7
BE 57-658 Eclipse
®
Model 706 Guided Wave Radar Transmitter – PROFIBUS PA output
1.4 Intrinsic Safety
The IEC 61158 physical layer supports Intrinsic Safety (IS)
applications with bus-powered devices. To accomplish this,
an IS barrier or galvanic isolator is placed between the
power supply in the safe area and the device in the
hazardous area.
IEC 61158 also supports the Fieldbus Intrinsically Safe
Concept (FISCO) model which allows more field devices in
a network. The FISCO model considers the capacitance and
inductance of the wiring to be distributed along its entire
length. Therefore, the stored energy during a fault will be
less and more devices are permitted on a pair of wires.
Instead of the conservative entity model, which only allows
about 90 mA of current, the FISCO model allows a maxi-
mum of 110 mA for Class II C installations and 240 mA
for Class II B installations.
FISCO certifying agencies have limited the maximum
segment length to 1000 meters because the FISCO model
does not rely on standardized ignition curves.
The Model 706 PA is available with entity IS, FISCO IS,
FNICO non-incendive, or explosion proof approvals.
2.0 Function Blocks
2.1 Overview
The Eclipse Model 706 Guided Wave Radar Level
Transmitter operates on the principle of Time Domain
Reflectometry (TDR).
The Eclipse Model 706PA is a Guided Wave Radar (GWR)
level transmitter with twelve PROFIBUS PA
™
Blocks (one
Physical Block, three Transducer Blocks, and eight Analog
Input blocks). The idea of Function Blocks, which a user
can customize for a particular application, is a key concept
of fieldbus topology. Function Blocks consist of an algo-
rithm, inputs and outputs, and a user-defined name.
The TRANSDUCER block output is available to the
network through the ANALOG INPUT blocks.
The ANALOG INPUT blocks (AI) take the TRANSDUCER
block measured values and makes them available as an
analog value to the network. The AI blocks have scaling
conversion, filtering, and alarm functions.
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