Construction
An instrument was placed at each end of the single-track section that they were to control. They were connected together electrically in such a way that operation of one would depend on operations carried out using the other.
There were various incarnations of instruments developed by Tyer & Co. Below are the more commonly found ones:
The Tyer's no. 7 tablet instrument consists of a wooden case, on top of which is a metal slide, a switch plunger, a bell plunger and an electric current indicator. On the front is an indicator which may show either of three indications: "Line Closed"; "Train Approaching" and "Train on Line". Below this there is a second slide, which has three positions: fully home, withdrawn half way, and fully withdrawn. The three indications correspond to the three positions of the slide. The case contains several tablets; they are removed from the instrument using the bottom slide, and replaced using the top slide. The instrument was so constructed that if a tablet had been withdrawn from either instrument of a pair, no further tablets could be withdrawn until the withdrawn tablet had been placed either in the other instrument, or in the same instrument from which it had been withdrawn.
The Tyer's no. 6 tablet instrument is cast iron framed 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. At the very top was the galvanometer. The signalling bell associated with the machine is separate so could be located on the block shelf or wall mounted above the instrument.
Read more about this topic: Tyers Electric Train Tablet
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