CBTC Overview

Question 1

Primary aim of CBTC

Answer 1

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.

Question 2

Safe separation distance

Answer 2

A dynamically calculate distance between trains based on operating speeds, braking curves and locations of the trains on the guideway.

Question 3

Safety distance

Answer 3

A fixed distance between the commanded stopping point of the following train and the confirmed position of the rear of the preceding train.

Question 4

Vehicle Control Centre

Answer 4

The VCC transmits the target point for trains to stop and calculates the safe separation distance for the following train.

Question 5

Automatic Train Protection

Answer 5

ATP is responsible for safe train movement:

1. Provides point interlocking
2. Provides safe train separation
3. Prevents hazards such as unscheduled door openings, roll back ect
4. Maintains continuous train location determination throughout the system.

Question 6

Automatic Train Operation

Answer 6

ATO is responsible for speed regulation, station stopping and door control:

1. Regulation of train speed within the limits imposed by ATP
2. Provide programmed station stop including door opening
3. Provide alarm monitoring and reporting

Question 7

Automatic Train Supervision

Answer 7

ATS provides a HMI via the system management centre:

1. Provides system admin capabilities
2. Provides a line overview
3. Routing trains
4. Regulated the operation of trains to maintain timetables
5. Displays KPIs

Question 8

VCC Overview

Answer 8

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.

Question 9

VCC Components

Answer 9

3 CPUs working in a 2-out-of-3 configuration
VCC Data Communication System
Input/output racks

Question 10

Station Controller Subsystem

Answer 10

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:

1. Emergency stop devices
2. Point status
3. Axle counters
4. Protection key switch
5. Peripheral equipment

Question 11

VOBC Overview

Answer 11

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.

Question 12

VOBC Communications

Answer 12

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.

Question 13

Transponders

Answer 13

The maximum distance between transponders is 75m. There must be 3 transponders every 100m. Four types of transponder:

1. Crossover transponder
2. Cross border transponder
3. Border transponder
4. Accurate stop transponder

Question 14

Crossover transponder

Answer 14

Basic transponder used by the positioning system. They replace crossovers found in a loop based system and are used to maintain positioning.

Question 15

Cross border transponder

Answer 15

Contain information to assist in establishing and maintaining positioning around virtual loop boundaries. They are placed on either side of a border transponder.

Question 16

Border transponder

Answer 16

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.

Question 17

Accurate stop transponders

Answer 17

Installed in stations 8-12m away from the TIU antenna stopping locations to minimise positional errors and improve stopping accuracy.

Question 18

Primary train tracking

Answer 18

The train is tracked using transponders

Question 19

Secondary train tracking

Answer 19

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.

Question 20

Controlled train

Answer 20

Automatic Mode (ATO)
Protected Manual (PM)

Question 21

Manual Train

Answer 21

Restricted Manual (RM)
Tripcock Protected

Question 22

ATO Mode

Answer 22

Doors are opened by t/op but everything else is controlled by the ATO system.

Question 23

PM Mode

Answer 23

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.

Question 24

RM Mode

Answer 24

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.

Question 25

On board train equipment overview

Answer 25

``` 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 ```

Question 26

Power Supply Unit

Answer 26

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.

Question 27

Data Communications Unit

Answer 27

DCU functions as the main radio interface between the VOBC, cab equipment and wayside equipment. It hosts the Mobile Radio Unit (MRU).

Question 28

Electronics Unit

Answer 28

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.

Question 29

Interface Relay Unit

Answer 29

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.

Question 30

Local Data Connector

Answer 30

LDC logs events.

Question 31

VOBC States

Answer 31

1. Dormant 2. Maintenance 3. passive 4, Active

Question 32

VOBC Dormant

Answer 32

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.

Question 33

VOBC Maintenance

Answer 33

VOBC moves to this state when a first line maintenance device (FLMD) is detected. VOBC provides diagnostic functionality.

Question 34

VOBC Passive

Answer 34

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.

Question 35

VOBC Active

Answer 35

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.

Question 36

Tachometers

Answer 36

2 Tachometers per VOBC. Used to derive velocity, position and travel direction.

Question 37

Accelerometer

Answer 37

1 Accelerometer per VOBC. Used to control the motor and brake demand so that excessive speed changes are avoided.

Question 38

Radio Antennas

Answer 38

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.

Question 39

Band Pass Filter

Answer 39

Filters signals from the antenna to reduce interference.

Question 40

Transponder Interrogator Unit

Answer 40

TIU consists of the tag reader and its auxillary antenna unit on the underside of the A end DM car.

Question 41

Enable Tripcock Device

Answer 41

ETD is used to exit a migration boundary. it forces latch relays into tripcock mode.

Question 42

Inhibit Tripcock Device

Answer 42

ITD is used for migration boundary entry. Forces the train latch relays into CBTC mode.