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 optical reference level created by a horizontally rotating laser. The multipoint measurement capability with 10 Hz sampling rate makes it unique compared to other measurement equipment, such as a total station theodolite. The DMM system can be applied for measuring bending of main girders during a bridge loading test or for long-term monitoring of various structures, for example.
Serially connected DMM units send measurement results to computer using a RS-485 data bus cable, which also serves power for the system. Communication between a DMM and a computer utilizes the MODBUS protocol which enables an easy connection to existing measurement systems. A bundled DMM Commander software, running in Windows, OsX or Linux, allows for a real-time evaluation of the measurement results.
Optionally a DMM unit includes bi-directional tilt and acceleration sensors and it also provides three input channels with 24-bit A/D converters for external voltage or current output sensors, such as a strain gauge or a displacement sensor.
In many applications it is possible to utilize super magnets or clamps for fixing, which makes the DMM system very flexible and easy to assemble.