PLC PLC Safety & Functional Safety 2

Question 1

Which IEC standard covers functional safety of electrical, electronic, and programmable electronic safety-related systems?

Accepted Answer

IEC 61508

Answer

IEC 61508 is the umbrella standard for functional safety of E/E/PE (electrical, electronic, and programmable electronic) safety-related systems.

Question 2

What does 'de-energize to trip' mean in safety PLC output design?

Accepted Answer

The safety output removes power to actuate the safe state, so a loss of power also triggers the safe state

Answer

De-energize to trip means the output coil de-energizes to initiate the safe state, ensuring that a wiring or power failure also drives the system safe.

Question 3

What is the Safe Failure Fraction (SFF) used to determine?

Accepted Answer

The proportion of failures that are either safe or detected dangerous failures within a safety component

Answer

SFF represents the fraction of all failure modes that result in safe or detected dangerous states, used to determine the maximum achievable SIL for a component.

Question 4

In functional safety terminology, what is a 'proof test'?

Accepted Answer

A periodic test of a safety function to detect dangerous undetected failures

Answer

A proof test is a scheduled functional test of a safety instrumented function to reveal dangerous undetected failures and restore the system to its designed SIL.

Question 5

Which safety architecture uses two independent channels where both must detect a fault to initiate a trip (voting logic)?

Accepted Answer

2oo2 (two-out-of-two)

Answer

A 2oo2 architecture requires both channels to agree that a fault exists before a trip is initiated, offering high availability but lower fault detection.

PLC - Programmable Logic Controller Certification Practice Test

PLC - Programmable Logic Controller Certification Practice Test

PLC PLC Safety & Functional Safety 2