The provision of one more distant signal is an essential requirement when the breaking distance has got increased due to increase in speed of train. In the sections where Rajdhani /Shatabdi Express are dealt the provision of second distant is mandatory to cope up with the increase in breaking distance for giving pre-warning to drivers. (In Railways the provision of second distant in such sections are in progress) The relevant provisions of GR regarding second distant are as follow, Ref.3.07. (6).
"Where necessary more than one distant signal may be provided. In such a case the outermost signal to be located at an adequate distance from the first stop signal, shall be called the distant signal and the other called inner distant signal, with the distant signal capable of displaying attention or proceed aspect only".
Accordingly, distant signal will have only two aspect and the normal aspect being attention (Double yellow). The inner distant will have three aspects viz. caution, attention and clear. The distant signal assumes clear for the reception on main line only. For all other cases, it displays attention aspect only. The inner distant signal however assume clear aspect only for run through. Except for this, the aspects of inner distant will be as in the case of normal distant signal.
The sequence and circuit for aspect control for distant signals will be:
-Fig.4.23 4.18.1 INDICATION CIRCUITS:
Indications are given on the panel for the guidance of operator and maintenance staff.
Following are the indications for the various functions. Indications are of two types: - Strip light type and spot light type.
Signals: Indication is given aspect- wise and route- wise through concerned ECR front contacts. Colour of indications, corresponds to the colour of aspects. When ever ECR is not used, indication transformer is used for indications. Circuits are as following:
-Fig 4.24
Fig 4.27
Track occupied indications 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 lamps are given to overcome the problems due to bulb failure. If one bulb fails at least other will maintain the indication. “Track circuit occupied” indication is very important for safety point of view.
In addition to this, following indications are also given on the panel. Route locked indication.
This will be “white” when the route is locked (ASR) and when no train has occupied the route and ‘Red’ when occupied. With the release of Route, this indication also disappears.
Fig. 4.28
4.18.1.1 Route locked indications : (Strip light type) are given through ASR back contact, since ASR dropped condition ensures route locking. The route locked indication is given from the foot of the signal to the next signal on the route already set excluding overlap.
4.18.1.2 Point Indication : Point indications are given through NWKR/RWKR front contact. Conventionally ‘white’ colour is used for normal and ‘green’ for reverse position. Point free indication can be given through WLR contacts.
4.18.1.3 Flashing Indications : Flashing indications are also given to indicate that the point is under operation or point indication has failed. Flashing supply is derived from a mercury pendulum flasher unit. Recently railways have gone for electronic flashers.
4.18.1.4 Power supply arrangement for indication Circuits : 12V DC or AC can be used for indications supply. 12V, 1.2W pencil type lamps are used. The DC is preferred to AC because of its stability and consequent increase in life of lamps. The power supply failure also do not affect indication if DC is used. If AC supply is used, it is desirable to make it stabilised and uninterrupted.
Recently LEDs are used to give indication to avail the benefits of long life and very less power drain. At 12V, 1.2W rated bulb consumes 100ma whereas LED drain will be around 2 to 5 ma only. However special attention are to be laid for managing with the problem of poor visibility due to the interface of external light.
4.18.2 SIGNAL LAMP FAILURE ALARM CIRCUIT :
This circuit is employed to give an audible and visual indication to the operator whenever any of the signal becomes blank due to Signal lamp fusing. The Circuit is given below. The functioning of the circuit is explained below
:-Relay GXJR picks up through any one of the ECR pick up contact of all the signals proved in Series. Hence this relay is normally energised relay. This relay is made slow to release to cater for the prevention of relay dropping due to aspect changing. If any signal becomes blank, the feed to GXJR Relay is cut and relay drops. Through the de-energised contact of this relay, the alarm rings, which will continue to ring till such time the ACK. Button is pressed and GXYNR Relay is energised. The visual indication also will appear as soon as GXJR is de-energised.
This indication remains till such time the fused bulb is replaced by a good one and GXJR is energised.
FIG 4.30
4.18.3 POINT FAILURE ALARM AND INDICATION CIRCUIT :
The functioning of this circuit is similar to the signal Lamp Failure Alarm Circuit explained earlier, except that the NWKR/RWKR energised contacts are proved in GXJR circuit, instead of ECR energised contacts.
The circuit is as following :
-4.19 INTERLOCKING OF LEVEL CROSSING GATE :