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.
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.
