Maricopa County Installs STC Optical Control at AZ Fire Station 132

TEMPE, AZ - 04/04/2012 - Maricopa County DOT (MCDOT) installed fire station flashers with optical operation at fire station 132 in Sun City, AZ during Q1 of 2012. The fire station is situated as a mid-block station on a four-lane street with a wide median. One of the key issues at the site were high voltage transmission lines over one side of the street.

Solar Traffic Controls performed a site survey for the county and determined the most reliable and least expensive method for control would be an all-optical approach. The system consists of an optical repeater station at the end of the fire station driveway and a total of three flashing beacon systems on the approach to the station.

The application site has a large median and two lanes in each direction. Two flashing beacons were placed on one approach, one on the median and one on the curb. The curb unit had visibility issues caused by the transmission line poles. The median unit helped to compensate for the obstacles.

The other approach required one flasher in advance of the driveway. The flashing beacon unit design was based on the STC SR product family which is a flashing beacon package designed to work with an external sensor drive. The sensor is a Tomar Strobe Switch optical detector which provides an open collector output. When a valid pre-emption emitter signal is detected the output goes low thereby registering as a change-in-state at the control logic.

The SR beacon package includes control logic with an LCD screen and a DPC2000 integrated charge/flasher control with built-in night dimming. Each unit includes an omni-directional confirmation beacon strobe and a solar-powered system designed to meet the location, load and duty cycle of the project. As with other advance STC designs, each system includes a self-test function to allow county personnel to verify operation of each unit.

The master control unit located at the end of the driveway consists of an STC solar-powered Optical Repeater (OR) system. The OR uses a Tomar Strobe Switch assembly to detect the pre-emption signal from trucks on call exiting. When detection occurs, the control logic activates two Tomar pre-emption emitter lamps, one facing each direction. These emitters trigger the flashing beacons through the Strobe Switch detectors on the flashers. To ensure the flashers are triggered the control logic pulses the emitters multiple times during the activation cycle. A built-in, self-test function is included to allow county personnel to test the OR station and trigger the flashing beacons.

One flasher location and the master station suffer from partial shading from nearby palm trees. STC was able to compensate by performing a shaded sizing report for the locations in question. The result is solar arrays for these two locations were increased in size commensurate with the shading effect. A site-specific issue such as this will typically not affect the battery bank since production of power is the primary impact of shading.

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