Block Detection
What is block detection ?
The ability to detect the presence of a train on a particular stretch of track is a requirement for automatic signaling which should in theory prevent more than one train being present on a section of track at any given time.
MRWAIN will be using a Digitrax BDL168 block detector that lets the system know via LocoNet when a detection section on the layout is occupied.
This data conveys the presence of a train to a SE8C signalling system that the track ahead is occupied.
Detection Section is a section of track gaped on one or both rails and connected to an occupancy detector, BDL168.
A BDL168 senses the presence of a locomotive (or specially equipped cars with resistor wheel sets) in a section of track that is set up for occupancy detection. Occupancy detectors also provide feedback in the form of a lamp on a control panel or it may be a feedback signal sent to a SE8C that can be used to set a signal head to a specific condition.
MRWAIN will be computer controlled using Traincontroller so the use of detection zones is a must. The software has to have feedback of data for it to know at any given time the location of a train. If it doesn't know where a train is it can't tell it to move somewhere else.
Just to make things a little bit more involved each detection block on my layout will have (3) three detection zones within that block.
There will be a detection zone at each end of the detection block and the third zone will be in the middle of the block.
The two end zones will be 125mm long and I need one each end because train movement on my layout is bi-directional meaning the train can enter that zone from either end.
To stop a train at a signal after entering a block, Traincontroller will begin slowing the train down in a controlled manner and this happens once the train has entered the detection zone at the end of the block. Upon entering the detection zone the BDL168 detects this event, advertises it on LocoNet with the result Traincontroller bringing the train to a controlled slow stop. The train hopefully will be positioned near the signal, just like the prototype.
Sounds really good in theory, lets see what happens in practice.
BDL168 (block detector) wiring schematic
Resistor Wheel Sets
Railway signaling is based on detection of trains. If a train is detected, then the signal system goes into action, setting up indications to show that the track section is occupied. At a grade crossing where a railway and a road intersect, the presence of a train starts the crossing signals and lowers the gates in time to stop traffic so the train can pass.
If you are into Centralized Traffic Control (CTC) like me then your railway must have block detection.
When a sensor detects electric current flow within a block the asumption is, that section of track is occupied
Powered locomotives and mobile decoders draw current, even when the locomotive is not moving. Cars with internal lighting provide the necessary detection component with their lights consuming a small amount of electric current.
Unpowered rolling stock has no electric current flow and is not detected so making the rolling stock "detectable" becomes important.
Resistor wheel sets have a resistive component that allows a small amount of electric current to flow from one rail to another. By doing so, non powered rolling stock on a track will be detected resulting in the signal system giving the proper signal indication, even if there is no locomotive present.
Jay-Bee resistor wheel set...36" & 33" inch RP-25 contour, 5.1K & 10K ohms
The image on the left depicts how the physical blocks on the layout are represented logically in TrainController's switchboard.
