PLC Safety & Functional Safety Flashcards
6 cards from real PLC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 PLC Safety & Functional Safety flashcards as text
Which international standard defines functional safety requirements for safety-instrumented systems in the process industry?
Answer: IEC 61511
IEC 61511 is the functional safety standard specifically for safety-instrumented systems in the process industry.
What does SIL stand for in the context of safety PLCs?
Answer: Safety Integrity Level
SIL stands for Safety Integrity Level, a measure of the reliability and risk reduction provided by a safety function.
A Safety PLC operating at SIL 2 typically requires which architecture to meet hardware fault tolerance requirements?
Answer: 1oo2 (one-out-of-two) redundancy
SIL 2 commonly requires a 1oo2 (1-out-of-2) hardware architecture to achieve the necessary hardware fault tolerance.
What is the primary purpose of a Safety Instrumented Function (SIF)?
Answer: To bring a process to a safe state when a hazardous condition is detected
A Safety Instrumented Function (SIF) is designed to take a process to a defined safe state upon detection of a hazardous condition.
Which term describes the probability that a safety function fails to respond when a dangerous condition occurs?
Answer: Probability of Failure on Demand (PFD)
PFD (Probability of Failure on Demand) quantifies the likelihood that a safety function will not operate correctly when called upon.
In a safety PLC, what is the role of the watchdog timer?
Answer: To detect processor faults and trigger a safe shutdown if the CPU stops cycling normally
A watchdog timer monitors the PLC CPU scan cycle and forces a safe state if the processor fails to reset it within the expected interval.