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herein.
Due to the client/server network nature of the Almos LLWAS system, the
number of supported display terminals, system consoles and printers is
practically unlimited. The provided network hub is may be linked to any
number of additional hubs, increasing the supported number of workstations
significantly.
A dedicated port can be set up to send data to an external network such as
the Official Airport System network. Using TCP/IP, the external connection can
access real-time data from the MetConsole server. This may be used for
connection to third party software of for remote diagnostics and data display.
This interface is called the External Data Interface and the default format is
described in detail below.
2.1.8.1 External Data Interface
The Almos LLWAS system gets data in from the wind sensor stations, from
threshold sensor stations and, in some cases, from other sensors around the
airport. This data is distributed to many modules in the system and various
calculations are performed on it.
MetConsole also makes the data from the LLWAS system available to external
users.
2.1.9 Algorithm Implementation
Almos LLWAS MetConsole uses an efficient LLWAS algorithm
implementation designed to perform all required calculations in a minimum
amount of time.
TELVENT Low Level Windshear Alert System
Almos
34
LLWAS
Low Level Windshear Alert System
F
i
g
u
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e
1
5
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LLWAS Data Input
Averaging (RC/Linear) is performed on the remote stations. RC and Linear
averaging constants are transmitted to the remote stations based on values
configured on the server. These configuration constants then can be updated
at any point without visiting the remote sites. Processing averaging on the
remote sites also means that only the final averaged values need be
transmitted to the master station, reducing transmission time and increasing
reliability.
Wind Gust computation is also partially computed
on the remote stations. Remote stations report 10
second average information to the master station,
which in turn computes a 10 minute gust using
the UAL Wind Gust Algorithm attached to this
document.
On the master station server, a timer calls various
components of the software every second. As
each component has an associated time period, it
can determine if the current ‘tick’ is appropriate
for executing its associated process.
For example, LLWAS has an associated ten second
time period. Even though LLWAS is called every
second it will only execute on the tenth second –
thus keeping in time with the LLWAS system
cycle.
Timer TICK
Threshold Sensor Interface
Master Station Controller(s)
Process MODULES
Arithmetic (Wind Gust etc)
UCAR LLWAS ALGORITHM
1. Data Preparation
2. Network Statistical Analysis
3. Divergence Analysis
4. Alert Analysis
5. Format Messages
SPES DQA
1. Bin Data per cycle
2. Process Periodic SPES Reports
DATABASE LOGGING
SERVER REPLICATION
DISPLAY
WIND
REMOTE
STATION LDL
MASTER STATION SERVER
KEYBOARD
& MOUSE
TELVENT Low Level Windshear Alert System
Almos
35
LLWAS
Low Level Windshear Alert System
Each process is designed to operate extremely efficiently, taking only a
number of milliseconds to complete. Therefore, all items executed by the
timer are completed well in advance of the next timer ‘tick’.
2.1.9.1 LLWAS Algorithm Functions
2.1.9.1.1 FAA Gust
Parameters
1. Time (seconds) of first variable average
2. Variable name
3. Gust calculation time period (seconds)
4. Gust variable name
5. Calculation intervals (seconds)
6. Peak_Wind_Threshold
7. CF_Threshold
8. Gust_Threshold
9. Calm_Threshold
The gust algorithm uses wind measurements from an LLWAS centrefield
station to determine gust wind speed.
The algorithm determines peak wind speeds over a 10-minute period and
compares these with a 2-minute average wind speed.
This is accomplished in two stages:
1. Wind speeds during the last minute that exceed the 2-minute centerfield
average by 5 knots are recorded, in order to determine a peak wind
speed.
2. Recorded peak winds measured over the past 10 minute period are
compared with the centerfield average wind speed, to determine a
maximum peak wind speed (gust).
The calculated gust wind speed is displayed for 10 minutes, unless the
maximum peak wind measurements fall to within 3 knots of the centerfield
average wind speed.
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