Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
125~51~
I
System ~or measuring particle transport in a ~ id.
The invention rela~es to a system for measuring partiCle transport
in a f luid.
A sy6tem which functions with acoustical waves and
elecero-acoustical tr~nsducers as transmitters and receivers is
described in "The in 6i~U measurements of sediment transport by means
of ultrasound scattering" by R.H.J. Jansen, Publ. No. 203, July 1978 o~
the Waterloopkundig Laboratorium in Delft (Delft Hydraulics
Laboratory~. ~his known system is used for measuring the
sediment crsnsport in coastal waters. In this prior art system, one
transducer transmits a narrou be~m of acoustical energy to a me~suring
volume. The particles ~hich are in the measuring volume will scatter the
acoustical waves and part of the scat~ered energy will be received by a
receiving transd~cer. The electrical signal at the output of the receiving
tran~ducer contains information both on the displacement velocity v and on
the concentration C of the particles in the fLuid. Therefore, the intensity of
the sign~1 at the output of the receîving transducer is a function of the
psrticle concentration C. Unfortunately however, this function comprises
a linear ter~ determined by the scattering in the measuring volume, and an
exponential term, reaulting from the extinction of the sound waves in the
propagation path bet~een transmitting and receiving transducerS. The
extinction is caused by scattering and absorption by particles and
absorption by the fluid itself. The extinction term results in a non-
linear relationship between the concentration and the signal intensity
and mskes thi8 rel~tionship ambiguous for higher concentrations.
An object of the invention is to indicate a way in which an extinction
correction term can be realized in the known system. In other words, a
way in which the influence of the exponentiallity in the signal
intensity of the received signal can be eliminated without introducing
further serious disadvantages in the system.
g6~
12SB5~L8
-- 2
Broadly stated a system for measuring the concentration
of particles in a fluid, said system comprising:
a transmitter under the control of an electrical control
signal for transmitting a wave beam in the direction of a first
measuring volume in the said fluid;
a first receiver within a first reception beam
receiving waves scattered by said particles in said first
measuring volume and generating therefrom a corresponding first
electrical reception signal, said first measuring volume being
determined by the intersection of said transmission beam and said
first reception beam;
a second receiver within a second reception beam
receiving scattered reflected waves from a second measuring
volume, determined by the intersection of said transmission beam
and said second reception beam, said second receiver generating a
corresponding second electrical reception signal upon reception
of said scattered reflected waves; and
a measuring apparatus receiving said electrical control
signal and said first and second electrical reception signals,
whereby the wave propagation path between said transmitter and
said second receiver is equal to n times said wave propagation
path between said transmitter and said first receiver wherein n
is an integer, said measuring apparatus comprising means for
forming a signal which can be expressed as said first electrical
reception signal raised to the nt h power, the result thereof
being divided by said second reception signal to form an output
signal representative of the concentration of particles in said
fluid.
The advantages of the system according to the invention,
possible embodiments of the system and further detailed
information will be given in the following part of the
description with reference to the attached drawings.
~258Sl~
- ~a -
Fig. 1 illustrates the above indicated prior art system.
Fig. 2 illustrates a principle diagram of a first embodiment
of the system, in which for the above-mentioned factor n the
value 2 is selected.
Fig. 3 illustrates in a graphical way the relationship
between the squared output signal of the second transducer and
the particle concentration for various particle sizes.
1258Sl~
Fig. 4 illustrates in a graphical way the relationshlp
between the squared output signal of the second receiver and the
particle concentration for various particle sizes.
Fig. 5 illustrates in a graphical way the output signal of
the measuring circuit as function of the particle concentration.
Fig. 6 illustrates a principle diagram of a second
embodiment of a system.
Fig. 7 illustrates a principle diagram of a third ambodiment
of a system.
Fig. 8 illustrates a principle diagram of a fourth
embodiment of a system.
Fig. 9 illustrates a modified measuring circuit.
The prior art circuit, which is already indicated above, is
illustrated in Fig. l.
