paroscientific, inc. digiquartz ® pressure instrumentation quartz crystal technology introduction...
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Paroscientific, Inc.Paroscientific, Inc.DigiquartzDigiquartz®® Pressure Instrumentation Pressure Instrumentation
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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• 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
Advantages of Quartz Resonant Sensors
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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 DrawingFlexure Relief
Isolator Spring
Input Force
Vibrating Beam
(Electrodes on Both Sides)
Isolator MassMounting Surface
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.
Single Beam Force Sensor
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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
Electrical Exitation Pads
Surface Electrodes
Dual Tine Resonators
Mounting Pad
Applied Load
Two tines vibrate in opposition to minimize energy losses
Applied Load
Double-Ended Tuning Fork Force Sensors
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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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0 Full Scale Compression
28
26
24
22
Full Scale Tension
10% Change in Period with Full Scale Load
Resonant Period (microseconds)
Output Period vs. Force
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Nominal Period of Oscillation=5.8 microseconds Nominal Temperature Sensitivity=45 ppm/0C
Electrical Exitation Pads
Dual Torsionally Oscilating Tines
Mounting Pad
Quartz resonator used for digital temperature compensation
Torsional Resonator Temperature Sensor
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The change in resonant period output is a measure of temperature used for thermal compensation of the pressure crystal output.
Wafer of Temperature Sensors
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Internal Vacuum
Balance Weight
Bourdon Tube
Quartz Crystal Resonator Force Sensor
Case
Quartz Resonator Temperature Sensor
BellowsPressure Input
Balance Weight
Quartz Crystal Resonator Force Sensor
Quartz Resonator Temperature Sensor
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.
Quartz Crystal Resonator Pressure Transducers
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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.
Digiquartz® Barometer
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Pressure Signal
Timebase Clock
Time N Periods
Time
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.
(fc)
Period Measurement Resolution and Sampling
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Sampling Time = NPeriod Resolution =+/- 1 Count/(Total Counts)=+/- 1 / (Nfc)
= +/- 1 / (Sampling Time) fc)
Force Resolution = +/- 10 / (Nfc) (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
ContinuedPressure Signal
Timebase Clock
Time N Periods
Time
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Force = C[1- 02/ 2] [1-D(1- 0
2/ 2)]
=Force Resonator Period Output
C=Scale Factor in Desired Engineering Units
D=Linearization Coefficient
0=Period Output at No Load (Force=0)
U=(Temperature Sensor Period)-(Temperature Period at zero 0C)
0= 1+ 2U+ 3U2+ 4U3+ 5U4
C=C1+C2U+C3U2
D=D1+D2U
Temperature =Y1U+Y2U2+Y3U3 (0C)
Linearization and Temperature Compensation
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Multiplexer
Counter
Microprocessor
Shift Store Pass On
Serial Interface
EEPROM
EPROM
15 Mhz Clock
Transducer
Pressure Signal Temperature Signal
RS-232 or RS-485 In RS-232 or RS-485 Out
Intelligent Instrumentation
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• Resolution• Static Error Band
– Non-repeatability– Hysteresis– Conformance
• Environmental Errors– Temperature– Acceleration
• Long Term Stability
Transducer Characteristics and Performance
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Noise Versus Record Length
Parts per billion in seconds
Parts per million for yearsHome Page
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DigiquartzDigiquartz®® Pressure InstrumentationPressure Instrumentation
Tsunami Detection (Earthquake Generated Tidal Waves)
Sensitivity of 1 mm of Water at Depths of 6000 meters
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Measured at 10,000 PSI +5 ppm
0
ppm 0 +0.25
Height (cm)
S/N 1064S’ Class 200 PSI/Kg Piston
-5 -0.25
Measuring piston wear to less than a nanometer
High Resolution Measurements of Dead Weight Tester Piston Taper
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Number of Units
Pressure Hysteresis in Microbars
0-10
-5
5 10
Mean Hysteresis -1.3 Microbars
Pressure Hysteresis Measurements on Twenty-Three Paroscientific Barometers
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Static Error Band(Non-Repeatability, Hysteresis, Non-Conformance)
-0.0100
-0.0080
-0.0060
-0.0040
-0.0020
0.0000
0.0020
0.0040
0.0060
0.0080
0.0100
600 700 800 900 1000 1100 1200
Pressure (hPa)
Err
or %
fs
Up1
Dow n1
Up2
Dow n2
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-0.03
-0.02
-0.01
0.00
0.01
0.02
0.03
-80 -60 -40 -20 0 20 40 60 80 100 120
Temperature (deg C)
Erro
r % fu
ll sc
ale
Zero
Mid-scale
Full-scale
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
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
1989 1991 1993 1995 1997 1999 2001
S/N 34264 Long-Term Stability
hP
a
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
1989 1991 1993 1995 1997 1999 2001
S/N 34266 Long-Term Stability
hP
a
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
1989 1991 1993 1995 1997 1999 2001
S/N 37131 Long-Term Stability
hP
a
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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.
Paroscientific, Inc. Overview
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Paroscientific, Inc.Paroscientific, Inc.DigiquartzDigiquartz®® Pressure Instrumentation Pressure Instrumentation
•Metrology
•Hydrology
•Meteorology
•Oceanography
•Aerospace
•Process Control
•Energy Exploration
Digiquartz® Application Areas
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