Monday, May 11, 2020



1) Route Set and Lock Indication Circuit

- Panel being an interface between yard status and the station master. It Pay an important role in smooth working of a train.

When route is not set, no indication is given on the panel.

 When a signal is take OFF, the route is set and locked,then a row of white/ Yellow lights light up the whole length of the route including overlap.

- Many time the same track circuit shall be common to many routes, but the indication circuit is designed in a such a way that while the route strip lights get illuminated for a route to which it is a part and it is not illuminated in any other situation.

These white/yellow strip lights are given through the back contact of ALSR and the relevant track circuit relay(TPR) front contacts.

-  When the train occupies the track circuits the lights turn to Red through the TR back contact. 

The point indications are given through point indication relay front contacts and signal indication through lamp proving relay, front contacts.

2) Track Indications :

- Track occupied indications(Red light) are given through the back contact of TPR.  

- This should appear at all times whenever a track is occupied, irrespective of route set or not. 

- Two led or more are given to overcome the problems due to led failure. 

- Here R means Red(Occupied) and W means White(Not Occupied) for Track no 1T

- R2 is nothing but a Group Red light for track no 1T 

- When R2 then 1TPR drop and when W2 then TPR up

-If one led fails at least other will maintain the indication. “Track circuit occupied” indication is very important for safety point of view. 


Circuits: When Track is not occupied
Circuits: When Track is occupied.

3) Point Indications :

- When a point is set and locked in N/R position, then two white/ Yellow strip lights are used to indicate the points position on the panel.

- Point indications are given through NWKR/RWKR front contact.

- Point free indication can be given through WLR contacts.  

- Point locked condition can be given with WLR dropped condition. 

- Point flashing indications are also given. Respective indication either Normal or Reverse will flash during the operation of point or due to failure.


Suppose take an example that we have one point in the yard whose number is 11 i.e Point 11 which is set and Lock in Normal condition.

Then 11A and 11C white strip light will be lit as per the given condition.

If Point in Normal then

If Point in reverse then

11 G -> 11RWKR() and 11ATPR()
11E -> 11RWKR() and 11BTPR()

Flashing indication during point operation.

The point indication remains flashing when the point is setting to either position till it is set ans lock, after which it become steady.

The Point Operation command is extended to point location only after the point indication relay NWKR, RWKR, NWKPRs, RWKPRs, NWSRs, RWSRs are dropped.

Therefore during the point operation , the white lights strip lights through the back contacts of indication relays(NWKR(↓) RWKR(↓)) will flash to whichever position the point is going to be set. On completion of any operation , when the point is set to normal and reverse , the indication become steady.

Example : Take the above yard and write the Point indication circuit of point number 51.

4) Flashing Indications

- Flashing indications are also given to indicate that the point is under operation or point indication has failed.  

- Suppose flasher fails and get stuck in high level then point failure indication will show steady instead of flashing.

- Flashing supply is derived from a mercury pendulum flasher unit or flashers

5) Signal Aspect Display:

Two methods of signal indication are prevalent in INDIAN RAILWAY 

These are:

  1. ON and OFF aspect are displayed on the panel.
  2. All aspects are available at the signal are replicate by the corresponding colour indications on the panel.  

Take the above yard diagram(example for S12) .

- C12 ECR (UP)

and the circuit are:


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