Tyger Mike s

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ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators

Topic: Hall Effect Rotary Encoders

Prepared by: Mike Tyger

Dept. of Electrical and Computer EngineeringUtah State University

3/06/2009


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11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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Outline

Reference List Explore Further Major applications Overview Basic working principle Typical Application Major Specifications Limitations


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Reference list Sensors, Understanding Integrated Hall Effect

Rotary Encoders,www.sensorsmag.com/sensors/article/articleDetail.js

p?id=383802. EDN, Rotary encoder mates with digital

potentiometer ,www.edn.com/article/CA278837.html

EDN, Automotive Hall-effect rotary-position sensoruses novel flux-concentrator technology www.edn.com/article/CA6492443.html


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To explore further

(survival pointers of web references etc) http://www.austriamicrosystems.com/eng/Products/Magnetic-

Encoders/Rotary-Encoders Leading manufacturer of hall effect rotary encoders. Data sheets for

complete product line http://www.everightsensors.com/index.shtml

Manufacturer of rotary encoders

http://en.wikipedia.org/wiki/Hall_effect

In depth discussion of the Hall effect
http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.everightsensors.com/index.shtmlhttp://en.wikipedia.org/wiki/Hall_effecthttp://en.wikipedia.org/wiki/Hall_effecthttp://www.everightsensors.com/index.shtmlhttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders


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Major Applications Measure:

Angular Velocity Angular Position Magnetic Field Strength


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Overview - General


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Voltage output of Hall sensor varies with thestrength and pole of the magnetic field.

http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i1_t.jpg


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Overview Angular position


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Multiple Hall sensors in an array are used to accuratelydetermine angular position



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Advantages Small Lightweight Low power Non-Contact Long life


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Advantages High degree of accuracy Simplified manufacturing compared to

optical encoder

Programmable zero-position


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Principle Field Strength


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The 4 Hall sensors in the array each measure a different magneticfield strength as the magnet rotates on the axis.



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Principle Sine and Cosine Signals


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The output of each sensoris a Sine or Cosine wave

= peak amplitude = magnet rotationalangle relative to thesensor


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Principle Differential Signals


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Differential amplificationof signals from oppositesensors in the array

results in a sine and acosine wave which can

be interpreted by theCORDIC algorithm


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Principle CORDIC Algorithm


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A CORDIC (coordinate rotation digitalcomputer) transforms the differentialsignal into angle and magnitude

A= measured angle = magnet rotational angle relative tothe sensor = peak amplitude

The final equation shows that themagnetic field amplitude can beeliminated from the calculation, resultingin the elimination of the effects of straymagnetic fields.


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Principle 360 Measurement


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The output of the CORDIC can accurately determine the angular position of the magnet relative to the sensors.



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Design Issues Resolution Accuracy Phase Error Offset Errors ADC nonlinearities Magnet nonlinearities


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Resolution and Accuracy


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Resolution Resolution is the smallest angle step that can be

measured by the sensor. Angle changes smaller thanthe resolution will not be read. Resolution is mainlydetermined by the resolution of the ADC and thecalculation depth of the CORDIC.

Accuracy Accuracy is the deviation between the indicated angle

and the actual angle.


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Typical Application


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http://news.thomasnet.com/images/medium/499/499091.jpg

Rotary encoder in industrial housing


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Major Specifications 360 contactless angular position encoding User programmable zero position High speed: up to 30,000rpm Direct measurement of magnetic field strength allows exact

determination of vertical magnet distance Wide magnetic field input range: 20 ~ 80mT Wide temperature range: -40C to 125C


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Limitations Highly susceptible to stray magnetic fields

Requires precise assembly Possible need for magnetic shielding


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Limitations Sensors must be placed very accurately around

the centerline of the rotational axis. Multiple sensors are typically contained in a single

package Sensor must be very accurately placed on PCB Small tolerances of sensor PCB mounting fixtures

can increase cost


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Other Considerations Robustness

The non-contact nature of a magnetic encodermakes it fairly robust. The CORDIC can be used toeliminate the effect of stray magnetic fields

Hall effect sensors are used in a wide variety ofapplications


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Other Considerations The ratio of sensor accuracy to sensor cost is

very good for a hall effect rotary encoder

11/11/2013 ECE5320 Mechatronics Assignment#1 Survey on sensors and actuators

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