August 29 - Signal Maintenance
There's been a lot of maintenance activity this summer. One area of concentration was the signals. Before going into the maintenance issues a quick review of the signal system operation is in order.
The image above shows the three states of a block. The green lights with white light at the top indicates that the block is empty. The yellow lights indicate the block is taken from this end; proceed with caution. The red lights indicate that the block is taken from the far end; do not enter block.
The image above shows a typical signal setup. The block starts across from the green switch stand. The Yellow switch stand is the Take switch --- on the right for those entering the block (traveling toward the signal). The Green switch stand is the Release switch on the right for those leaving the block (traveling toward the camera). So, as you approach the block if the signal is yellow or red you are to stop and wait until the signal is green. Once the signal is green, the block can be taken by operating the Yellow Take switch. If the take operation is successful the lights will change to yellow which indicates that you have the block and may proceed. When you get to the other end of the block you must operate the Green Release switch on your right to free the block for other users.
Eight Light Signal Heads: We have one other variation of signals; those with eight lights in the Signal Head. In addition to the pairs of red, yellow and green lights there is a pair of white lights located between the green and red lights. These signals are used where there is a diverting switch in the track just before the entrance to the block associated with the signal and the take switch is before that diverting switch. One case is at the south end of Sand Hill block where the switch diverts traffic to the west side of the main yard and on to Keim Block. Another case is at the other end of that track on the west side of the main yard where there is a siding switch just before the entrance to Keim Block. The third case is at the north end of Norats Block where there is a switch leading to a future roundhouse.
The operation of these units is identical to the six light units as long as the diverting switches are set so that traffic flows into the associated block. When those switches are thrown to the position to divert traffic from entering the block, the green, yellow and red lights are disabled and the white lights are turned on. In addition, since traffic will be diverted and can't enter the block the take switch is also disabled so one can’t take the block and then proceed on the diversion track without entering the block. In the case of the south end of Sand Hill Block the signal is reset when the switch is thrown to prevent one from taking and holding the block and then throwing the diverting switch and going onto the diverting track and possibly onto the Keim Block.
Signal Electronics: The signals are microprocessor controlled electronic circuits developed by Laura Walter. The first units were installed nearly ten years ago and after they proved to be very reliable all the previous relay based systems were replaced and all additional blocks have used the new system. The system uses two wires between the two ends with both power and control signals passed over the two wires. We control a total of eleven blocks with one block using radio control between the two ends and the other ten using the two wires between the ends. The signals are powered by 12 volt DC supplies and use only a few tens of milliamps per signal. Nine of the blocks have the power supplies connected to 115V AC and two (including the radio controlled block) are powered by solar cells. The electronics in each signal have evolved over the years, primarily to reduce fabrication effort. However, the signal protocol has not changed so that the very first units will work with the latest units (except of the course the radio controlled block). Those very first units have proven to be robust and the electronics part very reliable. Signal Posts: The design of the signal posts has also evolved from having the electronics in a box near the bottom of the post to housing the electronics in a box behind the lights in the latest design. The early design was a pain to work on and in some cases was below the water level during flooding. Another problem with the low boxes was that they were subject to ant invasions. The muddy water and ant residue caused the signals to fail. Amazingly, the electronics functioned again after the mud and ant residue was cleaned off. (However, there may be some long term corrosive effects.) This year we decided to rebuild all the early stands to match the latest design with the electronics housed behind the lights. We've also sealed the bases with foam to try to keep the ants out. The higher electronics box should help with the ants however this summer we found an ant nest at the very top of one of the signals.
Wiring: The original relay signals used four wires between the ends. The relays drew more current and heavier wire was used. Usually on-hand wire ranging from 14 to 10 gauge electrical power wire and in some cases communication cable was used. Later installations of the two wire system often used 26 gauge telephone cable. The wire was sometimes laid on the ground and sometimes buried. The wire has proven to be a major source of problems. The exposed wires are subject to damage from vehicles, derailments and mowers. The buried cable is subject to being cut by shovels and posts driven into the ground. Recently several of the long runs of direct buried 12 or 10 gauge stranded electrical wire have failed. These were from the original relay based four wire system. We used only two of the four wires for the new system. Over time one, two and then a third wire failed. One possible cause of these failures is stress due to freezing and thawing.
This summer it was decided to start to upgrade the system wiring to increase reliability and reduce maintenance effort. John Pennington suggested that we consider 18 gauge sprinkler wire intended for direct burial. We looked at the wire and decided it was our best option. Where possible the cable is run in ½” PVC conduit. (We recently had a failure in a 330 foot length of the power cable on Werner block. We were able to install the new cable in conduit in a couple hours. We buried the cable at the grade crossing and left the conduit unburied until we have the time to bury it. The time to install the new cable was less than spent trying to troubleshoot the old bad cable.) An added benefit of the smaller gauge cable is to increase the effectiveness of surge protection devices --- more energy is dissipated in the higher resistance cable.
The game plan is to not touch any of the buried cables that are working. However, once a cable fails we plan to replace it using the new 18 gauge cable in conduit. There are several cases where the wire is not buried and we will replace those cables as time permits before they fail. We have cable and conduit so these are real shovel-ready projects for anyone interested in getting a good back loosening exercise.
We are not the only railroad with signal wiring challenges. One railroad attaches PVC conduit to the ends all ties to be used for running signal cables. That design has worked great for many years. However, recently squirrels have taken to chewing through exposed conduit and then into the wires. We'll take ants over PVC chewing squirrels.
Control Switches: The Take and Release switches are subject to environmental issues (hot, cold, wet, insects) and abuse by the users. As one guys stated --- your goal should be to make it able to take a pounding from a ball bat and still keep working. We have a total of 50 of these switches and usually have to replace a couple during each meet --- expensive and a pain. We are currently testing a new design that should take a hit from a ball bat and keep working. It uses a plunger switch that is completely housed within the switch stand. It is operated by pushing down on the top of the stand. You can try it out at the Labor Day meet --- it is the release switch at the south end of Keim Block at the entrance to Barney Yard. Hopefully we'll have it painted green by the meet.