The transport of sediment particles T is defined as the
product of the mass concentration C and the velocity v of the
particles. In order to ensure that as little information as
possible is lost, C and v must be measured continuously,
instantaneously and simultaneously. The transducers T1 and T2
illustrated in Fig. 1 are identical piezo-electrical ceramic
discs. The area defined by the intersection of the narrow
transmitting beam and receiving beam is the effective measuring
volume V. The influence of eventual side lobes may be neglected
in practice. The particles which are in the measuring volume
will scatter the acoustical waves and part of the scattered
energy will be received by the receiving transducer. The
electrical signal at the output of the receiving transducer
contains information on both the displacement velocity v and the
concentration C of the particles in the fluid. When the
particles are moving, a frequency is observed between the
frequencies f and f' of the transmission signal and receiving
signal respectively due to the Doppler effect. The frequency
difference forms a measure for the velocity component along the
bisector of the angle between the transmission beam and the
reception beam. The velocity component can be written as:
~ 1258S18
vl =Ivlcos C~= cfd (I)
2 fdcos y/2
wherein vl=the velocity componenc Along che bisector of che angle
between che Cransmission beam and the recepCion beam
5¦v¦ = ~odulus of the velocicy vector
= angle bet~een che velocity veccor and the bisector
0 = angle between transmission and recepcion besm
fd = frequency difference
C = sound velocity.
The concentration C of the particles in the measuring volume can
be derived out of the signal intensity according to the formula:
2 kl
S = - Cle~p -m(k C ~ E) (2)
in ~hich S2 = signal intensity of the received signal
m = propagation path length between transmitter and receiver
Cl = concentration in the measuring volume
C2 = concentration along the propagation path
E = absorption coefficient of the medium
kl = constant determined by the transducer and particle
characteristics and by the Cransmitting po~er
k2 = constant determined by particle characteristics.
For~ula (2) is the product of two terms, a linear term determined
by the scaCtering in the ~easuring volume, and an exponential term,
resulting from the extinction of the sound waves in the propagation path
25 m. This extinction is caused by scattering and absorption by particles
and absorption by the fluid itsel~. The extinction term results in a
non-linear relationship between the concentration and the signal
intensity and makes this relationship ambiguous for higher concentrations.
Furthermore, because of ehe absorption coefficienc ~ the signal intensity is
30 dependent on the temperature and on furcher characceri5cic5 of the fluid in
~hich the particles are moving.
For instance when measuring the transport of sand particles in
seawater, the salinity of the seawater plays a role. Also, the
prcsence of mud will be eYpressed through the term.
An attempt has been made to eliminate the influence of this
exponential term by using a third receiving transducer, located
125~35~
vithin the transmitting beam of the transmitting t~ansducer at such a
distance thereof that the length of the sound propagation path between
the transmitting transducer and the third transducer is equal to the
length of the propagation path between the transmitting transducer and
S the already present receiving transducer. It appeared, however, that
thi~ ~ay of approaching che problem had a number of serious
di6advan~age6. By reflection of sound waves from the surface of ~he
second receiving transducer two effects appear:
l) The reflected waves interfere with the incoming waves and if an
integer number of half wave lengths "fits" between both transducers
then a standing ~ave ~ill be generated. l~ appeared that this process
is very temperature dependent. A temperature variation of 0,2 C results
in an amplitude variation of + lO~ which implies a variation of 20Z
in the concentration deter~ined on the basis thereof.
2) Secause of the reflection, the second receiving transducer
functions as ja~ming transmitter for the velocity measurement. ThUs not
only the velocity component along the bisector of the angle bet~een the
transmission beam and the reception beam of the second receiving
transducer results in a Dopp~er shift, but furthermore there is a
velocity component along the bisector of the angle between the jamming
transmitting beam from the third transducer and the reception beam Of
the second receiving transducer.
A further objectionto this approach is the
very unfavourable geometry of the measuring configuration in connection
vith the hydrodynamical disturbance of the fluid flow in the measuring
volume.
