WO1994008396A1 - Filtrage adaptatif de bruit periodique - Google Patents

Filtrage adaptatif de bruit periodique Download PDF

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Publication number
WO1994008396A1
WO1994008396A1 PCT/AU1993/000510 AU9300510W WO9408396A1 WO 1994008396 A1 WO1994008396 A1 WO 1994008396A1 AU 9300510 W AU9300510 W AU 9300510W WO 9408396 A1 WO9408396 A1 WO 9408396A1
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WO
WIPO (PCT)
Prior art keywords
signal
delay line
noise cancelling
noise
output
Prior art date
Application number
PCT/AU1993/000510
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English (en)
Inventor
Greig William Small
Original Assignee
Commonwealth Scientific And Industrial Research Organisation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Commonwealth Scientific And Industrial Research Organisation filed Critical Commonwealth Scientific And Industrial Research Organisation
Priority to AU51445/93A priority Critical patent/AU5144593A/en
Publication of WO1994008396A1 publication Critical patent/WO1994008396A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/028—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure
    • G01D3/032—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure affecting incoming signal, e.g. by averaging; gating undesired signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/035—Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
    • G01R33/0354—SQUIDS
    • G01R33/0356—SQUIDS with flux feedback

Definitions

  • This invention relates to synchronous noise filtering in systems measuring low level signals in the presence of periodic noise.
  • Low level measurements are frequently subject to interference from periodic noise sources arising from electrical power supplies, rotating machinery, structural resonances, and so on.
  • the a.c. mains power supply may produce an interfering signal which is of a greater amplitude than, or at least a comparable amplitude to, that of the signal to be measured.
  • Comb filters utilising analogue switches operating synchronously with the mains are a satisfactory means of reducing such interference in many situations.
  • the performance of these filters is limited by imperfections in the analog switches, notably leakage in the "off" state, leading to limited rejection of the unwanted signal and generation of significant high frequency noise.
  • USA patent 4344150 describes a digital filter within an operational amplifier for removing coherent noise from a signal.
  • the device refers in particular to the filtering of electrically induced noise from amplifying circuits of an echo analysis system, such as a radar, sonar or seismic echo system.
  • USP 4344150 provides improvements in amplification in environments suffering synchronous noise, it suffers a disadvantage in that, in order for the signal to be extracted faithfully, the signal measurement and processing system preceding the filter is required to transmit the signal and noise undistorted to the filter. If the noise is of larger amplitude than the signal the dynamic range, linearity, and slewing rate of the measurement and processing system may need to be increased beyond what would otherwise be required. In extreme cases the required performance may not be achievable in any practical implementation of the measurement system.
  • the present invention seeks to provide a comb filter technique implemented as a synchronous noise canceller operating at the input of an electrical system.
  • the technique provides a synchronous noise cancelling signal in the same physical energy form as the noise source, the effect of which is to be cancelled from the electrical system.
  • the present invention consists in a noise cancelling system for cancelling periodic noise present at an input of a physical parameter measurement system, wherein the physical parameter measurement system includes an input transducer to convert a measured parameter into a signal representative of the measured parameter and the measurement system has an output signal linearly related to the measured parameter, the noise cancelling system comprising an input arranged to accept the output signal from the measurement system, an accumulator arranged to maintain a continuously updated representation of the periodic noise present at the input of the measurement system by monitoring the output signal and transducer means arranged to synchronously feed a noise cancelling signal back to the input of the measurement system in the form of a parameter signal of the type detected by the measurement system, the noise cancelling signal being a function of the representation of the periodic noise.
  • Preferred embodiments of the invention accumulate the representation of the periodic noise using a delay line or similar storage device having a delay period which is equal to, or a multiple of, the noise period, the input to the delay line being fed a signal from a summing device which is the sum of a weighted value of the output signal from the measurement system and the current delay line output.
  • the noise cancelling output may be derived from the delay line input signal, the delay line output signal or the average of these two signals. It will be recognised, however, that the noise representation may be processed in other ways to derive the cancelling signal without departing from the spirit of the invention.
  • Embodiments of the invention may employ analogue recirculating delay lines, however, in preferred embodiments of the invention the delay line is a device arranged to hold a plurality of samples, such as a charged coupled device, a digital shift register, or other sample storage device, access to which is cycled at a rate corresponding to a sampling period p such that the delay through the delay line is m x p.
  • the measurement system output if an analogue form, is preferably digitised by an analog to digital converter (ADC) before being weighted and added to delay line output.
