Ashcroft A Series - N4 Pressure Switch - Manual (Page 2)

A-S ERIES S WITCH S AFETY M ANUAL
I&M009-10210
REV A - 4/19/2013
1 INTRODUCTION
This Safety Manual provides information necessary to design, install, verify and
maintain a Safety Instrumented Function (SIF) utilizing the A-Series pressure
switch. This manual provides necessary requirements for meeting the IEC 61508
or IEC 61511 functional safety standards.
1.1 Terms and Abbreviations
Safety Freedom from unacceptable risk of harm
Functional Safety The ability of a system to carry out the actions necessary to
achieve or to maintain a defined safe state for the equipment
/ machinery / plant / apparatus under control of the system
Basic Safety The equipment must be designed and manufactured such
that it protects against risk of damage to persons by
electrical shock and other hazards and against resulting fire
and explosion. The protection must be effective under all
conditions of the nominal operation and under single fault
condition
Safety Assessment The investigation to arrive at a judgment - based on evidence
- of the safety achieved by safety-related systems
Fail-Safe State State where solenoid valve is de-energized and spring is
extended.
Fail Safe Failure that causes the valve to go to the defined fail-safe
state without a demand from the process.
Fail Dangerous Failure that does not respond to a demand from the process
(i.e. being unable to go to the defined fail-safe state).
Fail Dangerous Undetected Failure that is dangerous and that is not being
diagnosed by automatic stroke testing.
Fail Dangerous Detected Failure that is dangerous but is detected by
automatic stroke testing.
Fail Annunciation Undetected Failure that does not cause a false trip or prevent
the safety function but does cause loss of an automatic
diagnostic and is not detected by another diagnostic.
Fail Annunciation Detected Failure that does not cause a false trip or prevent
the safety function but does cause loss of an automatic
diagnostic or false diagnostic indication.
Fail No Effect Failure of a component that is part of the safety function but
that has no effect on the safety function.
Low demand mode Mode, where the frequency of demands for operation made
on a safety-related system is no greater than twice the proof
test frequency.