Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
  • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters

Definitions

• Device and method for ultrasonic fluid flow measurement comprising a Sigma-Delta bandpass analog digital converter
• the present invention relates to a device and a method for ultrasonic measurement of fluid flow rate comprising an analog digital converter Sigma-Delta bandpass.
• An ultrasonic fluid meter includes two ultrasonic transducers which define a measurement path between them. Each transducer is used alternately in transmission mode and in reception mode.
• the principle of acoustic measurement of a fluid flow consists in determining the speed of the flowing fluid, by calculating the propagation times of the acoustic signal between the two transducers in the upstream and downstream directions of the flow of the fluid.
• the time of flight of the ultrasonic wave is calculated by means of a time measurement and / or a phase measurement.
• Fluid meters using the principle of ultrasonic flow measurement are completely autonomous, they do not depend on the electricity distribution network. These meters which integrate an increasingly sophisticated electronics, allowing the improvement of their metrological performances, offering consumers various information on consumption and allowing the remote reading of consumption and / or electronic toll collection of invoices, are powered by a battery of which longevity is limited in time and whose autonomy strongly depends on the architecture of the electronic circuits used.
• the architecture of a complete chain for acquiring and processing the measurements of an ultrasonic fluid meter according to the prior art is shown in FIG. 1.
• Such an ultrasonic fluid meter comprises two transducers 1 and 2 arranged in a cavity 3 in which a fluid flows.
• the two transducers are connected to a switching unit 4 so that when the first transducer 1 operates in transmission mode, the second transducer 2 operates in reception mode and vice versa.
• the transducer 2 receives said ultrasonic wave after a time characteristic of the speed of the flow and transforms the ultrasonic wave into a signal analog.
• the switching unit 4 is connected to a programmable gain amplifier 6 which provides full scale filtering and amplification of the analog signal intended for the analog to digital converter 8.
• the programmable gain amplifier 6 is connected to an 8 bit analog digital converter sampling frequency 320 kHz.
• the analog to digital converter 8 provides a digital signal necessary for determining the propagation times of the acoustic signal UW between the two transducers 1 and 2.
• the analog to digital converter 8 is connected to a RAM memory 10 of 2x256 bytes which stores the signals, waiting for their processing by the microcontroller 12.
• the microcontroller 12, which implements the processing of the stored signals and calculates the results relating to the bit rate, is connected to a set of different units 13 allowing for example the display, communication with the outside world, management of energy saving modes, storage of operating data.
• the microcontroller 12 is also connected to a sequencer 14.
• the sequencer 14 controls the firing sequences of the ultrasonic waves by the transducers 1 and 2 via a transmission buffer 16 comprising a digital analog converter and an amplifier, as well as the sampling carried out by the analog-to-digital converter 8 and the memorization of the signals by the memory 10.
• a battery (not shown) conventionally supplies the energy necessary for the operation of the devices through a set of connections (not shown) different components.
• the combination of the programmable gain amplifier and the analog-to-digital converter corresponds to a complex architecture, which consumes 30 to 40% of the needs of all the electronics of the meter.
• an analog-digital conversion device introduces quantization noise during digitization which degrades the accuracy of the measurements.
• Such a so-called conventional analog-to-digital converter converts a signal with the same resolution, the frequency of which can vary from continuous to half the sampling frequency.
• Sigma-Delta conversion is a principle of coding information on a small number of bits, sampled at high frequency in order to further increase the resolution.
• This conversion principle is based on an operating principle similar to that of the Delta conversion, which consists in coding the difference between the amplitude of a sample and the amplitude of the previous sample.
• the Sigma-Delta converter will output a binary train (alternating "0" and "1") consisting of a periodic regime whose fundamental period is proportional at the input voltage.
• the converter reacts like a voltage-frequency converter which is synchronized with a sampling clock.
• a digital filter known as a decimator filter placed at the output of the Sigma-Delta converter converts the signal coded on a small number of bits at high frequency into a signal of lower flow rate but coded on a greater number of bits.
