Ultrasonic pulse-phase method applied in fluid flow
measurements
V. Pavlovic
M.StojEev
B. Dimitrijevic
Lj. Go1ubovic
M.zivkovid
Lj.Stankovic
Indexing terms: Fluid flow measurements, Pulse phase method, Ultrasonicflow
Abstract: A novel pulse phase method for
ultrasonic flow measurement in pipes under
pressure is presented. It belongs to a group of
direct time measurement methods. The difference
in propagation (transit) time between two
ultrasonic beams transmitted in upstream and
downstream directions across the fluid flow is
measured. With a goal to achieve an accuracy
better than 1% each of the transit time intervals is
decomposed into two intervals. The first interval,
called ‘coarse’, points to an integer number of the
ultrasonic signal periods during propagation time,
and the second one, called ‘fine’, points to the
rest of its periods. Fluid flow velocity and volume
quantity are determined through involving the
calibration function. The main metrological
characteristics of the realised fluid flowmeter are
determined using available working etalons.
Experiments have shown that the total error of
the flowmeter described herein is within the
specified accuracy of 1%.
1
Introduction
Nowadays, accurate measurement of fluid flow velocity
and volume quantity is enormously important in contemporary industry. The methods and techniques
applied in such measurements are of great significance
for more efficent use of production capacity, and for
considerable savings in raw materials and energy consumption.
The existing flowmeters can be classified into several
different categories: mechanical, electromagnetic, ultrasonic and optical.
0 IEE, 1996
IEE Proceedings online no. 19960278
Paper first received 28th June and in revised form 18th December 1995
V. Pavlovic, M. zivkovic and Lj. Stankovic are with Ei IRIN d.d. NiS,
Bulevar Cara Konstantina 8&84, 18000 NiS, Serbia
M. StojCev and B. Dimitrijevit are with the Elektronski fakultet,
Beogradska 14, P.O. Box 73, 18000 NiS, Serbia
Lj. Golubovic is with the Tehnlki fakultet, Cara DuSana bb, 32000
Catak, Serbia
IEE Proc.-Sei. Meas. Technol.,Vol. 143, No. 5. September 1996
At present, three different types of noncontact fluid
flowmeters are on the market [l]: (i) electromagnetic
[2], (ii) optical [3], and (iii) ultrasonic [4, 51.
Recently, the ultrasonic fluid flowmeters have
become widely applied, since they are suitable for any
kind of fluid. Ultrasonic methods cause no flow distortion, enable velocity measurement of electrical conductive and nonconductive fluids, both in homogeneous
(clean fluid) and non homogeneous medium. They have
fast response, good stability, and a wide dynamic range
of measurement [6]. There are two ultrasonic measurement methods. The first one is known as the transient
time method, and the latter is based on the Doppler
effect.
Presently, three transient time methods are widely
employed. Their principles of operation are based on:
direct time measurements [7]; phase measurement [5];
and sing-around techniques [SI.
In industry, direct time methods are preferred, but
because of their shortcomings, their variants known as
the compensation methods have appeared. The most
popular of these are: time frequent and phase frequent
methods [l].
Compensation methods, compared with conventional
ones, provide a good background for realisation of
industrial fluid flowmeters. They fulfil the main
requirements with regard to low-cost, good reliability,
high linearity, wide measurement range, noncontact
measurement and simple installation.
In this paper we describe a realisation of the flowmeter’s functional structure, which belongs to a class of
the flowmeters based on time propagation measurement of ultrasonic signals in upstream tu, and downstream td, directions. Concerning the principle of time
interval measurement, t d and tu, a pulse phase method
is used. By the proposed method, first the flow velocity
is measured, and secondly, for the given pipe’s profile,
the flow volume quantity is calculated. This paper
addresses both of these problems. Bearing in mind a
complex function of the fluid’s movement along the
pipe, the fluid flow velocity and volume quantity are
determined through involving the calibration function.
Temperature influence, beam directivity, effect of
recesses, and path elongation are considered with
respect to the total measurement error. The functional
structure of the flowmeter is also described.
