INFRARED TRAIN DETECTION
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HOW INFRARED DETECTION WORKS IN OUR PRODUCTS:
The infrared emitter  sends out a modulated beam of infrared light. Objects above the emitter will reflect back some of this beam. When the infrared is reflected back onto the detector it distinguishes this from background infrared so detecting the presence of a train above it.
By using this method of detection our units work equally well in light and in dark..

Our units work by reflecting an invisible (infrared) beam off the underside of the rolling stock.  The infrared emitter and detector fit in a hole between the sleepers of the track. The emitter and detector are attached to an electronic circuit board that fits beneath the baseboard.  This board filters out background infrared and electrical noise. It also amplifies the detectors' electrical signal.. 
Both the emitter and sensor are supplied built on to the non component side of the circuit board. They are the parts covered in black heat shrink tubing.

The  infrared emitter and detector unit is built into many of our circuit boards including IRDOTs ( InfraRed Detection Of Trains) , IRDASCs ( InfraRed Detection And Signal Control),  MAS -Sequencer (Multiple Aspect Signalling), the SIMPLE SHUTTLE, , etc..
Below, using an IRDOT-1 as an example, we can show more clearly the working and positioning of a typical unit.
 

The diagram shows the IRDOT-1  fixed to the underside of the baseboard. The tips of the emitter and sensor are positioned level with the bottom of the sleepers..

