CMA ML36s User guide

BAROMETER/ALTIMETERML36S

USER’SGUIDE



CENTRE FOR MICROCOMPUTER APPLICATIONS

http://www.cma-science.nl

2|ML36sBarometer/AltimeterUser’sGuide

Shortdescription

TheBarometer/AltimeterML36smeasuresatmos phericpressurein therangeof300

hPato1,100hPa andcalculatestherespectivealtitudeinmetersassumingthatthe

average pressure exerted at sea level by the atmosphere is 1013.25 hPa (1

atmosphere).

The sensing element of the sensor is mounted inside the sensor housing.

 The

sensor’s electronics has an automatic internal temperature compensation to

minimizetheeffectofambienttemperaturechangesonthedata.

The pressure sensor is fairly durable but it is designed only for use with non‐

corrosive,non‐ionicworkinggassessuchasair,drygasesandthelike.Donot

getit

wet.

TheBarometer/Altimeter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 Barometer/Altimeter ML36s is a digital sensor that converts the measured

barometric pressure value to a digital value via 19‐bit analog‐to‐digital conversion.

The resolution of the sensor is ± 0.01 hPa. The maximal sampling frequency of the

sensoris10Hz(samplespersecond).



Thealtitudeiscalculatedbasedonthefollowingformula:



Altitude=44,300*(1‐(p/p

)^(1/5.255))



Where p is the measured barometric pressure, and p

 is the sea level standard

atmospheric pressure, which is 1,013.25hPa.

Practicalinformation

 Allowtheoutsideairtoeasilyflowontothesensorelement.

 Ifyouusethesensorinaclosedandpurelyventilatedroom,thesensorcangive

incorrectmeasurements.

 Themaximumpressurethatthissensorcantolerateis1,100hPa.

 Donotusethesensorin

ahotairflow.

 Donotallowwateroranyliquidscomeintothesensor.

ML36sBarometer/AltimeterUser’sGuide |3

Collectingdata

This Barometer/Altimeter 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.

Calibration

The Barometer is supplied with a factory calibration in hPa. The Altimeter is

calibrated in meters, which values are calculated based on conversion of the

measuredpressureassuming1atmosphere(1013.25hPa)of pressureatsealevel.In

that way the sensor gives relative rather than absolute values of altitude. If

 the

altitudeofyourmeasurementlocationisknown,valuescanbyadjustedbyusingthe

SettovalueoptionintheCoach6program.



Note:ThevalueforBarometricpressurereportedbyairportsandweatherstationsis

usuallygivenforthepressureatsealeveli.e.pr essureafterithasbeenadjustedtoits

equivalent at sea level. The valueobtained by this sensorwill be the pressure at its

currentlocation.

Suggestedexperiments

TheBarometer/Altimetercanbeusedinvariousexperimentssuchas:

 Measurementsoftheairpressureoveralongerperiodoftime(weatherstudies).

 Measurementsofthepressurein

liquidsbyconnectingthesensortoa

tube,whichissubmergedina

solution.

 Measurementsofpressure

differencesbetweendifferent

floors

ofbuildings.

 Altitudeinvestigations.



Figure1.Explorethepressureinsideanempty,

sealed, plastic bottle, before and after

squeezingthebottle.



4|ML36sBarometer/AltimeterUser’sGuide

TechnicalSpecifications



Sensorkind

Digital

on‐sensordigitalconversion

(19‐bitsresolution,communicationviaI2C)

Measuringrange Barometricpressure:300hPa..1100hPa

Calculatedrange Altitude:‐1000..9000m

Resolution ±0.01hPa

±0.25m

Uncertainty(accuracy)

Typical±1.0hPaat0to65℃,Max.±3.0hPa

Readingtime

Typical100ms 

Maximalsamplingrate 10Hz

Dimensions Sensorhousing:37x18x16mm

Connection 5‐pinsminijackplug



Warranty:

The Barometer/Altimeter ML36s  is warranted to be free 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.



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

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

Rev. 17/11/2011

CMA ML36s User guide

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