Wednesday, December 11, 2013

Airport runway light system testing

If you ever flown at night, you would have seen these bright lights and signs on the runway, directing the pilots to their correct paths and destinations.  Unlike the lights in our homes and offices, these lights are wired in series, not in parallel.  Each light is powered through an isolation transformer, so that if one light bulb goes out, the string does not go down, like the common Christmas lights which are also wired in series.  This series structure assures the same current going through each light in the string, and therefore guarantees the same brightness.  Depending on weather conditions, the runway operator would dial the current up or down to provide pilots with the optimal signage.  This is done electrically with a constant current regulator (CCR).  It is not uncommon for some CCR to output over 1000V in order to maintain the correct current.

One of Agilent’s customers, AGM, designs and manufactures these air field signs.  Throughout the sign creation process, handheld multimeters are used to verify the voltage and current of the airfield guide signs to ensure their proper operation. This requires the frequent use of the regulator switch on the CCR. Due in part to its size, at AGM the CCR resides apart from the shop floor. Depending on shop floor activities, signs under production can be located as far as 30 meters (98 feet) from this power source.   When deployed in airfields, signs can be hundreds of feet apart.
To obtain performance data of signs under production, typically one technician controls the CCR (to step it up or down), while a second technician records performance data at the signs under production. However, there are occasions when a single technician performs this process. He must make multiple trips between the signs and the CCR, which significantly hinders his productivity.
Today, AGM technicians use a Bluetooth®-enabled device equipped with an Agilent U1177A Bluetooth adapter, and free Android-based Agilent applications to perform remote monitoring.

Using the Agilent Mobile Meter application (which can monitor up to three meters and simultaneously display measurements), an AGM technician is able to monitor the sign data while operating the CCR from a distance. This has eliminated the need to use two technicians to perform testing when cycling CCR levels, and enhanced productivity by eliminating the walking required when the testing is performed by a single engineer. If any unusual behavior is observed during the testing, the technician uses the Agilent Mobile Logger application to monitor that particular component in the sign. When a performance issue is encountered, technicians are able to forward the captured data using the e-mail capability of the Agilent Mobile Logger application. This saves a great deal of time in addressing the issue. 

Foot notes:

The following diagram gives a detailed account of the circuit involved, quite distinct from commercial or industrial power circuits.

The reason for wiring in series:  light strings can be very long, over a mile perhaps.  Wiring in parallel will result in progressively dimmer lights as voltage drops over the distance.  Using constant current regulator will maintain fixed current draw on each and every light.  CCR runs from 2.5A to 6.6A selective against weather condition.  Bright in bad weather, light in good clear nights and energy savings mode.  The CCR can output from 2.5KV to 30KV depending on size.  At these high voltages cable insulation integrity is now paramount.