INTRODUCTION 1

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INTRODUCTION 1
What word comes to your mind to describe The
attempt by two objects to occupy the same space
at the same moment in time
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INRODUCTION
ACCIDENT
This is something which signal engineers work
towards ensuring do not happen while running
trains. Therefore we need identification of this
happening well in advance to ensure that trains
can be stopped before this can occur.
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TRACK CIRCUITS
Track circuits are used to identify the presence
of a train in particular section of a track and
protect against accidents occurring on account of
two trains moving to the same section of the
railway track. Track circuits use various
techniques and axle counting is one of them.
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AXLE COUNTER

• COUNTS AXLES
• COUNTS AXLES IN AND OUT OF SECTION

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HOW IT WORKS AS TRACK CIRCUIT

• IF AXLES IN NOT EQUAL TO AXLES OUT THEN SECTION
  OCCUPIED

SECTION IS OCCUPIED
IN 50
OUT 0
SECTION IS OCCUPIED
SECTION IS CLEAR
IN 50
OUT 40
IN 50
OUT 50
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ADVANTAGES

• INSULATED TRACK NOT REQUIRED
• INDEPENDENT OF BALLAST CONDITION
• TRACK CIRCUIT LENGTH CAN BE UNLIMITED
• VERY GOOD FOR PROVING BLOCK SECTION IS CLEAR
• CAN OFFER COST EFFECTIVE SOLUTION IN MONITORING
  YARDS WITH SHARED PROCESSOR AND MULITIPLE
  DETECTORS

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COUPLING OF SIGNAL FROM TRANSMITTER TO RECEIVER

• Audio frequency signal from transmitter coupled
  electro magnetically to receiver coil is
  interrupted by passage of wheels causing dips
  which are counted

Coupling above the rail
Coupling below the rail
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HOW DIPS ARE CREATED BY PASSAGE OF WHEEL

• Wheel interrupts the signal coupled above the
  rail

Coupling above the rail interrupted by wheel
Coupling above the rail
Coupling below the rail
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VECTOR DIAGRAM OF SIGNAL
With no wheel between the transmitter and receiver
The Resultant signal is large and of phase about
0 deg
With wheel between the transmitter and receiver
The Resultant signal is smaller and phase also
changes
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SIGNAL CAN INCREASE WITH WHEELS
Track devices do not necessarily have reduced
coupling of magnetic field in the receiver coils
when wheels traverse over it. In Siemens make
axle counter track device the signal strength in
the receiver coils increase when the wheels
traverse over it. The main idea is that the
signal changes as the wheel traverses over the
track devices and its detection.
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COUNTING OF AXLES

• Earlier Axle counters only monitored the
  amplitude of the signal from detectors.
• Present versions monitor both amplitude and
  phase. This gives additional discrimination
  between presence and absence of wheels.

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DETECTION OF DIRECTION

• Detection of direction of movement is important
  and it is done by having two detectors adjacent
  to each other.
• Depending on the direction of movement the
  sequence of dips of the two detectors changes.

Dip of A precedes that of B
A
A
B
B
Signal
Dip of B precedes that of A
A
A
B
B
Time
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COUNTING CIRCUITS

• Dips are analyzed using failsafe electronic
  circuits and systems.
• Older systems used discrete electronic circuits
  and then logic chips were used and presently
  processors are used
• Multiple detectors are used to monitor point
  zones and even complete yard using shared
  processing equipment thus reducing cost and
  equipment.

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DETECTION IN YARDS
Detector 2
Detector 1
Detector 3
Detector 4
Processor based evaluating unit
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DETECTION IN BLOCK SECTION
Processor can include suitable logic to transfer
information through radio or other
telecommunication link
Radio Link /OFC
Processor
Processor
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AXLE COUNTER WITH OFC INTERFACE
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TYPICAL MULTI ENTRY AXLE COUNTER CEL
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TYPICAL AXLE COUNTER SIEMENS
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TYPICAL AXLE COUNTER INDOOR EQUIPMENT
Power supply
CARDFILE
Input Card
Logic Card
Output Card
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TRACK DEVICE INSTALLATION
TRACK DEVICE INSTALLATION
The picture shows track devices fixed to the
track.
Receiver coil
Transmitter coil
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CLOSE LOOK AT TRACK DEVICE INSTALLATION
Receiver coils
Clamp
Transmitter coils
Base
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TRACK SIDE JUNCTION BOX CEL
The track side junction box provides matching of
the signals to and from the track side to the
Indoor processing unit. The junction box includes
receiver amplifier, a transmitter and power
supply. The transmitter is a audio frequency
sine wave generator. There are separate outputs
and inputs of the two transmitter and the
receiver coils. The cable length from the
junction box and the cable type is fixed to
maximize signal strengths and improve noise
immunity.
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SPECIFICATIONS OF AXLE COUNTER CEL
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SPECIFICATIONS OF AXLE COUNTER SIEMENS
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IMPLEMENTATION ISSUES 1
The output of the axle counter is fed to a relay.
This relay is picked up when the section being
monitored by the axle counter is clear of any
trains as detected by the track device at the
extremities of the section.
RELAY
EVALUATOR
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IMPLEMENTATION ISSUES 2
This relay drops when the section being monitored
by the axle counter is clear of any trains as
detected by the track device at the extremities
of the section. This relay contact is used in the
signalling circuit similar to track repeating
relay.
TRAIN
RELAY
EVALUATOR
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VALIDATION
When a axle counter is started up it does not
know the position of trains in the section it is
monitoring. There is therefore the need to ensure
that at start up it takes a safe state and that
is it assumes that the section is occupied. The
first train run and detected successfully is then
used to allow the monitoring of the section by
the axle counter. The signalling circuits are to
be designed implementing this principle.
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RESETTING
Instead of running a validation train another
method adopted is resetting of the axle counter
by manual means to start the monitoring of the
section. This can be safety risk and so normally
procedure for resetting ensures more than one
person will be be required to enable a
reset. Resetting causes the counts recorded by
the axle counter to be brought back to zero if
there are any residual counts. So even if not
used for validation is required to take care of
counts registered due to unknown reasons.
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MAINTENANACE
Track devices require maintenance as the relative
position of the transmitter coil, receiver coil
and the rail on which it is fixed requires to be
ensured for reliable detection of wheels of
trains as it traverses the track devices. For
proper adjustments dummy wheels are used which
are moved across the track devices and the dip in
the signal from the receiver coil ensured to meet
the specifications.
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PROBLEMS

• Some of the main problems faced are
• Unreliable wheel detection caused by
  installation of the track devices or setting of
  signal levels.
• Failure to detect fast trains caused by
  improper adjustment of the track device coils.
• Unreliable wheel detection during some periods of
  the day. Possibly due to defective track devices
  like fine cracks in the core material of the
  coils.