Orion Instruments Eclipse 705-51AX-XXX SIL Certified Safety Manual - Manual (Page 3)

3 57-651 Eclipse ® SIL Certified Safety Manual for Enhanced Model 705-51AX-XXX
1.0 Introduction
1.1 Theory of Operation
Guided Wave Radar is based upon the principle of TDR
(Time Domain Reflectometry). TDR utilizes high frequency
pulses of electromagnetic energy transmitted down a probe.
When a pulse reaches a surface that has a higher dielectric
than the air/vapor in which it is traveling, the pulse is
reflected. An ultra high-speed timing circuit precisely measures
the transit time and provides an accurate level measurement.
1.2 Product Description
The Enhanced ECLIPSE Model 705 is a loop-powered,
24 VDC level transmitter using GWR technology.
For Safety Instrumented Systems usage, the 4–20 mA ana-
log output is the safety variable. The analog output meets
the requirements of NAMUR NE 43 (3.8 mA to 20.5 mA
usable). The transmitter contains continuous self-diagnos-
tics, and upon internal detection of a failure, is programmed
to send its output to a user-selected failure state, either low
or high. This failsafe state is defined as the Faulted Mode.
Table 1 shows the version of the ECLIPSE Enhanced
Model 705 transmitter that has been certified for SIL 2/3
protection.
The Enhanced ECLIPSE Model 705 is classified as a Type B
Device as defined by IEC61508.
1.3 Determining Safety Integrity Level (SIL)
Safety Instrumented System designers using the Enhanced
ECLIPSE Model 705 must verify their design per applicable
standards, including IEC 61511-1.
Three limits must be met to achieve a given SIL level:
1. The PFD
AVG
numbers for the entire Safety Instrumented
Function (SIF) must be calculated. Table 2 shows the rela-
tionship between the Safety Integrity Level (SIL) and the
Probability of Failure on Demand Average (PFD
AVG
).
2. Architecture constraints must be met for each subsystem.
Table 3 can be used to determine the achievable SIL as a
function of the Hardware Fault Tolerance (HFT) and the
Safe Failure Fraction (SFF) for each subsystem in a safety
system (Type B–complex components as per IEC 61508
Part 2) of which the level transmitter is just one component.
1 Transmitters:
Model 705, 705-51A*-*** (HART)
NOTE: All transmitters shipped
after August 18, 2010 (serial numbers
667050-01-001 and later) are certified.
2 Probes:
All ECLIPSE probes can be utilized.
Refer to I/O Manual 57-600 for
complete probe offering.
Table 3
Minimum hardware fault tolerance
Type B sensors, final elements and non-PE logic solvers
SFF
Hardware Fault
Tolerance (HFT)
0 1 2
None: <60%
Not
Allowed
SIL 1 SIL 2
Low: 60% to <90% SIL 1 SIL 2 SIL 3
Medium: 90% to <99% SIL 2 SIL 3
High: ≥99% SIL 3
Table 2
SIL vs. PFD
AVG
Table 1
Enhanced ECLIPSE Model Numbers
Safety
Integrity Level
(SIL)
Target Average
probability of failure
on demand (PFD
AVG
)
4 ≥10 -5 to <10 -4
3 ≥10 -4 to <10 -3
2 ≥10 -3 to <10 -2
1 ≥10 -2 to <10 -1