Quartz Crystal Technology Introduction Design of Quartz Resonant

Quartz Crystal Technology • • • Introduction Design of Quartz Resonant Sensors Design of Pressure Transducers Transducer Characteristics & Performance Applications Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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 Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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 Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Design of Quartz Resonant Sensors • Single Beam Force Sensors • Double-Ended Tuning Fork Force Sensors • Torsional Temperature Sensors Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Single Beam Force Sensor Isolator Spring e orc ut F Single Beam Force Sensor Drawing Inp Flexure Relief Mounting Surface Vibrating Beam Isolator Mass (Electrodes on Both Sides) The beam is driven piezoelectrically at its resonant frequency. Isolator masses and springs act as a lowpass mechanical filter to minimize energy losses to the mounting pads resulting in high Q oscillations. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Double-Ended Tuning Fork Force Sensors Surface Electrodes Applied Load Electrical Exitation Pads Double-Ended Tuning Fork Force Sensors Drawing Mounting Pad Dual Tine Resonators Applied Load Two tines vibrate in opposition to minimize energy losses Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Double-Ended Tuning Fork Force Sensors Photo Produced on quartz wafers by photolithographic and chemical milling techniques similar to fabrication of watch crystals Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Output Period vs. Force Resonant Period (microseconds) 28 26 24 22 Full Scale Tension 0 Full Scale Compression 10% Change in Period with Full Scale Load Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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/0 C Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Wafer of Temperature Sensors The change in resonant period output is a measure of temperature used for thermal compensation of the pressure crystal output. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Quartz Crystal Resonator Pressure Transducers Internal Vacuum Balance Weight Bourdon Tube Quartz Crystal Resonator Force Sensor Case Quartz Crystal Resonator Force Sensor Quartz Resonator Temperature Sensor Pressure Input Bellows Quartz Resonator Temperature Sensor Input Pressures applied to the bellows or Bourdon tube load the Quartz Force Sensors to change the resonant frequencies. Quartz Temperature Sensors provide thermal compensation. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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. Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Continued Pressure Signal Timebase Clock Time N Periods Time 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=5 x 10 -7 Full Scale Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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 0 C) t 0= t 1+ t 2 U+ t 3 U 2+ t 4 U 3+ t 5 U 4 C=C 1+C 2 U+C 3 U 2 D=D 1+D 2 U Temperature =Y 1 U+Y 2 U 2+Y 3 U 3 (0 C) Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Intelligent Instrumentation Transducer Pressure Signal Temperature Signal Multiplexer Counter 15 Mhz Clock EPROM Microprocessor EEPROM Shift Store Pass On RS-232 or RS-485 In Paroscientific, Inc. Digiquartz® Pressure Instrumentation Serial Interface RS-232 or RS-485 Out Home Page

Transducer Characteristics and Performance • Resolution • Static Error Band – Non-repeatability – Hysteresis – Conformance • Environmental Errors – Temperature – Acceleration • Long Term Stability Home Page Paroscientific, Inc. Digiquartz® Pressure Instrumentation

Noise Versus Record Length Parts per billion in seconds Parts per million for years Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Tsunami Detection (Earthquake Generated Tidal Waves) Sensitivity of 1 mm of Water at Depths of 6000 meters Paroscientific, Inc. Digiquartz® Pressure Instrumentation ® Digiquartz Pressure Instrumentation Home Page

High Resolution Measurements of Dead Weight Tester Piston Taper S/N 1064 S’ Class 200 PSI/Kg Piston Measured at 10, 000 PSI +5 ppm 0 -5 ppm -0. 25 0 +0. 25 Height (cm) Measuring piston wear to less than a nanometer Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Pressure Hysteresis Measurements on Twenty. Three Paroscientific Barometers Number of Units 10 5 Pressure Hysteresis in Microbars 1 0 Mean Hysteresis -1. 3 Microbars Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

Static Error Band (Non-Repeatability, Hysteresis, Non-Conformance) Home Page Paroscientific, Inc. Digiquartz® Pressure Instrumentation

Total Error Band (Over Temperature at Various Pressures) Home Page Paroscientific, Inc. Digiquartz® Pressure Instrumentation

Long Term Stability Median Drift Rate= -0. 007 h. Pa = (-0. 0002 in. Hg) per year Paroscientific, Inc. Digiquartz® Pressure Instrumentation Home Page

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 longterm 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. Home Page Paroscientific, Inc. Digiquartz® Pressure Instrumentation

Digiquartz® Application Areas • Metrology • Aerospace • Hydrology • Process Control • Meteorology • Energy Exploration • Oceanography Home Page Paroscientific, Inc. Digiquartz® Pressure Instrumentation