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ME 311 Mechanical Measurements Instrumentation I 4/29/03

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ME 311 Mechanical Measurements Instrumentation I 4/29/03 Announcements The attendance sheet is being circulated. Please sign it before you leave! – PowerPoint PPT presentation

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Title: ME 311 Mechanical Measurements Instrumentation I 4/29/03


1
ME 311Mechanical MeasurementsInstrumentation
I4/29/03
2
Announcements
  • The attendance sheet is being circulated. Please
    sign it before you leave!
  • We are not meeting for lab tomorrow. Time to
    finish up testing and prepare for oral
    presentation.
  • How are your projects coming along? How many
    groups have finished their testing? Any general
    question?
  • If you have specific question, dont hesitate to
    contact your professors! We are here to help you.

3
Road Map of Lecture 7
  • Overview of a measurement system
  • sensor/transducer
  • signal conditioning (will be covered in greater
    details in ME 421)
  • data acquisition (will be covered in greater
    details in ME 421)
  • Focus on the sensor/transducer system in this
    course
  • How does it work? (operating principle)
  • Issues on range, resolution, sensitivity
  • System characteristics
  • Need for calibration
  • Terminology with system characteristics
  • Homework assignment (as a group)

4
Overview of a Measurement System
e.g. pressure, temperature, light intensity
Measurand
e.g. pressure gauge, thermocouple, photo-cell
e.g. amplification, band-pass filtering
e.g. display, record, storage
5
Basic Terminology
  • The measurand is a physical quantity, property,
    or condition that is being measured.
  • A sensor is the portion of a measurement system
    that responds directly to the measurand.
  • In the general sense, a transducer is a device
    which transforms one physical variable into
    another.
  • In most cases, the physical variable is
    transformed into an electrical signal.

6
Advantages of Electrical Transducers
  • Amplification or attenuation can be obtained
    easily
  • Inertial effects are minimized
  • Frictional effects are minimized (no moving part)
  • Remote indication of recording is feasible
  • Commonly susceptible to miniaturization
  • Majority of output/recording devices require
    electrical input

7
The Sensor/Transducer System
  • The fundamental function of a sensor/transducer
    system is to sense the desired input, excluding
    all others, and provide analogous output.
    (Example microphone for sound detection)
  • In reality, the sensor/transducer system always
    measures both the quantity of interest and some
    noise.
  • Can you name a few examples of transducer which
    you worked with in the first four labs and your
    project? What is the variable transformation in
    each case?
  • thermocouple (from temperature difference to
    potential difference)
  • thermistor (from temperature difference to
    resistance difference)
  • piezoelectric transducer (from stress/deformation
    to potential difference)
  • strain gauge (from strain/deformation to change
    in resistance)
  • photo-cell (from light intensity to change in
    resistance)
  • manometer (from pressure difference to height
    difference between fluid columns)

8
Issues to Consider
  • Knowledge of the measurand
  • static or dynamic (mean versus fluctuations)
  • time scale
  • amplitude scale
  • frequencies present (How large is the range?)
  • magnitudes
  • Knowledge of the sensor
  • operating principle (Does it imply any limitation
    on what can be measured?)
  • resolution (How does the resolution compare with
    the magnitude of the measurand?)
  • sensitivity
  • settling time
  • bandwidth (Is it large enough to capture the
    variation in the measurand?)

9
Characteristics of a Sensor/Transducer System
  • Viewing from a black-box perspective, every
    instrumentation is a dynamical system which has
    its own frequency response to the change in the
    measurand (amplitude and phase characteristics)
  • always has a lag time, no perfect (instant,
    exact) data transmission
  • recall the plotting device in Professor Olsons
    lab (Does anyone recall the highest frequency
    which can be tracked?)
  • the measurement system may be of first or higher
    order ranging from simple to complex response

10
More Vocabulary on System Characteristics
  • Time scales
  • time constant (for 1st order system)
  • rise time
  • settling time
  • Frequency response
  • Transient response
  • Bandwidth
  • Accuracy, range
  • Overshoot

11
Need for Calibration
  • One of the most overlooked procedures in
    conducting an experiment. (Did you do it for
    your project?)
  • Rather than just accepting the reading of an
    instrument, calibration firmly establishes the
    accuracy of the instruments.
  • Sometimes the manufacturers specifications may
    not be taken at face value.
  • It involves a comparison of the instrument with
    either
  • a primary standard (may be difficult to obtain),
  • a secondary standard with a higher and known
    accuracy than the instrument to be calibrated,
  • a known input source.

12
Many Types of Sensor/Transducer System
  • Acceleration
  • piezoelectric accelerometer
  • strain gage accelerometer
  • Force Torque
  • shaft torque sensor
  • dynamometer
  • Pressure transducer
  • Temperature
  • thermocouple
  • resistance temperature detector (RTD)
  • Flow rate
  • rotameter
  • turbine flowmeter

13
Homework Assignment
  • Each group chooses one of the sensor/transducer
    systems to research on.
  • Address the following key questions
  • What is the operating principle?
  • Range, sensitivity, resolution (based on the
    chosen model)
  • Any required accessories (signal conditioning)?
  • This homework is an attempt to get you involved
    in our second lecture on Instrumentation. It
    will be due at the beginning of the next lecture.

14
Suggested References
  • T.G. Beckwith, R.D. Marangoni, and J.H. Lienhard
    V, Mechanical Measurements, Addison-Wesley.
  • R.S Figliola D.E. Beasley, Theory and Design
    for Mechanical Measurements, Wiley.
  • J.P. Holman, Experimental Methods for Engineers,
    McGraw Hill.
  • A.J. Wheeler A.R. Ganji, Introduction to
    Engineering Experimentation, Prentice Hall.
  • SENSOTEC www.sensotec.com
  • OMEGA www.omega.com
  • DYNOmite www.land-and-sea.com/dyno.htm
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