A strain gauge is a thin strip of metal that is used in measuring of mechanical loads by changing its resistance when subjected to stretching or compressive stresses. Bridge circuits are used in these gauges in order to achieve precise measurements of resistance changes and also compensate the resistance variations due to temperature changes.They have wide uses in engineering profession.
These measuring instruments come in different types depending on the mode of manufacture and the application area to be employed. The common types in industry include the arc weldable, embedment and spot weldable strain gauges.
Fiber optic sensing is employed in detection and monitoring of strains and stresses along fiber lines whether at specific terminal points or the whole cable. The level of mechanical deformation and stress in capacitive types is indicated by use of variable capacitors. Simple models of these gauges can be applied in civil engineering works to measures stresses on cracks. The vertical and horizontal shifts of cracks can be monitored over a certain period of time and evaluated.
Temperature variation and changes is the biggest challenge faced in manufacture and application of these gauges. The metal strip narrow thickness will expand thermally due to variations in temperatures and this is always interpreted as a strain by the transducer. Thermal expansion of the strips will alter the strip resistance and hence affecting the preciseness of the measurement. To compensate this challenges caused by temperature variations specially made metal alloys are used which self compensate the changes. The other method of countering the temperature variation is by use of Wheatstone bridge having for gauges.
During the construction of this transducer an optimum combination of all affecting factors is paramount. A well constructed transducer should have optimum sensitivity to ensure measurement and detection of even small instances of stresses. It has to be free from temperature effects and other environmental changes. Good linearity and stability together with robustness are also relevant features of a good fabricated gauge.
Applications of weldable types in steel include the monitoring of stresses in structural members of steel buildings and supports during the period of construction and even after. They are also relevant in checking the performance of wall anchors and other tensioned systems together with monitoring the distribution of loads in pile sets. Areas of concentrated stresses in pipelines can effectively be checked by use of the weldable steel measuring instruments.
Application of strain gauges can be well discussed if divided into their specific areas of use. These transducers can tailor made to measure stresses in steel or stresses in concrete. Applications in measuring pressure in steel include monitoring stresses in the structural steel members of buildings, bridges and supports during and after completion of civil engineering works. They are also used in monitoring tresses in strutting systems foe deep excavations. Application in concrete includes measuring strains in reinforced concrete.
Strain gauges, Data Acquisition and Linear Position Sensor are reliable devices for measuring stresses in materials in the engineering fraternity for they are durable, less prone to errors when effectively used and the simple technology they apply.Proper maintenance of these devices also reduces the chances of breaking down.
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