# Proof test intervals

The proof-test interval shall be defined [ IEC 61511-1 ]. It is important that the proof-test interval is taken in account during the design of the process application since the proof-test interval affects the design of the application.

The proof test idea is to test the function as far as possible. It is more advisable to perform a proof test is when the process (factory) is stopped.

**Important Activities**

- describe the proof test procedures
- investigate if additional safety measures (monitoring, redundancy etc.) has to be adapted during the proof test interval.
- investigate if human aspects (forgotten bypass etc) could affect the safety during the proof test especially if the consequences could be catastrophic if the proof test goes wrong
- specify the required proof tests during the life-cycle
- the proof test activity shall be documented (the final result of the proof test)