Introduction; Terms And Abbreviations - ABB LLT100 Functional Safety Manual

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C h A p T E r 1

Introduction

The purpose of this safety manual is to provide information necessary to design, install, verify, and
maintain a Safety Instrumented Function (SIF) utilizing the LLT100. This manual provides the necessary
requirements for meeting the IEC 61508 functional safety standards.
This chapter defines terms, abbreviations and acronyms used in this document. It also exposes
reference documents and how to get product support.

Terms and abbreviations

Term
Basic Safety
Continuous Mode
Fail Annunciation
Detected
Fail Annunciation
Undetected
Fail Dangerous
Fail Dangerous
Detected
Fail Dangerous
Undetected
Fail No Effect
Fail-Safe State
Fail Safe
Functional Safety
high Demand Mode
Low Demand Mode
Multidrop
Meaning
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.
Mode where the safety function retains the EUC in a safe state as part of normal operation.
Failure that does not cause a false trip or prevent safety function but does cause loss of an
automatic diagnostic or false diagnostic indication.
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.
Failure that does not respond to a demand from the process (i.e. being unable to go to the
defined fail-safe state).
Failure that is dangerous but is detected by automatic stroke testing.
Failure that is dangerous and that is not being diagnosed by automatic stroke testing.
Failure of a component that is part of the safety function but that has no effect on the safety
function.
State where the output current is ≤3.6 mA (fail low) or ≥21 mA (fail high)
Failure that causes the current output to go to the defined fail-safe state without a demand from
the process.
The ability of a system to carry out the actions necessary to achieve or to maintain a defined safe
state for the equipment under control of the system.
Mode, where the frequency of demands for operation made on a safety related system is more
than one per year.
Mode, where the frequency of demands for operation made on a safety related system is not
more than one per year.
Multidrop Mode. In Multidrop Mode, multiple devices are connected in parallel to a single
wire pair. The analog current signal simply serves to supply power to the devices in two-wire
technology with a fixed current.