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”
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.
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.
AXLE COUNTER
• COUNTS AXLES
• COUNTS AXLES IN
AND OUT OF
SECTION
HOW IT WORKS AS TRACK
CIRCUIT
• IF AXLES IN NOT
EQUAL TO AXLES
OUT THEN SECTION
OCCUPIED
SECTION IS OCCUPIED
IN = 50
SECTION IS OCCUPIED
IN = 50
OUT = 40
OUT = 0
SECTION IS CLEAR
IN = 50
OUT = 50
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
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
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
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
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.
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.
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
A
A
B
B
Time
Dip of B precedes
that of A
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.
DETECTION IN YARDS
Detector 2
Detector 1
Detector 3
Detector 4
Processor based evaluating unit
DETECTION IN BLOCK
SECTION
Processor can include suitable logic to transfer
information through radio or other
telecommunication link
Radio Link /OFC
Processor
Processor
AXLE COUNTER WITH OFC
INTERFACE
TYPICAL MULTI ENTRY
AXLE COUNTER CEL
TYPICAL AXLE COUNTER
SIEMENS
TYPICAL AXLE COUNTER
INDOOR EQUIPMENT
Power supply
CARDFILE
Input Card
Logic Card
Output Card
TRACK DEVICE
INSTALLATION
The picture shows track
devices fixed to the track.
Receiver coil
Transmitter coil
CLOSE LOOK AT TRACK
DEVICE INSTALLATION
Receiver coils
Clamp
Transmitter coils
Base
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.
SPECIFICATIONS OF AXLE
COUNTER CEL
SPECIFICATIONS OF AXLE
COUNTER SIEMENS
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.
EVALUATOR
RELAY
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
EVALUATOR
RELAY
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.
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.
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.
PROBLEMS
Some of the main problems faced are
a) Unreliable wheel detection – caused by installation of the
track devices or setting of signal levels.
b) Failure to detect fast trains – caused by improper
adjustment of the track device coils.
c) 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.