Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Reexamination Certificate
1999-09-29
2001-03-27
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
C073S865500, C073S599000
Reexamination Certificate
active
06205848
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for the detection and identification of particles in a suspension, comprising the following steps:
a. generation of acoustic signals having the form of a beam using an acoustic source;
b. directing the acoustic signals at at least one measurement volume within the suspension, the boundaries of the measurement volume in the axial direction with respect to the acoustic source being defined with the aid of time windows;
c. reception of acoustic reflection signals produced by reflection of the acoustic signals by the particles in the at least one measurement volume;
d. conversion of the acoustic reflection signals into electrical reflection signals;
e. counting numbers of electrical reflection signals which have an amplitude in excess of a predetermined value and conversion thereof into numbers of particles which are larger than a certain size.
A method of this type is disclosed in British Patent 1,012,010, which describes a method and equipment for counting and measuring such particles, wherein acoustic samples are taken in various measurement volumes along the acoustic axis of the acoustic transducer in the suspension. By using suitable time windows when receiving reflected acoustic signals, the particles in, for example, four predetermined measurement volumes, which are each located a predetermined distance away from the transducer, are counted. By making use of a threshold voltage which the electrical signals produced from the acoustic signals must exceed in order to be counted, which threshold voltage is different for each zone, a minimum size for the particles to be counted is selected for each zone. Assuming that the particle distribution is the same in each zone, a rough estimate of the number of particles, subdivided according to particle size, can be obtained using this known method and using simple mathematical methods.
U.S. Pat. No. 3,774,717 describes a method and equipment for the detection and identification of small particles, for example biological cells, which, for example, are located in a medium which flows transversely to the direction of propagation of an acoustic signal. Each of the particles gives a specific scatter of the acoustic signal, depending on the size, the shape and the acoustic impedance of the particles. The acoustic signal has a wavelength and an effective cross-section of the order of magnitude of the particles to be detected and identified. Blood cells, for example, are detected with the aid of an acoustic signal of 860 MHz. Therefore, particles can be identified with the aid of techniques which are known from radar technology. The technique disclosed in this patent is unsuitable for in vivo detection and identification because the wavelengths used allow only very restricted depths of penetration in biological tissue.
The methods described above are based on the ultrasonic pulse-echo technique. With this technique use can be made of a so-called ultrasonic transducer, which converts an applied electrical pulse into an acoustic (ultrasonic) signal and which is also capable of converting an acoustic (ultrasonic) signal which is incident on the reception surface back into an electrical signal. Therefore, the transducer serves as transmitter and as receiver for ultrasonic signals. It is also possible to use independent transmitters and receivers. A high-frequency pulse-echo recording of the flowing suspension is made. A focusing transducer can be used for this. In
FIG. 1
the “illuminating” sound signal is shown diagrammatically in an arrangement known per se.
As is shown in
FIG. 1
, the principal axis z of the sound beam
20
generated by a transducer
23
is perpendicular to the direction of flow P of the suspension
21
flowing in a channel
24
and, consequently, to the direction of movement of the particles
22
present in the suspension. When a particle
22
passes through the sound beam
20
, the incident sound field will be reflected by the particle and the reflected signal will be captured by the transducer
23
. The received signal is converted by the transducer
23
into an electrical signal which is transmitted to the transmission and reception electronics
25
. The transmission and reception electronics
25
transmit the signal to a computer
26
, which in connected to a memory
27
for storing measurement data. The computer
26
is provided with suitable software for evaluation of the measurement data. The electrical signal from a single measurement is indicated diagrammatically by a and is a time signal, the time axis t indicating the propagation time of the sound. The response of the particle
22
in the measurement volume can be detected in the recording at that moment in time which corresponds to the propagation time of the ultrasonic pulse between transducer
23
and reflecting particle
22
and back again.
Only reflections within an applied time window [t
1
, t
2
] (see
FIG. 1
) arc processed in the analysis. The measurement volume is thus limited in the axial direction by z
1
=t
1
·c/2 and z
2
−t
2
·&sgr;/2 (c is the speed of propagation of the sound). In the lateral direction the measurement volume is limited by the shape of the acoustic beam.
A method for counting the number of particles using a measurement set-up of this type is described in the above-mentioned patents and in Croetech, J. G.: “Theory and application of acoustic particle monitoring systems”, Jr. Advances in Instrumentation and Control 45 (1990), Part 1. Generally-speaking, with this method a specific threshold value is chosen for the amplitude of the reflected signal. If the recorded signal within the time window [t
1
, L
2
] is in excess of this threshold value, this is interpreted as the presence of a particle in the measurement volume. On condition that the particle concentration is so low that the risk of the simultaneous presence of more than one particle within the measurement volume is negligible, the particle concentration can be estimated by counting the number of recordings in excess of the set threshold value.
This method takes no account of variations in particle size and no distinction is made between different types of particles which are possibly present in the suspension.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a reliable and wore precise method for the characterization of a suspension and the particles present in the suspension. In this context characterization in understood to be estimation of the particle concentration, the particle size distribution, the shape of the particles and the reflectivity of the particles.
A further aim of the invention is to provide a method for the characterisation of suspensions and the particles contained therein, with which method account does not necessarily have to be taken of the condition that no more than one particle may be present in the measurement volume at any one time.
The first-mentioned objective is achieved with a method of the above-mentioned typo, which method is characterized by the following steps:
f. composing at least one curve on the basis of a cumulative count of the number of reflection signals which have an amplitude in excess of a specific value as a function of the amplitude;
g. comparison of the at least one curve with predetermined standard cumulative count curves and deduction of at least one feature from a set of features comprising: material properties, particle concentration, particle shapes, particle size and standard deviation thereof and particle size distribution.
Material properties thus deduced may, e.g. be density and compressibility.
A method of this type can be used successfully where the suspension flows relative to the acoustic source, where the acoustic source is moved relative to the suspension (for example along the suspension), where, for whatever reason, the properties of the suspension change as a function of time and the acoustic source is fixed, and where an array of acoustic sources is used instead of a single acoustic s
De Kroon Mathilde Gertrudis Maria
Faber Gerard
Vos Hugo Cornelis Lucas
Bachman & LaPointe P.C.
Fayyaz Nashimya
Nederlandse Organisatie voor Toengepast-Natuurwetenschappelijk O
Williams Hezron
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