3
57-656 SIL Safety Manual for ECLIPSE Model 706
1.0
Introduction
1.1
Product Description
The ECLIPSE Model 706 High Performance Guided Wave
Radar Level Transmitter is a loop-powered, 24 VDC level
transmitter, based on Guided Wave Radar (GWR) technology.
NOTE: For Safety Instrumented Systems usage, it is assumed that the
4–20 mA output is used as the primary safety variable.
The analog output from the Model 706 meets the NAMUR
NE 43 standard (3.8 mA to 20.5 mA usable). The transmitter
contains self-diagnostics and is programmed to drive the
output to a user-selected failure state, either low or high,
upon internal detection of a diagnostic indicator. The device
can be equipped with or without a graphic liquid crystal
display (LCD).
Table 1 indicates the version of the ECLIPSE Model 706
transmitter suitable for SIL 2 applications based on the
hardware assessment.
1.2
Theory of Operation
Guided Wave Radar is based upon the principle of TDR
(Time Domain Reflectometry). TDR utilizes pulses of electro-
magnetic energy transmitted down a wave guide (probe).
When a pulse reaches a liquid surface that has a higher
dielectric constant than the air (
ε
r
= 1) in which it is traveling,
a portion of the pulse is reflected. The transit time of the
pulse is then measured via ultra high-speed timing circuitry
that provides an accurate measure of the liquid level. The
amplitude of the reflection depends on the dielectric con-
stant of the product. The higher the dielectric constant, the
larger the reflection.
1.3
Determining Safety Integrity Level (SIL)
The ECLIPSE Model 706 is classified as a Type B device
according to IEC61508.
Tables 2 & 3 define the criteria for the achievable SIL against
the target mode of operation in Demand Mode Operation.
• Table 2 shows the relationship between the Safety Integrity
Level (SIL) and the Probability of Failure on Demand
Average (PFDavg).
• Table 3 is used to determine the achievable SIL as a func-
tion of the Hardware Fault Tolerance (HFT) and the Safe
Failure Fraction (SFF) for the complete safety function
(Type B — complex components as per IEC 61508 Part 2)
of which the level transmitter is one component.
Model 706-511x-xxx (HART)
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. PFDavg
Table 1
ECLIPSE 706 Model Number
Safety
Integrity Level
(SIL)
Target Average
probability of failure
on demand (PFDavg)
4
≥
10
-5
to <10
-4
3
≥
10
-4
to <10
-3
2
≥
10
-3
to <10
-2
1
≥
10
-2
to <10
-1