  • ADC analog to digital converter
  • the noise cancelling signal is preferably converted to an analog signal by a digital to analog converter (DAC) before being fed to the output transducer means.
  • DAC digital to analog converter
  • the delay line is a digital storage device
  • the weighting of the output from the measurement system is achieved by shifting its digital form by n bits to give a weighting of 2 " .
  • the delay line is a random access storage device with addressing controlled by timing circuits and arranged to cyclicly output and update the samples held in the device.
  • the delay line and summing functions are performed by software running in a programme controlled device, such as a microprocessor or personal computer, the input to the programme controlled device being the digital signal from ADC and the output from the programme controlled device being fed to the DAC.
  • Embodiments of the invention effectively cancel interfering periodic noise at the input of an analogue measuring or sensing system and thus reduce dynamic range requirements and ease problems of overload, non-linearity and intermodulation distortion.
  • FIG. 1 is a schematic diagram of a first system embodying the invention
  • Fig. 2 graphically shows the amplitude response for three parameter settings of the system of Fig. 1;
  • Fig. 3 is a schematic diagram of a second system embodying the invention.
  • Fig. 4 graphically shows the amplitude response for three parameter settings of the system of Fig. 3;
  • Fig. 5 is a schematic diagram of a third system embodying the invention
  • Fig. 6 graphically shows the amplitude response for three parameter settings of the system of Fig. 5;
  • Fig. 7 shows a schematic fourth embodiment of the invention
  • Fig. 8 shows a schematic diagram of a fifth embodiment of the invention employing digital processing means
  • FIGs. 9 and 10 show schematic representations of two possible implementations of the embodiment of Figure 8.
  • Figs. 11 and 12 graphically show performance data pertaining to embodiments of the invention.
  • FIG. 1 a schematic diagram of a synchronous noise cancelling system for sensor systems is shown.
  • a linear sensor system 13 provides an analogue electrical output 19 which is proportional to the input physical signal 11.
  • the sensor system may include electronics for various purposes, for example for amplification, filtering and linearisation.
  • the input signal 11 may take any physical form, e.g. ultrasonic, magnetic, vibrational, etc. It comprises the desired signal to be measured plus interfering noise of a periodic nature having period T.
  • the analogue signal 19 passes through an adder 14 and delay line 15, the delay of the delay line being exactly equal to the period T of the noise signal.
  • a reference noise signal 20 and timing circuitry 16 are provided for the purpose of synchronisation.
  • the output of the delay line is recirculated to its input via adder 14.
  • the output of the delay line is also converted into the physical form of the input quantity via a transducer system 17, and added in opposite phase to the input of the sensor system. This addition is represented schematically by the adder 12.
  • the operation of the noise cancelling system is as follows. Periodic noise components at the sensor system output 19 add cumulatively into the recirculating delay line. Signals which are not synchronous with the reference signal 16 average out over time and do not accumulate in the recirculating delay line. Eventually a steady state is reached in which the periodic signal stored in the delay line, when fed back to the sensor input via transducer 17, accurately cancels the periodic noise signal present at the input 11. Under these conditions no further periodic signal is present at 19, and the cancelling signal stored in the recirculating delay line persists without change. Should there be any change in the level, period or waveform of the noise signal, the stored cancelling signal will automatically adapt to preserve cancellation at the system input.
  • Figure 2 shows the amplitude response
  • for three values of the transducer-sensor gain w: (a) w 0.2,
  • the transfer function is that of a notch filter removing components at frequencies equal to or close to multiples of 1/T.
  • the narrowness of the notches is determined by w.
  • Fig. 3 a second embodiment is illustrated in which the noise cancelling signal 18 is derived by weighting the output signal 19 from the measurement or sensing system and adding this to the output of the delay line 15, the summed signal being present at the output of the adder 14.
  • the embodiment of Fig. 3 is similar to that of Fig. 1, however, the resultant transfer function is now given by:-
  • Fig. 4 shows the amplitude response G(f) for the embodiment of Fig. 3, using the same 3 values of w as used to derive the response of Fig. 2.
  • the noise cancelling signal 18 in this case is derived as the average of the signals at the input and output of the delay line. This summation is performed in adder 38.
  • the resultant transfer function is given by:
  • Fig. 6 shows the amplitude response G(f) from the embodiment of Fig. 5 using the same 3 values of w as used to derive the responses of Figs. 2 and 4.
  • the third embodiment provides a system in which the amplitude of the response between the notches is least affected by the weighting factor w.
  • Some sensor systems commonly provide local feedback around the sensor as a means of achieving improved linearity or dynamic range, or for some other purpose. This is the case, for example, with SQUID (superconducting quantum interference device) magnetic flux and field sensors, whose response is a very non-linear (in fact, periodic) function of the input magnetic quantity. Where such local feedback is provided, the design of the noise cancelling system is considerably simplified, as illustrated in Fig. 7.
