Re: Signalling queries - Jointless tracks

[Eddie Oliver <eoliver@efs.mq.edu.au>]

Chris Downs wrote:

> >
> > A supplementary technique is the use of DPUs (data pick-up units) which
> > can subdivide a track circuit. These things, which look like metal ramps
> > alongside one rail, can be seen along some of the city stations, for
> > instance. If a track circuit is occupied, these things can tell whether
> > the occupancy is on one side or the other relative to their own
> > location.
> 
> These were also used for certain signals between Erskineville and Sydenham (&
> beyond?) when resignalled.  Considering the location of the DPUs in advance of
> certain signals, this forms part of the approach release system for these
> signals?

Probably. More generally, DPUs save the need for lots of short track
circuits, which are expensive and can start interfering with each other.
Allowing for overlaps, approach release and whatever, the closely
signalled areas may need lots of divisions in the tracks between
successive signals, so DPUs are an efficient way of helping to achieve
this. However they are also used in other contexts.