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Quartz Crystal Technology

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Presentation on theme: "Quartz Crystal Technology"— Presentation transcript:

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

2 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

3 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

4 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

5 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

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

7 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

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 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

16 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

17 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

18 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

19 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

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

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

22 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

23 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

24 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

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

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

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

28 Paroscientific, Inc. Overview
Paroscientific manufactures and sells a complete line of high precision pressure instrumentation. Resolution of better than % 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

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

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