327
Principle of measurement
2
In the proposed method, as shown in Fig. 1, the flowmeter measures a difference in transit times between
two ultrasonic beams transmitted upstream and downstream across the flow, respectively. If the ultrasonic
beams are transmitted at angles 0 and ?c-0 with
respect to the mean fluid flow velocity V, the corresponding transit times, in upstream and downstream
directions are given as follows:
D
td =
sin @ ( e a cos 0 )
+
D
t, =
(2)
sin O(c - .ilCOS 0 )
where t d and tu stand for transit times of the ultrasonic
beam in downstream and upstream directions, respectively; D = diameter of the pipe; c = velocity of the
ultrasonic wave across the fluid; and V = mean fluid
flow velocity on the path from the transmitter to the
receiver.
probe PI
I
\
\
I I
velocity
L
9
Fig. 1
Ultrasonic flowmeter bused on di&ence
measuremen ts
probe P2
time propagation
According to eqns. 1 and 2, and assuming that c2 >>
v2cose, we can write
c2tgO
(3)
20
where At t,-td, and tutd = (D/csin0)2.
Practical realisation of such a flowmeter, based on
eqn. 3, requires time interval measurement in several
steps (upstream and downstream direction), temporary
result storing, and their processing.
1
V$V = K(Q,) can be determined, and the volume flow
can be calculated:
Q = SOS = SK(QL)V
(6)
where QL is a mean fluid flow across the ultrasonic
beam area, and K(QL) is the calibration function determined experimentally. For more details, see [I].
4
Time interval measurement
The main problem, that has to be solved now, relates
to the accurate measurement of time intervals t d and tu
defined by eqns. 1 and 2. It is well known generally in
metrology that any time interval can be determined
more accurately than any other physical quantity, but
when the accuracy of the fluid flow measurement
greater than 1% is needed, several serious problems
arise. They are mainly related to a correct estimation of
the mean fluid flow velocity.
Transient time intervals t d and tu can be represented
in the form:
t d = NdT
Ard
(7)
+
tu = NUT+ Ar,
(8)
where Nd (Nu) stands for an integer number of the
propagation period in the downstream (upstream)
direction; and ATd (AT.,) = a rest of the time in respect
to the whole period of the ultrasonic signal being transmitted downstream (upstream).
According to eqns. 7 and 8, each of the time intervals
td and tu can be determined in two or more steps. First,
Nd or Nu, and after that AT^ or AT, are measured. Nd or
Nucan be determined by any standard counter method.
The counting process starts when the transmitting
probe is excited, and it finishes at the instant when the
signal at the receiving end is detected.
Intervals ATd or AT, are measured indirectly through
a phase difference between the transmitted and the
received signahwith the aim of increasing both the
resolution and the accuracy of the system, the measurement procedure should be realised in two steps. During
the first step the ‘coarse’ phase difference is measured,
while during the second the ‘fine’ phase shift is determined.
When Nd and Nu, and ATd and AT, are determined,
from eqns. 3, 6, 7 and 8 for 0 = 45”, the mean fluid
flow velocity along the path going from the transmitter
to the receiver V , and volume quantity Q, can be
expressed as:
3
Mean fluid flow velocity and volume quantity
estimation
In the ultrasonic method the mean velocity Vcos0 is
measured along the path L in the pipe’s flow cross-section S. Then
l
L
v=
?J(L)dL
(4)
zi
Of greater interest, however, is the mean velocity Vs
over the cross-section S, from which the volume flow Q
= VsS is obtained, i.e.
vs = -1 L , ( S ) d S
(5)
S
If the velocity distribution over the cross-section considered herein follows the definite law, the relationship
328
Bearing in mind the principle of time intervals td and tu
measurement, we say that this method belongs to a
group of the pulse phase methods.
5
Error consideration
Total measurement error of the fluid flow quantity Q
includes both systematic and random errors. Systematic
errors can be compensated by the calibration procedure
itself, by means of the referent fluid flow values under
real conditions. The errors, due to the parameters
whose values are randomly changed, are estimated by
the measurement procedure itself, because the multiple
fluid flow velocity measurement has been accomplished.
