I like the current-monitoring idea; you just have to divide the system into
subcircuits whose current you can resolve (as someone else noted, say, 20
bulbs per circuit, with 5% resolution), but maybe you have circuits fused
this way already anyway.  But this only works while current is flowing.
When the lights are off, can you leave a low, non-illuminating, voltage
running, and can you monitor that current?

Another idea: how about time-domain reflectometry (TDR?)  It's highly
successful and well developed in ethernet LAN wiring: send a sharp "ping"
down the wire and listen for the "echoes".  You can see shorts, opens, and
taps, resolved to a meter or so.  On an ethernet, it can be conducted while
the LAN is live -- I don't know whether the device sends a "keep off"
warning signal before the "ping" or if it just relies on the network's
normal error recovery.  In this lightbulb application, you have the
additional challenge of regognizing the signatures of hot bulb filaments as
well as cold ones, if you can can briefly remove line current (less than
1/30 second?) to strobe the circuit while lamps are on.

Peter F. Klammer / PKlammer@Racom.com
Racom Systems, Inc. / 6080 Greenwood Plaza Blvd / Englewood CO 80111
(303)773-7411 / FAX:(303)771-4708


-----Original Message-----
From: Pedro Drummond [mailto:pdrummond@IBM.NET]
Sent: Wednesday, May 20, 1998 2:52 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: How to prevent light bulb theft in airport runways ?


That's it, I have to come up with a solution. On small airports, people
steal light bulbs from the runway. How to prevent (detect) it ? And maybe
detect burn-out bulbs as well ?

Thanks in advance.


Pedro.