guided waves ppm encoded system using awg12 cables v2.0
TRANSCRIPT
GUIDED WAVES PPM ENCODED SYSTEM USING AWG12 CABLES
AS COMMUNICATION CHANNEL Gianpiero Trane
Rito Mijarez
Introduction• Guided waves long distance
propagation application:– Structural Health Monitoring
(SHM)– Non-Destructive Testing (NDT)
• SMH communication necessities:– Wireless communications– Harsh environments
• Fixed offshore oilrigs• Downhole oil reservoirs
– Use of existing infrastructure
• This work presents:– Guided wave– Pulse Position Modulation
(PPM)– Multiple-strand American
Wire Gauge (AWG)– Smart PZT based modulator– Real time off-line PZT based
demodulator– Experiments with 4m and
1m multiple strand wire AWG12
Guided waves theory• American Wire Gauge (AWG)
12 cables:– 19 copper wires– Polyvinyl chloride (PVC) insulator
• Analytical solution for the wave propagation does not exist– Inter-wire coupling– Dispersive nature– Multi-mode presence– Mode coupling
Wave propagation
• Dispersion curves were obtained with the commercial software Disperse©.
• Wave propagation in single wires– The so-called Pochammer
frequency equation of a solid, isotropic, homogeneous and traction free cylindrical rod
• Propagation modes:– Longitudinal L(0,m)– Torsional T(0,m)– Flexural F(0,m)
Frequency and signal selection• Guided waves in long range
applications require frequencies under 100 kHz
• For frequency selection on the dispersion curves– Spectrum of the transducer source
(PZT 5-H)
• Surface pressure loadings will excite longitudinal and flexural modes
• Under 300 kHz the number of excited modes increases– Multi-mode presence
• The frequency selected: 60 kHz• The signal generated: tone pulse
pulses
Pulse Position Modulation (PPM)
• Information modulated in the time delay between pulses (TDBP)– Effective in signals power limited rather than band
limited
• Δt = time slot• tr = time reference• ±ε = temporal
position of an acoustic pulse
PPM guided wave system• Active smart piezoelectric
– 9V Battery– Microcontroller– Signal buster– PZT element
• AWG12 cable– Insulator silicone
• Preamplifier• DAQ• LabVIEW based demodulator
PPM symbol codification
• 10 bit frames• Start and stop pulses
– 40 square pulses of 60 kHz (666 µs)• 8 data pulses
– 20 square pulses of 60 kHz (333 µs)• Time slot Δt of 1998 µs (six times bit pulse width)• Quantified values of ±ε of 999 µs (three times bit pulse
width)
PPM demodulation
• Finite Impulse Response (FIR) band pass digital filter (35 kHz – 50 kHz)
• Autocorrelation to increase SNR• Low pass filter tuned to the baud rate
– Smooth out the filtered signal• RMS operation threshold
– Continuous square pulse for each acoustic pulse• Temporal position demodulation of TDBP for each digital bit
Experiment setup an results
Guided waves propagation modes identification
• Dispersion curves 60 kHz: L(0,1) and F(1,1) – L(0,1) vg = 3.3718 m/ms– F(1,1) vg= 1.4760 m/ms
Guided wave symbol PPM identification
• 4BH ( 0 0 1 0 1 1 0 1 )
Conclusions• Novel guided waves PPM system using multiple-wire AWG12
cables as a communication channel has been designed, implemented and evaluated
• The system uses the electrical cable infrastructure as communication channel
• Successful transmission and reception of guided waves encoded PPM information
• Experimental results match with the theoretical Disperse© results• The feasibility of detecting dispersive energy guided wave
packets, provided sufficient SNR, has been proved• Next stage of this work is to carry out automatic real time PPM
demodulation
References