Assignment#01: Literature Survey on Sensors ECE 5320 Mechatronics Assignment#01: Literature Survey on Sensors Topic: Piezoelectric Quartz Accelerometers

ECE 5320 MechatronicsAssignment#01: Literature Survey on Sensors Assignment#01: Literature Survey on Sensors

Topic: Piezoelectric Quartz Accelerometers

Prepared by:Jared B. Bowler

Dept. of Electrical and Computer Engineering Utah State University

Email:[email protected]; Phone: (435)797-6612;

3/11/2005

03/10/05 ECE5320 Mechatronics. Assignment#1 Survey on sensors

Outline – Reference list– Links to explore this topic further– Basic working principles illustrated– Major applications– A typical configuration in application – Major specifications– Relevant issues in applications: advantages,

disadvantages, how to select, cost information, and places to purchase.

– Conclusion

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Reference list

• Mechatronics Handbook 20-57 to 60

• http://www.davidson.com.au/products/pressure/pcb/theory/piezo-accel-intro.asp

• http://www.sensorsmag.com/articles/0204/27/main.shtml

• http://www.pcb.com/techsupport/tech_gen.php

• http://news.thomasnet.com/fullstory/21307

• http://www.mmf.de/PDF/AN1E-Introduction.pdf

ECE5320 Mechatronics. Assignment#1 Survey on sensors

03/10/05

For further exploration…..(Survival pointers of web references)

• http://www.davidson.com.au/products/pressure/pcb/theory/piezo-accel-intro.asp

• http://www.sensorsmag.com/articles/0204/27/main.shtml

• http://www.pcb.com/techsupport/tech_gen.php

• http://news.thomasnet.com/fullstory/21307


Basic Working Theory:Piezoelectric Principles

• Piezoelectric effect discovered by Pierre and Jacques Curie in 1880

• They discovered that under certain conditions such as when quartz is stressed along its main axis, the quartz will generate an electrical field

• Now this effect is primarily used in sensing and actuating engineering applications


Classes of Piezoelectric Materials

• Natural, such as quartz

• Synthetic crystals

• Polarized ferroelectric ceramics

• Some Polymer films

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Piezoelectric Materials fall into 4 main categories


Classes of Piezoelectric Materials

• Most piezoelectric accelerometers use polarized ferroelectric ceramics or quartz crystal

• In accelerometers, lead zirconate titanate (PZT) and quartz crystals are most common

• High performance and physical robustness are two main reasons for using the above materials in engineering applications

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Piezoelectric Materials—Engineering


Overview: What it is

• “Most piezoelectric accelerometers are made of quartz crystal, piezoelectric ceramics, or, for high-temperature operation, tourmaline or lithium niobate. They obey Newton’s second law, F = ma, in that the force acting on the measuring element is directly proportional to the acceleration produced. Available in a wide range of configurations and operating specifications, these devices are used wherever shock or vibration is of interest.”


http://www.sensorsmag.com/articles/0204/27/main.shtml

Two types of quartz accelerometers

• High impedance: More versatile, most parameters can be controlled by an external charge amplifier, more robust.

• Low impedance: More customized application, can be cheaper, but not for broad applications


Why Choose Quartz instead of PZT?

• “Material stress limit of ~20,000 psi

• Temperature resistance up to 930°F

• Very high rigidity, high linearity, and negligible hysteresis

• Almost constant sensitivity over a wide temperature range

• Ultra-high insulation resistance (1014 ), allowing low-frequency measurements (<1 Hz)”



Basic Working Theory:Piezoelectric Effect in Crystals

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•“A) Longitudinal Effect. The size of the charge depends only on the force applied. The only way to increase this charge is to connect several plates mechanically in series and electrically in parallel.•B) Shear Effect. This effect, too, is independent of the size and shape of the piezoelectric element as well as of the charge distribution. The charge occurs at the surfaces under load; at n elements connected mechanically in series•C)Transverse Effect. In this case, a force in the direction of one of the neutral axes produces a charge on the surfaces of the corresponding polar axis.”



