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LED Approach Sequence Flashing System
SFL800D
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Content Scope of Application System Design and Functions Wiring diagrams Control Unit Flashing lights Customer benefits
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Scope of Application
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Scope of Application The SFL800D serves as approach sequential flashing light system and runway threshold identification flash lights (RTILS) on airports. The SFL system enables the pilot already to recognize the runway from a long distance and marks the active landing direction. The threshold identification lights indicate the begin of the runway. The system supports two different flash frequencies (1 / s or 2 / s). 3 intensity steps allow the adaptation to the actual metrological view.
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System Design The sequence flash system is installed complementary to the existing approach center line The common length is 900 m with a distance of 30 m between the flash lights The two Threshold Identification Lights (TIL) are placed beside the green threshold lighting. To avoid short distance glare to the pilot the last 300 m segment in front of the threshold is often not equipped with flash lights. This is especially the case in CAT II & III systems.
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Differences between Xenon and LED flashing systems
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Differences in electrical characteristics
Xenon LED Sensitivity to moisture Protections required Very robust Work safety High voltage issues (max. 15,000 V) Absolutely safe ( max. 70 VDC) Lifetime ~ 500 to 10,000 hours. High voltage circuitry requires maintenance attention. > 25,000 hours Light head dimensions Small (with separate Individual Control Cabinet) Requires larger optical output Inset lights available Very limited. Inset light conditions (moisture, condensation, vibration) not beneficial for high voltage Xenon. Yes, no restrictions. Max. intensity may be limited by the available optical aperture. Can be solved by twin light combination.
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Light output from Xenon and LED
Flash intensity shape is close to a rectangular flat light signal ( t ~ 50 ms [milli-secs]) According to the Blondel & Rey calculation, the total light output contributes to the effective intensity Xenon Flash is extremely short with a high intensity peak (t < 10 µs [micro seconds]) According to the Blondel & Rey calculation, parts of the rising and falling edges do not contribute to the effective intensity (optical losses)
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Let’s remember the Broca–Sulzer-Effect
Broca and Sulzer published in ~ that short pulses of definitely visible light of a certain duration will appear brighter than if the pulses lasted longer in time. It seems that the effect is a result of the visual signal evaluation in the human optic nerve and/or brain (till now no valid explanation available). The “Broca-Sulzer-Effect” has been confirmed by several scientific studies. The effect does not increase the physical amount of light but improves the perception! Broca-Sulzer brightness enhancement occurs at stimulus onset for high intensity incremental targets. Here flash brightness is plotted as a function of duration for flashes of different luminances. Data from Hart (1987) et al.
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What will be the optimized flash duration?
According the Broca-Sulzer-Effect a flash with a duration of 40 – 70 ms should appear VERY much higher than a longer or shorter flash.
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Selection of the Flash Duration
The best solution is a 50 ms flash It provides the best perception according the Broca- Sulzer-Effect. The LED current / thermal peak and the thermal dissipation can be handled. The required capacity voltage to provide the flash energy in the 50 ms time can be kept in the SELV range.
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What is the benefit of overlapping light pulses?
Short distance view The eye resolution can separate all sequenced flashing lights Recognized is the intensity of an individual light e.g. 15,000 cd Long Distance view The eye resolution cannot separate individual lights Recognized is a virtual light with an intensity formed by all lights covering the smallest viewing angle. (e.g. with 3 adjacent lights = 45,000cd) Flash Cluster in the Row Single Flash at the Threshold
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System Design and Functions
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The sequence flash system consist of:
Components The sequence flash system consist of: Control Unit with the power and communication interface to the field components Power Distribution Unit to feed the single flash light heads with SELV power and communication The flash lights (elevated or 12” inset) with the high power LEDs and the control electronics. Note: the inset lights may be installed by pairs
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Overvoltage Protection Unit
Principle Cabling The Control Unit placed in a sub-station supplies the flash system via a single power cable. The communication between the Control Unit and the flashes is achieved on separate wires of the same power cable. Inset lights may be installed by pairs to increase the photometric performances System Layout Overvoltage Protection Unit Control Unit
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Power and communication to the lights
Power Supply to the flashing lights 400 V / 50 Hz or 60 Hz power supply voltage on two wires of the supply cable. The Power Distribution Unit transforms that voltage down to 36 VAC supply voltage for the flash lights. The safe separation with the extra low voltage level provides a Safety Extra Low Voltage (SELV) with the highest work safety. Data communication to the flashing lights Control and monitoring by two other wires of the supply cable. The control unit sets the required intensity level and the system configuration of the entire system. Individual address of the flash head defines the time of ignition. After ignition each flash light sends automatically the actual status to the control unit. A pair of combined inset lights consists of a master and a slave unit. The function is defined by the internal configuration. Only the master communicates with the control unit.
