1. Quartz Crystal Technology
Introduction
Design of Quartz Resonant Sensors
Design of Pressure Transducers
Transducer Characteristics & Performance
Applications
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2. Introduction
The widespread use of digital computers and digital control systems have generated a need for high accuracy, inherently digital sensors.
This presentation will discuss the design, construction, performance, and applications of resonant quartz crystal pressure transducers.
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3. Background
Paroscientific is the leader in the field of precision pressure measurement. The company was founded in 1972 by Jerome M. Paros after a decade of research on digital force sensors. Application of this technology to the pressure instrumentation field resulted in transducers of the highest quality and superior performance. Precision comparable to the best primary standards is achieved through the use of a special quartz crystal resonator whose frequency of oscillation varies with pressure induced stress. A quartz crystal temperature signal is provided to thermally compensate the calculated pressure and achieve high accuracy over a wide range of temperatures.
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4. Material Properties and Characteristics of Quartz Sensors
Piezoelectric [pressure-charge generation]
Anisotropic [direction-dependent]
Elastic Modulus
Piezoelectric Constants
Coefficient of Thermal Expansion
Optical Index of Refraction
Velocity of Propagation
Hardness
Solubility [etch rate]
Thermal and Electrical conductivity
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5. Advantages of Quartz Resonant Sensors
High Resolution : More precise measurements can be made in the time domain than the analog domain.
Excellent Accuracy : The quartz crystal sensors have superior elastic properties resulting in excellent repeatability and low hysteresis.
Long Term Stability : Quartz crystals are very stable and are commonly used as frequency standards in counter-timers, clocks , and communication systems.
Low Power Consumption
Low Temperature Sensitivity
Low Susceptibility to Interference
Easy to Transmit Over Long Distances
Easy to Interface With Counter-Timers, Telemetry, and Digital Computer Systems
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6. Design of Quartz Resonant Sensors
Single Beam Force Sensors
Double-Ended Tuning Fork Force Sensors
Torsional Temperature Sensors
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7. Single Beam Force Sensor Drawing
Isolator Spring
Input Force
Flexure Relief
Mounting Surface
Isolator Mass
Vibrating Beam
(Electrodes on Both Sides)
The beam is driven piezoelectrically at its resonant frequency. Isolator masses and springs act as a low-pass mechanical filter to minimize energy losses to the mounting pads resulting in high Q oscillations.
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8. Single Beam Force Sensor Photo
Loads applied to the mounting pads change the resonant frequency of the beam. The change in frequency is a measure of the applied loads.
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9. Double-Ended Tuning Fork Force Sensors Drawing
Surface Electrodes
Applied Load
Double-Ended Tuning Fork Force Sensors Drawing
Electrical Exitation Pads
Mounting Pad
Dual Tine Resonators
Applied Load
Two tines vibrate in opposition to minimize energy losses
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10. Double-Ended Tuning Fork Force Sensors Photo
Produced on quartz wafers by photolithographic and chemical milling techniques similar to fabrication of watch crystals
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11. Resonant Period (microseconds)
Output Period vs. Force
Resonant Period (microseconds) 28 26 24 22
The high Q resonant frequency, like that of a violin string, is a function of the applied load - increasing with tension and decreasing with compression.
Usually the output signal gates a high frequency clock and the period output is measured. The change in period output with full scale load is 10%.
Full Scale Tension
Full Scale Compression
10% Change in Period with Full Scale Load
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12. Torsional Resonator Temperature Sensor
Electrical Exitation Pads
Dual Torsionally Oscilating Tines
Mounting Pad
Quartz resonator used for digital temperature compensation
Nominal Period of Oscillation=5.8 microseconds Nominal Temperature Sensitivity=45 ppm/0C
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13. Wafer of Temperature Sensors
The change in resonant period output is a measure of temperature used for thermal compensation of the pressure crystal output.
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14. Quartz Crystal Resonator Pressure Transducers
Internal Vacuum
Balance Weight
Balance Weight
Bourdon Tube
Quartz Crystal Resonator Force Sensor
Case
Quartz Crystal Resonator Force Sensor
Quartz Resonator Temperature Sensor
Quartz Resonator Temperature Sensor
Pressure Input
Bellows
Input Pressure
Pressures applied to the bellows or Bourdon tube load the Quartz Force Sensors to change the resonant frequencies.
