PLC PLC Safety & Functional Safety

Question 1

Which international standard defines functional safety requirements for safety-instrumented systems in the process industry?

Accepted Answer

IEC 61511

Answer

IEC 60068

Answer

ISO 9001

Answer

ANSI/ISA-88

Question 2

What does SIL stand for in the context of safety PLCs?

Accepted Answer

Safety Integrity Level

Answer

System Integration Logic

Answer

Signal Input Limit

Answer

Sequential Interlock Layer

Question 3

A Safety PLC operating at SIL 2 typically requires which architecture to meet hardware fault tolerance requirements?

Accepted Answer

1oo2 (one-out-of-two) redundancy

Answer

Single processor with no redundancy

Answer

1oo1 with diagnostics only

Answer

Quad-redundant 4oo4

Question 4

What is the primary purpose of a Safety Instrumented Function (SIF)?

Accepted Answer

To bring a process to a safe state when a hazardous condition is detected

Answer

To optimize throughput during normal operations

Answer

To log historical process data for reporting

Answer

To communicate between PLCs on a network

Question 5

Which term describes the probability that a safety function fails to respond when a dangerous condition occurs?

Accepted Answer

Probability of Failure on Demand (PFD)

Answer

Mean Time To Repair (MTTR)

Answer

Diagnostic Coverage (DC)

Answer

Safe Failure Fraction (SFF)

Question 6

In a safety PLC, what is the role of the watchdog timer?

Accepted Answer

To detect processor faults and trigger a safe shutdown if the CPU stops cycling normally

Answer

To record timestamps for audit trails

Answer

To schedule communication tasks between remote I/O modules

Answer

To manage PID loop execution timing