NEMA Traffic Signal Controller
This is the second real traffic controller in my collection. It is a NEMA (National Electrical Manufacturers Association) controller. The National Electrical Manufacturers Association developed the standard for this controller so that all NEMA controller parts can be interchanged between cabinets without compatibility issues.
This is just a basic set up. I do not have a NEMA cabinet, so I had to build a wood case to keep the controller locked up when it is running because of the obvious electrical danger. This is a four phase controller set up. It allows for main street and side street thru signals as well as left turn signals for both AND overlaps for both which would be a green and yellow turn arrow while the thru signal is green. It also has pedestrian signal capabilities for main street and side street. The controller panel also came with a police and tech panel. The police panel has only a few functions on it that are also available on the tech panel, so if I ever hook up any of these, I will only use the tech panel and not the police panel. The tech panel has switches on it for pedestrian signal push buttons and vehicle sensors which can be turned on or off. Right now I have the controller set to "think" it is constantly receiving pedestrian and vehicle "calls" so that it continuously sequences back and forth. In the future, I could hook up push buttons or motion detectors to simulate pedestrian and vehicle sensors.
This is the actual controller box itself. It is a Traconex 390. The programming menus for this controller are a bit intimidating at first, but eventually you can understand the basic layout of the menus. There are a lot of features on this controller that I will never need to use in my little basement display. There are also features I do not even understand. These controllers are capable of a lot of different things and are far more advanced than my other real controllers, the Eagle EF-15 and EF-70, the Marbelite M20 and the Crouse Hinds KS electro-mechanical controllers.
Here is a close up of the display on the controller. It is saying that phase 2 has a pedestrian call with the P indication. The 4 indicates that phase 4 timing is being displayed. Currently the phase 4 walk timing is being displayed by the WLK for WALK and 006 seconds left before DONT WALK flashing clearance begins. The RDD indication on the bottom is where phase 5-8 information would be displayed if this was an 8 phase controller, but since it is only a 4 phase, RDD is always displayed on the bottom. RDD stands for Red Dwell.
This is the conflict monitor. Its function is to monitor for problems, like a green light for conflicting phases, that could confuse drivers or cause an accident. If a problem is detected it puts the controller into flash and stops the controller box right at the point that the problem was detected.
This is a load switch. The controller operates the load switch with 24 volt DC. The load switch is like a solid state relay in that it turns on and off the 110 volt AC signal indications based on what the controller tells it to do. There are LED indications on the front of the load switch to show what signal lamp it has turned on at any given time. It also works with pedestrian signals, but the middle LED (yellow indication for vehicle signals) is not used with pedestrian signals.
This page was originally posted on 7/16/2002.