Application
EL beam sensors are used to monitor differential movement and rotation in structures. Typical applications include:
- Monitoring stabilization measures, such as pressure grouting and underpinning.
- Monitoring structures which may be affected by nearby tunneling and excavating.
- Evaluating the performance of bridges and beams under load.
- Monitoring the stability of structures in landslide areas.
- Monitoring the deflection and deformation of retaining walls.
- Monitoring convergence and other movements in tunnels.
Specifications
The beam sensor consists of an electrolytic tilt sensor attached to a rigid metal beam. The tilt sensor is a precision bubble-level that is sensed electrically as a resistance bridge. The bridge circuit outputs a voltage proportional to the tilt of the sensor. The beam, which is typically one to two meters long, is mounted on anchor bolts that are set into the structure. Movement of the structure changes the tilt of the beam and the output of the sensor
The voltage reading from the sensor is converted to a tilt reading in mm per meter. Displacements are then calculated by subtracting the initial tilt reading from the current tilt reading and multiplying by the gauge length of the sensor (the distance between anchors). When sensors are linked end to end, displacement values can be accumulated from anchor to anchor to provide a profile of differential movements or settlements.
Because the beam sensor has a very narrow range, it is necessary to "null" the sensor at installation time. This provides the maximum measurement range and also takes advantage of the sensor's best characteristics. The EL Nulling Device or the EL Data Recorder are convenient tools for the nulling operation.
Advantages
High Resolution:
The EL beam sensor can detect a change in tilt as small as one second of arc, equivalent to a movement of 0.005 mm per meter of beam.
Reliable Measurements:
Since the EL beam sensor has a defined gauge length, changes in tilt can be converted simply and accurately to millimeters of movement, regardless of the rigidity of the structure. Linked end to end, beam sensors can provide absolute displacement and settlement profiles.
Convenient to Install:
A low profile design makes the EL beam sensor practical to install in tunnels and other locations where clearance is important. The length of the beam can be modified to fit the structure, and special mounting brackets provide easy installation on curved or distorted surfaces.
Simple and Robust:
The electrolytic tilt sensor has no moving parts, and its insulated packaging provides thermal symmetry, shielding it from the effects of temperature gradients and radiated heat.
Remote Readout:
In construction-control applications, beam sensors are connected to a data acquisition system that continuously monitors movements and triggers alarms when threatening movements are detected. In less critical applications, beam sensors can be read manually at a remote terminal box with a hand held readout.
Cost Effective:
The EL beam sensor provides reliable, high-resolution measurements, is simple to install, and is easily connected to a data acquisition system. It represents an efficient and economical alternative to precision leveling surveys and settlement profiling systems.
