CMA ML26m User guide

MOTIONDETE CTORML26M

USER’SGUIDE

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CENTRE FOR MICROCOMPUTER APPLICATIONS

http://www.cma-science.nl

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2|ML26mMotionDetectorUser’sGuide

Shortdescription

The Motion sensor ML26m is a sonar device that emits ultrasonic pulses, which

reflect off an object. The sensor measures the time it takes an ultrasonic pulse to

travel from the sensor to the object and determines the distance from the object

based on the measured time and the speed of

 sound. The minimum range of the

sensor is 0.15 m and the maximum range is 6 m. While the sensor is operating, a

slight clicking sound from the sensor will be heard. The sensor is supplied with a

steelrod,whichcanbescrewedintoamountingthreadonthe

sensor.Therodcan

beusedforclampingintoasuitableholdingdevice,e.g.aretortstand.

The Motion sensor is an  I2C digital sensor, which gives calibrated values of the

measured quantity. This sensor can only be connected to special interfaces that

supportI2CdigitalsensorsliketheCMA MoLab

interface. The sensorcableneeded

toconnectthesensorto aninterfaceisnotsuppliedwiththesensor(sensorcables

aresuppliedwithinterfaces).

Sensorspecifications

The Motion sensor ML26m is a digital sensor that converts the measured distance

valuetoadigitalvaluevia16‐bitanalog‐to‐digital conversion.Theresolution of the

sensoris±0.001m.

Practicalinformation

The Motion sensor emits short bursts

of ultrasonic sound waves from the

goldfoilof itstransducer.Thesewaves

fill a cone shaped area about 18° off

theax isofthecenterlineofthebeam.

The detector then "listens" for the

echo of these ultrasonic waves

returningtoit.

The minimum

 distance between the

object and the Motion sensor should

be 0.15 m. Note that the motion

sensor will report the distance to the

closest object that produces a

sufficiently strong echo. Objects such

aschairsandtables,intheconeofultrasound,canbepickedupbythedetector.

For

accuratemeasurementstheobjectshouldhaveaflatfrontperpendiculartothe

line betweensensorandobject.Notethat themaximumdetectiondistanceof 6m

depends on the size, shape, orientation and surface of the reflecting object. This

ML26mMotionDetectorUser’sGuide |3

maximum distance can only be reached under ideal conditions, i.e. for a large, flat

surface (e.g. a wall) that is perpendicular to the detector. For smaller objects or

objectsthatarenotveryflat,themaximumdetectiondistancewillbesmaller.

Themeasurementinputrangealsodependsonthesamplingrate.

Keepinmindthat

increasingthesamplingratemayleadtoalowermaximumrange.

TipsongettinggoodresultswiththeMotionDetector

The most frequently reported problem with the motion sensor is that it does not

workbeyondacertaindistance.Herearesomethingstocheckifyouhaveproblems:

 Checkforastationaryobject(chair,table,etc.)intheconeoftheultrasound.This

object may be detected when you

 are trying to study an object further away.

Evensmallobjectscancausesuchproblems.Ifyouhavetroublewithastationary

object causing  unwanted echoes, try placing a cloth over it. This minimizes the

soundreflection.

 Also note that the cone of ultrasound beam extends downward from the

centerline. This can cause problems if you are using the sensor on  a horizontal

surface. In these cases, aim the Motion sensor slightly upward or place it

somewhathigherabovethesurface.

 Ifthereisanothersourceofultrasonicwavesinthesamefrequencyrange,(likea

motor, fan, air

 track blower, the sound made by air exiting the holes of an air

track,andevenstudentsmakingloudnoises),thiscancauseerroneousreadings.

 If the room in which the Motion sensor is being  used has a lot of hard, sound ‐

reflectingsurfaces,youcangetweirdeffects

causedbytheultrasoundbouncing

aroundtheroom.Standingwavescanbesetupbetweenthesensorandasound

reflector.Tryplacingaclothhorizontallyjustinfrontofandbelowthedetector.

Thissometimeshelpseliminateultrasoundthatis"skipping"intothesensor.

 Trychangingthes amplingrate.

Sometimesreflectedultrasoundpulsescancause

erroneousreadingsthatmaydisappearatothermeasurementfrequencies.

 Ifyouarestudying themovementof people, have them holdalarge,flat object

(e.g. a  large book) as a reflector. If you have an irregular reflecting surface,

sometimes the waves will be

reflected back to the transducer, and sometimes

not.Theresultwillseemerratic.

Collectingdata

This Motion sensor works only with specific interfaces. The sensor will  be

automatically detected when connected to such an  interface. For detailed

information about measurements with sensors consult the User Manuals of the

interfaceandtheCoach6software.

4|ML26mMotionDetectorUser’sGuide

Calibration

The Motion sensor is supplied with a factory calibration  in meters. The Coach 6

program allows shifting the pre‐define d calibration or creating a new  two‐point

linearcalibrationifneeded.Theusercalibrationisstoredinnon‐volatileusersensor

memory.

Suggestedexperiments

TheMotionsensorcanbeusedforstudyingavarietyofmotionsincluding:

 Walkingtowardandawayfromthesensor.

 Simpleharmonicmotion,suchasaweighthangingonaspring.

 Newton’slawsofmotion.

 Accelerationduetogravity‐freefall,objectsdroppedortossedupward.



Airtrackexperiments.

TechnicalSpecifications

Sensorkind Digital(16‐bitsresolution,communicationviaI2C)

Measuringrange 0.14to6m

Aperture(topangle/2) Approx.0.001m

Approx.18˚withrespecttothecentralaxis

Ultrasoundfrequency 62.5kHz

Resolution 0.001m

Accuracy

Typical:±0.1%atfullscale

±0.002mat25°C,measurementrange0.5m,and

samplingrate5Hz

Maximumsamplingrate

100 Hz

Currentconsumption

Typical

40mAatsamplingrate5Hz

Sensordimensions

51x29x64mm

Connection 5‐pinsminijackplug

Warranty:

TheMotion detector ML26mis warrantedto be fr ee from defects in materials and

workmanshipforaperiodof12months from thedateofpurchaseprovided that it

has been used undernormal laboratory conditions.This warrantydoes not applyif

thesensorhasbeendamagedbyaccidentormisuse.

  Rev.17/11/2011

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Note: Thisproductistobeusedforeducationalpurposesonly.Itisnotappropriate

forindustrial,medical,research,orcommercialapplications.   

CMA ML26m User guide

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