Paroscientific, Inc. Digiquartz ® Pressure Instrumentation Quartz Crystal Technology Introduction...

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

Paroscientific, Inc.Paroscientific, Inc.DigiquartzDigiquartz®® Pressure Instrumentation Pressure InstrumentationParoscientific, Inc.Paroscientific, Inc.

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


hP

a

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

1989 1991 1993 1995 1997 1999 2001


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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•Metrology

•Hydrology

•Meteorology

•Oceanography

•Aerospace

•Process Control

•Energy Exploration

Digiquartz® Application Areas

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Paroscientific, Inc. Digiquartz ® Pressure Instrumentation Quartz Crystal Technology Introduction...

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