Railway ⁽²⁾

Another of my hobbies, if you can call it that is that I volunteer at a heritage railway in the Signal and Telegraph (S&T) department. We maintain the signalling along the 4.5 mile railway which includes three signal boxes and numerous signals, points and telephones. Occasionally I get homework. This week it is working out the resistance needed to drop the voltage across the track at one point to a level suitable to power a relay. This is for a track circuit, in the case in question across a set of points. With the track circuits we use the section of track concerned, which is isolated from the rest of the railway by insulated block joints separating the bits of rail, power is fed to the rails at one end and a relay is connected at the other. The voltage needs to be sufficient to keep the relay up and this indicates that there is no train on that section of rail. When a train is on that track the voltage is shorted out across the wheels and the relay drops to indicate the presence of a train. The relay concerned is similar to the one shown below and has…

So this is my day job - well, not exactly a job and only one day a week - volunteering at a heritage railway. And here we are in the middle of nowhere... good job it isn't raining this time.