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Solid State Interlocking-Preparation of Estimate and Schedule
Ashok KumarManager/S&T
Rites Ltd.
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Consideration of yard for SSI
a) The outdoor arrangement is same in most of the cases for a
station with SSI or without SSI.
b) The signalling functions which control field gears is taken as vital
outputs
c) The signalling functions which are received from field are vital
inputs
d) Also some inputs/outputs connected to block instruments are vital
e) The key-in position of Crank handle is also a vital input
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Consideration of yard for SSI
e) All the control commands coming from panel are taken as Non-
Vital inputs.
f) The indications, counters, buzzers etc are taken as Non-Vital
outputs
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Power Supply Arrangements
Depending on the type of SSI being installed the power supply
arrangement will differ for different make of SSIs.
For example Microlok II uses 24v DC
Other manufacturers may use different voltages like Siemens and
AZD Praha
Accordingly the requirement of power for the SSI working to be
catered in the IPS or separately created
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Assessment of Interface with SSI
1. Vital and Non-vital I/O bit calculation
2. Vital and Non-vital board calculation
3. System configuration and serial communication
4. Power calculation
5. Interconnection of various racks and interlocking equipment
6. Manuscript of complete wiring diagram
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Vital Input and Output PCBs
No of Vital Outputs per output card No of vital inputs per card
Suitable for 12V , 24V or 60V DC application.
Spare vital inputs and outputs
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Non-vital Input/output PCB
Each Non-vital I/O PCB has 32 inputs and 32 outputs in
one PCB.
Suitable for 12V or 24V DC application.
Non-vital inputs are Panel push buttons and keys. Non-vital outputs are Panel indication LEDs, counters and
buzzers.
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Calculation of Vital I/O Bits
Gather following information from Interlocking plan:
1. Type of signals, no of aspects,
2. Points / Cross over and type of control / operation
3. Motor points / Hand operated points
4. Level crossings, siding control and crank handles
5. Track circuits
6. Axle counters
7. Block working and controls from and to the block
instruments
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Calculation of Non-Vital I/O Bits
Collect the following information from Panel Diagram:1. Number of push button controls/knob controls and key
controls. (if knobs are used one bit for normal and one bit for
reverse position to be considered)
2. Number of indications, counters, buzzers, bells etc
3. All output relays controlled by SSI are required to be read back
as per RDSO specification
From this information collected from Signalling Plan and
Panel Diagram Vital I/O and Non-Vital I/O bits can be
calculated respectively.
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Example of I/O Bits:
Out doorGear
Vital Output Vital Input Non-vitalInput
Non-vitalOutput
Relays
3A Signalwith routeindicator
DR
HR
UGR
COHR
DECR
HECR
RECR
UECR
COHECR
GN
or N & Rcondition of
knob
DGKE
HGKE
RGKE
COKE
ECR 4
UECR-1
3A Signal DR
HR
DECR
HECR
RECR
GN
or N & Rcondition of
knob
DGKE
HGKE
RGKE
ECR 3
2A Signal HR HECR
RECR
GN
or N & Rcondition of
knob
HGKE
RGKE
ECR 2
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Out doorGear
VitalOutput
Vital Input Non-vitalInput
Non-vitalOutput
Relays
Points NWR
RWR
NWKR
RWKR
WN or
N & Rpositions of
point knob
NWKE
RWKE
WFKE
QNN1 1
QNNA1 1
TrackCircuit
TPR TKE
TRKE
QNNA1 - 1
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Out doorGear
Vital Output Vital Input Non-vitalInput
Non-vitalOutput
Relays
CrankHandle
CHYR CHLR CHN CHKE
CHKRE
QNN1 - 1
SidingControl
KLYR KLCR KLN orKL N &
KL R
KLINKEKLOUTKE
KLFKE
QNN1-1
LevelCrossing
LXYR LXCR LXN or
LX N &
LX R
LXINKE
LXOUTKE
LXFKE
QNN1-1
QNNA1-1
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Calculation of BoardsAfter finding out final quantity of Vital and Non-vital I/O bits, quantity of various boards can be
derived :
Vital inputCard
Vital OutputCard
Mixed VitalInput/Output Card
Non-Vital InputCard
Non-Vital OutputCard
Microlok II 16 inputbits/Card
16 Output bits/Card
8 Output bits &
8 Input bits/Card
32 input bits and 32 Output bits/Card
AZD Praha ---------
Siemens 8 Inputbits/Card
4 Outputbits/Card
--------- 4 Input bits/Card 4 Output bits/Card
Calculation of Vital Input, Output cards and Non-Vital input, output cards is not
significant at initial estimate size, unless the tenderer quotes in the form of cards
It will be difficult to evaluate on the basis of cards Only the total number of vital inputs/outputs and non-vital inputs/outputs can be
projected, so that the requirement of cards is decided by the tenderer, as seen
from the above the bits per card vary from manufacturer to manufacturer.
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Configuration of SSI system
When the station provided with SSI is quite big, then more SSI units
are to be provided and synchronised
In that case whether the all the SSI units are to be kept at one
place or to be located at appropriate places to be decided
If requirement is to keep the SSI units at respective locations, their
synchronising with the use of OFC or twisted pairs
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Schedule for SSI system- Salient points
1. The SSI system should meet the latest RDSO specification and all
mandatory requirements of the specification need to be complied by
the supplier.
2. While preparing the schedule clear demarcation of work to be done
by indoor(SSI) contractor and similarly the demarcation of outdoorcontractor. As both indoor and outdoor contractors has to work
clubbing outdoor cables to indoor wiring, this is necessary.
3. Requirement of material for indoor work to be specific and clear.
4. Requirement of relays for indoor work whether to include in SSI
schedule or not to be decided. Where specific type of relays need to
be used in that case procurement of such relays to be decided (in
case of Siemens, Westinghouse etc)
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Schedule for SSI system- ..contd
6. Power supply requirements of the SSI and their arrangement
from IPS or individual supply.
7. Requirement of supplies for reading inputs, driving outputs and
interface with panel for indications, buzzers, counters and button
input reading to be decided.
8. Where more than one units are installed, requirement of
additional equipment and synchronisation of the units through
OFC or twisted pairs. In such cases cable paths need to be
different from reliability point of view.
9. Grounding, Surge protection and Earthing of SSI equipment and
measures to control EMI to SSI equipment.
10. Arrangement for protection from dust.
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Schedule for SSI system- ..contd
11. Provision of data logger
12. Both the Hardware and Software should be to SIL level 4
13. Spare capacity for expansion or alterations in the yard upto 20%
and facility for future alterations
14. Training of staff right from maintainer
15. Sufficient spares for the defect of cards and power supplies as
deemed necessary
16. The Software should be developed to Software engineering
standard such as CENELEC with special application to safety
critical application
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Schedule for SSI system- ..contd
17. Requirement of system architecture
1. Single Hardware with diverse software
1. Warm standby
2. Hot Standby
2. 2 out of 2 system with
1. Warm standby
2. Hot Standby
3. 2 out of 3 architecture
18. Requirement of flexibility in application software19. Any other requirements as per practice of individual railways
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Thanks
The End
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