1 / 22

Discrete Position Sensing

Discrete Position Sensing. Mechanical Optical Magnetic. Mechanical Sensing - Microswitch. Microswitch Operation. Switch exhibits mechanical hysteresis. Microswitch Actuators. Optical Sensing. LED’s and Photodiodes Transmissive/Reflective Modulated/Unmodulated Light-on/Dark-on

lisle
Download Presentation

Discrete Position Sensing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Discrete Position Sensing • Mechanical • Optical • Magnetic

  2. Mechanical Sensing - Microswitch

  3. Microswitch Operation Switch exhibits mechanical hysteresis.

  4. Microswitch Actuators

  5. Optical Sensing • LED’s and Photodiodes • Transmissive/Reflective • Modulated/Unmodulated • Light-on/Dark-on • Fiber optic

  6. Transmissive & Reflective Sensors

  7. Beam Pattern and Reflectance

  8. Specular Reflection

  9. Modulation • “Chop” LED on and off at many kHz rate • Bandpass filter after photodiode at the same frequency as chopping • Threshold circuit after BPF generates on/off output

  10. Magnetic Position Sensors • Reed switches (sense permanent magnet) • Inductive proximity sensors (eddy current) • Hall Sensors (sense permanent magnet)

  11. Inductive Proximity Sensor

  12. Inductive Proximity Sensors

  13. Hall Sensors • Hall effect: • constant voltage forces a constant current in semiconductor sheet • magnetic field flux lines perpendicular to current cause proportional voltage across sheet. • discovered by E.F.Hall in 1879 • Linear sensor needs voltage regulator and amplifier • Switch also needs threshold circuit, with hysteresis

  14. Hall Switch • Magnet motion • head-on • bypass or slide-by • Total effective air gap (TEAG) • Sensitivity, Hysteresis, & Temperature

  15. Other Discrete Position Sensors • capacitive • ultrasonic • variable reluctance (coil around magnet, senses moving ferrous material)

  16. Incremental Encoders

  17. Incremental Encoders • Encoders typically run on +5V, not +24V • Outputs are typ. not 24V compatible either

  18. Absolute Encoders • doubling resolution requires adding another photodiode/LED pair • cost is much higher than incremental • does not require seeking to establish reference location

  19. Potentiometer • A potentiometer (or pot) is a variable resistor wired to obtain a variable DC voltage proportional to position

  20. Magnetostrictive Pos. Sensor • Pulse sent down magnetostrictive material • Pulse reflects off position magnet’s field • Position is proportional to trcvd - tsent • Pulse propagates at ~2800 m/s • Resolution is ~.001” with tupdate ~1msec/in.

  21. Magnetostrictive Sensor

  22. Machine Vision Sensor

More Related