Sensors and Encoders

1. Sensors and Encoders Austin Kretz Pike October 4, 2010

2. Outline: • What is a sensor? • Where would I find a sensor? • What is an encoder? • Where would I find an encoder? • What should I consider before buying a sensor? • What should I consider before buying an encoder? • What are some common sensors? • What are some common encoders? • Review • References

3. What is a Sensor? • “A device that converts a physical stimulus or variable of interest into a more convenient form for the purpose of measuring the stimulus.” • In other words, a sensor changes one physical activity into a reaction more easily recognized. • [To obtain accurate measurements, a sensor must be calibrated to determine its transfer function]

4. Where would I find a sensor? • In the manufacturing process, sensors are located in the feedback control. • Sensors should be found paired with any specification that needs to be monitored for quality or control purposes.

5. What is an encoder? • “A device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.” • For most practical purposes, an encoder can be identified as the transducer portion of most measuring instruments. • An encoder takes the information provided by the sensor and returns a more useful form of that information.

6. Where would I find an encoder? • In the manufacturing process, encoders are found within the feedback control. • Encoders are used to control and monitor automated, and non-automated, processing.

7. What should be considered before buying a sensor? • Accuracy • Precision • Operating range • Speed of response • Ease of Calibration • Drift • Reliability • Cost (long and short term) • Space constraints • Ease of incorporating into manufacturing process • Possibility of using already established sensors to read additional variables • Additional sensors that may be required for a sensor to reach maximum utilization

8. What should be considered before buying a sensor? Consider a proximity sensor. • Detects the presence of an object within a certain distance. • Standard sensing distance is between 1.5 and 15mm • Standard accuracy is usually ±10% • Ferrous metals usually preferred • Sensing range decreases with non-ferrous metals. • Capacitive sensors need for non-metals

9. What should be considered before buying an encoder? • Required: • Accuracy • Environment • Resolution • Response time • Temperature • Torque involved

10. What should be considered before buying a nencoder? • Do you need an encoder or a resolver? • While similar, an encoder outputs pulses and a resolver returns wave functions. The wave eliminates the need for external counting; however, requires more extensive wiring. • Resolvers can be replaced by an encoder, unless: • Temperature reaches below -40C and above 100C. • Input devices cannot accept a constant value input. • Input devices need absolute position feedback. • Prices are relatively equal • Resolvers more accurate

11. Encoder Side Note • Absolute Encoders: • Also called parallel absolute encoders, these devices report the absolute measurement of the encoder to the electronics immediately without the need for indexing. • Incremental/Relative Encoders: • These devices report their measurements without any position information. To use the information from the encoder, an external electronic device must index the encoder’s output. The lack of reference makes the electronics report incremental changes.

12. Major Manufacturers and Vendors • Automation Direct • Autonic • Encoder Products Company • Heidenhain • IFM Efector Inc. • Renisha • Renco • Stegman • Omron

13. What are some common encoders? Price Range ($): 42.04 - 1,599.19 0.99 - 960.00 • Linear • Rotary • It should be noted that there are multiple types within these categories of encoders, they include: • Mechanical • Optical • Magnetic • Incremental • Absolute

14. What are some common measuring devices? Price Range ($): 8.36 - 1,499.99 6.53 - 6,900.00 4.18 - 688.00 1.00 - 584.00 48.39 - 9,417.00 0.01 - 1,729.23 24.99 - 723.00 49.50 - 723.00 29.99 - 3,345.00 1.90 - 762.79 • Accelerometer • Ammeter • Bimetallic switch • Bimetallic thermometer • Dynamometer • Float transducer • Fluid flow sensor • Fluid flow switch • Linear Variable Differential Transformer • Limit Switch

15. What are some common measuring devices? Price Range ($): 1.75 - 3,645.00 5.69 - 9,632.05 1.00 - 23,684.00 5.25 - 467.50 9.99 - 540.00 6.80 - 25,684.00 0.75 - 2,180.00 0.50 - 207.00 0.00 - 711.75 • Manometer • Ohmmeter • Optical encoder • Photoelectric sensor array • Photoelectric switch • Photometer • Piezoelectric transducer • Potentiometer • Proximity switch

16. What are some common measuring devices? Price Range ($): 39.99 - 7,440.00 19.96 - 4,030.00 5.00 - 3,223.00 20.00 - 580.00 0.65 - 349.97 0.31 - 4,365.00 2.00 - 1,684.00 5.99 - 864.00 • Radiation pyrometer • Resistance-temperature detector • Strain gage • Tachometer • Tactile Sensor • Thermistor • Thermocouple • Ultrasonic range sensor

17. Review and Questions

18. References For encoder and resolver comparison: • http://www.avtronencoders.com/encoder_vs_resolvers.htm For starting definitions of sensors and encoders: • http://en.wikipedia.org/ For pricing samples: • http://www.google.com/products • http://www.optoresolver.com/help/tutorials/resolver_v_encoder.htm For images: • http://www.supplierlist.com/photo_images/25932/Inductive_proximity_sensor.jpg • http://blogs.salleurl.edu/robotica/files/2009/06/encoder.jpg