|Signals and Telecommunication at the TSGR|
|The Teesside Small Gauge Railway has an extensive signalling system which is constantly undergoing improvements to make the whole system run safer and smoother. Signalling is important for us as we can run up to 3 trains (realistically) at a time on our 600' long track which requires concise control in order to achieve smooth operation. Our line, although simple in shape, has lots of points and therefore has many different possible route options requiring complex electronic interlocking.
We make use of LED colour light signals with three aspects (RED, YELLOW, GREEN). The original design of signals at the TSGR consists of three individual lenses (one for each aspect), each lens consisting of 9 super bright LEDs powered by an 18V DC power supply from the signal box. However, the latest signal design at the TSGR is of a three aspect signal with only one lens (similar to that of modern full-sized railway signals). This more modern design of signal has a slightly different configuration, but in effect does the same job. To prevent excessive weathering and also to avoid signals from being subject to criminal damage, the signals are removable from their bases and are stored indoors when we aren't operating.
History behind the system
In the early days of the TSGR (during the 90's), the signalling system started out as just a simple interface to control points with a few protecting signals and quite a shoddy wiring job. However, years later, with higher passenger numbers and ever-increasing electrical problems due to poor wiring, action was needed in order to renovate the old system.
In 2008, one of our members who has experience in electrical engineering set out to start from scratch and completely renew the electronic side of the signalling system. This job entailed reverse engineering the original system (as there were no wiring diagrams) and then drawing out diagrams for the old system and trying to work out how it worked. This then allowed for him to slowly start pulling out bits of the old system (worn out relays and cabling) so that he could replace them with newer and better components. This was a long-lasting job and actually took until spring 2013 to fully finish (5 years!) and then the P-Way Department (unofficial) decided they wanted to add a new passing loop in time for the Seven and a Quarter Inch Gauge Society AGM which was to be held at the TSGR. This would require a new electrically controlled point unit and a change in signal interlocking which just asked for more S&T work! It became apparent that this one off job of replacing the old system had turned into an ongoing job.
For many years, the raised track at the TSGR used an automatic signalling system which used solid state logic to work the signals. This proved to work well, so the decision was made to try and apply this to the ground level track. With an already complex system of relays used to control the system as it was, the extension of automatic control seemed quite impractical (if it was to rely upon relays). As a result, a small group of members (myself, and two others), decided we would experiment with using solid-state interlocking and control with the ground level track as well as prototyping train detection systems.
By summer 2014, the new system was installed after lots of head-scratching and trial and improvement.
The TSGR has continuously welded rail and about 75% of the line has steel plates welded between both rails to provide extra strength. Although this is a great idea for the mechanical side of the railway, this doesn't compliment the S&T side of the railway. This is because automatic signals normally rely upon a type of train detection called track circuits.
A track circuit is a system which detects the absence of a train on a track; a low-voltage electrical current is put through both rails which powers a relay and when a train's wheels and axels pass over the two rails, it connects them both (electrically) and short circuits the relay, causing it to de-energise. This is one of the cheapest and most failsafe ways to detect trains on railways, but due to the rails at the TSGR being welded together, it is impossible to use this system. Therefore, one of our members came up with a design for a sensor which would work on our line.
Originally, the design was going to be similar to that of the raised track train detection which uses a reed sensor to detect a train's wheels. This works by having a permanent magnet opposite a reed switch with about a 15mm gap between them for flange clearance. The gap isn't too big for the reed switch to be held closed by the magnet, but is big enough to allow wheel flanges to pass between them both. The theory behind this method of detection is that the flanges of the wheels (being made of steel) would shield the magnetic field of the magnet and therefore cause the reed sensor's contacts to open. This works very well for the raised track, but not so well for the ground level track as the flange clearance needed on the ground level track is much larger and really strong, expensive magnets would have been needed for the system to work properly.
However, an alternative design came about which was much simpler. This was to basically replace a short (about 6 inch) section of steel rail on one side of the track with an aluminium replica. The aluminium piece would be electronically isolated from the rest of the rail and connected to a power supply through a relay. The original steel rail on the other side of the track would be connected to ground which therefore meant that the presence of train's wheels would give the relay a negative return and would therefore energise the relay for the short time a train's wheels were on the sensor. This is basically a track circuit, but for only a 6 inch length section of track.
(the reason for the aluminium rail is because it conducts electricity better than rusty steel)
The new detectors were trailed and tested and proved to work very well so were installed throughout the system. An actual wiring diagram of the train detector can be viewed here.
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The TSGR makes use of radio handsets which were first introduced to the TSGR in time for the AGM event in 2013 in order to allow for smoother operations. They are still in use now and prove to be very useful in running the railway.
After the announcement that the TSGR would be host of the 2013 Seven and a Quarter Inch Gauge Society AGM, there was immediate action on working out how we would run the event smoothly. Club secretary, Ian Hall, visited a previous AGM event which was held at a different railway where he noticed that they used CCTV cameras placed around their running line to view the trains and see where they were.
This inspired the TSGR to adopt wireless, battery powered cameras which were mounted to metal poles and could be removed from the ground to be stored indoors. However, being wireless we had many problems with finding suitable locations for the cameras that compromised being an effective viewing spot with having a good wireless connection with the wireless receiver. We managed to get all cameras working well just in time for the AGM and the cameras served us well. Without the cameras, we would have struggled to run the AGM event due to the high frequency of locomotives that we had in operation.After the AGM, problems with the batteries used to power the cameras along with the fact that they weren't needed as much (due to the AGM event finishing), meant that they were forgot about. Currently, the cameras aren't in active operation, but could be used if needed.
Three aspect signal (original design)
Picture of the old electrical gubbins under the control board (2012)
Track sensor currently in use (Note the aluminium replacement rail on the right and the common supply on the left)
The Teesside Small Gauge Railway is a company limited by guarantee - Registered Number 3630949