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This architecture allows provision of any range of measurement averages,
from instantaneous to very long average periods. In an LLWAS environment,
the standard measurement period is the 10 second RC average (the System
Cycle).
2.1.5 Wind Masts
Most LLWAS systems are implemented with 10m, 15m or 20m poles. In most
case 10m is sufficient. Higher poles are sometimes installed to avoid
obstructions. While it is best that all poles are the same height, this is rarely
achieved in practice.
Poles need to be strong enough to withstand high winds and also to provide
easy access to equipment for maintenance.
Almos offers both frangible and non-frangible tilting masts.
2.1.6 RF and Land Line Data Links
2.1.6.1 Detailed Communication Specification
The remote station is supplied with facilities for both radio (RF) and landline
(non RF) communications.
2.1.6.1.1 RF communications
RF communications utilises a multi-drop radio protocol that allows up to 16
remote stations to communicate on the same radio channel.
RF communications uses digitally tuned Data Radios. The radio frequency and
other parameters are fully programmable. Assuming that there are no
obstructions and line-of-sight problems, reliable communications is assured
between the master station and any remote station up to a distance of 7
nautical miles. Under ideal conditions, transmission paths of up to 25 nautical
miles are possible.
TELVENT Low Level Windshear Alert System
Almos
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LLWAS
Low Level Windshear Alert System
9 element 9dB directional yagi antennas are used at the remote stations and
3dB omni-directional antennas are used at the master stations. The yagi
antenna is stainless steel. The omni-directional antenna has a stainless steel
mounting tube with a fibreglass radome.
2.1.6.1.2 Landline communications
Landline communications utilises a multi-drop modem configuration that
allows a number of remote stations to be connected together on a single
landline channel. The recommended maximum number of units on a landline
link is 20.
To prevent faulty remote stations from saturating the communication channel
the remote stations are fitted with a watchdog circuit that disables
transmission in case a remote station is not operating correctly.
The master station configuration may include several Master Station
Communication Sets (MSCS), enabling communications via any combination
of RF and landline links. Multiple RS232 communications ports are required on
the master station PC for communications to the remote stations.
2.1.7 Display Equipment
2.1.7.1 Overview
The Low Level Windshear Alert System (LLWAS) provides two methods of
displaying windshear and microburst alarm data on user workstations.
These are:
• AAD (Alphanumeric Alarm Display) – Text Only
• GAD (Graphical Alarm Display) – Text and Graphics
All display devices use a high resolution, high brightness LCD colour monitor
and may display either display format (graphics or text).
The AAD provides the user with data in a textual display. This screen shows
the current windshear status of the airport in textual form. It gives the status
of a selected number of runway thresholds and a centerfield location.
In order to use the AAD most effectively, the user can select a “runway
threshold configuration” that matches their current frame of reference. The
user can choose to view windshear information for a selected group of
available runway thresholds. This allows Air Traffic Controllers to concentrate
on areas that are within their specific sphere of control.
TELVENT Low Level Windshear Alert System
Almos
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LLWAS
Low Level Windshear Alert System
The GAD is used to show a map of the airport and the location of wind
sensors. If a windshear or microburst is detected, then the map will show,
using coloured highlights, those areas of the airport affected.
2.1.7.2 Alphanumeric Alarm Display (AAD)
AAD display screens are an integrated screen object displaying a number of
runway threshold winds & windshear reports, status variables and centrefield
information.
While the AAD simply reports the status of single data elements, these
elements can be configured to use backup sensors for centrefield and
threshold winds, providing ATC with constant data.
All parameters on the Almos AAD are completely configurable, including
number of lines per display (8 message + 2 status), colours & highlighting
rules, audible alarms and line formats.
Audible alarms are sounded through the PC sound card when a hazardous
wind shear is detected. The duration, in seconds of this audible alarm is
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