Paroscientific, Inc. Digiquartz Technology Overview. Paroscientific, Inc.

Transcription

1 Digiquartz Technology Overview

2 Quartz Crystal A quartz crystal resonator is the key sensing element in a Digiquartz pressure transducer. Quartz was chosen for the following inherent characteristics: High repeatability Low hysteresis Good elastic properties Long-term stability Low environmental sensitivity High Accuracy Ease of measurement in time domain A quartz crystal has piezoelectric effects: the ability of materials to generate an electric charge in response to applied mechanical stress. More information on Why Digiquartz:

3 Quartz Crystal Quartz Crystal Wafer Larger squares are mounting pads, smaller rectangles are electrical excitation pads.

4 Pressure Crystal The change in frequency of quartz crystal resonator is a measure of the applied load from pressure. Frequency increases with tension, decreases with compression. Surface Electrodes Electrical Excitation Pads Mounting Pad Applied Load Dual Tine Resonators

5 Temperature Crystal Digital temperature sensor consists of torsionally-oscillating tines whose resonant frequency is a function of temperature. Output is used to thermally compensate the calculated pressure and achieve high accuracy over a wide range of temperatures. Electrical Excitation Pads Dual Torsionally Oscillating Tines Mounting Pad

6 Transducer Mechanisms 1. Pressure transducer mechanisms employ bellows or Bourdon tubes as the pressure-to-load generators. 2. Pressure acts on the effective area of the bellows or Bourdon tubes to generate a force to load the crystal. 3. An evacuated cell, housing the crystal, serves as the absolute pressure reference and allows for maximum performance and stability of the quartz crystal. Bellows Bourdon Tube

7 Bellows Mechanism (0-500 PSI) Pressure acts on the effective area of the bellows to generate a force and torque about the pivot which compressively stresses (pushes) the resonator. The change in frequency of the quartz crystal oscillator is a measure of the applied pressure. Acceleration is compensated with balancing weights to reduce the effects of shock and vibration. Mechanism and crystal are hermetically sealed and evacuated to eliminate air damping and maximize resonant frequency.

8 Bourdon Tube Mechanism (1K-40K PSIA) Pressure applied to the Bourdon tube generates an uncoiling force which applies tension to the quartz crystal, increasing the resonant frequency. The change in frequency of the quartz crystal resonator is a measure of the applied pressure. Acceleration is compensated with balancing weights to reduce the effects of shock and vibration. The mechanism and crystal are hermetically sealed and evacuated to eliminate air damping and maximize resonant frequency.

9 Temp Compensated Pressure Calculation For a given T, an applied P will generate a specific crystal period. The relationship between the crystal period and pressure is known as the C,D,Tau equation. The coefficients used in C,D,Tau equation are unique to Digiquartz transducers, and are different for each transducer. Coefficients are determined during calibration using a proprietary algorithm.

10 Temperature Calculation T = Y 1 U + Y 2 U 2 + Y 3 U 3 U = X U 0 Where: T = Temperature (deg C) X = Temperature 25 deg C U = Temperature Period (μsec) U 0 (μsec) Temperature Coefficients: U 0, Y 1, Y 2, Y 3

11 Pressure Calculation P = 2 1 T0 1 T C( )[1 D( 2 2 τ τ 2 0 )] Where: P = Pressure τ = Pressure Period (μsec) U = Temperature Period (μsec) U 0 (μsec) C = C 1 + C 2 U + C 3 U 2 D = D 1 + D 2 U T 0 = T 1 + T 2 U + T 3 U 2 + T 4 U 3 + T 5 U 4 Pressure Coefficients: C 1 C 2 C 3 D 1 D 2 T 1 T 2 T 3 T 4 T 5

12 Calibration Coefficients Calibration coefficients come with every transducer Certificate of Calibration, Certificate of Conformance, Certification of Traceability also included Highly recommended to make copies of all paperwork received

13 Calibration Test Profile Each transducer is extensively tested against a primary pressure standard across the full scale/operating pressure range. Proprietary algorithm used during this process to determine coefficients. Used to provide information on hysteresis and repeatability. Capacity of transducers at one time 4 week standard lead time. f.s. Pressure 0-54 o C Temperature 107 o C

14 Important Terminology Accuracy Precision Resolution Linearity Repeatability Hysteresis More terminology:

15 Accuracy vs Precision Accuracy: how close is the measured value to the true value as established by reference standard. Precision: the ability of a measuring device to provide the same readings for the same input.

16 Resolution Paroscientific Normal Resolution MEMS-based Competition Resolution Resolution determines the smallest observable incremental change in pressure. Parts per million with normal resolution ( x full scale pressure) Parts per billion with nano resolution ( x full scale pressure)

17 Repeatability The difference in sensor output when the same pressure value is applied to it consecutively, under the same conditions and in the same direction. Error of Sensor (% fs) fs Applied Pressure

18 Hysteresis The difference in output, at any pressure value within the specified range, when the value is approached first with increasing and then with decreasing pressure. Error of Sensor (%fs) Applied Pressure fs

19 Linearity The closeness of a calibration curve to a straight line. NONLINEARITY Perfect linearity would result with output that lands exactly on a defined line.

20 Typical Accuracy Typical accuracy includes linearity, repeatability, and hysteresis. Typical accuracy of most transducers is better than 0.01% of full scale (each product defined by specification control drawing) Error % full scale Zero M id-scale Full-scale Temperature (deg C) Calibration test profile example

21 Long Term Stability hpa hpa S/N Long-Term Stability S/N Long-Term Stability Median drift rate of units tested over Twenty-one-year test period was hpa ( inhg) per year.

22 Nano-Resolution Technology Advances in counting circuitry and digital signal processing have improved resolution..... Parts-per-billion over an extended pressure spectrum Higher resolution to detect much smaller pressure changes. Increases to 1 part-per-billion (PPB) Tsunami Detection Sea-Floor Subsidence Infrasound Leak-Rate Testing Detecting Earthquakes Atmospheric Disturbances Faster update rates: 11 msec at 1 PPM Flight Test ROV Core Sampling for Enhanced Oil Recovery (EOR) Example: 4 ppb with 100 PSIA transducer.... Measureable change in pressure: PSIA (0.003 Pa, mmh2o) More information on Nano-resolution Technology:

23 Nano vs. Standard Resolution Standard resolution parts per million of full scale ( x f.s.) Nano-resolution parts per billion of full scale ( x f.s.) Surface Waves Detected at 900m Depths 0.2 Hz Microseisms (1mm Pressure Variations) TIDE TREND Effect of nano-resolution at MARS Observatory of the coast of California compared to normal resolution. More information on MARS nano-res experiment: