1. SMR/SMCR CIRCUIT
This relay is energized when the SM’s panel key is `IN’ and turned to Normal.
The Energisation of SMCR/SMR relay provides authorized operation of all the
functions on the panel.
When SM’s key is turned to reverse and taken out from panel by SM, prevents un-authorized operation and locks the panel in the last operated position.

2. TSR CIRCUIT
FOR SIGNALS 3,4,21 TSR IS COMBINED SINCE ALL THE THREE SIGNALS ARE CONFLICTING TO EACH OTHER

3. SIGNAL KNOB REVERSE RELAY(RR) CIRUIT
The switches/knobs used are 2 position type – NORMAL and REVERSE
NORMAL : Signal will be at ‘ON’ condition.
REVERSE : Knob reverse relay RR picks up provided conflicting RRs in drop. The signal will be taken off provided all other conditions are favourable.

4. RR SIGNAL KNOB REVERSE RELAY
Bridging of SMCR front contact with respective RR front contact facilitates locking up of SM’s panel after signal is taken off and prevents rising of signal when panel is locked.
Bridging of R band of signal switch with drop contact of SMCR prevents unauthorized normalization of signal in case SM locks up the panel.

5. UCR CIRCUIT
One signal will have one UCR. UCR will be named after the signal number.
This relay is normally de-energized relay. It energizes when ever signal knob is reversed
or signal knob reversed and route button pressed, provided all other required conditions
are available.
In UCR circuit all points in route, overlap and isolation (set& locked) are proved.
To achieve locking of conflicting signals, Front Contact of ASRs or back contacts of UCRs of
conflicting signals are proved in UCR circuit.
CH IN is also proved in UCR , so that once checking completed and route locked,
further route should not be altered mechanically by cranking.
UCR front contact is proved in HR circuit.
UCR back contact is proved in ASR circuit. This is utilized to drop ASR as soon as UCR
picks up i.e., to lock the Route as soon as it is checked. Back contact of UCR in ASR
circuit also ensures that Signal knob is normalized before releasing the route.

6. UCR CIRCUIT

7. ASR /ALSR CIRCUIT ALSR is a normally energized relay.
Every signal will have one ALSR .
Whenever a route is set and route-checking relay UCR is
energized it causes ALSR to drop and there by locks the
route.
The drop contact of ALSR is proved in HR circuit to ensure
locking of that signal route before the signal is cleared.
ASR can be combined for the signals which are conflicting to
each other

8. ASR/ALSR CIRCUIT CONSISTS OF 3 CIRCUITS
Indication locking.
Back locking.
Approach locking 

9. ASR CIRCUIT

10. ASR gets energized through 3 ways.
(i)    Only after the train travels on the entire route sequentially and
clears the route.
(ii)   On cancellation, with time delay when dead approach provided or
approach track occupied. 
(iii) On cancellation without any time delay when approach track is provided and clear.

11. When the train travels over the set route , ASR picks up only on the following conditions
The train has arrived completely and cleared the entire route.
The sequential route release relays UYR 1,2,3 have picked up indicating the sequential, directional movement and arrival of train.
The signal is put back to `ON’ and the controlling relays & indication relays have dropped.
The controlling switch if any, has been normalised .
The track circuits in the entire route upto Berthing track have picked up behind the train.

12. ASR CIRCUIT FOR S1

13. UYRs CIRCUIT

14. 3/4ASR COMBINED FOR S3&S4
In this circuit, ASR is combined for signals 3&4.
The approach path is provided for both starters.

15. Overlap Stick Relay Circuits - OVSR & OVJSLR
OVSR is normally energized and drops whenever the signal is taken ‘OFF’ leading towards that overlap.
OVSR UP is proved in the WLR circuit.

