Emerson Process Management Rev AA manual Proposed PROOF-TEST Procedure, Suggested Proof-test, Step

Functional Safety Manual

IP101/FSM, Rev AA

January 2012

Horizontal Float Switch

PROPOSED PROOF-TEST PROCEDURE

According to Section 7.4.3.2.2 (f) of the standard IEC 61508-2, proof-tests shall be undertaken to reveal dangerous faults which are undetected by diagnostic tests. This means that it is necessary to specify how dangerous undetected faults which have been noted during the Failure Modes, Effects, and Diagnostic Analysis can be detected during proof-testing.

Suggested Proof-test

Table 7.

Suggested Proof-test

(Low Level Alarm)

Table 8.

Suggested Proof-test

(High Level Alarm)

The suggested proof-tests (Tables 7 and 8) consist of switch operation tests in-situ.

1Inspect the accessible parts of the level switch for any leaks or damage

2Bypass the safety function and take appropriate action to avoid a false trip

3Disable any filling mechanism and drain the vessel to force the switch to the fail-safe state and confirm that the Safe State was achieved and within the correct time. INDEPENDENT PRECAUTIONS MUST BE TAKEN TO ENSURE THAT NO HAZARD CAN RESULT FROM THIS OPERATION.

4Reinstate the filling mechanism so that the vessel refills and confirm that the normal operating state of the switch was achieved.

5Remove the safety function bypass and otherwise restore normal operation

1Inspect the accessible parts of the level switch for any leaks or damage

2Bypass the safety function and take appropriate action to avoid a false trip

3Disable any drain mechanism and fill the vessel to force the switch to the fail-safe state and confirm that the Safe State was achieved and within the correct time. INDEPENDENT PRECAUTIONS MUST BE TAKEN TO ENSURE THAT NO HAZARD CAN RESULT FROM THIS OPERATION.

4Reinstate the drain mechanism so that the vessel refills and confirm that the normal operating state of the switch was achieved

5Remove the safety function bypass and otherwise restore normal operation

Proof Test Coverage

The Proof Test Coverage for the tests listed in the section “Proposed Proof-test Procedure” may be considered to be 100%, covering all components of the Mobrey level switch.