Full Route Emergency Cancellation :
Sometime it become necessary to cancel the route of a train. The reasons can be.
- The Signal failed to take OFF and need to be tried again.
- The train may be required to be admitted into another route or other train may need to be dealt first.
- In any case it must be first ensured that the signals are put back to ON(if already taken OFF) and train has not passed the signal and stopped in rear of the signal . In that case Emergency Cancellation is adopted.
While dealing with ALSR, it was explained that in case of Dead approach locking, the route will be released only after two minutes, if the train has not passed the signal.
Let us examine how the time delay, is made effective. This is made effective by one of the following means:
- Mechanical Time Release Relay.
- Thermal element relay (QJ1)
- Electronic Timer Relay.
Mechanical Time Release Relay.:
The rotation of a gear system makes the Reverse contact after two minutes. The reverse contact is used in picking up ALSR. This is not used now a days.
Thermal element relay (QJ1)
QJ1 is a Q series timer relay, which has a thermal coil and a bimetallic strip. This is used along with another Q series relay called NJPR.
The circuit is given below.
A common time element Relay is used for releasing routes of a group of signals or all yard signals. In that case, two more relays are used along with it, viz. RJPR & NJPR. In addition an individual ‘JSLR’ is provided, one for each signal or for a small group of conflicting signals. This, along with the common NJPR, provides for selection of time release in the concerned ASR circuit. While NJPR picks up at the end of JR operation, RJPR is used to prove the dropping of all concerned JSLRs, before a JR operation is initiated i.e., one timer operation for cancellation of one signal at a time.
When SM has to cancel the route, he puts back Signal switch to normal. With this HR drops following which HECR etc. drops JSLR picks up through ALSR drops. Through JSLR up contact the thermal coil gets feed. Due to the difference in the coefficient of linear expansion of Inver and brass, the bimetallic strip under goes an upward bend and this makes Hot contact. The thermal unit is fed through the back contact of JSR (JSR is the Neutral Relay in the same enclosure). As soon as hot contact is made, JSR picks up and sticks through its own contact. Once JSR picks up, the feed to the thermal coil gets cut off and the strip starts cooling down. After a time lapse, bimetallic strip goes back to original position and a set of contacts called cold contact will be made. (refer S5A for more details). The cold contact and JSR front contact together pick up JR or NJPR, which is a Q series relay connected externally. When JR picks up the ALSR energises and releases the route.
Electronic Timer Relay.
To get the required time delay, now-a-days electronic timers are used.
The electronic timers are having solid state electronic circuits inside.
This gives an output, two minutes after the input is given .
Since the Electronic circuits using semi conductors are not treated as fully reliable, it is a practice to use two Timers in parallel and their contacts in series for releasing the route as shown below.
Let us Understand by yard diagram.
Let us take OFF S-12 for Main Line .
By that time, the controller has instructed the SM on duty to receive train which is coming from Delhi first through Main line and put OFF the S1 first then receive the train from Howarh.
Then SM Presses the S12 and EGGN button to throw signal to danger.
Then SM releases EGGN and Presses the EUYN button alone with S12 to cancel the route.
After 120 sec, ALSR picks up and route get released.
And JN Circuit is given Below.
