Application of Kalman Filters for the Fault Diagnoses of Aircraft
Application of Adaptive Noise Cancelling Filters to …projects.npl.co.uk/power_energy/docs/1625...
Transcript of Application of Adaptive Noise Cancelling Filters to …projects.npl.co.uk/power_energy/docs/1625...
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Paul Wright & Paul Clarkson
Application of Adaptive Noise Cancelling Filters to
AC Electrical Measurements
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• Noise cancelling
technology has been around for several
decades.
• We are familiar with it in
audio products.
• This talk presents two experiments which
demonstrate the use of adaptive filters to improve
electrical measurements.
Introduction
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Motivation
• Need for on-site measurements at grid installations.
• Existing cabling and transformers not always well configured.
• Measurements subject to noise and “pick-up”.
• Investigate methods to reduce noise on measurements.
• Use DSP techniques such as digital and adaptive filters.
• Paper gives two examples of adaptive noise cancelling filters.
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Experiment 1: Cancelling Magnetically Coupled
Interference in Measurement Circuits
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Source
ADC Ch0
Adaptive
Algorithm
Σ
Φ Interference
ADC Ch1
ADC Ch2
ADC Ch3
Σ
3 Axis Pick Up
Measurement Circuit
Signal + interference
-
+
Filtered
Signal
wk(0)
wk(1)
wk(2)
xk(0)
xk(1)
xk(2)
yk
Software
Interference
estimate
ek
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3-Axis Magnetic Field Pick-up – Made from commercial relays glued together
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3 Axis Pick-up InputsSignal6 Channel DigitizerSampled data of 4 channels
Pick-up
2 Turn Loop to
Couple Noise
Source of Magnetic
Field Noise
Signal Generator
for Sample Clock &
Phase Lock Input
Calibrator,
10mV, 10Hz Signal
Magnetic Interference Pick-up Cancellation Experiment
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Low Signal on
3 Pick-up Channels
Magnetic Noise Source Switched-Off
Signal (calibrator output)
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Magnetic Noise Source Switched-ON
Detected Signal on
3 Pick-up Channels
Signal + Pick-up Noise
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Apply the Signal and the three-axis pick-up channels to the adaptive filter…..
The amount of noise on the signal improves as the filter adapts to the signals
(NB faster response is possible – reduced here to illustrate adaptive activity)
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Filtered Result Using and Least Mean Square Adaptive Filter…
Noisy Signal Error in RMS value from calibrator value: + 0.47%; THD: 9.2 %
Filter Signal Error in RMS value from calibrator value: + 0.01%; THD 0.7 %
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Filtered Result In the Frequency Domain
Signal
at
10 Hz
Pickup
at
50 Hz
Pickup
Harm’cs
Change in 10Hz Signal after filtering: -220 ppm
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Experiment 2: Frequency Beat Noise Cancellation
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Frequency Beat Noise Cancellation
Calibrator
Trans -
Conductance
Amplifier
230V mains,
50Hz ± 0.2Hz
5V
50Hz
5A
50 Hz
Strong Correlation between the
amplifier output and the cosine of
phase of the line voltage as it
varies relative to the calibrator
voltage.
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Calibrator
Trans -
Conductance
Amplifier
I to V
1V, 50Hz ± 0.2Hz
Signal + Noise
ADC Ch0
ADC Ch1
230:1230V mains,
50Hz ± 0.2Hz
5V
50Hz
Noise
Measure
Phase by
DFT
Adaptive
Filter
From
ADC Ch1
From
ADC Ch0
Filtered
Signal
Software
Σ
-
+
5A
50 Hz
1V
50Hz
Beat Noise Cancellation Experiment
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Application of a Recursive Least Squares Adaptive Canceller
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Conclusions
• Adaptive noise cancelling filters are important DSP tools.
• This talk has demonstrated their use in two poorly
configured electrical measurements.
• One wouldn’t chose these solutions in the lab! But in the
field there maybe no choice.
• It is intended this work be used and adapted to specific
field applications as required.
• Further work on optimization metrics for setting up the filters and on uncertainty issues need developments for
specific cases.