ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Resistance Strain Gage

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Resistance Strain Gage Prepared by: Jonathan Black Dept. of Electrical and Computer Engineering Utah State University T: (435)797-1000; F: (435)797-3054 (ECE Dept.) W: http:// 3/9/2007

2. Outline • Reference list • To probe further • Major applications • Basic working principle illustrated • A typical sample configuration in application (application notes) • Major specifications • Limitations • Neat Applications of strain gages • Conclusion ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list (no particular order) • Christopher S. Lynch (1999) “Strain Measurement” CRC Press LLC <http://www.engnetbase.com>. • Beckwith, Mar. (1993) “Mechanical Measurements” Addison-Wesley Publishing Company, Inc. • Lokos & Stauf (2004) “Strain-Gage Loads Calibration Parametric Study” NASA • http://www.shodor.org/~jingersoll/weave/tutorial/node4.html • http://www.omega.com/literature/transactions/volume3/strain.html • http://www.nakka-rocketry.net/strainlc.html • http://www.nlr.nl/eCache/DEF/424.html • http://www.michsci.com/Services/strain_gage_services.htm • http://www.cs.wright.edu/egr190/mechengr/PV-EGR191.pdf • http://www.dfrc.nasa.gov/gallery/photo/F-15B/Small/EC01-0124-1.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further • Search with this key words like strain gage, using search engines like Google. The USU library has a great electrical data base under the topics of engineering and technology, use EIcompendex • Searching for costs and specifications it is useful to use industrial supplier like Omega and globalspec.com ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major applications • Aircraft and aerospace industry • Force and load measurement sensors • Pressure sensors • Measure deflections of components • Automotive industry • Medical industry (ex. case studies on strains in anatomy) • Any application that calls for the monitoring strains, forces, pressures, etc. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. What is Strain? • Stain is the change in length per unit length. • Most materials strain in laterally as with longitudinally. • Ratio of lateral strain to longitudinal strain is called Poisson’s ratio Beckwith pg(480) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. How is stress related to strain? • Stress strain curve • Linear portion’s slope is known as Young’s modulus E • σ is the stress that causes the strain • Assumes thermo strains are zero with tensile strain test. http://www.shodor.org/~jingersoll/weave/tutorial/node4.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Equations involved in strain Where; E= Young’s modulus, εa= axial strain, εL= Lateral strain ν=Poisson’s ratio, σa= axial stress, L2 length after stress applied, L1 length before stress applied. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Basic working principle Wire with a measured electrical resistance have a voltage applied to it with a small current. When strained the cross-sectional area of the wire changes also changing the electrical resistance. This resistance is small but measurable. Beckwith pg(483) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. A typical sample configuration The strain gage resistances can be compared to other known resistance values with a Wheatstone bridge circuit. Arm 2 of the bridge is set near the strain gage in arm 1 to be at a similar temperature. This helps to cancel temperature effects. Beckwith pg(491) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Major Specs. on strain gages. • Gage Factor, this can be looked at like a transfer function constant. The greater the gage factor the greater the change in resistance per unit strain. • Resistively, the amount of resistance in the gage. Typically in ohms. • Operation temperature • Temperature coefficient of resistance. • Sensitivity (mV/V) • Requires High impedance ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Major suppliers of strain gages cost and differing types. Christopher S. Lynch pg(7) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Limitations • “While the higher unit resistance and sensitivity of semiconductor wafer sensors are definite advantages, their greater sensitivity to temperature variations and tendency to drift are disadvantages in comparison to metallic foil sensors. Another disadvantage of semiconductor strain gages is that the resistance-to-strain relationship is nonlinear, varying 10-20% from a straight-line equation. With computer-controlled instrumentation, these limitations can be overcome through software compensation.” www.omega.com • Optical strain gages are fragile not good for rough demanding industrial applications. • Attaching strain gages is very tedious • Gage circuit output very low about 100 mirovolts this makes it susceptible to unwanted noise. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Different configurations on strain gages Beckwith pg(484) Different rosettes of strain gages allow the measurement of strain in differing directions. Strain Gage on the bottom right can be used for pressurized diaphragms. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Neat applications of strain gages Make your own load cell. http://www.nakka-rocketry.net/strainlc.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Neat applications of strain gages http://engineering.union.edu/~rapoffa/MER214/laboratories/Lab%206%20Pop%20Can.pdf Measure the pressure with hoop stress equation of pressure vessel (soda pop can). http://www.cs.wright.edu/egr190/mechengr/PV-EGR191.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Neat applications of strain gages Measure the angle and deflections of helicopter Blades. Helicopter blades are very flexible so there positions and angles of attack need to be measured. http://www.nlr.nl/eCache/DEF/424.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Neat applications of strain gages By using spring amplifiers and slip rings. Strain gage signals from engine crank shaft can be measured. The strain measurements can be manipulated to tell torque of the engine. http://www.michsci.com/Services/strain_gage_services.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Neat applications of strain gages Lokos & Stauf, pg(3) Measure strains on aircraft wings (find limits on g force capability). Important for aluminum due to fatigue. http://www.dfrc.nasa.gov/gallery/photo/F-15B/Small/EC01-0124-1.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Conclusion • Resistance strain gages change their electrical resistance when strained. • Useful for any application that calls for the monitoring strains, forces, pressures, etc. • Limitations on strain gages include, low voltage output which makes it susceptible to noise. Nonlinearities like hysteresis. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators