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
related 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
Overview
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
4
3
safety
1
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.
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.
In XNX output signals, only 4-20 mA is considered a safety function.
Other output signals are optional signals and are not part of the
SIL2 compliance.
5
High demand or continuous mode of operation
(Probability of a dangerous failure per hour (PFH))
≥ 10 to < 10
-9
≥ 10 to < 10
-8
≥ 10 to < 10
-7
≥ 10 to < 10
-6
XNX Transmitter
IR Personality
board
mV Personality
board
EC Personality
board
XNX Gas Detector Transmitter
-8
-7
-6
-5
Sensor
IR sensor
mV sensor
EC sensor