Wednesday, April 29, 2020



The Steps of Signal Clearance will be as follows:

STEP 1 : For Clearing any signal, only authorized persons can make operations. 
             This is ensured by providing a SM key on the control panel.
              For That SM key must be ‘IN,’ and turned in On Position.

STEP 2 : Presses GN and UN Button together and release.   
             The respective GNR and UNR will Pick up and Route initialization will 
              happen. This is called route selection. 

STEP 3: A relay called “LR” will pick up which in turn operates the points in 
            Route,overlap and isolation to the required position.(provided that no 
            conflicting route is set)
STEP 4: if the point is free to be operated or the point is not engaged by any  
            other route, and the point zone is not occupied by train. 
            The relays NWKR/RWKR picks up when points are correctly set and 
            locked at site.

STEP 5: Once if the points in the route are operated, i.e., the route
            is set and locked. For route checking the relay called UCR picks up. 

STEP 6: Every signal will have one route checking relay (UCR) and it ensures 
             NWKR/RWKRs of points in the route, overlap and isolation etc.

STEP 7: After checking, the route has to be locked. Route Locking means,
            holding the point in the route and overlap in locked condition, after the
            clearance of signal. A relay called ASR OR ALSR is employed for this
            purpose. Normally this relay will be in picked up condition. When route
            is checked i.e.when the UCR picks up, ALSR drops. 

STEP 8: When ALSR drops, another relay called point lock relay(WLR) also 
            drops. When WLR drops, point cannot be operated. 

STEP 9: Now the ALSR picks up only when the train has arrived on proper signal
            with sequential operation of track circuits or if the route is cancelled 
            ensuring back locking, Indication locking and approach locking. 

STEP 10: For clearing signal, Signal control relay called HR is energized. 

For detail study we will take station layout which is given below


- SM’s key inserted and turned to ensure authorized operation(SMR/SMCR/SMPR up)

- Route initiation/selection is done (LRs up) by the authorized person.

- Route setting (operating the points to the required condition. (NWKRs/RWKRs up )

- Route checking (UCR up)

- Route Locking/Over lap locking (ASR/TRSR/TLSR/OVSR down), Electrical locking of points.( WLR down) 

In addition to the above, for Signal Clearance, the following conditions are also to be satisfied.

- The clearance of track in the route & overlap (TPRs up )

- One signal - one train feature (TSR up)

- No cancellation is initiated (JSLR down)

- Route Release Relays have de-energised after the last train movement ( UYR1, UYR2etc., are down) (In Southern Railways UYR 1 and UYR are called as TSSLR and TPZR respectively)

Route Indicator lamps are not lit for straight line (UHRs or UGR and UECR down)(compulsory in case of Junction type Indicator)

- Route Indicator lamps are lit for turn out (UGR or UHR and UECR up)

- 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.

- Concerned crank handles are `in’ and locked (CHR /CHLR up)

- Sidings in the route & overlap are kept normal and held (siding KLPR/NPR up)

- Aspect of signal ahead is displayed (GECR up or RECR/HECR/DECR UP)

- Cross protection is provided for the signal control (by the Front contact of ALSR or Backcontact of UCR ) These contacts are not favorable for signal clearance. 

Conflicting signals are proved either directly or indirectly by proving the front contact of ALSRs of conflicting signals in UCR circuit of the signal to be cleared.


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