On Tue, 14 Nov 2006, John Shelley wrote:

Tom Anderson wrote:

Using the running rails as a voltage reference would be the obvious way
to do it. AIUI, there is a voltage across them from track circuits, but
it's small enough that it shouldn't matter.

When the train is there the running rails are at the same potential, the
train axles providing the short circuit between them.

Doh! Of course.

tom

--
Come on thunder; come on thunder.