Structural Health Monitoring (SHM) / 結構健康監測
Today, the society has built an innumerable amount of buildings, with sometimes
complex architecture designs. Long-term monitoring, also known as SHM, has a
high degree of importance when the structures are subject to heavy physical
loads, aging, and other external factors (e.g. corrosion, seismic damage). It
involves the installation of many sensors fixed to critical areas in order to
track internal strains, microscopic deformations and frequency responses.
Wireless sensors communicate through radios and need a source of energy to
operate correctly. To increase the durability of the system, the power
consumption of each component – including the accelerometer –
should be as low as possible.
A small bias derivation improve the overall reliability of the sensor: each day,
they endure thermal variations and frequent switches, generating new errors
after each measurement. It is key to perform recalibration and have stable
sensors in order to avoid false alarms.
The Appropriate Technology
The number of sensors partially depends on the configuration and on the duration
of the monitoring. Piezoceramic sensors were the first to be selected for
standard SHM. They have a very large frequency bandwidth, however they cannot
measure DC signals. Wired SHM and crash testing are typical applications where
piezo sensors are implied.
More recently, MEMS capacitive
accelerometers (VC) proved to offer
good advantages, due to its simple yet efficient design. They need a very small
current to operate, as they function in an open loop configuration. MEMS VC
sensors are ideal for wireless long term monitoring, as they offer portability,
reliability and durability. Furthermore, piezo and VC sensors can be combined to
increase their overall performances.
Colibrys offers the
VS1000 series, a family of high performance, open loop vibration sensors.
This MEMS product has one of the largest frequency bandwidth, capable of
measuring signals typically from DC 0 Hz to 2500 Hz at ±5% FS, and up to 7000 Hz
at ±3 dB. The ranges considered for SHM would be ±2g, ±5g, and ±10g. With a
spectral density down to 7 µg/√Hz, and a non-linearity of 0.1% FS, the VS1000 is
considered as the most accurate vibration sensor made by Colibrys. It is
estimated that it can function during 11 months, as long as it is powered by two
AA batteries .