VCSO Mechanical Shock Compensation

Transcription

1 VCSO Mechanical Shock Compensation

2 Who are we? Team members: Max Madore Joseph Hiltz-Maher Shaun Hew Shalin Shah Advisor: Helena Silva Phonon contact: Scott Kraft

3 Project Overview VCSO and mechanical vibration Analog filter for compensation of 20dB Expand compensation to three axes

4 Original Goals Measure Instantaneous Frequency shifts and compare with accelerometer voltage output Design Compensation circuit based on frequency/voltage characteristics Test in and implement in 3 axis to determine the unique responses of each

5 Previous Work Last Year: Creation of Shock Tower for repeatable tests Comparison of two identical VCSOs Measurement Using Oscilloscope Problems: Unreliable Data Mismatched VCSO frequencies

6 Frequency Matching VCSO Nominal frequency of 400MHz Embedded Quartz crystal with varactor Voltage controlled with linear sensitivity between roughly 1V and 3V Frequency Generator Allows for precise matching to VCSO Controllable down to 10Hz

7 Phase Frequency Detector 2 inputs (Generator and VCSO) Output fed to operational amplifier for hardware filtering of noise and amplification for display Matched frequencies result in DC voltage

8 Shock Tower Product of previous work, controlled by 24 V source with intensity controlled by duration of pulse (typically 1.5ms) Foam Coating provides mechanical damping to reduce aftershock effects such as ringing Connected to DAQ which allows MATLAB program to shock during data collection period

9 Accelerometer ADXL Z Mounted to VCSO directly, responds synchronously with VCSO to feedback attenuated voltage. Output of Accelerometer was measured at 2.43V, changes with sensitivity of +3.3mV/G Fall semester we looked at raw data Spring semester involved filtering and attenuation for compensation

10 Data Acquisition Card

11 Test Setup Shock Accelerometer Filter Signal Generator Phase Frequency Detector VCSO Filter DAQ PC

12 Frequency Response VSCO The Control pin bias voltage ranges from 0-5 volts. Linearity of the frequency response was seen between 0-2 volts. Changes in frequency in linear region was 1.6kHz under standard operating region of V.

13 Problem solved with PFD Maximum Output of the VSCO is approximately dbm. Maximum input of phase frequency detector is 13 dbm. Attenuator was inserted in line with VSCO to reduce input voltage and eliminate noise. Improve data acquisition and protect the integrity of the component.

14 Shocking VCSO by tapping 3 finger tapping on VCSO appears to knock output signal out of phase Response remains at that phase until the other shock before it goes even further out of phase. Total phase shift represent the sum of the three individual shocks

15 Shocking by Solenoid Shocking by solenoid did not produce consistent data as finger tapping after repeat trials Results were inconsistent because more vibrations occur in SAW and possibly electromagnetic effect.

16 Problem with Accelerometer Accelerometer output was too high which exceeds input voltage on VSCO of 5V. Output of accelerometer produced oversensitive signals

17 Pre-Spring Break Results Filtering: Software lowpass butterworth filter

18 Pre-Spring Break Results Tap Testing: EM interference Code revised for manual tapping Insignificant disturbances

19 Pre-Spring Break Results Differential Op-Amp Low-noise DAQ inputs changed to single-ended Hardware + software filtering Wider voltage range O-scope test point

20 Post Spring Break

21 Vibration Reduction Oscillators secured with nylon straps VCSO s shimmed internally Wires taped and organized

22 New Accelerometers Faulty accelerometer: ADXL Only accelerometer in possession before spring break Output magnitude 5x too large Saturation at accelerations < 100g Confirmed with calibrated accelerometer New accelerometers: Also ADXL Single axis 500g 22kHz bandwidth Able to measure the acceleration levels necessary

23 Acceleration Sensitivity New accelerometers to move forward Most important task to achieving compensation Data processing and noise filtering have paid off Test each axis and superimpose compensations Accelerometer Output Attenuation Equation: Γ = Acceleration Sensitivity (1/g) F o = Oscillator Frequency (Hz) m = Frequency Control Curve Slope (Hz/V) S = Accelerometer Sensitivity (V/g)

24 Compensation Circuit Potentiometers for fine tuning attenuation level Accommodates 3 axes Operates around 1V (most linear region on the VCSO control input) Switches to toggle compensation Overall gain determined by VCSO acceleration sensitivity Voltage Divider VCSO Accelerometer Non-inverting Summing Amplifier

25 Compensation Circuit

26 Inherent with all scanning data acquisition units Capacitor voltage does not have time to change to the proper level Causing data corruption Attempted Remedies Decrease sample rate Increase Input Switching Time Still an issue as will be shown Ghosting

27 Ghosting Compensation On, Sample Rate = 200kHz

28 Ghosting Compensation On, Sample Rate = 500kHz

29 X-Axis Testing X Z Y

30 X-Axis Testing Compensation Off

31 X-Axis Testing Compensation On Actual attenuation ratio not corresponding to calculations yet Investigate possible ghosting in x-axis compensated result

32 X-Axis Testing

33 Y-Axis Testing X Z Y

34 Y-Axis Testing Ghosting Effect

35 Y-Axis Testing Accelerometer Input Grounded (Ghosting Removed) No compensation necessary

36 Y-Axis Testing

37 Timeline

38 Total Cost: $430 Budget Given Materials: National Instruments X series USB-6353 Data Acquisition Card NI-DAQmx software MATLAB 2009 Giga-tronics 6060B Signal Generator Phonon 400MHz VCSOs B&K 9130 triple output power supply Phase Frequency Detectors 2x Shock Tower Passive Circuit Components Materials to Purchase: Accelerometers $250 TLC2262CP op-amps $5 Nylon Straps $25 Phase Frequency Detectors $150