IEE Proc -Sei Mens Teclznol, Vol 143, No. 5. September 1996
5.1 Temperature influence on extension of
internal pipe's diameter principle of operation
The relative variation of a pipe's diameter as a function
of temperature variation A T is (ARIR,) = h.AT, where
h is a linear temperature coefficient of extension. For
steel with (0.1-0.6)% of carbon, h = l.2.lO-' [K-'1 [ l l ]
so that for temperature variation from 20 to 100°C we
have (ARIR,) <
This implies that the influence of the half diameter
R,, elongation due to temperature, can be neglected.
5.2 Beam directivity
During construction and installation of the probes on a
pipe, it is necessary to satisfy the following conditions:
(i) probe directivity diagram should be narrow, and
(ii) probes should be correctly directed one towards
another, so that maximal energy is transmitted.
5.3 Effect of recesses
During installation of the probes on to the pipe, some
recesses have appeared. They are filled with water. If
the flow velocity changes rapidly, these recesses will
cause some additional turbulence of the flow in the
vicinity of the probes.
Additionally, ultrasonic velocity variation in the
recesses is also influenced by temperature coefficient.
With the aim of compensating these influences we suggest filling the recesses with material for which AV as
the function of temperature is approximately equal to
zero. Error correction due to temperature influence can
be overcome through involving the calibration procedure.
5.4 Path elongation
In reality, due to fluid movement the velocity vector of
the ultrasonic signal changes from point to point along
the path L (i.e. anyzotrophy appears). This causes
curving of the beam path (i.e. elongation of the ultrasonic beam path between the transmitter and the
receiver [12]).
As shown in [12] the relative path variation is (ALIL)
= (iVc)~cosO.For 0 = 45" and ii < 5m/s, we obtain
(AWL) < 2.5~10-~.
This implies that, during the flow measurement with
an error near to 19'0, this term can be neglected. But, if
for larger fluid velocities, v > 5m/s, better accuracy is
needed, the influence of anyzotrophy, during ultirasonic
beam propagation, should be taken into account, and
has to be compensated. Usually this compensation is
done through involving the calibration function.
5.5 Delay through electronics
When standard electronic components (compa.rators,
logic gates, counters etc.) are installed, it is possible to
determine the time interval having a resolution better
than 1Qns. Concerning the errors obtained during
measurement of time intervals tu and tci, we have
adopted the value lQns for estimation of the flowmeter's error.
Random deviations during the measurement of tu
and tL,do not exceed the value of At. As an electronic
instrument, the flowmeter is comprised of a! large
number of analogue and digital electronic stages and
cables. Each of them involves its own delays
and
delay variations At,, where k is the ordinal number of
the stage under consideration. Thus, the total. delay
IEE Proc.-Sci. Meas. Technol., Vol. 143, No. 5, September 1996
through electronic stages t, and the corresponding variation At,, for m stages, is equal to
m
I m
The delay t, can be compensated at a zero fluid flow.
Thus, its influence on the accuracy of the fluid flowmeter can be neglected. The delay variation At,, which
relates to tu's and t i s time interval measurements,
depends on the characteristics of built-in electronic circuits. It can be estimated by choosing the suitable
methods related to the processing of measurement
results.
Contemporary technology in microelectronic components (TTL, STTL, HTTL, HCMOS, etc.) have a
declared standard delay variation of the order (1-2) ns.
For the flowmeter described in this paper, the blocks
for shaping and processing of output, referent and
receiving signals (CSL, SOS, UTR, CSB, ISC, PhC),
respectively, are dominant in influence on the delay
variation. During the flowmeter's realisation, special
care should be devoted to the construction of these
stages. In this manner the declared flowmeter's accuracy can be achieved. According to the previous analysis, the time intervals which also take the propagation
into account are given as:
where t",(tffd)= total time propagation of the ultrasonic
signal in the upstream (downstream) direction, .,(zd) =
time delay variation of the ultrasonic signal through
the measurement channel in the upstream (downstream) direction.
Determination of fluid flow quantity includes multiple time interval measurements trrnand t"d. Accordingly, the averaged values of time intervals t", and ttrd
are used for fluid flow quantity estimation. Thus, a
mean value of the time delay variation can be
neglected.
