DCC Block Detection

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Summary: Block Detection is a method for detecting rolling stock within a given section of track. It is also known as Occupancy Detection.

Occupancy Detection

  • Have you ever thrown a hidden turnout with a car over it?
  • Would you like to know when your train is at the end of your hidden staging track?
  • Have you ever hit the back wall of the engine house?
  • Which of your roundhouse stalls is occupied?

Knowing where trains are on your layout can be used for many purposes. It can be used for position indicators, operational signaling, automated control, or animation. To perform these tasks, a certain amount of blocking needs to be done for train detection. Even though this does take some work, it's easier to accomplish this with DCC than with block control. While it's not realistic, we'll say that the signal blocks in our example are less than 12 feet long.

Occupancy Detectors

Current Transformer Symbol. Current Transformers (CT) are often used to detect the presence of a train by sensing the current flowing to the track.

To get detection working, you will need occupancy detectors. These are devices that use electronic methods to sense the presence of a locomotive (or appropriately-fitted rolling stock) on a section of track.

There are two basic forms of block detectors. First, and usually the preferred form, is a block detector that detects trains and reports the status to your control system. These detectors are usually more expensive.

The second type of detector simply detects the trains, but requires additional circuitry to send the status to your command station. However, they are still useful without this, as they can operate a crossing gate without the command station even knowing.

Commercial Occupancy Detectors

A number of DCC manufacturers supply detection devices.

Lenz has the LB101. NCE has their BD120.

Digitrax offers the BDL168 and BD4, as well as the more sophisticated BXP88 and BXPA1.

See Occupancy Detectors for more information.

Preparing the Track

Here are the steps to prepare your track for detection:

  1. In order to get detection working, you first need to select a section of track you wish to detect if a train is on that track.
  2. Isolate this section of track by gapping one of the rails at the start and the end of the block.
  3. Wire the DCC feeds to this section of track via the detector

See Also

External Links