Omni Instruments supplied sensors for measuring temperature, humidity and air flow inside the main suspension cables of the Forth Road Bridge. The sensors were connected to data acquisition modules which converted the measured values to Modbus for transmission to a SCADA system.
The Forth Road Bridge is a legendary Category A listed suspension bridge and a vital artery of Scotland’s infrastructure. However, decades of exposure to harsh marine environments led to internal moisture build-up and corrosion within its massive, 60cm-diameter main cables, each comprised of 11,618 individual high-tensile steel wires. To prevent catastrophic strength loss, engineers undertook a groundbreaking, world-first retrospective dehumidification project.
To stop the high-tensile wires from corroding, the relative humidity (RH) inside the wrapped cables must be systematically reduced and maintained below 40%. At this dry threshold, atmospheric corrosion effectively grinds to a halt.
However, injecting dry air into a massive, airtight-sealed cable is only half the battle. To guarantee the system’s effectiveness and avoid over-pressurisation or undetected damp pockets, engineers needed continuous, real-time data from deep inside the cable wrap.
Omni Instruments supplied and integrated the critical “eyes and ears” of the dehumidification project. We provided high-reliability temperature. humidity and air flow sensors and data communication components designed to withstand the extreme conditions of the Firth of Forth.
By providing highly accurate, reliable environmental data, Omni Instruments helped the bridge authority safely manage the drying phase and verify when the cables were securely dry.
The dehumidification system successfully halted the progress of wire corrosion, dramatically extending the lifespan of this crucial landmark and saving taxpayers millions in potential replacement costs.
As the view above demonstrates, the Firth of Forth is the only location in the world where the absolute pinnacle of bridge technology from three consecutive centuries stands side-by-side. We are proud that Omni Instruments were able and an integral part of ensuring the continued preservation of this historic and iconic landscape.
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