Device and method for ultrasonic measurement of a fluid flow...

Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters

Reexamination Certificate

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C073S861250

Reexamination Certificate

active

06696843

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an ultrasonic fluid flow measuring method and apparatus including a sigma-delta bandpass analog-to-digital converter.
An ultrasonic fluid meter comprises two ultrasound transducers defining a measurement path between them. Each transducer is used alternately in emission mode and in reception mode.
The principle of measuring a fluid rate acoustically consists in determining the speed of the flowing fluid, by determining the time the acoustic signal takes to propagate between the two transducers both in the upstream direction and in the downstream direction relative to the fluid flow. The travel time of the ultrasound wave is calculated on the basis of measuring time and/or measuring phase.
The flow rate and the volume of fluid that has flowed over a given length of time can then easily be determined on the basis of the measured fluid speed.
BACKGROUND OF THE INVENTION
Such ultrasound apparatus is well known to the person skilled in the art and is described, for example, in European patent application EP 0 807 824. The same applies to the acoustic measurement method as described for example in European patent application EP 0 852 725.
Fluid meters relying on the ultrasound principle to measure flow rate are entirely self-contained and they do not depend on an electricity distribution network. These meters contain electronics that is becoming ever more sophisticated, and they make it possible to improve measurement performance, giving consumers various kinds of information about consumption and enabling consumption to be read remotely and/or bills to be paid remotely, and they are powered by means of a battery of limited lifetime, which lifetime depends very strongly on the architecture of the electronic circuits used.
The architecture of a complete system for acquiring and processing measurements in a prior art ultrasound fluid meter is shown in FIG.
1
. Such an ultrasound fluid meter comprises two transducers
1
and
2
placed in a cavity
3
along which a fluid flows. The transducers are both connected to a switch unit
4
in such a manner that when the first transducer
1
operates in emission mode the second transducer
2
operates in reception mode, and vice versa. When the first transducer
1
emits an ultrasound wave UW which propagates in the fluid flow, the transducer
2
receives said ultrasound wave after a length of time that is characteristic of the flow speed, and it transforms the ultrasound wave into an analog signal. The switch unit
4
is connected to an amplifier
6
having programmable gain which serves to provide full-scale amplification and filtering of the analog signal for application to an analog-to-digital converter
8
. The programmable gain amplifier
6
is connected to an 8-bit analog-to-digital converter operating at a sampling frequency of 320 kHz. The analog-to-digital converter
8
delivers a digital signal as is required for determining the propagation time of the acoustic signal UW between the two transducers
1
and
2
. The analog-to-digital converter
8
is connected to a random access memory (RAM)
10
having capacity of 2×256 bytes which stores the signals, until they can be processed by the microcontroller
12
. The microcontroller
12
which processes stored signals and calculates results relating to flow rate is connected to a set of various units
13
serving, for example, for the purposes of display, communication with the outside, managing energy saving modes, and storing operating data. The microcontroller
4
is also connected to a sequencer
14
. The sequencer
14
controls the sequences of ultrasound waves fired by the transducers
1
and
2
via a transmission buffer
16
comprising a digital-to-analog converter and an amplifier, and it also controls the sampling performed by the analog-to-digital converter
8
and the storing of signals in the memory
10
. A battery (not shown) operates in conventional manner via a set of connections (not shown) to provide the energy necessary to enable the various components to operate.
The combination of a programmable gain amplifier and an analog-to-digital converter corresponds to architecture which is complex and which consumes 30% to 40% of the energy requirements of the electronics of the meter. In addition, such an analog-to-digital converter introduces quantization noise while digitizing, thereby degrading measurement accuracy. Such a “conventional” analog-to-digital converter converts a signal with constant resolution providing its frequency lies in the range DC to half the sampling frequency.
It is known to the person skilled in the art that transformation of an analog signal into a digital signal by means of an analog-to-digital converter is a major source of error commonly known as quantization noise. A technique known to the person skilled in the art for reducing such quantization noise is using sigma-delta conversion (see for example “Delta-sigma data converters—theory, design, and simulation” by Steven R. Norsworthy et al., IEEE Press, New York, 1997). Noise reduction is obtained by sigma-delta conversion because the architecture of a sigma-delta converter enables it to take account of the conversion errors made during past conversions in order to correct future conversions.
Furthermore, another aspect of sigma-delta conversion relates to the particular way the information that results therefrom is encoded. Sigma-delta conversion is a principle for encoding information on a small number of bits, sampled at a high frequency so as to enable resolution to be increased subsequently. This conversion principle is based on operation that is analogous to that of delta conversion, which consists in encoding the difference between the amplitude of a sample and the amplitude of the preceding sample. For example, when encoding on a single bit, a sigma-delta converter generates a binary output stream (alternating “0s” and “1s”) constituted by a periodic regime whose fundamental period is proportional to the input voltage. The converter responds as a voltage-to-frequency converter which is synchronized on a sampling clock. A “decimator” digital filter is placed at the output from the sigma-delta converter and converts the signal encoded on a small number of bits at high frequency into a signal at a lower bit rate but encoded on a larger number of bits.
The principle of sigma-delta conversion can be extended to converting signals centered around a particular frequency. The converter used is then a bandpass sigma-delta converter. The filter of the converter which was previously an integrator is replaced by a resonator. The digital filter at the outlet from the sigma-delta converter is no longer a decimator but a bandpass filter followed by a demodulator. In the field of telecommunications, and in particular in the field of digital radio, it is known to use bandpass sigma-delta analog-to-digital converters in order to eliminate quantization noise (see for example “A fourth-order bandpass sigma-delta modulator” by Steven A. Jantzi et al., IEEE Journal of Solid State Circuits, Vol. 28, No. 3, March 1993, pp. 282 to 291).
The object of the present invention is to remedy the drawbacks of the measurement acquisition and processing system of prior art ultrasound fluid meters, and in particular to reduce the complexity and the power consumption of the digitizer.
Another object of the present invention is specifically to reduce quantization noise during digitization of the analog signal and to increase the performance of the converter.
In the invention, these objects are achieved by replacing the prior art digitizing system by a sigma-delta converter.
More precisely, the present invention provides ultrasound apparatus for measuring a fluid flow rate, the apparatus comprising:
first and second transducers placed in the fluid whose flow rate is to be determined, one of the transducers, also referred to as the “emitter” transducer, operating in emission mode while the other transducer, also referred to as the “receiver” transducer, operates i

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