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Wiring diagrams
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Safety Extra Low Voltage
Principle Wiring Diagram and Voltage Levels 400 VAC HO7RN-F 4-core cable 2 wires for power (400V) 2 wires for control and monitoring Cable joint (contractor-made) Overvoltage Protection Unit Power Distribution Unit ( = separation transformer) Safety Extra Low Voltage (SELV) < 50V Control Unit Cable joint (contractor-made) Optional connector (e.g. for electrical frangibility on approach masts) Connector of the light E.g. for elevated light with breakable coupling
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Control Unit
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Control Unit Input: 400 V 3 phases Output: 4-core cable – 2 wires for power (400 VAC), 2 wires for communication Interface to remote Control and Monitoring System (CMS) via parallel or serial interface. Local control for the basic functions. Detailed maintenance and configuration of the system can be done over an external maintenance computer with the optional service software lucDMC.
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Local Control and Monitoring
Local control for maintenance purposes on the internal control module 5 push buttons to select function (TIL, SFL, flash frequency...) + 1 rotary switch for brightness and remote/local control 9 LED indications show the actual status of the system. Note: The use of the internal local control should be limited to trained electricians. With opened Control Unit the suitable safety regulations must be applied!
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Remote Control Interfaces
Parallel (multiwire) interface with in- and outputs on 24 VDC level. 2 redundant CAN-Bus ports For an optional serial interfacing with any other CMS brand the following interface can be provided on request: RS-485 (EIA-485) MODBUS/RTU, RCOM, RCOMplus ETHERNET MODBUS/TCP PROFIBUS DP
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Flashing lights
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Flashing lights – which photometric requirements?
Flashing lights are not specified in ICAO Annex 14 or ADM However, it seems logical that the beam dimensions should be the same as steady burning lights. But what about the intensity? Average intensity of 20,000 cd is often excessive and produces glare. FAA limits the intensity to a maximum of 20,000 cd, with a minimum of 8,000 cd for elevated lights and 5,000 cd for inset lights. Many lights of this type installed worldwide. Ideal solution: Use the ICAO beam angles Average intensity for elevated lights: 10,000 cd to avoid glare (meaning peak intensity 15,000 cd as most FAA lights) Inset lights should be approx. 60% of elevated lights as per FAA, as they are seen at shortest distance.
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Elevated flash light Flashing lights The elevated type is available as
as a standard light with 12,500 cd * nominal intensity. or a extra high intensity light with 20,000 cd * for best far distance operation under low vis. Choosing the standard light helps to increase the LED lifetime. 12” inset flash light The single inset light provides a nominal intensity of cd *. To increase the operational effective intensity, two synchronized insets next to each other can be combined to form a single point of light. * Typical values of the effective Intensity on the highest brightness step.
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Customer benefits
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Approach lighting is different!
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Reduced maintenance thanks to
Customer benefits Reduced maintenance thanks to the reliability and long life time of the LEDs (xenon flash tubes have a very short life) IP68 for all outdoor equipment, including the elevated lights This is extremely useful for approach lights installed on masts, outside the airport perimeter, above fields, roads or sea...
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Low power consumption: 20VA per light
Customer benefits Low power consumption: 20VA per light Inexpensive and easy installation: Standard low voltage cable (HO7RN-F), of small diameter; typically: 2,5 mm² from the Control Unit to the first light then 1,5 mm² to the end of the line Same 4-core cable used for both the power supply and the communication. No separate bus. No individual electronic cabinet: only a simple transformer that can be installed in a transformer pit Safety: SELV at the level of the lights, instead of 400 or 2000V.
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LED Flashing Lights First LED Approach Flasher has been operating in Kassel, Germany since April 2013. Further installations are in Muenster (Germany) Nordholz (mil) (Germany) Frankfurt (Germany) Geilenkirchen (mil) (Germany) Finkenwerder (Germany) Dubai (UAE) Iasi (Romania) Innsbruck (Austria) Warsaw (Poland) Many more are due to be in operation soon.
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