KROHNE SU 501 EX EN - Manual (Page 25)

9 Functional safety
9.1 General
This safety manual applies to the SU 501 Ex signal
conditioning instrument. The instrument corresponds to a part
system of type A.
In combination with a vibrating level switch, the signal
conditioning instrument can be used as measuring system for
level detection meeting the special requirements of the safety
technology, e.g.
l
Mode "max." = A-mode for overfill protection
l
Mode "min." = B-mode for dry run protection
The measuring system is qualified in both modes to meet the
following requirement degree acc. to IEC 61508-2/IEC 61511:
l SIL2 with architecture 1oo1D (single channel)
l
SIL3 with architecture 1oo2D (double-channel/redundant)
The safety function of the signal conditioning instrument is the
recognition of the meas. currents stated below and the
conversion into a respective switching signal on the relay
contact or the transistor output. The safe condition depends on
the mode:
l
In mode "max.": 16 ±1 mA for condition "covered"
l
In mode "min.": 8 ±1 mA for condition "uncovered"
l
IEC 61508-1, -2, -4
- Functional safety of electrical/electronic/programmable
electronic systems
l
IEC 61511-1
- Functional safety – safety instrumented systems for the
process industry sector – Part 1: Framework, defini-
tions, system, hardware and software requirements
The failure limit values for a safety function, depending on the
SIL class (of IEC 61508-1, 7.6.2)
Safety integrity level Low demand mode High demand mode
SIL PFD
avg
PFH
4 >=10 -5 up to <10 -4 >=10 -9 up to <10 -8
3 >=10 -4 up to <10 -3 >=10 -8 up to <10 -7
2 >=10 -3 up to <10 -2 >=10 -7 up to <10 -6
1 >=10 -2 up to <10 -1 >=10 -6 up to <10 -5
Validity
Area of application
Safety function
Relevant standards
Safety requirements
SU 501 Ex - Signal conditioning instrument 25
Functional safety
27953
-EN
-050616