Basic Working Theory:Manufacture of Piezoelectric Quartz

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“Figure 1. Piezoelectric crystals that are cut so that they exhibit the longitudinal effect (A) are sensitive to compression forces. They are used primarily to measure force, pressure, strain, and acceleration. The transverse effect (B) makes it possible to obtain a greater charge by suitable shaping and arrangement of the piezoelectric elements, and is used primarily in pressure sensors. Shear effect elements (C) are chiefly used in accelerometers and 3-component force sensors. They have low base-strain sensitivity (the amount of strains in an object under test that are transmitted via the base plate to the sensor element) and a well-behaved response to rapid temperature changes because these influences act in a direction perpendicular to the sensitive shear axis.”



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Major applications of Piezoelectric Quartz Accelerometers I

• “Aerospace. Modal testing, wind tunnel, and shock tube instrumentation; landing gear hydraulics; rocketry; structures; ejection systems

• Ballistics. Combustion, explosion, and detonation• Engine Testing. Combustion and dynamic

stressing”



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Major applications of Piezoelectric Quartz Accelerometers II

• “Engineering. Materials evaluation, control systems, reactors, structural analysis, auto chassis structural testing, shock and vibration isolation, and dynamic response testing

• Industrial/Factory. Machining systems, metal cutting, and machine health monitoring

• OEMs. Transportation systems, rockets, machine tools, engines, flexible structures, and shock/vibration testers”



Quartz Accelerometers: Specifics


•Active electrical systems•Produce an output only when there is a change in the load•Best suited for dynamic measurements•However, with the proper hardware, they can also accurately measure relatively static systems

Typical Configuration:Wilcoxon Accelerometers

• These sensors are hermetically sealed. Outer housing is 316L stainless steel, which is corrosion resistant. These sensors are particularly appropriate for industrial environments, due to their ability to work even in harsh operating conditions.


Example: Wilcoxon Model 785ALow Profile Industrial Accelerometer

• Sensitivity........................................100 mV/g

• Acceleration Range..........................80 g peak

• Amplitude non-linearity..................1%

• Frequency Response (3dB).............1.0 - 12,000 Hz

• Resonant Frequency........................30 KHz

• Transverse Sensitivity.....................5% of axial03/10/05

Major Specifications : Dynamic


Model PDA130 High Speed Piezoelectric Micro-positioning Motor.

• Power Requirement: voltage source ........................... 18 - 30 VDC

• current regulating diode .............................................. 2 - 10 mA

• Electrical Noise, equiv. g, nominal:

• Broadband 2.5 Hz to 25 kHz ...................................... 1,260 μg

• Spectral 10 Hz ............................................................ 11 μg/√Hz

• 100 Hz ........................................................................ 6 μg/√Hz

• 1000 Hz ...................................................................... 6 μg/√Hz

• Output Impedance ...................................................... 100 Ω

• Bias Output Voltage, nominal ................................... 12 VDC03/10/05

Major Specifications: Electrical


Advantages• “Extremely wide dynamic range, almost free of noise -

suitable for shock measurement as well as for almost imperceptible vibration

• Excellent linearity over their dynamic range

• Wide frequency range, high frequencies can be measured

• Compact yet highly sensitive

• No moving parts - long service life

• Self-generating - no external power required

• Great variety of models available for nearly any purpose

• Integration of the output signal provides velocity and displacement”


http://www.mmf.de/PDF/AN1E-Introduction.pdf

Disadvantages

• Relative high price• Need higher power• System must be changing somewhat,

purely static measurements are impossible to make


Criteria for Selection

• Type of sensing needed (force, shocks, etc)

• Temperature Range

• Nature of the environment (temperature)

• Nature of the system measured (static, dynamic)

• Resolution

• Cost


Cost information

• Can range widely from a few dollars to hundreds of dollars

• Wide variety of configurations available

• The example looked at was priced at $150 USD


Places to purchase

• Do a Google or Froogle search for “piezoelectric accelerometers,” there are many results

• One distributor found Reliability Direct, which distributes Wilcoxon Accelerometers

• http://www.reliabilitydirect.com/accelerometeraccessories/wilcoxon.htm


Conclusion

• Piezoelectric Accelerometers offer unique characteristics due to their design that are not often found in other types of sensors. However, they are not necessarily for every application. Be sure to weigh the pros and cons and take a close look at the sensor specs


Documents

Assignment#01: Literature Survey on Sensors ECE 5320 Mechatronics Assignment#01: Literature Survey on Sensors Topic: Piezoelectric Quartz Accelerometers