1. Instrumentation Symposium 10/9/2010 Nigbor 1 Instrumentation Selection Strategies Robert Nigbor nees@UCLA

2. 2 Some sources of instrumentation selection informationSome sources of instrumentation selection information Common types of measurements in NEES researchCommon types of measurements in NEES research Introduction to the Operating Range concept for sensor + data acquisition selectionIntroduction to the Operating Range concept for sensor + data acquisition selection OUTLINE Instrumentation Symposium 10/9/2010 Nigbor

3. Training & Information on Instrumentation Selection A question for the audience – how many universities have hands-on instrumentation courses as part of the CE curriculum?  Example: Prof. Muratore’s ME Instrumentation & Data Acquisition course at Rice Professional Organizations  ASCE  IEEE Vendors  IOTech  National Instruments Instrumentation Symposium 10/9/2010 Nigbor 3

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5. 5 www.mccdaq.com/handbook/handbook.aspx

6. Instrumentation Symposium 10/9/2010 Nigbor 6 www.mccdaq.com/handbook/resource_center.aspx

7. Instrumentation Symposium 10/9/2010 Nigbor 7 www.ni.com/academic/measurements_curriculum.htm

8. Review of Basic Instrumentation Issues Instrumentation Symposium 10/9/2010 Nigbor 8

9. Basic Instrumentation Blocks Graphics from www.ni.com DAQ Fundamentalswww.ni.com 9 Instrumentation Symposium 10/9/2010 Nigbor

10. Sensor Bridge Completion Amplification Low Pass Filter Sample and Hold Excitation Analog To Digital Converter Multiplexing and data transmission Typical Analog-to-Digital Instrumentation System Signal Conditioner Data Acquisition Unit Microvolts to Volts depending on the sensor Volts Bits Recording, Storage and Display From John F. Muratore’s course 10 Instrumentation Symposium 10/9/2010 Nigbor

11. What it really looks like! Instrumentation Symposium 10/9/2010 Nigbor 11

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14. Instrumentation Symposium 10/9/2010 Nigbor 14 NEES Experiments typically use tens or hundreds of sensor channels, compared to hundreds or thousands in Aerospace, Mechanical, Physics, and Geophysics applications.

15. The Most Common NEES Measurements: Position, Motion, Strain, Force, Pressure  Linear Position  Angular Position  Linear Velocity  Angular Velocity/Rate  Acceleration  Strain in steel & concrete  Force via Strain  Pressure via strain 15 Instrumentation Symposium 10/9/2010 Nigbor

16. PositionVelocityAcceleration – proportional to force LinearPosition – Direct measurement by moving electrical element (potentiometer, Linear Variable differential transformer (LVDT)), measuring time of flight (laser, sonar), Velocity- Direct measurement by Doppler (sound or radio), Integrate acceleration (inertial) or differentiate position Acceleration – accelerometer – measure a force, divide by mass Pressure – force per unit area AngularAngle –Angle shaft encoder, synchro-resolver, rate integrating gyro, Rotary Variable Differential Transformer (RVDT) Angle rate – direct measurement by rate gyro, Angular acceleration – differentiate rate gyro. Measure a torque, divide by moment of inertia From John F. Muratore’s course 16 Instrumentation Symposium 10/9/2010 Nigbor

17. String Potentiometer From www.spaceagecontrol.com 17 Instrumentation Symposium 10/9/2010 Nigbor

18. Linear Variable Differential Transformer (LVDT) LVDT core centered – no signal Typically core is attached by a shaft to the object whose position is being measured Core left – magnitude is a function of position in same phase as Ein Core right – magnitude is a function of position in opposite phase as Ein 18 Instrumentation Symposium 10/9/2010 Nigbor

19. CEE125, Spr10, Lecture 4 19 Accelerometer Types of Accelerometers: Electronic : transducers produce voltage output Servo controlled: use suspended mass with displacement transducer Piezoelectric: Mass attached to a piezoelectric material, which develops electric charge on surface. Generally accelerometers are placed in three orthogonal directions to measure accelerations in three directions at any time. Sometimes geophones (velocity transducers) are attached to accelerometers to measure the seismic wave velocities. Principle: An acceleration a will cause the mass to be displaced by ma/k or alternatively, if we observe a displacement of x, we know that the mass has undergone an acceleration of kx/m.

20. CEE125, Spr10, Lecture 4 20 Earthquake Sensors – Accelerometer Example: Kinemetrics EpiSensor

21. Strain Gage As the material to which the gage is bonded increases in length (tension), the cross sectional area of the wire in the strain gage decreases. As area decreases, the resistance increases because resistance is inversely proportional to wire cross sectional area 21 Instrumentation Symposium 10/9/2010 Nigbor

22. Typical Implementation via Bridge Circuit: Change in Resistance  Change in Voltage 22 Instrumentation Symposium 10/9/2010 Nigbor

23. Load Cells – Linear Force Strain gage bridge measures elastic strain in material due to applied force 23 Instrumentation Symposium 10/9/2010 Nigbor

24. Capacitance Pressure Transducer Piezoelectric Pressure Transducer Strain gage pressure transducer Basic Pressure Sensor Types 24 Instrumentation Symposium 10/9/2010 Nigbor From John F. Muratore’s course

25. Measurement Needs and Constraints Instrumentation design must consider amplitude, time, and frequency needs and constraints ALL measurement systems have limitations in all three domains A large part of the ART of instrumentation design and implementation is the optimization of needs and constraints Instrumentation Symposium 10/9/2010 Nigbor 25

26. Example: Static versus Dynamic Displacements Instrumentation Symposium 10/9/2010 Nigbor 26 LVDT’s here work for slow (quasi-static) motions but not for vibrations/dynamic motions, due to resonance of sensor and frame

27. Example: Piezoelectric Accelerometers & Earthquake Motions Instrumentation Symposium 10/9/2010 Nigbor 27 Not Sensitive to <1Hz Motions, an important part of earthquake shaking

28. “Operating Range” Tool for considering both amplitude & frequency ranges in an instrumentation system Tool for comparing instrumentation operating range with measurement need Time must be considered separately, but this is often a data acquisition issue instead of a sensor issue Instrumentation Symposium 10/9/2010 Nigbor 28

29. Instrumentation Symposium 10/9/2010 Nigbor 29 Frequency Amplitude, usually in narrow band like 1/3-octave Operating Range Diagram Maximum or Clip Level Resolution or Noise Level Lower Corner Upper Corner Operating Range of Component or System

30. Instrumentation Symposium 10/9/2010 Nigbor 30 Frequency Amplitude, usually in narrow band like 1/3-octave Operating Range Diagram Maximum or Clip Level Resolution or Noise Level Lower Corner Upper Corner Operating Range of Component or System Phenomenon 1: Within Operating Range, is OK

31. Instrumentation Symposium 10/9/2010 Nigbor 31 Frequency Amplitude, usually in narrow band like 1/3-octave Operating Range Diagram Maximum or Clip Level Resolution or Noise Level Lower Corner Upper Corner Operating Range of Component or System Phenomenon 2: Outside Operating Range, not OK

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34. Instrumentation Selection Strategy 1. Understand amplitude, time & frequency limitations/constraints of potential instrumentation components and systems (sensor + signal conditioning + digitizer). 2. Compare with amplitude, time & frequency needs of your particular measurement challenge. 3. Make sure your particular phenomenon lies within the operating range of the instrumentation 4. The Operating Range Diagram is a useful tool for this comparison Instrumentation Symposium 10/9/2010 Nigbor 34