wls data acquisition
TRANSCRIPT
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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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