16. At HR stage all the conditions to be satisfied for clearing a signal are proved.
Crank handles are ‘in’, i.e. proved by CHLRs up and CHFRs down.
Route Release Relays have de-energized after the last train movement i.e UYR1, UYR2 etc., are down.
No cancellation is initiated i.e. JSLR down.
Interlocked LCs if any in the Route and overlap are locked and closed against Road traffic (LXPR up) and held locked till the passage of that train is over.
Conflicting signals are at ‘ON’ is proved by proving the front contact of ASRs or back contacts UCRs of conflicting signals.
All points in the route, overlap and isolation are set and locked i.e. Concerned NWKRs, RWKRs are in up condition.
Concerned to its own signal i.e
-        RR is up
-        UCR is up
-        ASR is down
-        One signal - one train feature (TSR up)

17. At HR stage all the conditions to be satisfied for clearing a signal are proved.
All Back lock & and controlling tracks are clear i.e. TPRs concerned are up.
Signal ahead is not blank (GECR up or RECR/HECR/DECR UP)
Route Indicator lamps are not lit for straight line (UHRs / UGRs and UECR down) compulsory in case of Junction type Indicator
Route Indicator lamps are lit for loop lines (UGR or UHR and UECR up)
Sidings in the route & overlap are kept normal and held (siding KLPR/NPR up).
Cross protection is provided for the signal control relay, by the Front contact of ASR or Back contact of UCR.
Double cutting is provided by UCR up & ASR down

18. HR CIRCUIT FOR S1

19. NCR/RCR circuit

20. WLR CIRCUIT

21. WLR CIRCUIT

22. PCR CIRCUIT With WLR up, the PCR heavy duty relay picks up.

23. PCR CIRCUIT With PCR up 110v DC is extended to point location.

24. NWKR/RWKR CIRCUIT With WLR, RCR/NCR picked up, NWKR/RWKR drops.
NWKR/RWKR CIRCUIT
With WLR, RCR/NCR picked up, NWKR/RWKR drops.
Thereby all indication relays& its repeater relays (NWKPRs, RWKPRs, NWKSRs, RWKSRs) drop.

25. NWR/RWR CIRCUIT
With WLR up, all indication relays drop, NCR/RCR up, NWR/RWR will pick up at location

26. POINT OPERATION CIRCUIT AT LOCATION
With NWR/RWR picks up, WJR picks up.
There by WXR picks up and sticks with its own front contact.
With WXR picking up, normal feed to WJR removed but WJR held in pick up through time delay condenser circuit.

27. WCR CIRCUIT
With WXR, WJR, NWR/RWR up and WNKR/WRKR drop, WCR (QBCAI relay) picks up.

28. POINT OPERATION
With WCR & NWR/RWR up, 110V DC available on bus bar is extended to point machines at A end & B end parallelly.
Both points are set to Normal or Reverse.

29. WNKR/WRKR CIRCUIT
There by WNKR/WRKR picks up.

30. NWKR/RWKR CIRCUIT
Energisation of WNKR/WRKR results in dropping of WJR, WCR, and NWR/RWR.
With NWR/RWR dropping, WXR drops.
Due to all controlling relays (WCR, WJR, WXR, NWR, RWR) at location dropping and WNKR/WRKR picking up, energizes indication relay NWKR/RWKR at relay room.  

31. POINT OPERATION
Energisation of NWKR/RWKR results in dropping of WLR and locks the point electrically.  
De-energisation of WLR in turn drops PCR1 /PCR2, thereby 110V DC is withdrawn from the location bus bar.
In nutshell it can be concluded that point operation initiated, point unlocked, point operated & set, all point controlling relays de-energized, point indication obtained and point locked again.

32. INTERLOCKING OF LEVEL CROSSING GATE

33. INTERLOCKING OF LEVEL CROSSING GATE
Method – I
The level crossing annunciation relay (LCAR) is
kept normally energized in the gate lodge when
no route over the level crossing has been set.
Any route is set, the concerned ASR/TRSR/TLSR
drops which in turn de-energizes LCAR.
This causes the road signal on either side of the level crossing to display red aspect and the bells also start ringing.
The Gate-man closes the gate and locks it, by taking out the key.

34. LC GATE INTERLOCKING

35. LC GATE INTERLOCKING

36. LC GATE INTERLOCKING

37. LC GATE INTERLOCKING