• the principle of Sigma-Delta conversion can be extended to the conversion of signals centered around a particular frequency.
• the converter used is then a Sigma-Delta bandpass converter.
• the converter filter which was previously an integrator is replaced by a resonator.
• the digital filter at the output of the Sigma-Delta converter is no longer a decimator but a bandpass filter followed by a demodulator. It is known in the field of telecommunications and in particular of digital radio to use analog to digital converters
• An object of the present invention aims to remedy the drawbacks of the acquisition and processing chain of the measurements of the ultrasonic fluid meters of the prior art and in particular to reduce the complexity and the consumption of the digitization device.
• Another object of the present invention is, in particular, to reduce the quantization noise during the digitization of the analog signal and to increase the performance of the converter.
• the invention relates to an ultrasonic device for measuring a fluid flow rate comprising:
• transducer transmitter being intended to emit an ultrasonic wave in the fluid
• receiving transducer being intended to transform said ultrasonic wave into an analog signal
• said analog signal processing means comprise a Sigma-Delta bandpass converter comprising:
• a digital analog converter forming a feedback loop, connecting the output of the analog digital converter to the input of said filter.
• the transducers used in the device according to the invention are piezoelectric type transducers having a band-pass transfer function limited in frequency, for example 40 kHz ⁇ 1.5 kHz. Since the useful information is found only in this frequency band, it is advantageous to amplify and convert only the signals located in this frequency band.
• the device for ultrasonic measurement of a fluid flow rate is characterized in that the bandpass loop filter of the Sigma-Delta bandpass converter is constituted by the receiver transducer.
• the transducer alternately plays the role of receiver but also of band pass filter in the loop of the Sigma-Delta band pass converter, which makes it possible to optimize the analog-to-digital conversion in the interesting frequency band.
• the present invention also relates to an ultrasonic fluid flow measurement method comprising a Sigma-Delta bandpass analog digital converter.
• the method of ultrasonic measurement of a fluid flow rate between two transducers according to which the fluid flow rate is determined by means of a measurement of propagation time and / or a measurement of acoustic phase shifts of the acoustic signals propagating in the fluid flowing between two transducers in the upstream and downstream directions of the fluid flow comprises: - an emission step consisting in emitting an acoustic signal. UW in the fluid whose flow is to be determined, an acoustic-analog conversion step consisting in transforming said acoustic signal UW into an analog signal S2,
• the analog-digital conversion step of order N comprises: an estimation step consisting in determining an estimate of the quantization error q N _, committed during the step of order Nl digitization, for the order of digitization step N. a subtraction step consisting in subtracting the estimate of the quantization error q N. , from the analog signal S2,
• a digitization step consisting in digitizing the analog signal S2 subtracted from the estimate of the quantization error q N .
• the acoustic-analog conversion step consisting in transforming said acoustic signal UW into an analog signal S2 comprises: a step of converting the acoustic signal UW into an analog signal SI, and - a step of truncating the analog signal SI into a analog signal S2.
• the step of determining the acoustic phase shifts and the propagation times consisting in determining the acoustic phase shifts and the propagation times from the digitized signal S3 comprises: - a step of filtering the digital signal S3 into a filtered digital signal S4, and a step of calculating the acoustic phase shifts and the propagation times from the filtered digital signal S4.
• the estimation step consisting in determining an estimate of the quantization error is implemented by the receiver transducer.
• FIG. 2.a is a temporal representation of the signal S 1
• FIG. 2.b is a spectral representation of the signal S 1
• FIG. 2.c is a temporal representation of the signal S2
• FIG. 2.d is a spectral representation of the signal S2
• FIG. 2.e is a temporal representation of the signal S3,
• FIG. 4 represents the timing diagrams of the switch control signals when the transducer 1 is transmitting and the transducer 2 is receiving, for the device according to figure 3
• figure 5 represents the timing diagrams of the switch control signals when the transducer 1 is receiver and the transducer 2 is transmitter, for the device according to figure 3
• - figure 6 represents the different stages of the process according to the invention
• FIG. 7 represents an alternative embodiment of the device of FIG. 3.