6
Pulse phase flowmeter
In the sequel a detailed description of the functional
structure and principle of the flowmeter's operation is
proceeding.
6.I Global functional structure
The block scheme of the flowmeter based on the pulse
phase method is shown in Fig. 2. The flowmeter represents a small embedded system. Its achitecture is a
combination of the programmable microprocessor core
with a memory and hardwired programmable peripheral interface devices accompanied by other processing
logic. Hardware and software together form the system. The microcomputer (MC) generates all necessary
control signals k l , kz, k3 and k , in defined time intervals. The ultrasonic transmitter is excited by sinewave
signals of frequency 2.2MHz (exact value is
2.216767 MHz). The excitation signal is obtained by
dividing the frequency of 17.73414MHz, generated at
the output of the block crystal oscillator (OSC). Division is accomplished by a counter logic as a constituent
part of the block counter-shift-logic (CSL). Shaping of
the rectangular pulses into a sinewave is accomplished
in the block shaper-output-stage (SOS). The SOS is
329
kgf
1
J kl
k2
(MC)
6
-
(ADC)
U0
+-
(InT)
V
Uln
-
-+t-P,
BlnPut
(PhC)
kL
+I42
-c
Ainput
.c--
a
Y
I
sc
1E
IE-1 I R
I
UkLSx
U2LIPX
.
3-L
(CSB)
Uka
0
(ISC 1
4
(UTR)
J
realised as a two-stage bandpass amplifier with resonant frequency of 2.2MHz. The amplitude of the output signal UILcpl can be discretely adjusted into two
levels. The state of the signal kA defines the magnitude
of the output signal UILcp,.The signal kA is generated
by the countinggsynchronisation-block (CSB).
The ultrasonic-transmitter-receiver (UTR) block
incorporates a pair of ultrasonic probes P1 and P2.
Each probe, in accordance with the proposed measurement method, operates alternatively either as the transmitter or the receiver. Switching function is provided
through fast electronic switches. States of the electronic
switches are defined by the control signal k4.
The signal from the receiving probe U2Lcp,, excites
the input stage of the block input-stage-comparator
(ISC), where it is first amplified and then shaped into
rectangular pulses. The ISC generates two types of output signals UkLq, and U k A , respectively. The signal
U,, drives the counting-synchronisation-block (CSB)
while the signal U,Lcp, drives the A i n p u t of the
phase-comparator (PhC).
The phase cpx of the received signal U, depends on
the fluid velocity.
The B-input of the PhC is driven by the referent signal U D L q D . The duty cycle of the signal U,, obtained at
the output of the PhC is proportional to the phase difference Acp = cpx-cpD.
Further, in the processing chain, an integration is
performed. Namely, a train of rectangular pulses is
averaged in the block integrator (InT). Activities of
InT, related to the setting of the initial condition, enabling of the integration period etc., are regulated by
control signals k l and I,. The output voltage U,,
obtained at the output of InT is proportional to Arp
and is led to the analogue-to-digital-converter (ADC).
The ADC provides an interface between the analogue
and digital parts of the electronics. Data transfer
between the MC and ADC is regulated by the control
signals k2 and SC.
The CSB is a specifically designed interface block
controlled by a MC. In defined time intervals it generates control signals needed for correct operation of the
330
flowmeter’s constituents (i.e. start-of-conversion (SC)
for ADC, integrator reset (IR)for InT, enabling operation (IE) of PhC, output amplitude setting of SOS etc.).
6.2 Principle of operation
Estimation of the flow Q is based on determination of
the fluid flow velocity, v (i.e. by measurement of the
transit time intervals tu and t d of the ultrasonic signal in
upstream and downstream directions, respectively). In
Fig. 3 the global time diagram depicting the flowmeter’s operation is given. T, is a total measurement
period. The measurement starts at the instant to. During T I the propagation time of the ultrasonic beam
from the transmitter to the receiver is determined. During the subinterval [tl,t2],the MC initialises the system.