  • the local feedback consists of the sensor system 13, additional electronics, for example amplifiers and integrators, 22, and the transducer 17 providing a feedback signal added in antiphase at the sensor input 12. It may be shown that a signal added into this local feedback loop at adder 21, traversing the loop in the direction of the arrows, and returning to the output point 19, is subject to a gain close to unity. Thus a nett transducer-sensor gain w may be achieved by means of a signal attenuator 23 having a gain or weighting factor equal to w.
  • the adder 14 and synchronous delay 15 complete the noise canceller. The requirement for an accurately timed unity gain delay can be conveniently met using a digital sampled data system, as shown in Fig. 8.
  • 11 is the input physical signal with periodic noise interference
  • 13 is a sensor system providing an analogue electrical output 19.
  • the analogue signal passes through an optional anti-aliasing low-pass filter 24 to an analogue-to-digital converter (ADC) 25.
  • a digital sampled data representation of the analogue signal is passed to a digital processor 26 implementing the function of a recirculating delay line.
  • the output of the digital processor 26 passes through a digital-to-analogue converter (DAC) 27, optional smoothing low-pass filter 28, and transducer system 17 providing an analogue feedback signal in the same physical form as the original signal 11.
  • the feedback signal is added in antiphase to the input signal as represented by adder 12.
  • Digital clocks 29 synchronised to a reference noise signal 16 determine the sampling and data transfer rates of the ADC, DAC and digital processor. Digital output data are available at 30.
  • y(i) y(i-M) + w d x(i-M) (4)
  • the digital embodiment of Fig. 8 may also be used to obtain results similar to those obtained from the embodiments of Figs. 3 and 5, having transfer functions (2) and (3) respectively. To achieve a transfer function (2) the digital processor would be required to effect the following algorithm:
  • phase shifts associated with the low-pass filters may cause instability in the feedback circuit. This problem can be overcome in some cases by introducing lead compensation in the digital algorithm. If the phase shifts are exactly or nearly equivalent to a delay of m sampling periods, or mT/M seconds, alteration of the algorithm (4) as follows may be advantageous:
  • y(i) y(i-M+m) + w d x(i-M+m)
  • This algorithm yields a transfer function differing negligibly in performance from that of (1) .
  • frequency components higher than the filter cutoff frequency can be trapped in the digital recirculating delay line.
  • Such high frequency components can be generated by overload conditions, for example. In the absence of high frequency feedback such components - 1 .1 -
  • Figs. 9 and 10 show schematically two possible implementations of the digital processor.
  • the weighting factor w is achieved by means of a digital shift of the input sampled data I entering the digital adder A.
  • Implementation of algorithms (4) and (5) is effected by a choice of timing at the output while algorithm (6) requires some additional hardware.
  • the delay comprises a random access memory (RAM) M and an address counter C which is synchronised to the reference input signal R by means of a phase-locked loop. This type of circuit is capable of high accuracy.
  • RAM random access memory
  • C address counter
  • FIG. 9 is for a filter designed to remove noise at mains frequency (50 Hz) and its harmonics from biomagnetic ' signals. Such noise may exceed the wanted signal by 2 orders of magnitude.
  • the input and output samples have 16-bit accuracy and the adding circuitry and RAM are each 24-bits wide. An 8-bit shift gives a weighting factor
  • Fig. 10 shows schematically a software implementation of the digital processor using a microprocessor 36 and associated random access memory (RAM) 37.
  • Input data 33 from the ADC is processed in accordance with one of the algorithms (4), (5) or (6) using the RAM 37 to provide a delay, and output data 35 is passed to the DAC.
  • the microprocessor is timed by clock signal 34 which may or may not be phase-locked to the noise reference signal. If the clock signal is phase-locked to the noise, timing of the ADC and the DAC may be invested in the microprocessor itself. If the microprocessor clock is asynchronous, a separate phase-locked timing signal will be required to pace the microprocessor and to synchronise the ADC and DAC.
  • a microprocessor-based mains (50 Hz) noise canceller has been built for a SQUID magnetometer system. This system is designed for detection of very weak magnetic fields, for example the biomagnetic fields of the human heart, brain etc. Typically in the operation of such a system, magnetic fields due to mains currents in the environment will be several orders of magnitude larger than the wanted signal.
  • the SQUID system is operated with its own local feedback forming a so-called "flux-locked loop".
  • the mains canceller and SQUID electronics may be represented schematically as shown in Fig. 7.
  • Fig. 11 and 12 illustrate the performance of this system.
  • Fig. 11 shows a frequency spectrum of the system output 19 with the mains canceller switched off. The peaks seen are all interference components at the mains frequency 50 Hz and its harmonics.
  • Fig. 12 shows a frequency spectrum of the system output to the same scale as Fig. 11 with the mains canceller, having equation (1) as its transfer function, in operation.
  • the 50 Hz component has been reduced in amplitude by approximately 60 dB (1000 times) and the harmonics have been reduced to a magnitude which is too small to be displayed on the scale of the figure.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Indication And Recording Devices For Special Purposes And Tariff Metering Devices (AREA)