• FIG. 2 represents the diagram of the acquisition chain of an ultrasonic fluid meter and more particularly the analog to digital conversion chain according to the invention.
• the rest of the measurement acquisition and processing chain is identical to that shown in Figure 1 and is no longer shown in Figure 2.
• a battery (not shown) conventionally provides through a set of connections (not shown) the energy necessary for the operation of the various components.
• the ultrasonic wave UW from which the time and phase measurements are made is a narrow band signal whose frequency is centered on the so-called transducer emission frequency, for example 40 kHz.
• This ultrasonic wave UW will give rise, by direct piezoelectric effect, to an analog signal SI at the terminals of the receiver transducer.
• the analog signal SI the variations of which as a function of time are shown in FIG. 2.a is a signal centered on this resonant frequency of the transmitting transducer, as shown in FIG. 2.b.
• the analog signal S 1 from the receiver transducer 2 is amplified by the amplifier 20 connected to the output of the receiver transducer 2 via the switching unit 4.
• the analog signal SI undergoes a time truncation, which allows d '' eliminate parasitic echoes from successive reflections of the ultrasonic wave in the cavity.
• the temporal and spectral shape of the analog signal S2 having undergone truncation is shown in FIG. 2.c and 2.d respectively.
• Amplifier 20 is connected to a Sigma-Delta bandpass converter 21.
• the Sigma-Delta converter comprises a bandpass loop filter 22 whose input is connected to the output of amplifier 20, an analog to digital converter 24 whose the input is connected to the output of said bandpass loop filter, and a digital analog converter 26 disposed in the feedback loop connecting the output of analog digital converter 24 to the input of said loop filter 22.
• the analog to digital converter 24 is a 1 bit analog to digital converter, for example a comparator, and the analog to digital converter 26 is a 1 bit analog to digital converter.
• the analog signal S2 has been transformed into a digital signal S3 whose temporal shape represented in FIG. 2.e corresponds to a binary train.
• the signal S3 of FIG. 2.e is a signal coded on 1 bit at a high sampling frequency of, for example, 320 kHz. It can be seen in FIG. 2.f that the noise spectrum is distinct from the spectrum of the useful signal, which will make it possible to effectively eliminate the parasitic noise by filtering.
• the output of the Sigma-Delta bandpass analog converter 21 is connected to a bandpass filter 28.
• the role of this filter is the rejection of noise outside the useful band for better synchronous detection at the output of the converter 21 but also the coding of the signal on a greater number of bits at a frequency lower than the sampling frequency. .
• the resulting signal is shown in Figure 2.g and its spectral shape in Figure 2.h.
• the bandpass filter 28 is connected to the RAM memory 10.
• the Sigma-Delta analog band-to-digital converter provides a very high signal-to-noise ratio in a frequency band configurable by the architecture of the converter used. On the other hand, the conversion noise is very important outside this frequency band.
• an analog digital converter Sigma-Delta band pass allows to optimize the analog digital conversion in the interesting emission band of the transducer.
• the signal is converted to a single bit, which considerably simplifies the digital processing which follows the Sigma-Delta band pass analog to digital converter.
• This simplification of the analog part of the analog to digital converter in particular by the fact that the analog digital converter Sigma-Delta band pass no longer requires the use of a programmable gain amplifier, makes it possible to reduce considerably, up to 40 %, the total consumption of the electronics of the ultrasonic fluid meter.
• significantly improved metrological performance results from the use of the Sigma-Delta bandpass analog digital converter in the acquisition and processing chain of the ultrasonic fluid meter measurements.
• FIG. 3 represents the diagram of the acquisition chain of the device for ultrasonic measurement of a fluid flow rate according to the preferred embodiment of the invention.
• the preferred embodiment of the invention consists in replacing the band pass filter 22 of the device in accordance with FIG. 2, by the receiver transducer itself.
• the transducer is used as a receiving transducer, but also as a filter in the feedback loop of the Sigma-Delta converter.
