IRDOT-2D

The IRDOT-2D operates a built-in changeover relay and lights an LED "same outputs as the IRDOT-2". As a train passes above the IRDOT-2Ds sensor, the relay and LED switch on and remain on whilst the train is above the sensor.After the train leaves, the relay and LED remain on for a further 4 seconds.The delay prevents the IRDOT-2D continually switching the relay off and on, due to the gaps between the wagons, as the train crosses over it.The delay is also useful when the IRDOT-2D is used for moving trains automatically in storage sidings as it keeps the trains separated.

Operation

When the IRDOT-2D detects a train, it lights an LED and operates a relay.Terminals 3 and 4 are connected when a train is detected.Terminals 2 and 4 are connected when no train is detected "LED not lit". The IRDOT-2D is supplied with a 5mm diameter red LED connected to the correct screw terminals.This provides an aid while installing the IRDOT-2D to check for reflections off obstructions.

After installation, the LED is wired to the control panel.Ensure that the long leg is wired to terminal 5.If several IRDOTs are used, all the short legs of the LEDs may be connected together and a single connection taken to one of the terminal 6 connections.The LED will be damaged if it is connected directly to the power supply.It requires a current limiting resistor which is built into the IRDOT-2D.

Power Supply

The diagram below shows how to connect a number of IRDOTs to the same power supply.

As the current consumption is low, many units can be powered by the same supply.The supply should be between 12 and 16 volts.The units work with either AC or DC.If DC is used, the positive connection of the power should connect to every terminal 1.If AC is used, it is important to be consistent and connect all terminals to the same power supply terminal.

Automatic storage for a row of trains

IRDOT-2D units can be used to store a queue of trains, automatically moving trains up into empty sections. The IRDOT-2Ds also provide LED indication of the occupied sections.

The diagram above shows 3 storage sections A, B, and C separated by isolation breaks in the positive rail.Each section has an IRDOT-2D positioned at "X" "no delay is necessary at C, so either an IRDOT-2 or IRDOT-2D can be used at this position".Electrical connections from the isolated sections are through a diode and the IRDOT-2D relay contacts back to the controller.When no trains are over the IRDOT-2Ds, the relay contacts 2 and 4 are connected, powering sections of the track through the diodes. "Relay contacts 2 and 4 refer to the numbering of the terminal blocks of the IRDOT-2D". Further track sections may be added to the left.

Suppose a train moves from the left into section C.Power will be connected onto the track through the relay contacts until the front of the train is detected by the IRDOT-2D.The relay will then open.If there is no train in section B, the track in section C will still be connected to the controller through the second diode and section Bs relay contact.When a train is in section B, the train in section C will be isolated and will stop when it is detected by the IRDOT in section C. When the train leaves section B, the train in section C will move up into the next empty section. A train moving into section A will be isolated and stopped when detected.The push button switch is used to connect power to the track to restart the train in section A.The switch should be a normally open type.

Note : This arrangement will not work with feedback controllers, as the diodes block the feedback signal from the engine to the controller. This will cause the controller to think that the train is moving, and so the controllers voltage will increase to maximum.

Diodes

The diodes are used to prevent unwanted connections between the sections.They are one way valves for electricity, with the band indicating which way the electricity can flow. "our diodes are black with a silver band at one end".Looking in the direction a train is travelling, the right hand rail will be positive and the left hand rail negative.Hence for the electricity " current" to flow back to the controller so that the train can move, the band needs to be towards the positive rail as shown in the diagram.If the isolation breaks are in the negative rail, the diode band would need to be away from the rail.Note that feedback controllers will not work with diodes because the diode prevents the feedback signal reaching the controller.If feedback controllers are used, 2 pole relays can be used in place of the diodes.

Controller and train speeds