Leuze sensors played an important role in the reconstruction of the Bay Bridge in San Francisco.
The five lane double deck toll bridge that connects Oakland and San Francisco carries some 300 000 vehicles each day. Following a severe earthquake in 1989, it was decided to replace a damaged part of the bridge. This required removing a 1100 m, 3200 ton section of the old structure and slotting a new 3600 ton section into the resulting gap. All this had to be done 50 m above ground and completed within a three day period. Syrinx Industrial Electronics was contracted to develop a central monitoring system for the project to provide a visual display of all the bridge parts as they were being moved.
Precision and reliability
Gerry Bryant, managing director of Countapulse Controls, says that a total of 31 Leuze laser distance sensors and 16 pressure sensors were chosen for this specialised solution that had to function under exacting conditions. The ODSL 96B laser sensors provided a visible display that allowed the measured values to be read on the spot. “This eliminated the need for personnel to move between the central laptop and the sections of the bridge where parts were being moved,” he says.
Each of the sensors was fixed to a mounting plate which was kept in place by strong magnets. During the move, the bridge was pushed upward at four points for approximately 300 mm and then moved horizontally by means of hydraulic winches. The height and position of the various winches were converted to 4-20 mA signals with the aid of the distance sensors. The horizontal movement was over a distance of 30 m and was also measured using these sensors.
The ODSL 96B features RS485 output and special electronics was designed to convert this information to an exact 4-20 mA signal. This made it possible to attain greater precision over the entire measurement range up to 50 m. Eight measurement boxes were also developed by Syrinx and all laser and pressure sensors were connected to these. This formed the measurement network that was connected to the laptop. This in turn was connected to a monitor where the movement processes were visualised.
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