Deflection Multi Meter (DMM) is a new measurement concept for structural health monitoring of large load-bearing structures, such as bridges.
The DMM system measures vertical deflection from many locations, in real-time, utilizing the reference level created with a horizontally rotating laser. The multipoint measurement capability combined with high speed operation makes it unique compared to other measurement equipment, such as tachymeter. DMM system can be applied e.g. for measuring bending of main girders during a bridge loading test or for long-term monitoring. The system is also suitable for monitoring sag on a construction site. Horizontal measurement of deflection is possible by utilizing a vertically rotating laser.
Integrated into each DMM unit are an optical deflection sensor, bi-directional tilt and acceleration sensors, as well as input channels for three external voltage or current output sensors, such as a strain gauge or displacement sensor. Serially connected DMM units use a RS-485 data link in communication with a computer, which saves the measurement data or sends it to a cloud storage. A bundled DMM Commander software, running in Windows, OsX or Linux, allows also for realtime evaluation of the measurement results.
The DMM unit is also available as a battery operated WLAN version. In many applications it is possible to utilize super magnet based fixing method, which makes the DMM system very flexible and easy to assemble.