Automatic Block System

Introduction

This article presents a realistic automatic digital block system based on the Uhlenbrock IB-Switch route controller and 63350 LocoNet feedback module. Prototypical train motion at the block signals is reproduced by MZE Brake Modules, which gradually start and stop digital locomotives equipped with high-efficiency propulsion 6090x and mfx).

A unique feature of this block system is that it relies on contact track sections to control the block movements, in place of the usual circuit tracks. The use of contact tracks allows trains with multiple pickups to be operated, such as railcars (ICE, TEE, etc.) and lighted coach consists, which would otherwise cause false triggering of a circuit track block system. In addition, this system takes advantage of the IB-Switch's capability to activate accessories and routes on both positive (OFF-to-ON) and negative (ON-to-OFF) feedback events. This feature, in combination with the use of contact tracks, provides control of the signals and block movements in a way that is very prototypical. Block entry signals are switched immediately upon entering a block and each block is cleared for entrance as soon as a train has exited, which is not easily accomplished with a system of circuit tracks.

Contact tracks are also used as feedback sensor inputs to control the setting of the Brake Modules to give smoother operation. By installing a contact track section within the "brake" track of each Brake Module, and arming it through a relay contact, the locomotive is able to bypass the "transition" track of the module. This eliminates the discontinuity in speed that is caused by the locomotive passing over the module's low-voltage transition track before entering the brake track section.

The visual presence of the contact track based triggering system is also virtually undetectable with only a small gap required between adjacent rails, and no plastic actuators in the center of the roadbed. The security of this type of system is greatly improved as well, since the wheel-to-rail contact is much more predictable and reliable than circuit track operation.

The example that follows is of a four-block system, and can be easily expanded to fit any size layout and any number of blocks by additional components of the same type.

Required Components

Uhlenbrock Intellibox 65000 or 65050

Uhlenbrock IB-Switch 65800

Uhlenbrock Feedback Module 63350

MZE Brake Modules (4)

MZE Z83/84 Decoders (4)

Signals (4)

Contact tracks (8 sets)

Operation

The basic operating principle of any block system is that each block of track can only be occupied by one train at a time. The entrance to each block is protected by a signal, which prevents a second train from entering before the first has exited the far end of the block. On a model railroad, digital components can be used to simulate this functionality:

Each block contains a signal, relay, brake module, and two contact track sections connected to the feedback module. The first contact section is positioned immediately at the entrance of each block to indicate its occupation status. When this section is activated, the IB-Switch will acknowledge the feedback "ON" event and sets the block's entry signal to Stop to show that the block is now occupied. The feedback input remains ON (positive) until the last set of car wheels has left the contact track, when it will change to OFF (negative). At this point, the first train has completely vacated the preceding block, which should now be cleared for entrance by the next train.

These actions are carried out by a route stored in the IB-Switch, which is set to activate on the negative feedback event of the first contact section. The first step of the route protects entry into the occupied block by setting the relay to "arm" the second contact section, which is located in front of its entry signal and within the brake module's braking track. The subsequent steps within the route set the vacated block's entry signal, relay, and brake module to Go, which allows the next train to enter that vacant block.

When the oncoming train activates the second contact section, the IB-Switch sets the brake module guarding the occupied block to Stop and gradually stops the train. Setting the brake module in this way allows the locomotive to bypass the module's transition track, and prevents this low-voltage track from creating a discontinuity in the locomotive's speed. The result is a much more realistic and seamless deceleration of the locomotive. Note that the transition track is still required to provide an electrical barrier between the mainline track and the braking track for any cars that may be equipped with a pickup.

Construction

The components within each block are activated by digital accessory decoders. In this example, a single MZE Decoder Z83/84 controls the signal and Brake Module in each block, and supplies the relay contacts to arm the second contact section as well. As an alternative to this configuration, you may also use a mixture of Viessmann 5211 and 5213 decoders, or 5211 decoders with additional external relays.

To monitor the contact track sections, the Uhlenbrock 63350 LocoNet feedback module is used. The input response time of this module is adjustable, and should be programmed with a positive event reporting delay of around 30 milliseconds and a negative event delay of 2 seconds for all inputs. These settings provide an adequate filtering of the contact noise generated by the wheels on the contact sections, and insure that a negative feedback event will not be falsely reported. Additionally, the length of each entry contact section should be at least the same as the longest operated car to avoid "bridging" the section when a train is stopped between two blocks. The second contact section in each block, used to trigger the brake module, must be a minimum of 3 inches long. It should also be positioned far enough into the brake track to insure that the locomotive is completely within the brake section when the module is activated. (Refer to the Brake Module instructions for the suggested lengths of each of its track sections.)

Route & Sensor Programming

Programming of the IB-Switch sensor events and routes follows from the sequence described in the Operation section. The feedback input connected to the entry contact section of each block should be assigned to set that block's signal to Stop when the input is turned ON (positive). The same feedback input will be assigned to activate the preceding block's entrance route when the input turns OFF (negative). The route first switches the occupied block's relay to the Stop position to arm its brake module, then sets the vacant block's entry signal to Go, then its relay to Go, and lastly its brake module to Go. As an option, a delay can also be inserted between the last two steps of each route to reproduce the reaction time of the engineer responding to the signal change.

The feedback input connected to the second contact track of each block should be assigned to set its entry brake module to Stop when the input is turned ON (positive), and with no OFF (negative) event. The following tables summarize all of the IB-Switch programming information for the block system:

Table 1. Route Programming Steps for the IB-Switch

Table 2. Sensor Event Programming for the IB-Switch

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