Application
Vibrating wire arc-weldable strain gauges are used to measure strain in steel or strain in concrete and masonry structures. Typical applications include:
- Monitoring structural members of buildings and bridges during and after construction.
- Monitoring load in struts used to brace deep excavations.
- Measuring strain in tunnel linings and supports.
- Monitoring areas of concentrated stress in pipes.
- Monitoring distribution of load in pile tests.
- Monitoring cracks in concrete (may require long-base strain gauge).
Operation
The strain gauge operates on the principle that a tensioned wire, when plucked, vibrates at its natural harmonic frequency, and by measuring that frequency, we can calculate the strain in the wire. The gauge is constructed so that a wire is held in tension between two mounting blocks that are welded to the structural member. Loading of the structural member changes the distance between the two mounting blocks and results in a change in the tension of the wire. An electromagnet is used to pluck the wire and measure the frequency of vibration. Strain is then calculated by applying calibration factors to the frequency measurement.
Installation
The strain gauge is supplied with two mounting blocks which are arc-welded to the steel surface. For applications on concrete, small holes are drilled into the structure and groutable mounting blocks are used.
Advantages
Field-Adjustable: The strain gauge can be adjusted so that most of its range is available to measure compression or tension, as required by the application.
Permanently Attached Coils: The coils used to excite and read the vibrating wire cannot be accidentally separated from the body during installation and wiring operations.
Built-in Temperature Sensor: The temperature sensor is useful for temperature corrections when the gauge is installed on materials that have a different temperature coefficient.
Easy Installation: The mounting system ensures that the gauge is not damaged during installation of the mounting plates. Also, this mounting system allows repositioning or reuse of the gauge.
Reliable Signal Transmission: The strain gauge provides a strong signal which can be transmitted reliably over long distances with properly shielded cable.
