Tuesday, May 5, 2020



Approach (Lock) Stick Relay Circuits (ASR/ALSR) - Part 1

After checking the Route, it is to be locked( locked all the points in the route including in overlap & isolation ). For locking the route, ALSR to be de-energised. 

It is necessary to lock the route before a signal is taken off.  

- Every signal will be having one ALSR and the drop contact of ALSR is proved in HR pick up circuit to ensure locking of that signal route before the signal is cleared.  

-  ALSR stands for Approach Lock Stick Relay. ALSR is normally an energiesed relay with stick path provided .

- UCR checks the route whenever a route is set , if set route is found correct, UCR energises , which causes the ALSR to drop.

- In other word ALSR drops as soon as UCR picks up, since UCR back contact is proved in ALSR circuit.

- Dropping of ALSR causes OVSRs and TLSRs/TRSRs to drop .Thereby all points in route , overlap and isolation are locked as the front contact of ALSR, OVSR and TLSR/TRSRs are proved in NWLR/RWLR or WLR circuit. 

- The drop contact of ALSR, OVSR, and TLSR/TRSR are proved in HR circuit to prove that route is locked before signal is taken Off.

ALSR mainly consists of 3 circuits 

(a) Indication locking. (b) Back locking. (c) Approach locking 

- In Addition to the above locking , UCR  back contact is proved .

- All NRRs back contact concerned to that signal is also proved.

- Sequential route release and emergency cancellation circuits are take off from the circuit as shown in the diagram  .

Once ALSR picks up the locking effect on the signal route is released and all the points will become free.  Hence before a route is released, it must be ensured that the signal is normal and the movement is completed and the route tracks are clear.  To achieve that indication locking, route locking & approach locking applicable to a signal,  are proved in ALSR circuit.  

(a) Indication locking.

- Before releasing the Route i.e ALSR picking up, Signal assumed 'ON' aspect Proved in Indication Locking.

- For Color Light Signalling , RECR front contact is not used to prove the integrity of ON Aspect of signal Lamps, As Red Lamp Failure may cause the route Locking condition,thereby causing delay to traffic.

- To avoid the above under delay , instead of proving an energised contact of RECR , all the de- energised contact of signal controlling relays and there lamp checking relay (ECRs()) are proved.

(b) Back Or Route Locking

- After the train passes the signal , is shall not be possible for SM to alter the route unless the train clear the entire route. To achieve this Back or Route Locking is provided.

- All the track circuits just after the signal to the last point zone track in the route will be proved in back/route locking.

- where sectional route release is used , first Route section is directly controlled by ALSR concerned.

- The subsequent section is controlled by TLSR/TRSRs. Therefore only first route section tracks are proved in back locking of ALSR.

(c) Approach Locking

- Approach Locking is provided in ALSR circuit to prevent releasing of route in the face of an approaching train and to prevent the route being altered.

- Approach locking is providing in three parallel path. i.e
  1. Sequential route release path
  2. Cancellation path (Full route emg.. cancellation)
  3. Approach track path
- The above three path are the way to Energised ALSR .

When ALSR drops, the WLRs of points concerned drop and points become inoperative.  It is already understood that WLR should be in picked up position for any point to get operated.  This is the reason why WLR is controlled by ALSR and TPRs contact and WNR and WRR are controlled by WLR contact.  It will be also seen that ALSR and WLR back contacts will be proved in HR circuit to ensure that, both route and point are locked before signal is taken off.

ALSR can be energized in  4 ways. 
  1. Sequential route releaseOnly after the train travels on the entire route sequentially and clears  the route. i.e., the back lock TPRs are picked up.  (As we know the route shall not be released when the train is on route).  This condition is achieved by proving back lock track circuit relays in ALSR circuit and is known as back locking.
  2. Full Route Emg.. Cancellation: On cancellation with time delay when dead approach provided  or approach track occupied. 
  3. Approach track not occupied : On cancellation without any time delay when approach track provided and not occupied by train.
  4. Calling on cancellation : When ever due to Back locking track circuit failures, the route is locked (ASR not picked) then calling on knob reversed and calling on ASR drops. Immediately calling on knob is normalized and calling on cancellation is applied (CO-CAR up) calling on NJPR picks up after 240 seconds time delay which picks up the Main signal ASR.This way the route is released with out S&T Person’s intervention.

Note: we will discuses energization of ALSR in detail in next lesson


ALSR is normally picked up (through its own stick path)
ALSR when energized, indicates that the route is free / signal concerned is not taken off.
Each signal will have one ALSR or if a group of signals have common points and only one signal can be taken off at a time, as in the case of starters they may have a common ALSR.

ALSR front contact is used in WLR, TRSR/TLSR, TSR and conflicting UCR circuit.
To prove that a signal is not taken off, its ASR front contact can be used.  This feature is used to achieve locking of conflicting signals.  In fact ALSR is the ideal relay to achieve interlocking between two conflicting signals.  As ALSR can pick up only when the train has arrived and cleared backlock tracks.

ALSR back contact is used to give route locked indication on the panel.
ALSR back contact is used in HR circuit to prove that route is locked before signal is taken  ‘off’.
ALSR back contact is also used in picking up route release relays i.e., UYRs to ensure that, they pick up only when the train is arriving on proper signals.

ALSR back contacts are used in Timer circuits also to ensure that the timer is initiated only when the route is locked.


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