Orion Instruments Eclipse 705 - Manual (Page 39)

39 57-600 Eclipse ® Guided Wave Radar Transmitter
2.8.3 Device Configuration
Device Descriptions
The function of a Fieldbus device is determined by the
arrangement of a system of blocks defined by the Fieldbus
Foundation. The types of blocks used in a typical User
Application are described as follows:
Resource Block describes the characteristics of the Fieldbus
device such as the device name, manufacturer, and serial
number.
Transducer Blocks contain information such as calibration
date and sensor type. They are used to connect the sensor to
the input function blocks.
Function Blocks are built into the Fieldbus devices as needed
to provide the desired control system behavior. The input
and output parameters of function blocks can be linked
over the Fieldbus. There can be numerous function blocks
in a single User Application.
An important requirement of Fieldbus devices is the inter-
operability concept mentioned above. Device Description
(DD) technology is used to achieve this interoperability.
The DD provides extended descriptions for each object and
provides pertinent information needed by the host system.
DDs are similar to the drivers that your personal computer
(PC) uses to operate peripheral devices connected to it. Any
Fieldbus host system can operate with a device if it has the
proper DDs for that device.
The most recent DD and Common File Format (CFF)
files can be found on the MAGNETROL web site at
magnetrol.com or fieldbus.org.
2.8.4 Intrinsically Safe
H1 supports Intrinsic Safety (IS) applications with bus
powered devices. To accomplish this, an IS barrier is placed
between the power supply in the safe area and the device in
the hazardous area.
H1 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. 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 maximum of 110 mA for Class II C
installations and 240 mA for Class II B installations.