Quartz Crystal Technology Introduction Design of Quartz Resonant Sensors Design of Pressure Transducers Transducer Characteristics & Performance Applications 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. 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. 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 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 Home Page

Design of Quartz Resonant Sensors Single Beam Force Sensors Double-Ended Tuning Fork Force Sensors Torsional Temperature Sensors Home Page

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. 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. Add descriptive text: Home Page

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 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 Add descriptive text: Home Page

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 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/0C 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. Home Page

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. 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. 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. Home Page

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 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 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) Home Page

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 Home Page

Transducer Characteristics and Performance Resolution Static Error Band Non-repeatability Hysteresis Conformance Environmental Errors Temperature Acceleration Long Term Stability Home Page

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

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

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 Add descriptive text: Measuring piston wear to less than a nanometer Home Page

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 Home Page

Static Error Band (Non-Repeatability, Hysteresis, Non-Conformance) Home Page

Total Error Band (Over Temperature at Various Pressures) Home Page

Long Term Stability Home Page Median Drift Rate= -0.007 hPa = (-0.0002 inHg) per year Add descriptive text: 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 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. Home Page

Digiquartz® Application Areas Metrology Hydrology Meteorology Oceanography Aerospace Process Control Energy Exploration List and link to main page applications Home Page