9. Safety design and specifications of 11-301
STO design main requirements
Parameter Value
PFD
AVG
2.58x10
-4
PFH
D
1.18x10
-8
PL d
MTBF 8,096 years
DC
AVG 84%
Abbreviations:
SIL Safety Integrated Level
PFHD Probability of Dangerous failure Per hour
MTBF Mean Time Between Failures
MTTR Mean Time to Repair. ( hour)
Safety Function Requirement Specification SIL2
Initiating devices User connected sensor or other safety devices
Hazard Rotation of the motor (To be derived from hazard assessment)
Consequence Human harm or damage to machinery.
Safe State PWM removed, therefore No Voltage output from the drive.
Required Action Detect Safe input signals and remove PWM signal.
Response Time
8ms (from STO input signal detection to the final action of
STO)
Target SIL SIL = 2, PL d, category 3
Demand Rate High demand rate
Mode of
Operation
Continuous
PFHD The PFHD of STO function shall be less than 0.5* 10-6
MTBF The MTBF of drive system shall be more than 100,000 hours
Trip Mode De-energize to trip
MTTR No more than 4 hrs (No field repair, only change new board)
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