Applications Arc-weldable strain gauges are used to measure strain in steel.  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. Operation The body of the strain gauge is a sealed steel tube with weldable  mounting-blocks at both ends. Inside the body is a magnetic coil and a steel  strip, which is held in tension between the ends of the body. When the steel  strip is magnetically plucked by the coil, it vibrates at its natural frequency. Strain in the structural member is transferred via the welded mounting-blocks  to the body and the steel strip, causing a change in the tension of the strip.  To ensure that the full strain is transmitted to the steel strip, a short  section of the body is specially formed to reduce its stiffness. When the strip is plucked and set into vibration in the proximity of the  magnetic coil, a frequency signal is induced in the coil and transmitted to the  readout device. The readout device processes the signal and displays a reading. Installation The arc-weldable strain gauge is supplied with two weldable mounting-blocks.  The mounting-blocks are attached to a setting-rod and then welded to a clean,  flat surface. Afterwards, the setting-rod is removed and the strain gauge is  inserted in its place. The tension of the strip is then adjusted to ensure that  the gauge has sufficient range to measure compression or tension, as required by  the application. Advantages Superior Stability: Each end of the steel strip is fixed with  precision welds. This eliminates the high local stresses and potential for creep  inherent in the mechanical swages used in other designs. 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. 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: A setting-rod is substituted for the gauge during  welding, eliminating possible dam-age to the gauge from heat-induced stresses.  The gauge can also be re-positioned in a different set of end pieces. Reliable Signal Transmission: The arc-weldable strain gauge provides a  strong signal which can be transmitted reliably over long distances with  properly shielded cable.