• the feedback takes place physically via a mechanical quantity at the level of the receiving transducer.
• the transducers 1, 2 advantageously consist of a piezoelectric plate comprising two opposite surfaces, said surfaces being metallized to be connected to the connection terminals of the transducer.
• One of the two terminals of each of the transducers 1 and 2 is permanently connected to ground 35.
• the other terminal of the transducer 1 or 2 is connected to switches 31, 32, 33, or to switches 41, 42, 43 respectively.
• the switches 31, 32, 33 and 41, 42, 43 are produced by two separate multiplexers.
• the transducers 1 or 2 can be connected to ground 35 via the switch 32 or 42 respectively.
• the transducer 1 is connected to an amplifier 20 via the switch 33.
• the output of said amplifier 20 is connected to an analog to digital converter 24.
• this analog to digital converter is a lbit analog to digital converter, for example a comparator .
• a digital analog converter 26 is arranged in the feedback loop associated with the transducer 1, the input of said analog digital converter 26 being connected to the output of analog digital converter 24 by means of switch 61.
• the output of said digital converter analog 26 being connected to transducer 1 via switch 31.
• analog digital converter 26 is a 1 bit digital analog converter.
• the transducer 2 is connected to the amplifier 20 via the switch 43.
• a digital analog converter 46 is disposed in the feedback loop associated with the transducer 2, the input of said analog digital converter 46 being connected to the output of analog digital converter 24 by means of switch 51.
• the output of said digital converter analog 46 being connected to transducer 2 by means of switch 41.
• analog digital converter 46 is a 1 bit digital analog converter. The transducer 2 is thus disposed in the feedback loop when the switch 51 and when the switches 41 and 43 are closed successively.
• At least one additional purely electric bandpass filter 110 is connected in series in a conventional manner between the amplifier 20 and the analog to digital converter 24.
• the role of this additional filter is to improve the performance of the Sigma-Delta converter.
• the output of the analog-to-digital converter 24 is connected to the input of a filter 28.
• the output of the filter 28 is connected to a RAM memory 10.
• the RAM memory 10 is connected to a microcontroller 12.
• the microcontroller 12 is connected via the switch 62 or 52 to the digital analog converter 26 or
• a battery (not shown) conventionally provides through a set of connections (not shown) the energy necessary for the operation of the various components.
• FIG. 3 The operation of the device of FIG. 3 will now be described, firstly with reference to FIG. 4 for the emission of an ultrasonic wave from the transducer 1 to 2, and then with reference to FIG. 5 for the emission of an ultrasonic wave from the 2 to 1 transducer.
• the state of the switches 51, 52; 61, 62; 31, 32, 33; 41, 42, 43 is represented as a function of time, the state "1" or "0" corresponding to a closed or open switch respectively.
• the opening and closing of all the switches are conventionally controlled by the microcontroller.
• the microcontroller is connected to the switches via appropriate wiring (not shown).
• the signal Se corresponds to the signal generated by the microcontroller 12 to excite the transmitter transducer.
• the excitation signal Se is a square signal formed for example of 8 periods at a frequency of 40 kHz and whose amplitude at the output of the digital analog converter 26 or 46 is, for example, 200 raV peak to peak.
• the acquisition of the ultrasonic signal having passed through the cavity lasts approximately 800 ⁇ s and begins approximately 400 ⁇ s after the start of the excitation of the transmitter transducer by the signal Se, this duration corresponding to the time of flight between the transmitter transducer and the receiver transducer.
• the square signals controlling the opening and closing of the switches concerned during the acquisition phase have a frequency of, for example, 320 kHz. It should be noted that the scale of the timing diagrams in Figures 4 and 5 for switches 41, 42, 43 or 31, 32, 33 during the acquisition phase is not the same as for the other switches and for the signal Se.
• the microcontroller 12 controls a sequence of emission of an ultrasonic wave by generating a square signal Se.
• the switches 62 and 31 are closed, the square signal from the microcontroller is transformed into an analog signal which will excite the transducer 1 at its resonant frequency.
