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Digital blocking systeem

Project Waldberg is a good example of a layout that is completely controlled by the computer. The trains run just like real trains in a computer controlled blocking system. To put such a blocking system together you need a computer and a special programme like Railroad & Co. A computer controlled blocking system is the most advanced way of controlling your layout. You could also use a blocking system without a computer or even stick to your old analogue blocking system.

Signals play an active role in the blocks of a traditional analogue blocking system. Each signal is preceded by a short piece of track that is switched off when the signal shows red. The train stops abruptly when it reaches the powerless track. The signal is operated automatically by contact tracks or manually via switches. The lights, smoke generator and built-in sound module of the locomotive will not work while it is waiting for the signal, because there is no power going to the locomotive.

A traditional digital blocking system is more or less similar to a traditional analogue blocking system. The only big difference is that trains are now running on digital power and not on analogue DC or AC power. The trains are stopped by cutting the power to a small section of track in front of the signal. The trains will stop abruptly. The lights, smoke and sound module are also switched of as long as the signal is showing red. You can solve these problems by adding a special signal module. The signals are operated via contact tracks, switches or decoders. It is no surprise that the possibilities of such a blocking system are somewhat limited.

A computer controlled blocking system works very differently. A computer controlled blocking system does not switch off the power in front of the signal. The computer knows which train is closing in on a red signal and reduces its speed by sending successive speed commands to the decoder of the locomotive. The last command stops the train just before it reaches the signal. Exactly the opposite happens when the signal turns to green. The train accelerates when it receives successive speed commands from the computer. The big advantage of this method is that everything can be controlled from the computer desktop. Maximum speed, acceleration and deceleration can be set for each individual locomotive and block. This will yield a much more realistic behaviour.

The blocking system will only work if the programme knows where each train is. This means adding train detection contacts to each block, e.g. with the BMD16N or BMD16N-SD. Most programmes work well with three contacts in a block. The first contact is right at the beginning of the block. As soon as a train passes the first contact, the block is regarded as occupied and the preceding signal is set to red. The second contact is located roughly halfway the block and about one to two meters before the signal (in H0). The computer will start braking the train when it reaches this contact, but only if the signal is showing red. The second contact is also called the ‘brake contact’. The train decelerates to a minimal speed and slowly moves on until it reaches the third contact in front of the signal. The computer now stops the train. The third contact is also called ‘stop contact’.

Not all programmes work in exactly this way, but the principle will be about the same. The number of contacts you have to use varies from programme to programme. It is better to decide on a programme first and read all the documentation, before you start changing your layout or planning your new one.

But what do you do if you have a beautiful layout and you do not want to rip apart to add the train detection contacts? There is a trick. You probably have a traditional analogue blocking system installed that works with powerless sections in front of the signals. You can use the existing connections of the block by means of current detection. The block is split up into two detection sections. The first section combines the first two detection sections that are normally used. This trick only works if your programme supports the use of only two sections in a block. Most good programs will do so, but results might vary from programme to programme.





Download all illustrations as PDF to take a closer look.

blockingsystem.pdf (260 kb)

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