VCSO Mechanical

Shock Compensation

Who are we?

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

• VCSO and mechanical vibration

• Analog filter for compensation of 20dB

• Expand compensation to three axes

Project Overview

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

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

VCSO •Nominal frequency of 400MHz

•Embedded Quartz crystal with varactor

•Voltage controlled with linear sensitivity between roughly 1V and 3V

Frequency Matching

Frequency Generator •Allows for precise matching to VCSO

•Controllable down to 10Hz

•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

Phase Frequency Detector

•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

Shock Tower

•ADXL001-500Z

•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

Accelerometer

Data Acquisition Card

Test Setup

Shock Accelerometer

VCSO

Filter

Filter

Signal Generator

Phase Frequency Detector

DAQ PC

•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 1.0-1.1V

.

Frequency Response VSCO

• Maximum Output of the VSCO is approximately

10-12 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.

Problem solved with PFD

• 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

Shocking VCSO by tapping

• 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.

Shocking by Solenoid

•Accelerometer output was too high which exceeds input voltage on VSCO of 5V.

• Output of accelerometer produced oversensitive signals

Problem with Accelerometer

Filtering:

• Software lowpass butterworth filter

Pre-Spring Break Results

Tap Testing:

• EM interference

• Code revised for manual tapping

• Insignificant disturbances

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

Pre-Spring Break Results

Post Spring Break

Vibration Reduction

• Oscillators secured with nylon straps • VCSO’s shimmed internally • Wires taped and organized

New Accelerometers

• Faulty accelerometer: • ADXL001-500 • Only accelerometer in possession before spring break • Output magnitude 5x too large • Saturation at accelerations < 100g • Confirmed with calibrated accelerometer

• New accelerometers: • Also ADXL001-500

• Single axis • 500g • 22kHz bandwidth

• Able to measure the acceleration levels necessary

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) • Fo = Oscillator Frequency (Hz) • m = Frequency Control Curve Slope (Hz/V) • S = Accelerometer Sensitivity (V/g)

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

Accelerometer

Voltage Divider

Non-inverting Summing Amplifier

VCSO

Compensation Circuit

Ghosting

• 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

Compensation On, Sample Rate = 200kHz

Ghosting

Compensation On, Sample Rate = 500kHz

X-Axis Testing

X

Y

Z

X-Axis Testing

Compensation Off

X-Axis Testing

• Actual attenuation ratio not corresponding to calculations yet • Investigate possible ghosting in x-axis compensated result

Compensation On

X-Axis Testing

Y-Axis Testing

X

Y

Z

Y-Axis Testing Ghosting Effect

Y-Axis Testing

• No compensation necessary

Accelerometer Input Grounded (Ghosting Removed)

Y-Axis Testing

Timeline

Budget

Total Cost: $430

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