Sensor Report: Strain Gauges

1. Sensor Report: Strain Gauges Utah State University March 11, 2010 Steve Gunderson chapodecalifornia@hotmail.com (916) 662-4244

2. Acknowledgements • Dr. YangQuan Chen: Research background and technical instruction

3. Overview Impact of Engineering Principle of Operation Types Implementation Application Major Specifications Limitations Purchasing References Agenda Typical Foil Strain Gauge http://en.wikipedia.org/wiki/Strain_gauge

4. Strain gauges are used to measure the mechanical strain on an object or the junction between two objects The strain can be measured as a force or as a torque Other indirect implementations include those measuring acceleration, displacement, pressure, and temperature Overview

5. Strain gauges can be used in common applications to increase safety and efficiency of other technology in our daily lives Bridges, for example, can have strain gauges implemented on them to monitor their structural integrity and ability to carry loads Safety monitoring has benefits worldwide Impact of Engineering

6. Basic electronic strain gauges use a basic 2-dimensional foil array As strain is placed planar to the foil, the resistance of the foil changes The resistance change is monitored by circuitry Principle of Operation Typical Foil Strain Gauge http://en.wikipedia.org/wiki/Strain_gauge

7. Strain gauges can be constructed as either purely mechanical or mechanical/electrical Electrical gauges are implemented in numerous ways and their possibilities range from a 2-dimensional foil array to an actual semi-conductor chip Types

8. Typically, a Wheatstone Bridge circuit configuration is used to monitor the resistance change in the strain gauge This is also one of the most basic circuit configurations to monitor the sensor Implementation Wheatstone Bridge http://en.wikipedia.org/wiki/Wheatstone_bridge

9. Rx represents the variable strain gauge sensor As it changes in resistance, the sensor Vg can decode the output and relate it to a particular amount of strain on the sensor Implementation Wheatstone Bridge http://en.wikipedia.org/wiki/Wheatstone_bridge

10. Other resistor values are chosen to vary the sensitivity and resolution of the sensor circuitry Multiple resistance values can be varied in this bridge to implement sensors under both tension and compression Implementation Wheatstone Bridge http://en.wikipedia.org/wiki/Wheatstone_bridge

11. A multi-sensor implementation of the Wheatstone Bridge gives a bridge constant Bridge constant k equals the general bridge output divided by the bridge output with only one active gauge Implementation Wheatstone Bridge http://en.wikipedia.org/wiki/Wheatstone_bridge

12. Care must be taken with the type of gauge being used as some have operational areas of non-linearity Linear approximation can be used with most sensors of this type Implementation Wheatstone Bridge http://en.wikipedia.org/wiki/Wheatstone_bridge

13. Countless types of strain gauges are in use today all throughout the world A wide variety of markets can take advantage of them for monitoring safety and reliability as well as product testing Strain gauges can also be used as a general measurement device of forces and torques Application

14. This sensor was used for fatigue and durability testing A manufactured part can then be tested more accurately to meet product specifications Application Strain Gauge http://blog.prosig.com/2006/05/17/fatigue-durability-testing/

15. This worker is installing a strain gauge on a bridge Measurements taken can be used to assure the safety and longevity of the bridge itself Application Strain Gauge http://www.timedla.com/blog/huey/default,date,2008-05-29.aspx

16. Sensitivity and resolution greatly depends upon the size of the sensor and the materials used to construct it Strain gauges can be used to measure strain on anything from small delicate tissues to large concrete and steel bridges Larger strains cause the characteristic equation of the gauge to become more non-linear Major Specifications

17. Strain gauges can be difficult to attach to small parts as there needs to be some type of spacing between both attachment points 3-dimensional stress analysis also can be complicated if there is not an easy way to mount sensors on all axis Limitations

18. Strain gauges may be readily purchased from many online retailers Small semi-conductor and electronic strain gauges are found at digikey.com or mouser.com Large-application gauges may be obtained from specialty manufacturers and retailers Purchasing

19. Wikipedia.org “Mechatronics – An Integrated Approach” by Clarence W. de Silva References

20. Questions?