Fig. 2 illustrates a principle diagrsm of a system embodying the present
invention. This system comprises three electro-acoustical transducers: the
transmitting transducer Tl and the receiving transducers T2 and T3. As
appears from the Figurethe above described measuring operation is in fact
carried out ~ice, namely for waves which from Tl along the path ml arive
at ~he receiving transducer T2 and waves which from the transmitting
transducer Tl along the path m2 arrive at the receiving transducer T3.
The signal intensity S2 of the signal of both transducers T2 and
T3 is cxpressed by the above formula (2):
125~51~
2 kl 6
Sl - -- Clexp -m(k2C2 + a) (3)
S2 ~ - C3exp -m(k4C4 + ~) (3)
If the concentration C of the partlcles ln the fluid 1~ coo61dered
homogeneous, then C - Cl ~ C2 ~ C3 ~ C4 and k2 8 k4 .
Therefore the quotient of Sl2 ralsed to the n-th power and S22 can
be expres~ed a6:
(S12)n k~Cn-lD,
2 - exp -(nml ~ ~2)(k2C + ~) (5)
S2 k3ml
If the length of the path m2 is selected such that M is equal to n
times ml: 2
m2 ~ n-ml (6)
then the formula (5) can be slmpllfied to:
(Sl) _ k n-l wlth k ~ kl n
S22 . k3 mln l
The result 16 an eliminatlon of the exponential term in formula (2).
Preferably n ls selected to equal 2 in which case the quotient of
Sl raised to the n-th power and S2 is linearly dependant on
25 the concentration and multiplied by a proportionality factor
determined by:
the transmission power ,
the characteristlc~ of the transducer~; and
the difference in sound path length .
In Fig. 2 the signal Sl at the output of the transducer T2 i8
squared by multipller lo The signal S2 at the output of the
recei~ing transducer T3 is 6quared by multlpller 2. Output
signals from both multipliers 1 and 2 are divided by divider 3
resulting in output signal Sl2/S22. This slgnal ls applied to
multipller 4, and multiEjlied to the output signal of multiplier l.
The resultant output signal of multiplier 4
corresponds with above indicated formula (7), where n = 2, and is
proportional to the concentration C.
In the Figures 3, 4 and 5 results~ obtalned wlth the 6ystem
are indicated in a graphical way. The system
~as used ln a flowlng fluld to whlch sand wlth a predetermlned partlcle
~:2S8S~B
size wa8 added. The oueput slgnals, measured and ffquared by means of
the system are shown in the Figures 3 and 4
along the vertlcAl axes. The concentratlon of sand particles, determined by
taking samples afterwards, are shown in Figures 3 and a along the
h~rizontal axes. In each of the Fiqures measurement values are
indicated for sand particles havin~ sizes of lOO,um, 150,um a~d 200~m.
In Fig. 3 the squared output slgnal S12 of the first transducer
T2 is lllustrated. From ~his Figure it i6 clear that S12 ls
repre~ented by a ~on-linear curve.
In Flg. 4 the squared oueput signal s22 of the further recelving
transducer T3 is indlcated as functlon of the concentration.
Fromthis F~gure,lt appears that the exponentLal te~ in the formula
S22 not only causes the non-linearity of the functlon but further~ore
makes the function ambiguous.
IQ Fig. 5 the output signal of ~ultiplier 4 ln Fia. 2,
which signal should be proport~onal to the particle concentra~ion, lfi
lllu6trated ~s function of the concentratlo~. It iS clearly shown that
the influence of t~e e~ponentlal ter~ in the obtained formuls is substantially
eliminated and that a near linear relationship is obtained between
the output signal of the system and th~ partlcle concentratlon ln the
fluld.
By comb~nlng the slgnals S12, S22 and the output signal
(S12)2/S22 it i8 also posslble to deter~ine the particle size for
concentratlons above ~ ehreshold value, which in the illustrated
e~ample lles spproxi~ately at 1000 mg/l. Por example, suppose that the
output signal nas a value of 350 mV, then it appears from Fig. 5,
taking into account some dispersion, that the concentration is
between 2300 and 2700 mg/l. If simultaneously for S2 , a value of
700 mV is measured then it appears fro~ Fig. 4, that after
combining the 700 mV with the obtained concentration between 2300
and 2700 mq/l the average particle size is 120 ~m. Also, if Sl
is simultaneously measured then the result can be verified in Fig.3.
