Tyer’s Electric Train Tablet system is a form of railway signalling for single line railways. It was first devised in Great Britain by engineer Edward Tyer after the Thorpe rail accident of 1874, which left 21 people dead. It was used in New Zealand for close to 100 years until June 1994. The system uses a hard disk called a tablet, a form of token.
The purpose of the system is to use the tablet as a physical guarantee to the train crew that their train had exclusive right of way on the single line section of a railway. Without this they could not proceed beyond the section signal which protected entry to the single line.
The Tyer’s no. 6 tablet instrument is typically a cast iron framed item that has a movable drawer at the front which issues and receives the tablets. On the left hand side is a lever to reseat the tablet when it is replaced into the magazine. It has wooden side cheeks to access the complicated mechanism and a tombstone shaped wooden case on the top which houses the bell plunger, commutator and the tablet indicators for up and down trains.
Tablets are in the form of a disc made of metal or fibre (with a gunmetal weight at the top of the magazine) about 4.5 inches (110 mm) in diameter, engraved with the names of the stations between which it is valid, and also provided with notches (also called configurations) or other indentations to ensure that it would fit only one pair of instruments. (Source: Railway Signs and Signals of Great Britain and Wikipedia).Back To Signal Boxes