Sensors monitor bridge safety

Using linear differential variable transducers is an inexpensive method of monitoring the safety of bridges.

The recent tragic bridge collapse in Minneapolis- St.Paul, USA, really emphasizes the fact that many of our very important but ageing bridge structures may now be reaching overload due to increased weights and traffic volumes on steel structures that may be either weakened by corrosion or suffering early metal fatigue.

Peter Smith of RDP Electronics comments "in this technological age there is no reason why the public should be exposed to this daily gamble if the relevant authorities were adequately funded to install monitoring equipment at strategic points in the structures".

"There are many ways that this can be done, but the most simple and well proven method is to attach linear differential variable transducer (LVDT) inductive sensing devices to give long and short term indications of the movement and strains being experienced by the beams".

RDP Electronics manufactures these devices and associated instrumentation, as well as special products for use where high-temperatures, corrosive, high-pressure, radiation and cryogenic environments are involved.

It has provided equipment for monitoring motorway road bridges in the UK, measurement of stresses in sea submersible applications, monitoring structural movement in nuclear installations, monitoring movements in rock strata during tunnel boring in the Channel Tunnel and even monitoring the movement of the dome of Saint Paul's Cathedral in London.

The LVDT approach is relatively inexpensive when several points need to be monitored over a long distance such as a bridge structure.

By using a two-wire "bus" system in conjunction with a PC, the wiring installation can be considerably reduced.

The LVDT can be supplied with or without its associated electronic circuitry incorporated within the device, or it can be used alongside a separate signal-conditioning module.

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