Hi,

for a project I have designed a PIC based tamper detector.  It
works with an OMRON reflective IR switch, which consists of an
IR Led and a photo transistor orientated in a certain angle
to each other in the plastic case.

I use it to detect whether the case has been opened (triggers
countermeasure function).   Therefore I measure the "dark"
voltage (IR led off) of the photo transistor circuit, and the
"light" volts (IR led on).

My concern is that the measurement can be influenced by a) mobile
phones and b) airport security x-ray machines.  To a degree that
false triggers occur.

While I can test a) at home (and have done it already), I'm having
a hard time at the X-RAY thing. Unfortunately I'm not a frequent flyer,
so I can only occasionally "test" the circuit, nowhere near exhaustivly.

I found no references on the web on how those machines work.  Ie is
X-RAY near enough to visible light / IR light to make a phototransistor
conduct?   Is the X-RAY in such machines continous or pulsed? Pulsed at
what frequency typically?

Currently I make two measurements with ~15ms in between, and both
have to indicate positive before the trigger is accepted.

I appreciate any info or web pointer you can provide. Thank you!