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PRINTER
PAPER TRAY
POWER SUPPLY
MODEM
PC SWITCH
M/S
SRV-A
KVM EXTENDER
LAN HUB
PATCH PANEL
M/S
SRV-A
MOXA-A-1
MOXA-A-2
MOXA-B-1
MOXA-B-2
TELVENT Low Level Windshear Alert System
Almos
14
LLWAS
Low Level Windshear Alert System
A 19” CRT monitor, keyboard and mouse are provided external to the rack for
use as a System Console.
Controller Software
The Master Station Communications Set (MSCS) communicates with remote
stations using a selective-retry, multi-drop binary communication protocol.
The efficient design of this system was demonstrated during testing and trials
with the FAA during the commissioning phase of the Almos LLWAS MSCS
design in 1997. For a very detailed discussion on the communication protocol,
please see below the section under RF and Land Line Data Links entitled
Detailed Communication Specification.
The system is designed to provide reliable communications in line with FAA
LLWAS specifications. This reliability has been proven to representatives of
the FAA Phase III LLWAS program.
All communications between the Remote Stations and the Master Station is
performed at 2400 baud. Due to the extremely high efficiency of the protocol
it is not necessary to use a higher baud rate in order to satisfy the data
transfer rate requirements of the system.
Low baud rates like 2400 are considerably more noise immune than high
baud rates like 19,200 baud and therefore are a much better option in noisy
environments, such as radio communications surrounding an airport.
Bit error rate: <10-5
Communications Reliability: > 99.9% (48Hr MER < 10-4, 1Hr MER < 10-3)
The remote station communication
system uses a highly advanced binary
communication protocol. This was
developed specifically for the FAA Phase
III LLWAS programme and has been
proven to exceed the strict
communication efficiency requirements
that were defined for that specification.
The MSCS polls all the remote stations
at the beginning of the system cycle,
which is typically 10 seconds, and then
waits sufficient time for all the units to
respond.
REPOLL
SAMPLE 4 STATION POLL CYCLE
RS3 REPLY
MISSING REPLY
RS2 REPLY
RS1 REPLY
POLL
REPOLL
RS4 REPLY
MISSING REPLY
TIME
TELVENT Low Level Windshear Alert System
Almos
15
LLWAS
Low Level Windshear Alert System
All units for which a response was not received are then selectively repolled
until the end of the data acquisition time. This period is calculated to
leave sufficient time for the data processing, display and archiving functions
of the system.
RC and Linear averaging is performed on board the Remote Station WAWS
unit. This reduces the transmitted packet size and greatly enhances the
reliability of the communications system. This approach was witnessed and
approved by FAA personnel during type testing.
For Centrefield wind gust, the WAWS unit reports ten-second gust
information. This data is then processed by the MetConsole Server and
displayed on Operator Workstations.
2.1.2.5 LLWAS Software
Almos systems’ implementation of the UCAR Phase III Algorithm uses an
efficient implementation based on and tested against the Version 1990.02
Algorithm Specification. The system is designed to allow easy expansion to
accommodate FAA approved enhancements to this algorithm.
2.1.2.5.1 LLWAS Configuration
All MetConsole stations are configured through a single shared configuration
database. This database file contains configuration information pertaining to
the role of each station on the network (primary server, secondary server,
archiving PC, SPES workstation, operator workstations, displays etc). In
addition, the configuration database contains LLWAS parameters contained in
the ACF, SPES thresholds & parameters, DCF configurations and other
configuration data.
Figure 1 - LLWAS System Configuration (Typical)
SYSTEM CONFIGURATION (SCF) and
MAINTENANCE CONFIGURATION
(MCF) (Averaging constants,
Displays, Parameters, etc)
AIRPORT CONFIGURATION FILE
(ACF)
DISPLAY CONFIGURATION FILE
CONFIGURATIO
DATABAS
(METCFG.MDB
AAD DISPLAY
SYSTEM
INPUT DEVICE
ARCHIVE STATION
KEYBOAR
D &
MOUSE
AAD DISPLAY
SYSTEM
INPUT DEVICE
AAD DISPLAY
SYSTEM
INPUT DEVICE
RAW CONFIGURATION FIL ES
& PARAMETER S
SHARED
(BOTH
LLWAS MetConsole
Overvie
TELVENT Low Level Windshear Alert System
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