Quartz Crystal Technology

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Quartz Crystal Technology

• Introduction
• Design of Quartz Resonant Sensors
• Design of Pressure Transducers
• Transducer Characteristics Performance
• Applications

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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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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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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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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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Design of Quartz Resonant Sensors

• Single Beam Force Sensors
• Double-Ended Tuning Fork Force Sensors
• Torsional Temperature Sensors

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Single Beam Force Sensor Drawing
Single Beam Force Sensor
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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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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Double-Ended Tuning Fork Force Sensors Drawing
Double-Ended Tuning Fork Force Sensors
Surface Electrodes
Applied Load
Electrical Exitation Pads
Mounting Pad
Dual Tine Resonators
Applied Load
Two tines vibrate in opposition to minimize
energy losses
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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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Output Period vs. Force
Resonant Period (microseconds)
28
26
24
22
0
Full Scale Compression
Full Scale Tension
10 Change in Period with Full Scale Load
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Torsional Resonator Temperature Sensor
Electrical Exitation Pads
Dual Torsionally Oscilating Tines
Mounting Pad
Quartz resonator used for digital temperature
compensation
Nominal Period of Oscillation5.8 microseconds
Nominal Temperature Sensitivity45 ppm/0C
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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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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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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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Period Measurement Resolution and Sampling
(fc)
tSensor Output Period 1/Resonant
Frequency NNumber 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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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
time1 second
then the Force Resolution5x10-7 Full Scale
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Linearization and Temperature Compensation
Force C1- t 02/ t 2 1-D(1- t 02/ t 2) t
Force Resonator Period Output CScale Factor in
Desired Engineering Units DLinearization
Coefficient t 0Period Output at No Load
(Force0) U(Temperature Sensor
Period)-(Temperature Period at zero 0C) t 0 t 1
t 2U t 3U2 t 4U3 t 5U4 CC1C2UC3U2 DD1D2U T
emperature Y1UY2U2Y3U3 (0C)
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Intelligent Instrumentation
Pressure Signal
Temperature Signal
RS-232 or RS-485 Out
RS-232 or RS-485 In
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Transducer Characteristics and Performance

• Resolution
• Static Error Band
• Non-repeatability
• Hysteresis
• Conformance
• Environmental Errors
• Temperature
• Acceleration
• Long Term Stability

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Noise Versus Record Length
Parts per billion in seconds Parts per million
for years
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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

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High Resolution Measurements of Dead Weight
Tester Piston Taper
Measuring piston wear to less than a nanometer
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Pressure Hysteresis Measurements on Twenty-Three
Paroscientific Barometers
Number of Units
0
-10
-5
5
10
Pressure Hysteresis in Microbars
Mean Hysteresis -1.3 Microbars
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Static Error Band(Non-Repeatability, Hysteresis,
Non-Conformance)
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Total Error Band (Over Temperature at Various
Pressures)
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Long Term Stability
Median Drift Rate -0.007 hPa
(-0.0002 inHg) per year
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Paroscientific, Inc. Overview

• Paroscientific manufactures and sells a complete
  line of high precision pressure instrumentation.
  Resolution of better than 0.0001 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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Digiquartz Application Areas
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