Namely, it defines the state of the control signals and
sets the following blocks into initial operating conditions : InT, ADC, CSL and other parts of the electronics. The control signal k3 (Fig. 2) enables transmission
at instant tl. During the subinterval [ t l , t2]the transmitting probe is driven by a sinewave signal of amplitude
Ulo, while during [t2, t3], by a sinewave of amplitude
Ull. The amplitude of signal Ulj ( j = O,l), is defined by
the control signal kA (kA = {O} * Ull; kA = { I }
==, U,,).
TI
7
T2
-I
At t5 the receiving signal of the amplitude U,, is
detected. As can be seen from Fig. 3, the transmitting
probe is excited with a signal of two different amplitudes ( U l o and Ull). This helps us to overcome the
problem related to precise measurement of time intervals tli and t,. Ambiguities during precise deterrnination
of til and tu are mainly caused by probe’s inertion (i.e.
its integration effects).
Instants t3 and t6 point to completions of the transmitting and receiving processes in a downstream direction, respectively. The start and termination of the
transmission process (i.e. duration of the time-interval
[ t l , t3])is controlled by the MC. The instant t4, when
the receiving process starts, is defined by fluid flow
velocity, and it cannot be determined in advance.
According to Fig. 3, the time interval t d is equad to
t d = t 4 - tl = t s - t 2
(14)
Time interval td is defined as
t d = NdT Ard
(15)
where Nd = integer number of the clock periods of frequency 2.2MHz in the subinterval [ts, tz];T = period of
the sinewave signal (f= 2.2MHz); and Atd = part of the
period T. The value Nd is determined by a suitable
counter measurement method during the subinterval
[t2, tslAt the output of the PhC the signal U, is obtained.
Its duty cycle corresponds to the phase difference
Durbetween the signal U,<and U,, (i.e. Acp = ‘pX-qD).
ing the subinterval [ t s , t6]the signal U, drives the TnT.
At the end of the integration period, the voltage at the
output of the InT is proportional to AQ.
From the instant t6 up to t7 the MC accepts data
from the ADC and processes them. The transmitting
process finishes at t7.
After t7 the ultrasonic beam is transmitted in the
opposite direction. This means that now it is necessary
to determine tu. Both from a program and a functional
point of view the activities in the following subintervals: [ t 7 , tsl and [to, t11, [ts, t9I and [ t ~t21,
, [t97 t101and
it2, t3i, [til, t12iand it4, tsi, itl2, tI3iand [t5,t61,. it13, tlpl
and [t6, t,], are identical. Due to different ultrasonic
+
Fig. 4
signal propagation, in downstream and upstream directions, the intervals [t3, t4] and,[tlo, til] are not of equal
durations. In accordance to Fig. 3, we have:
tu = [ t l l , t 8 ] = [ t d s ]
(16)
According to eqn. 8, we have tu = NUT+ AT,, where Nu
= integer number of the sinewave periods (f=2.2MHz)
in the subinterval [t9,tI2]and AT^ = part of the period
T. Nu and AT, are determined similary as Nd and A-cd.
When Nd, Nu, AT, and A-cUare determined, according
to eqns. 9 and 10, the fluid flow velocity V and volume
quantity Q are calculated, respectively.
7
Flowmeter calibration
To determine the main metrological characteristics of
the realised ultrasonic fluid flowmeter, by means of the
available working etalons of flow, the calibration procedure is provided. In Serbia such working etalons are
in the possession of Legal Hydrotechnique Laboratories of the Institute for Hydrotechniques ‘Jaroslav
Cerni’ in Beograd and in the Civil Engineering Faculty
in Nis. As far as the working etalons’ characteristics
are concerned, the flowmeter calibration is more convenient for lower fluid flow values, but for higher fluid
flow values, the hydrodynamic etalons are preferred.
The measuring equipment of the Laboratory for
hydrotechniques of the Institute for Hydrotechnique
‘Jaroslav Cerni’ in Beograd, was used (Fig. 4).
