 0
When Circuit breaker fails due to “Does not open” then, in case of electric discharge, PLC can be damaged but probability of that damage is 0,1 so our Critically number will be:
Cm = 0,05 x 0,49 x 0,1 x 100%.
I think this is correct but…..
Electrical discharge is very rare – I can estimate that 1 per year.
What to do whit that ??!! If i should change DC for that failure mode or meybe change the beta value for example:
beta = probability of electric discharge X probability of PLC electric damage due to electric discharge
beta = (1/365???? [days , hours]) X 0,1
What to do??????
Ok and another question……
We have a temperature sensor which send information to the regulator about temperature then regulator control cooling.
One of temperature sensor Failure Modes is “improper output”. In our case “improper output” can has different effects for example.
If “improper output” (wrong signal – wrong temperature indication) does exceed the regulator limits (< -100oC i >100oC) then PLC know about the sensor failure and everything is OK.
If “improper output” (wrong signal – wrong temperature indication) does NOT exceed the regulator limits (>-100oC i <100oC) then there is a problem! If in that case temperature sensor understatement temperature then it is OK but if overestimates then this can be CRITICAL.
So how to calculate beta in that case?
beta = probability of exceeding the limits x probability of overestimates
In my opinion if can be always 50/50
beta = 0,5 X 0,5 = 0,25 for CRITICAL effect?
I can’t find answer anywhere please help me last time.