PDF《Highway IDEA Program》

20867 will significantly reduce maintenance personnel'

s exposure to hazardous situations and will produce appreciable reductions in traffic-lamp maintenance expenditures. DESCRIPTION AND METHOD OF OPERATION OF THE CONSERVATION TRAFFIC CONTROL LOAD SWITCH The CTCLS Model 20867, a microcomputer that functions as a load switch, was designed to extend the life of incandescent traffic lamps by four times, providing significant savings to DOTs in maintenance expenditures. The load switch is the last possible access to the alternating current (AC) line voltage prior to reaching the lamp filament coil. By applying this technology to the load switch, there is no interference or damage to other critical components in the signal cabinet. The load switch is the only interchangeable component in the signal cabinet which provides the ease of replacement with maximum control over the AC line voltage. This is accomplished through three distinct features: ? Soft-Start: During the normal operation of an incandescent lamp, molecules of tungsten are constantly evaporating, which causes a notch, or weak spot, to develop on the tungsten filament coil. When AC is applied to a cold filament, an in-rush surge of 8-10 times normal load resistance occurs to the tungsten filament coil, causing stress to any notch or weak spot, which ultimately breaks the filament coil, and the lamp fails. The soft-start feature of the CTCLS Model

20867 softens this in-rush current or stress on the filament coil. The soft start, or the gradual increase of the initial AC voltage, preheats the filament coil over a period of

45 msec which is not perceptible to the human eye. ? Regulation: The Model

20867 regulation feature accomplishes two different functions. First, the microprocessor utilizes advanced series of algorithms to soften or cushion the voltage fluctuations, absorbing a substantial portion of the shocks and peaks that occur in all normal AC line voltage. This fluctuation is another leading cause of incandescent lamp failure. Second, the regulation feature regulates the AC line voltage down to a preset voltage point by looking at the AC line voltage

120 times per second and adjusting the AC applied to the lamp. This aspect of the regulation feature substantially cools the burning temperature of the lamp and slows the tungsten evaporation, which prolongs the life of the filament coil by reducing the development of the notches or weak spots on the coil. To obtain the maximum lamp-life benefits from the Model 20867, with the Institute of Transportation Engineers (ITE) standard for lumen output is specified at

1750 lumens, the CTCLS requires that a higher rated luminous output lamp be used to meet ITE specifications. ? Fail-Safe: When compared to a conventional load switch, the CTCLS Model

20867 provides an additional safety feature. In the unlikely event of microprocessor failure, the CTCLS Model

20867 reverts the unit back to a conventional on-off load switch through a built-in fail-safe, which helps to ensure uninterrupted traffic flow. The mechanical packaging is same as the standard National Electrical Manufacturers Association (NEMA) traffic control load switches. The connector and housing are exactly the same as existing units to ensure that no retro-fit will be required. ACCOMPLISHMENTS Two hundred CTCLS Model

20867 units were produced and distributed to

100 DOT and municipal signal laboratories throughout the country to: 1. Verify test results. 2. Complete all normal and customary testing of a traffic control load switch/tri-switch-pak to assist in the certification and specification processes. 3. Obtain recommendations for additional features. 4. Introduce the device to the DOT and municipal signal laboratories and obtain their feedback on its performance.