Lesson 2 - Semaphore Practices
In Lesson 1 we learnt how to add basic routes to our panel - and how to draw a panel, we will now expand on this basic building block and add some signals.
Some simple rules I will follow, signalling was an art form, nowadays its more of a science with strict rules to follow, in the "old" days there were many different companies with their own rules, within these companies were districts with their own rules and often even individual signal boxes on occasion had unique rules - I intend to do generic signalling for the time being, I will build a working panel for a prototype location in the future.
The layout to be signalled is a simple up and down line, with a distant / home / starting on each line, a crossover between the lines and a shunt signal at each end of the crossover - this is easily drawn from the toolbar but we find our first "gotcha" - there are no semaphores ! - be patient we will solve that problem soon, so lets draw our simple panel and add the signals (no routes for now)
You should have a panel like this, clicking on the signals will change their aspects and they should all be red/green only (Fig 1)
Fig 1
To continue we need to make some decisions on the interlocking and the easiest way to do this is to draw up what the prototype called a locking chart, basically a list of levers and then some columns detailing what happens to them - there are many complications and variations so I will again deal with a vanilla - plain - chart, we will create 3 columns, the lever number, what, if any lever combinations release it and what if any levers it locks when reversed (pulled over) - in this example the locking chart will be drawn on the panel, it is recommended that a spreadsheet be used and kept as documentation for "real" panels. Fig 2 shows our blank locking chart. Note we do not consider levers which are normal in the frame in the "released by" section, only those levers which are required to be pulled.
Fig 2
An easy example - In a semaphore based signalling location it is not possible to clear the distant signal unless all the stop signals for that signal box have been cleared, so in our panel, signal s1 cannot be cleared unless s2 and s3 are cleared, "s1 is released by s2 and s3" - so we add this onto our locking chart (Fig 3)
Fig 3
When we pull lever 2 we do not want to be able to set either of the points on the crossover road, it is customary on a crossover to have one point released by the other (this saves on the locking as we only need to lock the first point, the second is automatically locked unless we pull the first) - for our crossover I will have lever 5 as the first half and lever 6, the second half, is therefore released by lever 5, (Fig 4)
Fig 4
Pulling lever 2 should lock the crossover points, so we prevent lever 5 being pulled, so "lever 2 locks lever 5"
Lever 3 is a free lever, it would be probably locked by the instruments in reality, but for our example we will leave it free.
Lever 4 requires the crossover road to be set, so "lever 4 is released by lever 6" (note this is the second half of the crossover and therefore ensures the whole crossover has been set (lever 6 requires lever 5 remember)) but we also want to ensure that once lever 4 has been pulled we cannot pull the signal for the other way so we lock lever 7 to prevent this, "lever 4 locks lever 7"
Lever 5, the first half of the crossover, when pulled must prevent trains being signalled along the main lines so "lever 5 locks levers 2 and 8"
Lever 6, the second half of the crossover, is simply "released by lever 5"
Levers 7-10 are very similar to the above but apply to the opposite direction moves.
Why not have a go at completing the chart before looking at the solution ?
Fig 5 shows the completed locking chart
Fig 5
Download a zip file containing the working files for this basic plan.
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Last updated : January 20, 2008 23:00