WLS data acquisition

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    SUMMER INTERNSHIPSUMMER INTERNSHIP

    Ashwin B N

    09MC05F

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    ContentsContents

    IntroductionTransducers

    Strain Measurement

    Strain gaugeStrain Gauge measurement

    Data Acquisition Systems for Strain GaugeMeasurements

    Cantilever beam dimensions and material

    properties

    Comparision of results

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    IntroductionIntroductiony Data acquisition involves gathering signals from measurement

    sources and digitizing the signals for storage, analysis, and

    presentation on a PC

    y components when building a basic data acquisition system:

    Transducers and sensors

    Signals

    Signal conditioning

    DAQ hardware

    Driver and application software

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    TransducerTransducer

    y Data acquisition begins with the physical phenomenon to be

    measured. This physical phenomenon could be the temperature of a

    room, the intensity of a light source, the pressure inside a chamber,

    the force applied to an object, or many other things.

    y Table below shows a short list of some common phenomena and the

    transducers used to measure the

    Phenomenon Transducer

    Temperature Thermocouple

    Strain Strain gauge

    Acceleration Accelerometer

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    STRAIN MEASURMENTSTRAIN MEASURMENT

    y Strain is the amount of deformation of a body due to an applied

    force. More specifically, strain (e) is defined as the fractional

    change in length, as shown in Figure

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    STRAIN GAUGESTRAIN GAUGEy While there are several methods of measuring strain, the most

    common is with a strain gage, a device whose electrical resistance

    varies in proportion to the amount of strain in the device.

    y The metallic strain gage consists of a very fine wire or, more

    commonly, metallic foil arranged in a grid pattern.

    y The grid is bonded to a thin backing, called the carrier, which is

    attached directly to the test specimen.

    Therefore, the strain experienced by the

    test specimen is transferred directly to the

    strain gage, which responds with a

    linear change in electrical resistance.

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    y A fundamental parameter of the strain gage is its sensitivity to

    strain, expressed quantitatively as the gage factor (GF). Gage factor

    is defined as the ratio of fractional change in electrical resistance to

    the fractional change in length (strain):

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    STRAIN GAUGE MEASURMENTSTRAIN GAUGE MEASURMENTy

    In practice, strain measurements rarely involve quantities larger

    than a few millistrain (e x 10-3).

    y To measure such small changes in resistance, strain gages are

    almost always used in a bridge configuration with a voltage

    excitation source. The generalWheatstone bridge, illustrated in

    Figure 3, consists of four resistive arms with an excitation voltage,

    VEX, that is applied across the bridge.

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    y Now if I replace R4 with Rg , i.e strain gauge .Then, the strain-

    induced change in resistance, DR, can be expressed as DR =

    RGGFe, from the previously defined Gauge Factor equation. Now

    equation becomes VO/VEX as a function of strain

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    Data Acquisition Systems for StrainData Acquisition Systems for Strain

    Gauge MeasurementsGauge Measurementsy Requirements

    NI USB- 9234

    Bus powered

    Built-in excitation up to 10 V

    Up to 50 kS/s/ch sample rate

    Simultaneous acquisition

    with four ADCs

    Quick sensor connect

    with RJ50 connectors

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    Cantilever beam dimensionsCantilever beam dimensions

    and material propertiesand material properties

    y Length = L =35 cm

    y Width = b = 27 cm

    y Thickness = t = 0.25 cm

    y Area of cross section = A= b*t m2

    y Moment of inertia= I = (b*t^3)/12 m4

    y Youngs modulus of the material (Al) =E = 7*1010 N/m2

    y Mass density = 2700 kg/m

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    COMPARISION OF RESULTSCOMPARISION OF RESULTS

    Analytical LabView MATLAB

    29.30Hz 32Hz 31Hz

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