SBZ 321 Instrumentation

• What are the requirements for instrumentation? 


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  • Reliability
  • Simplicity
  • Quality
  • Sufficient performance
  • Accuracy
  • Precision
  • Resolution
• Order of reliability


  • Optical
  • Mechanical
  • Hydraulic
  • Pneumatic
  • Electrical
• Name 9 electric measurement instruments

  • Foil strain gauge instruments
  • Potentiometer (rotary and linear)
  • Electrolytic level
  • Geophone
  • LVDT
  • Vibrating wire strain gauge instruments
  • Piezoelectric bender element
  • Piezoelectric accelerometer
  • Force balance accelerometer
• Name the advantages of electric instrumentation


  • Versatile
  • Control over signal conditioning circuitry
  • Can log output
  • Being able to access information from a distance
• Electrical measurement instruments


  • Force balance accelerometer
  • Piezoelectric bender element
  • Piezoelectric accelerometer
  • Geophone
  • LVDT
  • Rotary potentiometer
  • Linear potentiometer
  • Electrolytic level
  • Foil strain gauge instruments
• What does a Potentiometermeasure?

  Measures displacement
• What are the advantages of a Potentiometer?

  • Low cost
  • Elementary circuitry
  • High output voltage (no amplification required)
• What does a Rotary potentiometer measure?

  Measures displacement
• Linear potentiometer


  Measures displacement
• Electrolytic level


  Measures inclination
• Electrolytic level


  • Low cost
  • High accuracy (± 50 arc-sec)
  • Excellent precision (± 0.3 arc-sec)
  • Elementary circuitry
  • Fragile
  • Not suitable if vibrations occur
• What does a Geophone measure?

  Measures vibration velocity
• What are the advantages of a Geophone?


  • High sensitivity (30V/m.s-1)
  • No excitation voltage required
  • Large signal (no amplification required)
  • Low cost
  • Frequency range (5 to 1500Hz)
• What does a LVDT measure?

  Measures displacement
• LVDT - Linear Variable Differential TransformerAdvantages 


  • High accuracy (± 0.03µm)
  • No friction
  • No hysteresis
  • Submersible
  • Suitable for dynamic measurements
  • Good long term stability
• LVDT needs other measurement equipment to use in soil tests
• What does a vibrating wire strain gauge measure?


  Measures strain
• Vibrating wire strain gauge advantages: 


  • Good long-term stability
  • Measures frequency (not voltage)
  • Avoids: noise, cable effects, amplifier drift, etc.
• Vibrating wire transducers can be coupled with any sensor to measure pressure, strain, temperature, load and displacement etc
• What does a vibrating wire pressure transducermeasure?


  Measures fluid (pore) pressure in soil.
• Piezoelectric bender element


  Measures stiffness and shear wave velocity
• What does a Piezoelectric accelerometer measure?


  Measures vibration acceleration
• What are the advantages of a Piezoelectric accelerometer?


  • Large frequency range (5 to 10 000Hz)
  • Large accelerations can be measured (50g to 10 000g)
  • Charge amplifier required
  • High cost
• Home made tilt meter

  Measures inclination
• What does a force balance accelerometer measure? 


  Measures acceleration or inclination
• What are the advantages of a force balance accelerometer?


  • High sensitivity
  • Good precision (± 50 arc-sec)
• Piezo ceramic


  • High cost
  • Housing
  • Mass
• How piezo ceramic tilt meter works


  As the housing vibrates, it compresses the mass and the piezo crystal releases the electricity
• Home made tilt meter


  • Pendulum
  • Mass
  • Housing
  • Hinge
  • Position detector
• In a home made tilt meter


  The housing tilts while the pendulum remains vertical, the angle alpha is how much the housing has tilted
• Proximity transducer


  Position detector that measures the distance between the transducer and the mass
• In a home made tilt meter, eventually the mass touches the proximity transducer
• Force balance accelerometer


  • Measures acceleration or inclination
  • Applications: tilt meter, inclinometer, vibration measurement
  • Advantages: high sensitivity, good precision (± 50 arc-sec)
  • Limitations: slow response (0 to 100Hz), zero drift, high cost
• Force balance accelerometer has good performance of 1 degree/3600 sec but it can't be buried for years as it will give incorrect readouts
• Inclinometer with wheels


  We measure the inclination by pulling the inclinometer up 1m at a time from which we get the profile of our borehole crest
• What are the advantages of non-electric instrumentation?


  • More reliable than electric instruments
  • No electronic circuitry required
• 0.1mm = 100µm, 10µm is the size of a human hair, a cloud water droplet can not be seen with the naked eye
• Dial gauge resolution


  The range is 0.2m, the big dial will change 0.2m in one revolution, the smaller dial scale tells us how many times the big dial can rotate
• Vernier caliper


  • Type: Mechanical
  • Measures: thickness, width, depth
  • Advantages: low cost
  • Limitations: accuracy (50 - 100µm), susceptible to environmental effects
• Vernier caliper resolution is 0.02mm, reading is 12.46mm