Overview - Honeywell XNX Safety Manual

XNX Universal Transmitter

2 Overview

IEC 61508 is a generic functional safety standard. Functional safety
is defined in this standard as "part of the overall safety relating to the
Equipment Under Control (EUC) and the EUC control system which
depends on the correct functioning of the E/E/PES
systems, other technology safety-related systems, and external risk
reduction facilities."
A system is considered to be functionally safe if the random and
systematic faults do not kill or injure humans, pollute the environment,
and do not result in the loss of equipment or production.
A systematic fault is defined as a failure with a definite cause. A random
fault can happen at any time and the cause is unclear. The terms fault
and failure can be used interchangeably.
A Safety Integrity Level-certified system can detect the majority of
safe and unsafe failures. XNX is SIL 2 capable per IEC 61508. XNX
is SIL 3 capable in a redundant system per IEC 61508.
Table 2 below outline a system's safety integrity level in relation to its
average probability of failure to perform its design function on demand
and probability of dangerous failure per hour.
Table 1. Average Probability of Failure to Perform Its Design Function on Demand (Low Demand
Safety Integrity Low demand mode of operation (Average probability of
Level failure to perform its design function on demand (PFD))
4
3
2
1
1 Electrical/electronic/programmable electronic systems
Overview
safety related
1
Table 1
System)
≥ 10 to < 10
-5 -4
≥ 10
to < 10
-4 -3
≥ 10
to < 10
-3 -2
≥ 10 to < 10
-2 -1
Table 2. Probability of a Dangerous Failure Per Hour (High Demand System)
Safety Integrity
Level (Probability of a dangerous failure per hour (PFH))
4
3
2
1
NOTE:
The XNX system is Type B. A Type B system uses controllers
or programmable logic per IEC 61508.
The XNX product consists of a main board, a personality board, and
a sensor. The information presented in this manual is based on the
combination of the main board and personality board.
XNX Transmitter
and
XNX
main
board
Note: Only one personality board per XNX main board
This manual outlines the proof test procedure, a required operation to
maintain the XNX's functional safety under low demand applications.
4
High demand or continuous mode of operation
≥ 10
to < 10
-9 -8
≥ 10
to < 10
-8 -7
≥ 10 to < 10
-7 -6
≥ 10 to < 10
-6 -5
Sensor
IR Personality
IR sensor
board
mV Personality
mV sensor
board
EC Personality
EC sensor
board
XNX Gas Detector Transmitter