Emerson Mobrey Series, Руководство по функциональной безопасности

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9
Functional Safety Manual
M310/FSM, Rev BA
Designing a Safety Function Using the Level Switch
April 2017
Designing a Safety Function Using the Level Switch
Table 3-2. Failure Rates for Level Switch, 6-contact Versions – Types D6, P6, H6, and B6
Table 3-3. Failure Rates according to IEC 61508, 4-contact Versions – Types D and P (FIT)
Table 3-4. Failure Rates according to IEC 61508, 6-contact Versions – Types D6, P6, H6, and B6 (FIT)
3.6 Connection of the level switch to the SIS logic solver
The Mobrey level switch should be connected to the safety-rated logic solver which is actively
performing the safety function as well as automatic diagnostics (if any) designed to diagnose potentially
dangerous failures within the level switch. The Mobrey Magnetic Level Switch
Reference Manual gives
installation details for the level switch.
3.7 General requirements

The system and function response time shall be less than the process safety time. The Mobrey level
switch will change to its defined safe state in less than this time with relation to the specific hazard
scenario.

All SIS components, including the Mobrey level switch must be operational before process start-up.

The user shall verify that the Mobrey level switch is suitable for use in safety applications by confirming
the level switch nameplate and model number are properly marked.

Personnel performing maintenance and testing on the Mobrey level switch shall first be assessed as
being competent to do so.

Results from periodic proof tests shall be recorded and periodically reviewed.

The Mobrey level switch shall not be operated beyond the useful lifetime as listed in the section
“Useful lifetime” on page 13 without undergoing overhaul or replacement.
Failure category
Failure rate (FIT)
(1)
1. FIT is the abbreviation for Failure In Time. One FIT is 1x10
-9
failure per hour.
Maximum detection Minimum detection
Fail Safe Detected 0 0
Fail Safe Undetected 168 197
Fail Dangerous Detected 0 0
Fail Dangerous Undetected 327 298
No Effect 34 34
Device

SD
(1)
1. FIT is the abbreviation for Failure In Time. One FIT is 1x10
-9
failure per hour.

SU

DD

DU
Level switch, maximum detection 0 88 0 243
Level switch, minimum detection 0 117 0 214
Device

SD
(1)
1. FIT is the abbreviation for Failure In Time. One FIT is 1x10
-9
failure per hour.

SU

DD

DU
Level switch, maximum detection 0 168 0 327
Level switch, minimum detection 0 197 0 298