A camera for other applications has a frame rate that provides a known and=
=20
accurate time base. So measuring distance traveled between successive frame=
s=20
is accurate or even counting the frames in which the target appears.

Would a IR detector, in a tube to limit it angle of view, detect each hot=20
wheel as it passed? Or a photo transistor in a similar tube, detect the am=
=20
binate light from the other side of the tunnel with the wheels interrupting=
?

One thing no one has mentioned is that the engine has a large electric=20
source of electro magnetic stuff coming from it. As well as the "third rail=
"=20
pickup. This may be a way to detect passage or might just gum up things lik=
e=20
Pookie eating peanut butter.

Bill


--=20
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