A 'block' is nothing more that a portion of track isolated by several means to keep trains separated.

On older DC model railroads they were sections electrically isolated from the next section by means of block control switches that could be turned on or off.

Transformer power was first routed to the switch block and then on to the track. This kept passing tracks, yards, and siding electrically isolated from the rest of the layout for parking trains or locomotives waiting to go.

You can set up DCC the same way, even though unless you are in command of the locomotive it won't go anywhere until you tell it too. Setting up DCC this way helps troubleshooting electrical Gremlins by isolating one block at a time until the problem is narrowed down to a particular block. It is not absolutely necessary though for independent operation of locomotives.

 

A 'block' is nothing more that a portion of track isolated by several means to keep trains separated.

I think Michael's definition gets to the heart of what a block is for. Its a method of keeping trains separated physically. When planning blocks, you should think of the logical boundaries where you want just a single train to occupy that space. Then those boundaries become places where trains are stopped before entering or leaving that space so only one train is in the block. (There are of course some exceptions to this rule such as a storage track where you might want to store multiple engines.)

Block boundaries often occur around turnouts because you have 2 or more tracks leading into a turnout and you need to make sure 2 trains don't both try to enter the turnout at the same time. Your case of a crossing is another example where blocks would be used to ensure trains don't collide.

The next question that arrises is once you have blocks and block detectors in place, what do you use to enforce stopping of trains so they don't collide? In the real world, an engineer would look for the signal lights that would tell him if he/she can proceed or not. In the modeling world, you can replicate those signal lights and then rely on you as the train driver to heed the signals. The other way to do this is to use electronics to control the trains and send messages to the DCC locomotives to slow down and stop. One way of accomplishing this is to use full blown computer software to monitor all the trains and track and control them as they move from block to block. TrainController is a popular software program that can do this. I think there are less expensive and less sophisticated ways of doing this with discreet control boards, but I'm not familiar with their capabilities and limitations. Hopefully others can chime in with their knowledge.

Hope this helps.

Mark

 

Thank you and I should have added that I meant in a DCC world.

From your answer, in a DCC layout, it is just a "portion of track" -- but it still needs to be isolated electrically from other blocks or portions of the track, right?

 

From my previous question, on my layout I will want to know when a train is approaching the 90* crossing, so I'd need a block leading up to the crossing. I'm assuming it is electrically isolated somehow so that a "block detector" or "occupancy detector" will know the train is "in" the block, right?

Or does DCC eliminate this and through the magic of electronics they can detect the train without the tracks being isolated?

 

Block detectors can be used for block signaling, but the 'block' need not be electrically isolated from the rest of the layout. It's not like DC.

The signaling can work with IR detectors or block detectors specifically made for the purpose. Some use the detection of current draw of the locomotive and cars in the section of track they are currently in for the signaling.

Google Viessmann Signals. They are signal specialists and have a variety of systems and signals.

 

Yes it helps. Yes, I intend to use TrainController or similar (not sure yet).

Reference the attached.

1. Would this be the correct way to define block location?

2. Is there electrical isolation required between A1 and A2? Between the A's and B's?

I think I might be over-thinking this.

 

paisley has a circuit for that http://www.circuitous.ca/Diamond.html

 

I do believe that you've got your block boundaries correct, but I don't have any crossings on my layout, so I don't have direct experience. Fredrick or Rudy and some others would probably know better than I do. If you don't get confirmation in this thread, you might try searching the TrainController forum as I'm sure this is a common question.

I think all crossing track pieces will have electrical isolation of the A and B tracks, so you shouldn't need to worry about that. Best to double check with a meter. If you're going to use block detecters that work on electrical current flow, you'll have to put in your own insulated track joiners between A1 and A2 and between B1 and B2.

Mark

 

Light came on

Mark is correct about the way a crossing is 'wired'.

The NS rails are not electrically connected to the
EW rails. The current is, however, passed through
in each direction.

If you are using current measurement for occupancy
detection you would need to use insulated joiners
to create isolated 'blocks' approaching the crossing.
If you use IR or photo electric detection no blocks
or insulated joiners needed.

Don

Thanks gentlemen. I get it now.

 

Mark is correct about the way a crossing is 'wired'.

The NS rails are not electrically connected to the
EW rails. The current is, however, passed through
in each direction.

If you are using current measurement for occupancy
detection you would need to use insulated joiners
to create isolated 'blocks' approaching the crossing.
If you use IR or photo electric detection no blocks
or insulated joiners needed.

Don

 

Auto stop blocks

Jackpresly;

Another possible use for blocks approaching a crossing is automatic stopping for safety. On a real railroad, the crossing and the tracks leading to it, would be an "interlocking." This is an area of track where only one train is allowed inside the "interlocking plant" at a time, to prevent collisions. On my model railroad I have a crossing that has electrically insulated sections at the approaches. In my case, there are turnouts nearby which select which route through the crossing will be used. (My crossing is for two of the three tracks in a wye.) The contacts of the turnout's switch machines are used to control power distribution to the crossing's approach tracks. Only one route can have power applied at a time.
A train approaching "the wrong way" will encounter a dead rail and stop. This works with either DCC, which I use, or with DC.
If your track layout does not include conveniently-placed turnouts, you could use a simple toggle, or slide, switch to regulate which route gets power. With extra contacts, the same switch could operate "interlocking signals" that would let the engine crew know if they were cleared through the crossing, or not.
BTW, the square shaped, two storied, tower model called an "Interlocking tower" (or sometimes "switch tower") would be logically located near the crossing. In the steam era, a human operator in the tower, would control the signals and any turnouts and/or derails in the interlocking plant. Today interlockings are computer controlled from a distant point.

Another thing you might want to consider adding would be some curved track joining two, or more, of the straight approach tracks, with turnouts at the junction of each curve/straight track junction and maybe a siding or two if you can fit them in.
The idea here is that the two tracks crossing one another belong to two different railroad companies. What you now have is an "interchange." Cars from railroad 'A' can be forwarded to railroad 'B' via the curved tracks, or left on one of the sidings. This interchange becomes a "universal industry" where cars of any type can be dropped off and later picked up. It's a lot more realistic than leaving a cattle car at the oil refinery!

I've used a lot of terms here that may be new to you. The attached "Model Railroad terminology" pdf file will define any words you're not familiar with.

regards;

Traction Fan:smilie_daumenpos:

View attachment Model Railroad Terminology 2.1.pdf