Strain Sensors

The strain gauges selected for SHOX are the "1-LY41-20/120" & "K-LY4-1-11-120-3-1" coming from the HBM Manufacturer. These are linear gauges that come with a Constantan measuring foil and polyamide carrier. Their temperature response matches the response of steel with and come with integrated soldering tabs. All gauges tested had a resistance of 120 ohms. The estimated power to be dissipated for 5 and 10V excitation is about 52 and 208mW respectively in each arm of a Wheatstone bridge. Considering the electrical noise environment and an analog-to-digital (A-D) conversion processing requirement, an excitation voltage of 10V was considered ideal. The strain-gauges are operated in a Bridge Completion Module (Wheatstone bridge) circuit. The bridge is initially balanced with an adjust-ment potentiometer as shown above. A water proof barrier using a compound, such as M-COAT JA, is built after initial testing of gauges. In the present testing, the strain-gauges are bonded to steel-rebars and a force is applied. The strain is found indirectly, by measuring the change in voltage due to variation in resistance. The same load was applied a number of times and the average strain was noted.