What is sign testing?
The checks that prove a sign works and is safe: function, electrical tests, light and position, compared with the baseline and recorded.
Sign testing proves a sign works and is safe, rather than assuming it does. It is done at commissioning, after any repair, and on the airport's routine programme, and every result is compared with what the sign gave before.
1Check it works
First the function: the sign lights, the whole message shows evenly with no dark segment, and each brightness step the circuit offers gives a clear change. The face is checked for cleanliness and the correct colours.
2Test the electrics
With the circuit isolated, locked out and proved dead, the sign's wiring is checked for continuity and its insulation is measured to earth with an insulation-resistance test. The earth bond is checked too. Connectors are part of this, since a damp or poor joint shows up as a low reading.
3Compare and record
A healthy sign gives steady results close to its baseline. A low or falling insulation reading, or a changing continuity reading, points to moisture, damage or ageing. Position and legibility are checked from where a pilot or driver sees the sign, and the result, conditions and date are recorded.
| Test | What it shows |
|---|---|
| Function | Sign lights fully and evenly at each brightness step |
| Continuity | The sign's wiring and connectors form an unbroken path |
| Insulation resistance | Insulation to earth is high and steady, with no damp or damage |
| Earth bond | Metal parts are properly bonded to earth |
| Light and legibility | Brightness, colour and message are clear at distance |
| Position | Sign is upright, aligned and not blocked |
Frequently Asked Questions
Q1What is sign testing?
Checks that prove a sign is working and safe: that it lights fully and evenly, that its wiring is sound and well insulated, that its light output and legibility are right, and that it sits in the correct position.
Q2What electrical tests are done on a sign?
Continuity of the sign's wiring and connectors, an insulation-resistance test to earth, and a check of the earth bond. The circuit is de-energised, isolated and locked out first.
Q3How are results judged?
Against the commissioning baseline and earlier records. A healthy sign gives a steady reading close to its past values. A low or falling insulation reading, or a changing continuity reading, points to moisture, damage or ageing.
Q4When is a sign tested?
At installation and commissioning, after any repair or replacement of a part, and as part of the airport's routine programme or after a fault report or event such as impact or jet blast.
Q5Is it safe to test a sign?
Only after the circuit is isolated, locked out and proved dead. A sign normally sits on a series circuit through an isolating transformer, so the primary must not be opened while it is energised, the secondary must not be left open-circuit on an energised circuit, and both are treated as live. Where a sign is fed from a local low-voltage supply instead, isolate and prove that supply dead.
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