What is the AGL series circuit principle?
Lights connected end to end on one loop with one current — so every light gives the same output.
The series circuit principle is how airfield lighting is powered: the lights are connected one after another along a single loop and fed by a CCR that holds the current constant. The brightness of a lamp follows its current, and a series path carries the same current through every lamp, so every light gives the same output, whatever its position or the length of cable.
A parallel supply would hold the voltage constant instead, but voltage drops along long airfield cables and far lamps would shine dimmer. The trade-off is that there is only one path: a break stops the whole loop, so the loop is kept complete and each lamp is fed through an isolation transformer. See constant-current circuit and series circuit architecture for the detail.
- Connect. Join the lights one after another into a single loop.
- Supply. Feed the loop from a constant-current regulator.
- Set. The CCR fixes the current for the chosen brightness step.
- Pass. That same current flows through every light in turn.
- Match. Every light gives the same output, wherever it is.
- Protect. Keep the loop complete, since a break stops all of it.
Frequently Asked Questions
Q1What is the series circuit principle in AGL?
The lights are connected one after another along a single loop and supplied by a CCR with a constant current. Because the same current flows through every light, they all give the same output.
Q2Why are AGL lights connected in series rather than in parallel?
Light output depends on the current through a lamp. A series loop forces exactly the same current through every lamp, so brightness is equal along the whole airfield without having to control the voltage at each one.
Q3What would go wrong with a parallel supply?
Airfield cables are long, and the voltage drops along them, so lamps far from the supply would receive a lower voltage and shine dimmer than those near it. A series loop is not affected in this way.
Q4What is the main disadvantage of a series circuit?
With only one path, a break in the loop stops the current for the whole circuit. The loop therefore has to be kept complete, and each lamp is fed through an isolation transformer so that a failed lamp does not normally break it. See series circuit fault path for a break in the cable.
Q5What does the CCR do in this principle?
It holds the loop current at the value set for the chosen brightness step by adjusting its output voltage. See constant-current circuit for how it does this.
Q6Is the voltage the same at every light?
No. The current is the same everywhere, but each load and each length of cable drops its own share of the voltage, and the shares add up to the CCR output voltage. See series circuit voltage.
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