Slide #1.

Position Sensing • Mechanical • Optical • Magnetic
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Slide #2.

Mechanical Sensing Microswitch
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Slide #3.

Microswitch Operation Switch exhibits mechanical hysteresis.
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Slide #4.

Microswitch Actuators
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Slide #5.

Optical Sensing • LED’s and Photodiodes • Transmissive/Reflective • Modulated/Unmodulated • Light-on/Dark-on • Fiber optic
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Slide #6.

Transmissive & Reflective Sensors
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Slide #7.

Beam Pattern and Reflectance
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Slide #8.

Specular Reflection
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Slide #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
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Slide #10.

Magnetic Position Sensors • Reed switches (sense permanent magnet) • Inductive proximity sensors (eddy current) • Hall Sensors (sense permanent magnet)
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Slide #11.

Inductive Proximity Sensor
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Slide #12.

Inductive Proximity Sensors
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Slide #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
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Slide #14.

Hall Switch • Magnet motion – head-on – bypass or slide-by • Total effective air gap (TEAG) • Sensitivity, Hysteresis, & Temperature
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Slide #15.

Other Discrete Position Sensors • capacitive • ultrasonic • variable reluctance (coil around magnet, senses moving ferrous material)
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Slide #16.

Incremental Encoders
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Slide #17.

Incremental Encoders • Encoders typically run on +5V, not +24V • Outputs are typ. not 24V compatible either
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Slide #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
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Slide #19.

Potentiometer • A potentiometer (or pot) is a variable resistor wired to obtain a variable DC voltage proportional to position
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Slide #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.
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Slide #21.

Magnetostrictive Sensor
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