• the voltage applied to the terminals of the transducer 1 creates a force by reverse piezoelectric effect, at the origin of an ultrasonic wave UW1-2 which propagates in the fluid flow towards the transducer 2.
• the switch 51 can already be closed during the transmission phase.
• all of the other switches 52; 61; 32, 33; 41, 42, 43 are open.
• the switches 52; 61; 32, 33 remain open and the switch 51 is closed.
• the position of the switches 62, 31 is indifferent, they can for example be kept closed.
• the switches 41, 42, 43 are successively closed and open at a frequency of, for example, 320 kHz so that when a switch is closed for a period equivalent to 1/3 of a period, the other two are open.
• Each period with a duration of 3.125 ⁇ s comprises three successive phases, a writing phase when the switch 41 is closed, a stabilization phase when the switch 42 is closed, and a reading phase when the switch 43 is closed.
• the 1-bit analog-to-digital converter 24 outputs a high voltage level corresponding to a logic "1” if its input is subjected to an input voltage greater than a threshold voltage in absolute value.
• the analog-digital converter 24 supplies at output a low voltage level corresponding to a logic "0" if its input is subjected to an input voltage lower than the threshold voltage in absolute value.
• Comparator 46 is an inverter digital-to-analog converter which outputs a positive reference voltage + Nref if its input is at "0", and a negative reference voltage -Vref if its input is at "1".
• the output of the analog digital converter 24 is randomly in a "1" or "0" state. Take for example the case where the output is in a state "1”, the voltage applied by the comparator to the receiver transducer 2 during the writing phase by the closing of the switch 41 will be + Vref.
• the switch 42 is closed during the stabilization phase, the two terminals of the receiver transducer 2 are then connected to ground 35.
• the transducer constituted by a piezoelectric plate being a resonator, the fact of subjecting it at a voltage + Vref during the writing phase and then at a zero voltage during the stabilization phase, will cause the receiver transducer to be forced into oscillation.
• the position of the piezoelectric blade during its oscillation will then be determined during the reading phase by means of the closing of the switch 43.
• the acquisition phase begins shortly before the arrival of the signal ultrasonic UW1-2 at the level of the receiving transducer 2, so that a stationary oscillation regime is established at the level of the receiving transducer 2. This stationary oscillation regime will give rise to a binary train, alternating states "0" and "1" in the loop of the Sigma-Delta converter.
• This binary train makes it possible to maintain the stationary regime of oscillation of the transducer by means of looping via the digital analog converter 46.
• the integration of the receiving transducer in the loop of the Sigma-Delta converter creates a servo-control, the train binary keeping the piezoelectric blade stationary on average around its equilibrium position.
• the measurement of the ultrasonic wave UW1-2 will be carried out by detection of the fluctuations of this regime established during the arrival of the ultrasonic wave UW1-2 at the level of the receiver transducer 2.
• the oscillation will be the sum of the displacement that is forced during the writing phase and the disturbance due to the ultrasonic signal reaching the receiving transducer.
• the binary train will thus be modified to cancel the effects of this disturbance in order to enslave the piezoelectric plate thanks to the electrical feedback so that it remains stationary on average around its equilibrium position.
• the receiving transducer is a resonator, it plays the role of a memory in the sense that the longer the acquisition phase, the more the oscillation will be modified by the sum of the disturbances and the more the converter will be able to detect a small signal.
• the voltage across the transducer is based on the principle of superposition, the sum of the contribution from the ultrasonic wave and the contribution from the electrical feedback.
• the operation of the device is completely similar with regard to the emission of an ultrasonic wave UW2-1 from the transmitter transducer 2 to the receiver transducer 1. Reference may be made to FIG. 5 for the operation of all of the switches in the case of the acquisition of an ultrasonic wave UW2-1.
• the device according to the invention has a direct digital output, which completely replaces the conventional acquisition chain, while considerably simplifying it.
• the device according to the invention makes it possible to eliminate the quantization noise from the bandwidth of the signal.