Quartz Temperature Sensors provide thermal compensation.
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15. Digiquartz® Barometer
Balance weights provide acceleration compensation. The mechanism is hermetically sealed and evacuated. The internal vacuum maximizes the crystal “Q” and serves as the reference in absolute pressure sensors.
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16. Period Measurement Resolution and Sampling
Pressure Signal
Timebase Clock
Time N Periods
Time
(fc)
t=Sensor Output Period= 1/Resonant Frequency
N=Number of Periods
Transducer period output, t, gates a high frequency clock, fc, for N periods and the clock pulses are counted.
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17. Example: If clock =20 MHz and sampling time=1 second
Pressure Signal
Timebase Clock
Time N Periods
Time
Continued
Sampling Time = Nt
Period Resolution =+/- 1 Count/(Total Counts)=+/- 1 / (Nt)(fc) = +/- 1 / (Sampling Time) (fc)
Force Resolution = +/- 10 / (Nt)(fc) (Only 10% of the counts are related to Force)
Example: If clock =20 MHz and sampling time=1 second
then the Force Resolution=5x10-7 Full Scale
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18. Linearization and Temperature Compensation
Force = C[1- t 02/ t 2] [1-D(1- t 02/ t 2)]
t =Force Resonator Period Output
C=Scale Factor in Desired Engineering Units
D=Linearization Coefficient
t 0=Period Output at No Load (Force=0)
U=(Temperature Sensor Period)-(Temperature Period at zero 0C)
t 0= t 1+ t 2U+ t 3U2+ t 4U3+ t 5U4
C=C1+C2U+C3U2
D=D1+D2U
Temperature =Y1U+Y2U2+Y3U3 (0C)
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19. Intelligent Instrumentation
Transducer
Pressure Signal
Temperature Signal
Multiplexer
Counter
15 Mhz Clock
EEPROM
EPROM
Microprocessor
Shift Store Pass On
Serial Interface
RS-232 or RS-485 In
RS-232 or RS-485 Out
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20. Transducer Characteristics and Performance
Resolution
Static Error Band
Non-repeatability
Hysteresis
Conformance
Environmental Errors
Temperature
Acceleration
Long Term Stability
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21. Noise Versus Record Length
Parts per billion in seconds
Parts per million for years
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22. Tsunami Detection (Earthquake Generated Tidal Waves)
Sensitivity of 1 mm of Water at Depths of 6000 meters
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Paroscientific, Inc.
Paroscientific, Inc.
Digiquartz
Digiquartz
Pressure Instrumentation
Pressure Instrumentation

23. High Resolution Measurements of Dead Weight Tester Piston Taper
Measured at 10,000 PSI +5
ppm
+0.25
Height (cm)
S/N 1064
S’ Class 200 PSI/Kg Piston -5
-0.25
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Measuring piston wear to less than a nanometer
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24. Pressure Hysteresis in Microbars
Pressure Hysteresis Measurements on Twenty-Three Paroscientific Barometers
Number of Units
-10 -5 5 10
Pressure Hysteresis in Microbars
Mean Hysteresis -1.3 Microbars
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25. Static Error Band (Non-Repeatability, Hysteresis, Non-Conformance)
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26. Total Error Band (Over Temperature at Various Pressures)
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27. Long Term Stability Home Page Median Drift Rate= -0.007 hPa
= ( inHg) per year
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28. Paroscientific, Inc. Overview
Paroscientific manufactures and sells a complete line of high precision pressure instrumentation. Resolution of better than % and typical accuracy of 0.01% are achieved even under difficult environmental conditions. Other desirable characteristics include high reliability, low power consumption, and excellent long-term stability. Over 30 full scale pressure ranges are available - from a fraction of an atmosphere to thousands of atmospheres (3 psid to 40,000 psia). Absolute, gauge, and differential transducers have been packaged in a variety of configurations including intelligent transmitters, depth sensors, portable standards, water level systems and meteorological measurement systems. Intelligent electronics have two-way digital interfaces that allow the user to adjust sample rates, resolution, engineering units, and other operational parameters. Digiquartz® products are successfully used in such diverse fields as hydrology, aerospace, meteorology, oceanography, process control, energy exploration, and laboratory instrumentation.
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29. Digiquartz® Application Areas
Metrology
Hydrology
Meteorology
Oceanography
Aerospace
Process Control
Energy Exploration
List and link to main page applications
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