TFL06 General Instruments

TFL06 General Instruments - Velocity, Acceleration, Load,...

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1 1 Velocity, Acceleration, Load, and Pressure 2 Unit Objectives • Describe devices used to measure mechanical quantities (e.g. force, etc.) • Present analyses associated with measuring mechanical quantities • Examine operating issues associated with mechanical quantity measurement
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2 3 Velocity Transducer I • Principle is identical to an electrical generator •e o = B×l×v i • Moving coil or core • Typical Characteristics Sensitivity o 50 to 500 mV/(mm/s) Frequency Response o 100 Hz to 1500 Hz Mass o 20 g to 1.5 kg N S e o v i 4 Velocity Transducer II • Permanent-Magnet Tachometer N S Permanent Magnet Output Signal Electrical Windings Tachometer Case
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3 5 Accelerometers • All devices employ a mass/spring system • Accelerometer mass can affect system dynamics • Multi-dimensional systems available • Jerk can be measured by differentiating acceleration, however a jerk transducer is available (i.e. a Donner Jerk Meter) 6 Accelerometer Dynamics x o x x i M R K i o x x x M K s M R s s s X s X i o 2 2 ) ( ) ( i i x a M K s M R s s A s X i o 2 1 ) ( ) ( ) ( ) ( x x R x x K x M i i
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4 7 Accelerometer Response Gain log ( ) Accelerometer Response Gain log ( ) Vibrometer Response 8 Accelerometer Configurations • Strain Gauge • Piezoelectric • Capacitive • LVDT
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5 9 Typical Characteristics • Range - 10 g to 10,000 g • Natural Frequency - 500 Hz to 50 kHz • Sensitivity - 10 mV/g to 1000 mV/g • Linearity - less than 1% • Mass - 10 gm to 30 gm • Size - 20 mm × 20 mm × 10 mm 10 Piezoelectric Accelerometer log ( ) Gain Piezoelectric Accelerometer Response Working Range
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6 11 Load Cells • Force measuring transducers • Added elasticity associated with a load cell • Multi-dimensional cell available Three-dimensions of Force Three-dimensions of Torque Three-dimensions of Force and Torque 12 Load Cell Configurations • Strain Gauge • Piezoelectric • Capacitance • LVDT
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7 13 Strain Gauge Operation The strain is then taken to be related to change in resistance via the following equation R R G 1 If this is then combined with the voltage equation for the resistance bridge then 2 GV V Then for a cantilever case, the force ( F ) is related to the bridge voltage difference (
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TFL06 General Instruments - Velocity, Acceleration, Load,...

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