CBTC Overview Flashcards
Primary aim of CBTC
Provide fail safe rail signalling operating, preventing hazards such as collisions between trains. It also allows trains to travel at the maximum speed consistent with safety.
Safe separation distance
A dynamically calculate distance between trains based on operating speeds, braking curves and locations of the trains on the guideway.
Safety distance
A fixed distance between the commanded stopping point of the following train and the confirmed position of the rear of the preceding train.
Vehicle Control Centre
The VCC transmits the target point for trains to stop and calculates the safe separation distance for the following train.
Automatic Train Protection
ATP is responsible for safe train movement:
- Provides point interlocking
- Provides safe train separation
- Prevents hazards such as unscheduled door openings, roll back ect
- Maintains continuous train location determination throughout the system.
Automatic Train Operation
ATO is responsible for speed regulation, station stopping and door control:
- Regulation of train speed within the limits imposed by ATP
- Provide programmed station stop including door opening
- Provide alarm monitoring and reporting
Automatic Train Supervision
ATS provides a HMI via the system management centre:
- Provides system admin capabilities
- Provides a line overview
- Routing trains
- Regulated the operation of trains to maintain timetables
- Displays KPIs
VCC Overview
VCC provides ATP and commands vehicle operation and route setting. It is responsible for safe train separation and safe movement of points. 14 VCCs on the 4LM network.
VCC Components
3 CPUs working in a 2-out-of-3 configuration
VCC Data Communication System
Input/output racks
Station Controller Subsystem
SCS communicates with the VCC and other SCSs. It is responsible for the safety of the system within its area of control. Receives inputs from:
- Emergency stop devices
- Point status
- Axle counters
- Protection key switch
- Peripheral equipment
VOBC Overview
The VOBC provides ATP and ATO. It is responsible for train movement within the speed/distance permission from the VCC. Each S Stock has two VOBCs fitted for redundancy.
VOBC Communications
The TIU mounted on the underframe reads information from the track mounted transponders. The VOBC uses this information to determine its position on the guideway. The VOBC via the DCU transmits this information to the wayside equipment.
Transponders
The maximum distance between transponders is 75m. There must be 3 transponders every 100m. Four types of transponder:
- Crossover transponder
- Cross border transponder
- Border transponder
- Accurate stop transponder
Crossover transponder
Basic transponder used by the positioning system. They replace crossovers found in a loop based system and are used to maintain positioning.
Cross border transponder
Contain information to assist in establishing and maintaining positioning around virtual loop boundaries. They are placed on either side of a border transponder.
Border transponder
These replace loop crossovers/boundaries in a loop based system and are used to maintain and establish positioning. They also replace EFID loops at transition zones so positioning can be established when entering the system from non-CBTC territory.
Accurate stop transponders
Installed in stations 8-12m away from the TIU antenna stopping locations to minimise positional errors and improve stopping accuracy.
Primary train tracking
The train is tracked using transponders
Secondary train tracking
The train is tracked using axle counter blocks. An ACB is a section of track inbetween two axle counter blocks. The train is counted in and then another train cannot occupy the ACB until the initial train is counted out.
Controlled train
Automatic Mode (ATO) Protected Manual (PM)
Manual Train
Restricted Manual (RM) Tripcock Protected
ATO Mode
Doors are opened by t/op but everything else is controlled by the ATO system.
PM Mode
Train is under the control of the t/op but is supervised by the ATP system. SID displays the maximum speed allowed and the authorised distance to go.
RM Mode
The t/op is responsible for the control of speed, motoring, coasting and braking. Speed limit of 15km/h is enforced by the propulsion system.
On board train equipment overview
VOBC rack mounted equipment: 1 Power supply unit (PSU) 1 Data communication unit (DCU) 1 Electronics Unit (EU) EMC Ferrites 1 Interface Relay Unit (IRU) 1 Local Data Collector (LDC) 1 Cable Kit
VOBC peripheral equipment: Tachometers Accelerometers 2 Radio Antennas 2 Band Pass Filters (BPF) Transponder Interrogator Unit (TIU) Relay Box
Power Supply Unit
PSU is a single Line Replaceable Unit (LRU) subrack and is powered from the 110dc train supply. It provides the operating voltages for the VOBC EU, LDC, DCU , TIU and Tachometers.
Data Communications Unit
DCU functions as the main radio interface between the VOBC, cab equipment and wayside equipment. It hosts the Mobile Radio Unit (MRU).
Electronics Unit
The EU is the vital controller of the VOBC. It provides the ATP and ATO functions. It receives and decodes information from the VCC and generates and transmits responses to the VCC.
Interface Relay Unit
IRU provides output interlocking and ensures the vital and non-vital outputs are disconnected from the EU when the train is in manual driving modes.
Local Data Connector
LDC logs events.
VOBC States
- Dormant
- Maintenance
- passive
4, Active
VOBC Dormant
Default after power up, VOBC reset or automatic restart following a self test.
Does not control the train, provides no ATO and limited ATP functionality.
Default when in non-CBTC areas.
VOBC Maintenance
VOBC moves to this state when a first line maintenance device (FLMD) is detected. VOBC provides diagnostic functionality.
VOBC Passive
Passive VOBC does not control the train, provides no ATO and limited ATP functionality. Communicates with the VCC so it can control the train when commanded active.
VOBC Active
The EU controls the safe operation of the train. Only one VOBC can be in this state on a train at a time. VOBC supervises all ATO and ATP functions.
Tachometers
2 Tachometers per VOBC. Used to derive velocity, position and travel direction.
Accelerometer
1 Accelerometer per VOBC. Used to control the motor and brake demand so that excessive speed changes are avoided.
Radio Antennas
DCU has two antennas mounted on the front of the vehicle. used to transmit and receive the messages sent to and from the VCC and VOBC.
Band Pass Filter
Filters signals from the antenna to reduce interference.
Transponder Interrogator Unit
TIU consists of the tag reader and its auxillary antenna unit on the underside of the A end DM car.
Enable Tripcock Device
ETD is used to exit a migration boundary. it forces latch relays into tripcock mode.
Inhibit Tripcock Device
ITD is used for migration boundary entry. Forces the train latch relays into CBTC mode.