 Track
Baseboard
Circuit Board

The two images below show the two sides of the IRDOT -1

The image above shows the component side of the IRDOT-1. The LED is shown in the position as received and before being removed to the control panel.
Two wires are required from a power source to the IRDOT-1		 The image above shows the detection side of the IRDOT-1. This side is fixed to the underside of the baseboard. The two vertical projections are the emitter and the detector which  fit into a predrilled hole in the baseboard. 
When correctly located the tip of the detection device is level with the bottom of the sleeper.
All materials reflect infrared in varying amounts.  Rolling stock of any colour, constructed of plastic, metal or card is detected. 
As the infrared is emitted in a cone, its intensity falls off with distance. This allows the detectors to work inside tunnels.  Matt black paint on the tunnel ceiling reduces the infrared reflected from it allowing the units to operate inside tunnels with only two or more inches of headroom.  Alternatively a thin piece of foam may be fitted to the tunnel ceiling (foam is a very poor infrared reflector).
IRDOTs and IRDASCs
ADVANTAGES
Infrared train detection has the following advantages:
   The units detect all rolling stock in a train. This is particularly useful when trains may run in reverse.
   The infrared detectors are inconspicuous and are usually fitted with the circuit board under the baseboard.
   They are simple to install and can be fitted to existing track.
   No modifications are necessary to the track wiring or the rolling stock. 
   They are electrically separate from the track. This makes wiring simple.
   They work in both light and dark.
   The detectors are suitable for Z, N, HO, OO and O gauge.
TYPES OF UNIT
We manufacture the following Infrared Units:
IRDOT-1: The basic unit. This lights a (control panel) LED. It has an electronic "train detected" switch to activate our other units, a second green "not detected" LED, or a relay. It is also possible to operate a bicolour LED to give for example green "not occupied", red "occupied". The switch may also operate a relay or opto-isolator for interfacing to a computer etc.
Main Uses:
  • Train detection in hidden sidings. The unit is supplied with a 5mm diameter red LED which lights when a vehicle is above it.
  •  Train detection in conjunction with our SA range of shuttles, passing loops, station stops, block sections etc. The advantages over reed switches are that no magnets need to be fitted to the engine and the detector can be positioned where the front of the train is meant to stop rather than where the train mounted magnet will finish.
  • Train detection for uncouplers. When uncoupling at a distance from the controller it is difficult to judge when the couplings are aligned over the uncoupling magnet. The gaps between the vehicles can be detected by positioning the IRDOT-1 between the sleepers on the outside of the rails, these sleepers being adjacent to the magnet fitted within the rails.
IRDOT-1D: Outputs are identical to the IRDOT-1. It detects the train immediately but takes 4 seconds to  undetect, this is to provide continuous detection of the train. As a train crosses the IRDOT-1 the LED will flicker off at each gap between  wagons or coaches , the IRDOT-1D's LED will remain lit during these gaps due to the 4 second delay.                                                                                                                                               
Main Uses:
  • To detect the whole of a moving train without the LED  flickering.
IRDOT-2: This operates an LED and a built-in changeover relay.
Main Uses:
  • Automatic isolation of trains in storage sidings.
  • Relay contacts are electrically separate from the IRDOT-2's power thus allowing the IRDOT-2 to provide a replacement for reed switches.
  • The relay contacts provide electrical isolation to enable interfacing to computers, programmable logic controllers, etc. As well as detecting trains they have been used as proximity detectors for movement of model crane arms etc.
IRDOT-2D: This has the same outputs as the IRDOT-2, but also has a 4 second undetect delay to prevent the LED flickering and the relay repeatedly switching as the train travels over it.
Main Uses:
  • System of moving up trains in storage sidings.
  • Operation of lineside accessories as the train passes.
IRDOT-3: This has a built in double pole relay and the facility to also operate both detect and undetect LED's or a bicolour LED.. The size and voltage specifications are the same as the IRDOT-3D.    
Main Uses:
  • The same as the IRDOT-2 where a bicolour display is required.
  • The first set of relay contacts can be used for automatic stopping, the second set for interfacing with a computer.
IRDOT-3D: As the above with the addition of the following selectable delays: 3, 6, 9, 12, 15, 18, 21, and 24 seconds. These are selectable by connection to the terminal block.
Main Uses:
  • The same as the IRDOT-2D where a bicolour display is required.
  • Longer delay can be used to isolate a crossing line to prevent collisions.
  • Longer delay can be used as a switch for level crossing lights.
  • Simple 2 Aspect signalling. The unit is placed ahead of the signal and timing is selected to be long enough to keep the signal at green until the train has passed.
The following units use infrared detection to control signals and points
IRDOT-P: This operates solenoid (PECO SEEP etc) point motors on detecting a train.  It also has a train detected LED.  These units can be used to operate automatic reverse loops and storage sidings.
MAS- Sequencer-4: This operates a 3 or 4 aspect signal on an adjustable time system. A feature is its very simple wiring.
IRDASC-4: These units operate 3 or 4 aspect signals. The signal aspect depends upon the aspect of the next signal or the presence of a train in the next section. The unit may either follow a MAS-SEQUENCER or be part of a chain of IRDASC-4 units. Units are also available for junctions including operating route indicators.
IRDASC-5: This works as described for the IRDASC-4 with the addition of a relay to provide  track isolation when the signal is at red.
IRDASC1 IRDASC-2 IRDASC-3: These units operate 2 aspect bulb LED and semaphore signals with  block sections, interlocking to points, and interlocking to track isolation.
POWER SUPPLY: All our modules can be powered from 12 to 16 Volts AC or DC.  A controller accessory output is a suitable power source.  The low power consumption of the units (less than 20ma for the IRDOT-1) allows many modules to be powered from the same supply.
INSTALLATION OF INFRARED DETECTION MODULES:
Units with built in infrared detection are designed to be screwed to the underside of the baseboard with the infrared emitter and detector located in a hole between sleepers. See diagram at the top of the page. They can also operate on their sides.
It is easiest to install the units after the track is laid.  Drill a small pilot hole between the sleepers.  Fit an 8mm drill bit marked with tape for slightly less than the base board thickness.  Drill from underneath the baseboard following the pilot hole.  Cut or file the small amount of baseboard material left between the sleepers.  Install the unit and then fill the remainder of the hole with modelling material.  Blu-Tack will hold the units in place temporarily.  Use 1.2mm holes for the self-tapping screws that hold the units permanently in place.
When fitted to Z or N gauge track the gap between sleepers will be less than the diameter of the infrared detector and emitter.  However, the modules work well provided they are adjusted to fit close to the sleepers. This positioning prevents reflections off the sleepers causing detection.
For base boards thicker than 22mm  (i.e. the height of the infrared devices), or where there are obstructions, the units can be supplied with the infrared emitter and detector fitted to wire leads up to 400mm / 18 inches long.