Last time we have discussed about the block working in Indian Railways, there I have mentioned about a term Block Instrument. So you may be confused about what the Block Instrument actually mean and what it does. A Block Instrument is the apparatus kept at a block station where station master use this to give line clear to or receive line clear from adjacent block station. It is basically a communication equipment between two block station used to implement absolute block working. They are available in 2 categories:

• Single Line Block Instrument
• Double Line Block Instrument

We will discuss them one by one.

Single Line Block Instrument

This type of Block Instruments are used in that block section where only single line is provided i.e the same line is being used for both up and down movement. The Block Instruments available under this category are-

• Neale's Ball Token Block Instrument
• Tokenless Push Button type Block Instrument
• Single Line Universal Failsafe Block Instrument

Neale's Ball Token Block Instrument

This is the oldest type of block instrument invented by J.E Neale, who was a Telegraph Superintendent of The Great Indian Peninsular Railway. This Block Instrument was designed to implement absolute block working and simultaneously preventing trains from opposite direction. This Instrument use small steel balls as tokens that is handed over to driver of the proceeding train to proceed upto next adjacent station. This instrument also prevent trains from opposite direction as once a token is extracted from either of the Block Instrument another token cannot be extracted from opposite side so preventing other block station to give authority to proceed.Lets see the details how this device works.

1. Station Master of sending station will attract the attention of the recieving station's Station Master by giving bell codes (bell is mounted on left side of instrument).
2. Recieving station Station Master will acknowledge the bell codes and start talking to sending station's Station Master on Block Telephone (mounted on the right side of instrument).
3. Sending station's Station Master will details of train going to leave and ask for line clear by giving bell codes.
4. Recieving Station will acknowledge the bell codes and turn the bottom operating handle of instrument to TCF(Train Coming From) position(arrow on right side).
5. Sending station will move the bottom operating handle to TGT(Train Going To) position(arrow on left side) and a steel ball called as token will come out of the instrument of sending station.
6. The token is handed to the driver of the train going to leave and signal is taken off by sending station's Station Master.
7. When the train leaves sending station's Station Master will give bell code for train departed and recieving station will acknowledge it.
8. When the train arrives at the recieving station Station Master will check complete arrival of the train and recieves token from the driver.
9. Recieving station's Station Master will put the token into the instrument by opening the top cover,putting inside it and turning the top operating handle.
10. After that he will give bell code for train arrival and turn bottom operating handle to Line Closed(arrow up) position.
11. On recieving bell codes sending station's Station Master will acknowledge the bell codes and turn bottom operating handle to Line Closed position.

In this way this Block Instrument works,it may be little complicated for you to understand but once you understand you will be amazed how great this technology was at that time.

Tokenless Push Button Type Block Instrument

This Block Instrument is developed to overcome shortcomings of Neale's Ball Token Block Instrument as it was very time taking to operate it and driver could sometimes lose the token while on his way and many more. So as the name suggests this Block Instrument does not use any type of tokens or tablets and it is easy to use compared to previous Block Instrument and it does not require any action from the recieving station's Station Master. Let's see how this Block Instrument is used to take line clear from recieving station and move trains upto it.

1. The procedure for attracting attention of recieving station's Station Master through bell codes is same as Neale's Ball Token Exchange System.
2. Station Master of recieving station will acknowledge the bell codes and give line clear message through block telephone.
3. The sending station's Station Master will press "Bell Code" button and "Train Going To" button together and a "Train Going To" indicator light glows on sending station's Block Instrument.
4. Similarly a "Train Coming From" indicator light glows on recieving station's Block Instrument.
5. When train enters Block Section as detected by track circuits, the indication changes to "Train On Line" on both the Block Instrument.
6. When train arrives at the recieving station as detected by track circuits buzzer sounds on the reciever station's Block Instrument to announce arrival of train after that Station Master of that station will give bell codes to sending station's Station Master that the train is recieved and after recieving his acknowledgment recieving Station Master will press "Line Closed" button and the "Line Closed" indication will glow on both the Block Instrument.

This is the working of Tokenless Push Button Type Block Instrument.

Single Line Universal Failsafe Block Instrument

This the picture of a Single Line Universal Failsafe Block Instrument. This Block Instrument is just an extension of previous Block Instrument we just discussed above. A human error is possible on the above two block instrument we discussed like closing the line without properly ensuring complete arrival of train and not checking the block section is empty or not before giving line clear or taking line clear, this system comes to your rescue. In this system an Axle Counter is provided at the entry and exit of the Block Section. When train enters the Block Section the axle counter will count the number of axles the train is having currently and informs the axle counter at the exit of the Block Section. When train enters the recieving station that axle counter will again count the number of axles and verify that no coach or rolling stock is left behind and after ensuring that the line will be closed automatically with an alert to both sending and recieving end Station Masters.

Double Line Block Instruments

This type of Block Instruments are provided where there are 2 lines are in a same Block Section one for Up and other for Down. It consists of-

• Standard Double Line Block Instrument
• Double Line Universal Failsafe Block Instrument

We will discuss them one by one.

Standard Double Line Block Instrument

This is the image of a Standard Double Line Block Instrument. It has 2 dials with needles and an operating knob at bottom with bell plunger. Let's see how it works.

1. Station Master of sending station will ask for line clear by the bell codes.
2. Station Master of recieving station will acknowledge it and move the operating knob towards "Line Clear" position, by this action needle in the lower dial of recieving station's Block Instrument will point towards "Line Clear" position and same happens to the needle in the upper dial of sending station's Block Instrument.
3. After seeing the position of upper dial's needle sending station's Station Master will lower the signal and depart the train.
4. When the train enters the Block Section a buzzer will sound at the sending station's Block Instrument and after acknowledging the buzzer Station Master of sending station will give bell code of train entering block section to recieving station's Station Master.
5. Recieving station's Station Master will move the operating knob to "Train On Line" position. By this needles of both lower dial of recieving station Block Instrument and upper dial of sending station Block Instrument will point to "Train On Line" position.
6. When the train arrives the recieving station buzzer will sound at the recieving station's Block Instrument and after acknowledging that and ensuring complete arrival of train Station Master will move the operating plunger towards "Line Closed" position that will result in needles of both lower dial of recieving station and upper dial of sending station will come to "Line Closed" position.

In this way this Block Instrument works.

Double Line Universal Failsafe Block Instrument

This Block Instrument works same as Single Line Universal Failsafe Block Instrument. This Block Instrument will also avoid human errors, check clearance of Block Section before giving line clear and also check the integrity of train before closing the line. It is the most advanced technology Block Instrument ever used. It is operated the same way as Tokenless Push button type Block Instrument is operated and it is very easy to operate.

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