Although not lndicated in dets11 in Fig. 2,the output slgnals of
the tran6ducers T1, T2 and T3 are not used directly, These signals
are first supplied to a clrcult In which product signals are formed
from the transmitter control siqnal and the amplified signals from
the receiving transducers. The product signals are in fact used as
Sl and S2, both for the above described concentration calculation as
well as for the determination of the velocity component along the
bisector of the angle be~ween the transmission and reception beams on
, .
1258~
d
the basls of the above lndlcated formula (l). For further detalls of
veloclty ~es6urement reference is made to the earlier
mentloned publlcstlon.
Wlth the 6ystem lndlcated ln Flg. 2,only the veloclty component
along the blsector of the angle between the transml6slon and receptlon
dlrectlons can be determlned~ Wlth this embodlment, only one
veloclty factor component 16 obtalned. Fig. 6 lllustrates a modlfled
embodlment of the system accordlng to the ~nventlon In whlch ~o-dimensional
veloclty components, l.e. ln the plane of the dra~lng, can be
determined. In t-~i5 ca6e,the mea6urlng dlrec~lon of T2 is not equal to
the mea6urlng dlrectlon of T3. However, the requlrement that the length
of the path ~l ~8 half the length of the path m2 should be
fulfllled. The component6 ll, 12, 13 and 14 have function6
corres~onding to the functlon6 of the components 1, 2, 3 and 4 in Fig.
15 2.Therefore the output signal of multiplier 14 corresponds to the
output 61gnal of multipller 4. It will be clear that with the circult
of Fig. 6 not only the veloclty co~ponent vl can be mea~ured,but al60
the velocity component v2. By combining both component6,the veloclty
componen~ in the plane of the drawlng can be obtained.
Flg. 7 lllustrste6 in a sche~atlcal way,an embodlment of the
system accordlng to the lnvention, comprls~ng a transmittlng
transducer Tl and three receivlng transducers T2, T3 and T4. The
transmlttlng transducer Tl 16 posltloned at the lnter6ectlon of the
coordlnate axes X and Y and transmlt6 a beam of electro-acou6tlcal
energy along the Y-axls. Each of the recelving transducers ls
posltloned such that the 60und propagat~on path between Tl and T2 is
half the ler.gth of the sound propagatlon path between Tl and T3. The
length of the last ment~oned path ls ln turn half the length of the
propagatlon path between Tl snd T4. Furthermore,the receivlng
tran6ducers ln thl6 embodlment are positioned in a plane through the
coordlnate axe6 X' and Y'. The plane ls posltloned A~ a dlstance dl
above the plane through X and Y. Therefore the varlous dlstances
d ln ~he Flgure,fulfll the expression dl = d2 ~ d3 ~ d4. With this
configuration, it is possible to measure three different
dlrected spaclal veloclty components v8, vb and VC from whlch the
three-dlmenslonal veloclty vector can be determined. If thls
conflguratlon ls u6ed for measurlng ~he eransport of par~lcles ln a
fluld, where prlncipal dlrectlon of movement of the particles is
ln the plane through X and Y, then a further advantage of this
conflguratlon 16 thst the pOsitioning of tile recelvlng transducers in
~258518
prlnclple does not disturb the hydrodyn~lcal flo~ pattern becnuse
these transducers are ao to 6peak elevated~ out of the measurlng
plane. Preferably che dlstance6 d2, d3 and d4 are selected such that they are
equal to each other because of an eventual vertical concentration
5 gradient between the measuring plane and the plane through X' and
Y', This gradient for each combination of transmitting transducer
and receiving transducer has the same influence.
In the above dl6cussed embodlments of the system
dlfferent measurlng volumes are used, for
each recelvlng tran6ducer. If one trles to elimlnace posbible
problems in relatlon to ~n eventual concentratlon gradlent,then
the embodlment Illuqtrated ln Flg. 8 can be used.
