Moore Industries STA - Section 7 - STA in Safety Instrumented Systems

www.miinet.com Moore Industries-International, Inc.
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User’s Manual
225-748-00P
August 2024
Programmable RTD, T/C, Ohms, mV and Potentiometer Safety Trip Alarm
STA
TPRG
SECTION 7
Section 7 - STA in Safety Instrumented Systems
The STA is designed for use as an element of a safety instrumented system as dened by
IEC61508-4 para 3.4.1.
This user manual contains all of the information needed to congure, install, operate and
maintain this product. For safety applications the STA must only be used in accordance with this
information and the restrictions and limitations as detailed below.
Functional Safety Description
The STA has been certied, by exida ®* to IEC61508:2010 for systematic integrity up to SIL3
and for random integrity up to SIL2. This means that an STA is approved for single use in Safety
Instrumented Systems (SIS) up to SIL2 and in a redundant architecture (1oo2, 2oo3, etc.)
up to SIL 3. It is classied as a Type B device according to IEC 61508. Therefore, table 2 in
IEC61508-1 and table 3 in IEC61508-2 provide the Safety Failure Fraction (SFF) and PFDAVG
requirements for a given SIL rating.
The STA is a programmable alarm which accepts RTD, T/C, Ohms, mV and Potentiometer as
input for Low-Level (TPRG) units. Two programmable relays, used as process trip alarms, and
one SPDT relay, used as the fault relay are provided as outputs. An optional Analog Output (AO)
is also provided. Operating power is supplied external to the unit. For safety systems, the STA
performs as an alarm trip and/or transmitter which processes the input signal(s) and sets the
output trips and optional 4-20mA output current according to its conguration. The safety output
is either congured as an output trip or as an analog output. In both cases the fault relay must be
used to detect faults.
Note: For units with rmware V1.2 or earlier, the STA is certied to 61508:2000 by TUV
Rhineland. For units with rmware V1.3, the STA is certied to 61508 by both TUV Rhineland
and exida
®
. For units with rmware V1.5 and later, the STA is certied to 61508:2010 by exida
®
.
Failure Rate Data
The STA FMEDA report (Moore Industries’ Document No: 700-702-32) provides the failure
data (including PFD and SFF) required for calculations to use the STA as part of a Safety
Instrumented System.
Product life
The product life of the STA is 20 years (based on worst case component life data).
However, IEC 61508-2, section 7.4 states that a useful lifetime based on experience has more
weight than the calculated gures; Note 3 in the section comments that the useful lifetime of a
transmitter is most often within 8 to 12 years.
Installation
No special installation is required in addition to the standard installation practices in this user
manual. Refer to the specications table of this user manual for ambient conditions and required
power input.
Prior to use in a safety function, the user must validate the operation of the device o󰀪ine (see
bench check in Section 2).