Ashcroft Pressure Switch User Manual

A-SERIES SWITCH SAFETY MANUAL

I&M009-10210
REV A - 4/19/2013

Safety Manual

A-Series Pressure Switch

Document: I&M009-10210

REV A - Release 4/19/2013

Table of Contents:

Section pg.

1. Introduction……………………………………………… 2

2. Device Description……………………………………… 4

3. Designing A SIF Using a Manufacturers Product…… 4

4. Installation and Commissioning……………………….. 7

5. Operation and Maintenance…………………………… 7

6. Start-up Checklist………………………………………. 9

A-SERIES SWITCH SAFETY MANUAL

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.

A-SERIES SWITCH SAFETY MANUAL

I&M009-10210
REV A - 4/19/2013

1.2 Acronyms

FMEDA Failure Modes, Effects and Diagnostic Analysis

HFT Hardware Fault Tolerance

MOC Management of Change. These are specific procedures often

done when performing any work activities in compliance with
government regulatory authorities.

PFDavg Average Probability of Failure on Demand

SFF Safe Failure Fraction, the fraction of the overall failure rate of

a device that results in either a safe fault or a diagnosed
unsafe fault.

SIF Safety Instrumented Function, a set of equipment intended

to reduce the risk due to a specific hazard (a safety loop).

SIL Safety Integrity Level, discrete level (one out of a possible

four) for specifying the safety integrity requirements of the
safety functions to be allocated to the E/E/PE safety-related
systems where Safety Integrity Level 4 has the highest level
of safety integrity and Safety Integrity Level 1 has the lowest.

SIS Safety Instrumented System – Implementation of one or more

Safety Instrumented Functions. A SIS is composed of any
combination of sensor(s), logic solver(s), and final element(s).

1.3 Product Support

Product support can be obtained from:

Ashcroft Inc., 250 East Main St., Stratford Ct. 06614

www.ashcroft.com

[phone]

1.4 Related Literature

Hardware Documents:

• Ashcroft A-Series Switch Installation, Operation and Maintenance

Instructions

Guidelines/References:

• Safety Integrity Level Selection – Systematic Methods Including Layer of

Protection Analysis, ISBN 1-55617-777-1, ISA

• Control System Safety Evaluation and Reliability, 2nd Edition, ISBN 1-

55617-638-8, ISA

• Safety Instrumented Systems Verification, Practical Probabilistic

Calculations, ISBN 1-55617-909-9, ISA