ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Linear Position Sensors (LPS)

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Linear Position Sensors (LPS) Okan Gurdil Email: okang@cc.usu.edu Phone: (435)797-6203

2. Outline • Reference List • To Explore Further … • Major Applications • Resistive • Capacitive • Inductive • Linear Variable Differential Transformers (LVDTs) • Magnetoresistive • Laser Interferometry • Major Specifications • Cost vs Accuracy

3. ReferenceList • Nyce, David S. (2003). Linear Position Sensors – Theory and Application. New Jersey: Wiley-Interscience • http://www.mtssensors.com/Linear.htm • http://www.beiduncan.com/html/products/linear/linear.htm • http://www.sensorsmag.com/articles/1199/38_1199/main.shtml • http://www.sensorland.com/HowPage006.html • http://www.ee.polyu.edu.hk/staff/eencheun/WebSubject2/chapter1.htm • http://zone.ni.com/devzone/conceptd.nsf/webmain/ • http://www.daytronic.com/products/trans/lvdt/default.htm • http://www.ssec.honeywell.com/magnetic/datasheets/linearpositionsensing.pdf • http://www.feanor.com/laser_principles.pdf

4. To Explore Further • http://www.novotechnik.com/ • This website produces linear position sensors and you can pick what specifications you would like. • http://www.engineeringtalk.com • Provides more specific discussion of various sensor technologies. • http://zone.ni.com/devzone/ • Explanations and usage guides for various linear position sensor technologies

5. Major Applications • Resistive – Volume, tone, and similar controls • Capacitive – Detection of a moving metal target • Inductive – Valve positioners • LVDTs – Mission critical military applications • Magnetoresistive – Motion detection in industrial machinery, automotive, aviation, elevators • Laser Interferometry – Machining, surveying, surface profiling

6. Resistive Linear Position Sensor:Basic Working Principle • Measures a physical variable • A voltage potential is applied across a resistive element • A slide, or brush, contacts the resistive element and is wiped across it • Creates a voltage divider, where V is the measured data

7. Resistive Linear Position Sensor:Typical Sample Configuration (6)

8. Resistive Linear Position Sensor:Advantages/Disadvantages • Disadvantages • Moving parts • Limited lifetime due to wear of brushes • Limited frequency response • Advantages • Low Cost • Low Tech • Ease of use

9. Capacitive LPS:Basic Working Principle • Consists of a target, a capacitive sensing element, and support electronics and mechanics • “[An] electronic circuit drives the sensing element with an alternating current, the sensing element changes capacitance due to changes in the measurand, and the resultant signal is demodulated by the electronic circuit.” (1)

10. Capacitive LPS:Typical Sample Configuration (6)

11. Capacitive LPS:Advantages/Disadvantages • Disadvantages • Must be close to the measurand target • Not a directly measurable output • Measurement accuracy is effected by the environment the sensor is installed in • Advantages • Can be used to measure moving parts • No wear on parts, low maintenance • Low cost

12. Inductive LPS:Basic Working Principle • Uses the property of inductance in electrical conductors • Consists of a coil within an appropriate housing, a movable core piece and pushrod, and support electronics to condition the output (7)

13. Inductive LPS:Typical Sample Configuration Courtesy http://www.balluff.com/

14. Inductive LPS:Advantages/Disadvantages • Disadvantages • Shorter range • Contact with measurand must be made • Lower precision • Advantages • Small size • Simplistic design • Low cost • Can be made with no moving parts, thus eliminating maintenance needs

15. LVDT LPS:Basic Working Principle • Linear Variable Differential Transformers • Very similar to the Inductive linear position sensor • Consists of a tube with a primary coil in the middle, and two secondary coils, one on either end of the primary • A core moves in the middle of the coils • “If the core is displaced from "null" position, in either direction, one secondary voltage will increase, while the other decreases.  Since the two voltages no longer cancel, a net output voltage will now result.” (8)

16. LVDT LPS:Typical Sample Configuration (8)

17. LVDT LPS:Advantages/Disadvantages • Disadvantages • Must be calibrated more frequently • Contact with measurand must be made • Advantages • Very Accurate • Can be sealed and used in hostile environments • Robust application range

18. Magnetoresistive LPS:Basic Working Principle • Uses three elements: an array of sensors, a magnet attached to the measurand and associated electronics • Operates by detecting the change in resistance when a magnetic field is applied to a current-carrying conductor • The longer the array of sensors, the longer the measured displacement can be

19. Magnetoresistive LPS:Typical Sample Configuration (9)

20. Magnetoresistive LPS:Advantages/Disadvantages • Disadvantages • As range is extended, cost goes up • Not as accurate as other methods • Sensitive to interfering magnetic fields • Advantages • Range can be extended almost infinitely • Can operate in a broad temperature range • Non-contact

21. Laser Interferometry LPS:Basic Working Principle • Consists of a laser and a beam splitter • One beam is sent to a fixed mirror for reference purposes • The other beam targets a mirror fixed to the moving object • The position change of the object is calculated from the resulting interference of the beams recombining

22. Laser Inteferometry LPS:Typical Sample Configuration (10)

23. Laser Interferometry LPS:Advantages/Disadvantages • Disadvantages • Sensitive to temperature of measuring environment • Cost • Complexity • Advantages • Extremely accurate • Non-contact • Can be extended to multiple axes • Longer range

24. Major Specifications • Contact – contact or non-contact • Dimensions – Single or multi-dimensional • Range of Measurement • Physical Size/Weight • Environment – Temperature, Humidity, Corrosive • Installation – Simple, Complex • Accuracy • Lifetime - Hours of Continuous Operation • Cost

25. Cost vs Accuracy in Different Technologies (7)