Functional Safety Manual M310/FSM, Rev AA January 2012 Horizontal Float Switch Mobrey Magnetic Level Switches Functional Safety Manual www.mobrey.
Functional Safety Manual M310/FSM, Rev AA January 2012 Horizontal Float Switch Contents Introduction Scope and Purpose of the Safety Manual ........................................................... page 3 Skill Level Requirement ....................................................................................... page 3 Terms, Abbreviations, And Acronyms .................................................................. page 3 Documentation and Standards...............................................
Functional Safety Manual IP101/FSM, Rev AA January 2012 Horizontal Float Switch Magnetic Level Switch Functional Safety Manual INTRODUCTION Scope and Purpose of the Safety Manual This safety manual contains the information to design, install, verify and maintain a Safety Instrumented Function (SIF) utilizing the Mobrey magnetic level switch.
Functional Safety Manual Horizontal Float Switch M310/FSM, Rev AA January 2012 FIT FIT is the abbreviation for Failure In Time. One FIT is 1x10-9 failure per hour FMEDA Failure Modes, Effects, and Diagnostics Analysis. Functional Safety Part of the overall safety relating to the process and the BPCS which depends on the correct functioning of the Safety Instrumented System (SIS) and other protection layers. HFT Hardware Fault Tolerance.
Functional Safety Manual IP101/FSM, Rev AA January 2012 Documentation and Standards Horizontal Float Switch This section lists the documentation and standards referred to by this safety manual. Table 1. Associated Documentation Documents IEC 61508-2: ed2, 2010 Exida EM 10/08-36 R001 IP101 M310 Table 2. Associated Standards Standards IEC 61508: ed2, 2010 IEC 61511 (ANSI/ISA 84.00.
Functional Safety Manual M310/FSM, Rev AA January 2012 Horizontal Float Switch PRODUCT DESCRIPTION Level Switch Purpose Mobrey magnetic level switches are ideal for high and low liquid level alarm, overfill alarm, and pump control duties. Figure 1. Application Example: High and Low Level Alarm Operation Principle The level switch is designed to open or close a circuit (“switch”) as a changing liquid level within a vessel passes the level of the float (the Switch Point).
Functional Safety Manual IP101/FSM, Rev AA January 2012 Horizontal Float Switch Figure 3. Level Increases – Float Pivots Upwards Contact B-B Float Pushrods N Contact A-A s s N Float Magnet Cross-section of the Level Switch NOTE: For all product information and documentation downloads, visit www.mobrey.com. Ordering Information Level switch models fitted with options listed on pages 14 and 15 of this manual have been externally assessed and certified to IEC 61508.
Functional Safety Manual Horizontal Float Switch M310/FSM, Rev AA January 2012 DESIGNING A SAFETY FUNCTION USING THE LEVEL SWITCH Safety Function A change in liquid level through the operating range of the float causes the switch to operate. It may be used in high level or low level safety related applications. In either case, it is recommended to use the set of contacts (A-A or B-B) which are Open in the Fail Safe State.
Functional Safety Manual IP101/FSM, Rev AA January 2012 SIL Capability Horizontal Float Switch Systematic Integrity The Mobrey level switch has met manufacturer design process requirements of Safety Integrity Level 2 (SIL 2). These are intended to achieve sufficient integrity against systematic errors of design by the manufacturer.
Functional Safety Manual Horizontal Float Switch Connection of the Level Switch to the SIS Logic Solver M310/FSM, Rev AA January 2012 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. NOTE: For all product information and documentation downloads, visit www.mobrey.com.
Functional Safety Manual IP101/FSM, Rev AA January 2012 Horizontal Float Switch OPERATION AND MAINTENANCE Proof-test Requirement During operation, a low-demand mode SIF must be proof-tested. The objective of proof-testing is to detect failures within the equipment in the SIF that are not detected by any automatic diagnostics of the system. Undetected failures that prevent the SIF from performing its function are the main concern.
Functional Safety Manual Horizontal Float Switch M310/FSM, Rev AA January 2012 SPECIFICATIONS Useful Life USEFUL LIFETIME According to Section 7.4.9.5 of IEC 61508-2, a useful lifetime based on experience should be assumed. Although a constant failure rate is assumed by the probabilistic estimation method (see FMEDA report), this only applies provided that the useful lifetime(1) of components is not exceeded.
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.
Functional Safety Manual M310/FSM, Rev AA January 2012 Horizontal Float Switch LEVEL SWITCHES CERTIFIED TO IEC 61508 Tables 9, 10, and 11 lists all of the Mobrey magnetic level switch options that are certified to IEC 61508. In general, this is the entire range with the exception of the marine versions, pneumatic switch mechanisms, and some floats. Refer to Mobrey product data sheet IP101 for the full specifications. Table 9.
Functional Safety Manual IP101/FSM, Rev AA January 2012 Horizontal Float Switch Table 10.
Functional Safety Manual M310/FSM, Rev AA January 2012 Horizontal Float Switch Mobrey Level Solutions Emerson provides a wide range of Mobrey products for level measurement applications. POINT LEVEL DETECTION CONTINUOUS MEASUREMENT Vibrating Fork Liquid Level Switches Ultrasonic Continuous Level Transmitters and Controllers For high and low alarms, overfill protection, pump control, including wide pressure and temperature requirements, and hygienic applications. Flexible mounting.