Table 1: Measured data
I
1
2
3
4
5
6
7
8
9
10
Q,,[//s] 0.11 0.25 0.60 1.05 1.87 2.34 2.75 3.19 3.60 5.56
Q,,[//s] 0.17 0.35 0.63 1.46 1.86 2.33 2.77 3.21 3.57 5.08
I
11
Q,,[//s]
7.00 8.00 9.00 9.47 10.0 13.9 15.0 16.8 21.5 25.0
12
13
14
15
16
17
18
19
20
Q,,[//s] 6.60 7.40 8.60 9.20 9.60 13.8 14.9 16.5 21.0 24.3
i
21
22
23
24
25
26
27
28
29
30
Q,,[//s] 26.0 28.1 29.0 30.0 32.0 33.0 34.0 35.1 36.0 37.0
Q,,[//s] 25.3 27.4 28.0 29.2 31.2 32.5 33.6 34.6 35.7 36.7
Laboratory calibration equipment
IEE Proc.-Sci Meus Tecluiol. Vol. 143, No. 5, S e p t e d w 1996
331
The calibration procedure of the flowmeter consists
of three phases as follows:
(i) collection of the measured data, as shown in
Table 1
(ii) estimation of the calibration function K(Q,) and its
parameters
(iii) implementation of the calibration procedure for
correction and data displaying.
Measured data given in Table 1, and in Fig. 5, represent the fluid flow measurement results obtained by the
etalons Q, and fluid flow values QL. The measurement
results, obtained in this manner, are used for static calibration [ 131. According to the difference among measured values QL,-Qei (i = 1-30) we suppose that its
random variations exist, so that the function QL, =
f(Q,,) can be represented by a straight line as:
Q L ~=
aQez + b
(17)
where a and b are the coefficients determined by the
least mean square method.
Di
....
-
..
di
quantity of flow, Qel, I / s
Fig. 5 Diagrams o j linear regression line
QLr = AQ,,) and the dependences, D,, dz,QL, = +, QL, = -
Applying the correlation and regression methods, it
is estimated that those measured results are in close
correlation (i.e. coir (Q,, QL) = 1). Accordingly, the
coefficients of the regression line (eqn. 17) are: a-slope
( Q L , Q,) and v-intercept of (Q,, Q,), so that the calibration function is:
Q L =~ 0.982Qe - 0.042
(18)
Diagrams of the linear regression line (eqn. 18) and
dependence Q,, = f(Qe,) as well as the differences D,=
QLr,-QL, and d, =
are given in Fig. 5.
Standard deviations of the differences D,and d, in a
concrete case are:
&,-e,,
stdev(D,) = 0.235 l/s
and
stdev(d,) = 0.33 1/s
The relative error in approximation of the measurement results, by using the calibration function (eqn. 18)
for a full-scale range of the flowmeter was stdev(D,)/
Qem,;100% = 0.636%. By correction of the calibration
function for the parameter b = -0.042, the relative
approximation will not be changed, so that a final calibration function can be written as
QL = 0.98Qe
332
(19)
Using the estimated calibration function, calibration of
the fluid flowmeter’s indication is marked in the units
of flow [Us] or flow velocity [mis]. The flowmeter calibrated in this manner was ready for the final testing
and certification in accordance to the regulations of
Legal Metrological Laboratories in Beograd.
8
Conclusions
During realisation of the ultrasonic flowmeter and minimisation of the inevitable errors, both the problems of
theoretical and practical nature were met.
The main problem, from the technical and metrological point of view, is how to determine time intervals t d
and t, with better accuracy. Namely, estimation of the
small ratio VIC is especially critical (in practice v-lmis,
c-l500m/s). This problem is mainly caused due to the
small difference At = t,,-td with respect to time intervals
td and tu. Realisation of the flowmeter with an accuracy
better than 1% requires measurement of the time intervals td and tu, with an error of order 0.001% (i.e. more
accurate than three orders of magnitude [2]).To fulfil
this requirement, it is necessary to measure the time
intervals in several steps with a high resolution (better
than 211s). We suggest a two-step method including
’coarse’ and ‘fine’ time interval measurement. The ‘fine’
interval is measured over the phase difference by using
the tracking technique.
During practical realisation of the flowmeter,
described in this paper, special attention is paid to signal processing and to construction of the essential
building blocks. Shape of the measured signal is
selected so as to contain only the basic harmonic.