In Flg. 8~the three transducers are each dlrected to the same
measurlng volume V. Also ln ~his case,lt applfes for the sound
propagatlon path that n(ml + m2) = ml + m3, and furthermore that
m3 8 ml + 2m2'
As will be clear ~rom the above descrlptlon,it is no~ pos61ble
wlth thls configurAtlon to measure the concentration C without any
lnfluence of an eventual concentratlon gradlent. Also,the velocity in
the plane of the dra~lng can be determlned ~lth this conflguratlon. A
slmllar solutlon ls applicable to the e~bodlment described
~lth reference to Flg. 7.
As already dlscussed with reference to Fig. 2 the division in the
measuring circult should be carrled out by divider 3. If very small
concentrAtions nre measured then correspondirlgly small signals are
obtained at the outputs of the receiving transducers. Such s~all
signals could result in problems for the division in divider 3.
As appeArs from the Figures 3 and 4, the influence of the
e~ponential term becomes slgnlficant,only if relatlvely strong slgnals
are involved. Therefore,lt mlght be preferable to insert a threshold
detector bet~een the measuring circult and At least one of the
recelvlng transducers, The detector thereby provides a signal in case the
slgnal level at the outpu~ of the transducer falls below a
prede~ermlned value. For example the signal can be used to supply the
output blgnal of multlpller l lnstead of the ou~put slgnal of
multlpller 4.
Further to p~oblems ln relatlon to very smAll 61gnals,
problems can also appear in relation to the desired range of
values. A multlplier vl~h a usable voltage range of lOmV to IOV at ~he
output allovs ~or lllstance a maxlmum dyn~mlc varldtlon of 30 : I for
125~5~
the Lnput 6~gnAI~. Ihec 1~ ~u~t sufflclent fo~ 8 Concentr~tlon rao8e of
10 to 10.000 ~g/1. ~o~ever, the deQsnd~ made upon the 8nalogue
componene6 of the ~ea~urlag clrcult cno be very heavy and vlll
Bo~e~Lme~ result in a circuit which is not realizable in practice. Tc
S Holve th~6 probleQ lt ~ preferred 60 real~e the mea~urlng clrcul~ for
the larger part ~n a dlgl~al form.
Flg. 9 llluserates a practlcal embodlment of ~ Qeaaurlng clrcult
ln ~h~ch a dlg~tal proce~60r Ls used. The ou~pu~ 61gnal~ of the
trin6ducer6 T2 and T3 are Ln ehe AtD convertor~ Z0 a~d 21 perlodlcally
converted loto dlgl~al values whlch, ln a slQllar vay Afl ~ deBCrlbed
vlth refereuce to Flg. 2, are used ln the proces60r 22 to provlde by
mean6 of multlplylng nnd dlvldlng a dlgl~sl output slgn~l proportlonal
to the concentratlon.
~ remarked ~hat there are at thl~ moment proce660r~ vlth
bullt-ln tJD convertor6 avallable on the msrke~, for instance chip
#2920 manufactured by the INTEL Corporation, which is suited for
application in a measuring circuit of this type.
Although in the above descrlptlou of the vArlou6 e~bodiment6
reference 16 made to the use of ~cou6tlcal vave6 lt 1~ al60 pos61ble to
reallze 61mllar 6y6tems functlonlog wlth llght uaves. Such sy6~em~ c~n
for lu6tsnce be u~ed ln sltuatlons 1n whlch the fluld 16 6ufflclently
llght trsn6parent. If ~n lnc~nde6cent lamp 16 u6ed then lt 18 only
po~61ble to determine the concen~rg~lon of the partlcle6~ AppllcAtlon
of a la~er llgh~ source, hovever, provlde6 the po~slbllley also eo
ZS determlne the veloclty of the partlcle6.
It 1B furthermore pos61ble to apply high-frequent electromsgnetic
v~ves, for lnstance ln ehe rAdar rsnge. In thst case the eystem cAn be
u~ed for ln6tsnce for meteorologlcnl Appllcaelons, envlroomentsl
pollutlon mes6urlog sysee~s, eec.