Abstract

Système de suppression de bruit pour un système de mesure (13) paramétrique, consistant à utiliser une ligne à retard (15) pour mémoriser une représentation du bruit périodique en cours de suppression. Le retard de la ligne à retard est un multiple de la période du bruit, un circuit de synchronisation (16) effectuant la synchronisation. Sa représentation est continuellement mise à jour par l'addition de la sortie de la ligne à retard et la sortie pondérée du système de mesure (13) dans l'additionneur (14), et par l'introduction de la somme dans l'entrée de la ligne à retard. Des signaux qui ne sont pas synchrones par rapport au signal de référence (20) s'équilibrent en moyenne avec le temps et ne s'accumulent pas dans la ligne à retard (15) circulant à nouveau (15). La sortie (18) de la ligne à retard (ou une fonction de cette sortie) est introduite dans un transducteur (17) qui convertit ce signal en un signal du même type ou de même énergie, tel que mesuré par le système de mesure (13), de sorte que le signal de suppression est appliqué en opposition de phase par rapport à l'entrée du système de mesure (13) tel que représenté par le point de totalisation (12).
PCT/AU1993/000510 1992-10-05 1993-10-01 Filtrage adaptatif de bruit periodique WO1994008396A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU51445/93A AU5144593A (en) 1992-10-05 1993-10-01 Adaptive filtering of periodic noise

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPL507492 1992-10-05
AUPL5074 1992-10-05

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WO1994008396A1 true WO1994008396A1 (fr) 1994-04-14

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999050679A3 (fr) * 1998-03-30 1999-12-16 3Com Corp Estimateur de frequence faible complexite, suppression d'interferences, et dispositif correspondant
EP1130831A1 (fr) * 1999-12-16 2001-09-05 Nokia Mobile Phones Ltd. Méthode et filtre pour la sépareration de signaux périodiques
WO2020110253A1 (fr) * 2018-11-29 2020-06-04 理化工業株式会社 Dispositif et procédé d'élimination de bruit d'onde sinusoïdale
WO2022062599A1 (fr) * 2020-09-25 2022-03-31 大唐恩智浦半导体（徐州）有限公司 Circuit de mesure d'impédance de batterie

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4232381A (en) * 1979-06-08 1980-11-04 Northrop Corporation Noise cancellation using tracking filter
US4878188A (en) * 1988-08-30 1989-10-31 Noise Cancellation Tech Selective active cancellation system for repetitive phenomena
GB2222053A (en) * 1988-08-17 1990-02-21 Topexpress Ltd Signal processing means for sensing a periodic signal in the presence of another interfering periodic noise
US5029218A (en) * 1988-09-30 1991-07-02 Kabushiki Kaisha Toshiba Noise cancellor
US5138664A (en) * 1989-03-25 1992-08-11 Sony Corporation Noise reducing device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4232381A (en) * 1979-06-08 1980-11-04 Northrop Corporation Noise cancellation using tracking filter
GB2222053A (en) * 1988-08-17 1990-02-21 Topexpress Ltd Signal processing means for sensing a periodic signal in the presence of another interfering periodic noise
US4878188A (en) * 1988-08-30 1989-10-31 Noise Cancellation Tech Selective active cancellation system for repetitive phenomena
US5029218A (en) * 1988-09-30 1991-07-02 Kabushiki Kaisha Toshiba Noise cancellor
US5138664A (en) * 1989-03-25 1992-08-11 Sony Corporation Noise reducing device

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999050679A3 (fr) * 1998-03-30 1999-12-16 3Com Corp Estimateur de frequence faible complexite, suppression d'interferences, et dispositif correspondant
US6498820B1 (en) 1998-03-30 2002-12-24 3Com Corporation Low complexity frequency estimator and interference cancellation method and device
EP1130831A1 (fr) * 1999-12-16 2001-09-05 Nokia Mobile Phones Ltd. Méthode et filtre pour la sépareration de signaux périodiques
US6847689B1 (en) 1999-12-16 2005-01-25 Nokia Mobile Phones Ltd. Method for distinguishing signals from one another, and filter
WO2020110253A1 (fr) * 2018-11-29 2020-06-04 理化工業株式会社 Dispositif et procédé d'élimination de bruit d'onde sinusoïdale
JPWO2020110253A1 (ja) * 2018-11-29 2021-09-02 理化工業株式会社 正弦波ノイズ除去装置及び正弦波ノイズ除去方法
JP7109727B2 (ja) 2018-11-29 2022-08-01 理化工業株式会社 正弦波ノイズ除去装置及び正弦波ノイズ除去方法
WO2022062599A1 (fr) * 2020-09-25 2022-03-31 大唐恩智浦半导体（徐州）有限公司 Circuit de mesure d'impédance de batterie

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