Thus, sensor operation at the resonant frequency
(2.2MHz) is provided, and electronic circuits are simple
in construction. The resonant frequency is chosen
according to the minimal phase difference, and amplitude variations of the measured signal for the selected
probes.
The flowmeter structure is based on the microcomputer. Built-in software and hardware allows us to perform multiple measurements in a short time interval
(i.e. to obtain a fast response of the system). For the
fluid flowmeter having a pipe of D = O.lm in diameter,
the following results are obtained. Time interval is
measured with the resolution of 0.1211s. According to
that the estimated velocity resolution is 1.12mmis and
the volume quantity resolution is 8.8ml/s. The instant
flow movement sampling is performed in intervals less
than 60ms, and processing and result display are performed in time intervals less than 0.5s.
The ultrasonic fluid flowmeter described in this paper
belongs to a group of the soft real-time embedded systems and fulfils almost all of the requirements concerning contemporary fluid flowmeters for industrial
applications with respect to sensitivity, automatic zero
and measurement range linearity adjustment, self-testing, displaying and transferring of the measured results
to the host. The accuracy of the flowmeter is better
than 1%. This flowmeter can measure different kinds of
liquids, and operates as an autonomous measurement
equipment or as a part of the complex measuring system.
IEE Proc.-Sci. Meas. Technol.. Vol. 143, No. 5, September 1996
9
References
1 BOBROVNIKOV, C.N., NOVOZILOV, B.M., and SERAFANOV, V.G.: ‘Non-contact flowmeters’ (Mahostroenie,
Moskva, 1985) (in Russian)
2 BERNARD, H.:
‘Ullraschnell-DurchfluBmessing’,
Messen
Prujen/Autornut., 1983, 18, pp. 258-263, (in German)
3 FIEDLER, 0.: ‘Moderne StromungsmeBtechnik’, MewStemenBegeln, 1983, 26, (3), pp. 122-128, (in German)
4 BARNEY, G.C.: ‘Intelligent instrumentation microprocessor
applications in measurement and control’ (Prentice Hall Intermational, New Jersey, 1985)
5 SANDERSON, M.L., and HEMP, J.: ‘Ultrasonic flow-meters - a
review of the State of the art’. International conference on
Advances in flow measurement techniques, University of Warwick,
England, 1981, pp. 157-178
6 CHANDE P.K. and SHARMA P.C.: ‘Ultrasonic flow velocity
sensor based on picosecond timing system’, ZEEE Trcms., 1986,
IE-33, pp. 162-165
LEE Proc.-Sci. Meti.\. Tdinol., Vol. 143, N o . 5, Sc‘pteniher 1996
7 APPEL, J., BRUERE, A., DUNAND, F., and HAZIZA, E.:
‘Microcomputer-controlled measurement application to flow
measurements and to spectrometry’, ZEEE Trans., 1979, IM-28,
pp. 263-269
8 WATSON, C A . : ‘Ultrasonic floy meters’ in DIJSTELBERGEN,
Flow measurement of fluids’
H.H., and SPENCER,, E.A.:
(yrth-Holland Publishing Co., Amsterdam, 1978), pp. 571-577
9 0 HIGGINS, P.J.: ‘Basic instrumentation, industrial measurement’ (McGraw-Hill Inc., New York, 1966), pp. 170-173
10 CARLSON, B., and HOOTMAN, J.: ‘Improve converter resolution with pP tracking techniques’, Electron. Des., 1988, 36, pp.
97-101
11 KRAUT, V.: ‘Handbook on mechanics’ (TehnicXa knjiga Zagreb,
1982) (in Croatian)
12 GOLUBOVIC, L.J. and PAVLOVIC, V.: ‘Ultrasonic method for
fluid flow velocity estimation’. Proceedings of the Yugoslav conference on Electrical measurement, JUKEM, Sarajevo, 1990, part
I, pp. 542-541
13 CHESTER, N.L.: ‘Instrumentation and control: fundamentals
and applications’ (John Wiley & Sons, Inc., New York, 1990), pp.
63-67
333