• High precision can be obtained with a device according to the invention, without a complex implementation because a simple comparator can make it possible to achieve, after filtering at the output of the Sigma-Delta converter, a resolution greater than 16 bits in the passband. of the signal.
• the device according to the invention no longer requires the use of a programmable gain amplifier to obtain a full-scale signal for the analog-to-digital converter, which has the consequence of reducing the complexity and the energy consumption of the conversion.
• FIG. 6 represents the various stages of the ultrasonic measurement method of a fluid flow rate according to the invention.
• the fluid flow rate is advantageously determined by combining both a propagation time measurement and / or a measurement of the acoustic phase shifts of the signals. acoustic propagating in the fluid flowing between the two transducers in the upstream and downstream directions of the fluid flow.
• the first step 90 of the ultrasonic measurement process of the fluid flow consists in emitting an acoustic signal UW in the fluid whose flow is to be determined, for example in the upstream direction.
• the acoustic signal UW is transformed into an analog signal SI during the acoustic-analog conversion step 92, via a receiver transducer.
• the shape of the signal SI is shown in Figure 2. a.
• the signal SI is temporally truncated during a truncation step 94. This truncation is carried out practically by controlling the start and stop signal acquisition via switches.
• the analog signal S2 resulting from this time truncation is shown in Figure 2.c.
• the analog signal S2 is then transformed into a digital signal S3 during an analog-to-digital conversion step 95 via processing means 21.
• This analog-to-digital conversion step 95 uses the conversion principle
• the digital signal S3 represented in FIG. 2.e is coded on 1 bit with a sampling frequency of 320 kHz.
• the Sigma-Delta converter makes it possible to determine an estimate of the conversion error q.
• this estimate of the conversion error q will be subtracted from the analog signal S2 to be digitized, during a subtraction step 99, so that the Sigma-Delta converter refines its estimate of the error of digitization q as successive conversions.
• the Sigma-Delta converter subtracts an estimate of the quantization error q N.
• the analog signal subtracted from the estimate of the quantization error S2-q N _, is then digitized during the digitization step 96.
• the analog signal S2 subtracts from the estimate of the quantization error q N _, will give rise to a determination of an estimate of the quantization error q N committed during the digitization step 96 of order N. This estimate will be used to improve the digitization next of order N + l.
• the digital signal S3 at the output of the Sigma-Delta converter is a signal coded on 1 bit at high frequency.
• the step of converting the acoustic signal UW into an analog signal SI, and the step of determining an estimate of the quantization error q committed by the analog to digital converter are implemented successively by means of the transducer used both as a receiver and then as a bandpass filter in the Sigma-Delta converter.
• the signal S3 is converted into a lower bit rate signal but coded on a greater number of bits by means of a digital filter.
• the signal S4 resulting from this filtering step 100 is represented in the figure
• the acoustic phase shifts and the propagation times are determined from the digitized signal S4 during the determination step 102.
• the flow rate can be determined from propagation time measurements and / or measurements of the acoustic phase shifts of the acoustic signals propagating in the fluid flowing between the two transducers in the upstream and downstream directions of the flow of the fluid.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Measuring Volume Flow (AREA)
• Compression, Expansion, Code Conversion, And Decoders (AREA)

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• 1998
  • 1998-12-29 FR FR9816608A patent/FR2787880B1/fr not_active Expired - Fee Related
• 1999
  • 1999-12-22 EP EP99961156A patent/EP1163494A1/de not_active Withdrawn
  • 1999-12-22 CN CN99815318A patent/CN1332841A/zh active Pending
  • 1999-12-22 US US09/869,396 patent/US6696843B1/en not_active Expired - Fee Related
  • 1999-12-22 AU AU17860/00A patent/AU1786000A/en not_active Abandoned
  • 1999-12-22 KR KR1020017008262A patent/KR20010089728A/ko not_active Application Discontinuation
  • 1999-12-22 JP JP2000591392A patent/JP2002533709A/ja active Pending
  • 1999-12-22 WO PCT/FR1999/003266 patent/WO2000039538A1/fr not_active Application Discontinuation

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