What is a proof test and why is it necessary?

• A. A diagnostic check performed automatically during operation.
• B. An emergency stop procedure used only during a fault.
• C. A test that verifies safety functions are capable of performing as intended and remain within safety parameters.
• D. A design review conducted after production.

Answer: (C)

A proof test is a deliberate check that safety functions can actually perform as intended and stay within their defined safety limits. It involves exercising the safety-related parts of the system under controlled conditions to make sure, when a fault is present or when a safety function is required, the system activates correctly, reaches the safe state, and does so within the required timing and parameter ranges.

Why it’s necessary: components wear, drift, or develop latent faults over time that routine operation might not reveal. By performing a proof test, you verify that the safety function still provides the intended risk reduction, that it responds quickly enough, and that its outputs and fault indications behave correctly. This helps ensure ongoing compliance with safety standards and gives confidence that the system will actually protect people and equipment when needed.