Abstrict A method for triggering an ultrasonic flow meter comprising a synchronized
ring circuit, consists of periodically turning the ring circuit
on and off by trigger pulses whose repetition period is varied within
the range of possible changes of the repetition period of autocirculation
pulses of the synchronized ring circuit until an autocirculation
pulse is matched with a trigger pulse. At such point, the application
of trigger pulses to the synchronized ring circuit is discontinued
by matching the frequency of the trigger pulses with that of the
autocirculation pulses via continuous automatic phase control of
the trigger pulse frequency. With no autocirculation pulses in the
synchronized ring circuit, the application of trigger pulses is
resumed.
Claims What is claimed is:
1. A method for triggering an ultrasonic flow meter having a synchronized
ring circuit, said method comprising the steps of
applying a train of trigger pulses to said synchronized ring circuit;
periodically turning said synchronized ring circuit on and off
by said trigger pulses;
varying the repetition period of said trigger pulses within the
range of possible changes of the repetition period of autocirculation
pulses of said synchronized ring circuit until an autocirculation
pulse is matched with a trigger pulse;
discontinuing the application of said trigger pulses to said synchronized
ring circuit at the moment an autocirculation pulse is matched with
a trigger pulse, by continuous automatic phase control to match
the frequency of the trigger pulses with that of the autocirculation
pulses; and
resuming the application of said trigger pulses to said synchronized
ring circuit as soon as there are no autocirculation pulses in said
synchronized ring circuit.
2. A method as claimed in claim 1 wherein said synchronized ring
circuit is turned on for periods of time which are not in excess
of the trigger pulse duration.
3. A method as claimed in claim 2 wherein the trigger pulse duration
is limited at the instant an autocirculation pulse of the synchronized
ring circuit is matched with a trigger pulse.
4. A method as claimed in claim 1 wherein the trigger pulse repetition
period is varied with a pitch which is not greater than the trigger
pulse duration.
5. A method as claimed in claim 1 wherein the moment an autocirculation
pulse of the synchronized ring circuit is matched with a trigger
pulse is recorded and serves to indicate that the triggering is
over and that the ultrasonic flow meter is in operation.
6. An ultrasonic flow meter, comprising
at least one synchronized ring circuit;
a shaping amplifier in said synchronized ring circuit, said shaping
amplifier having an input and an output;
an inhibitor in said ring circuit, said inhibitor having a first
input connected to the output of said shaping amplifier, a second
input and an output;
an excitation pulse former in said ring circuit, said excitation
pulse former having a first input connected to the output of said
inhibitor, a second input and an output;
a first electroacoustical transducer electrically connected to
the output of said excitation pulse former;
a second electroacoustical transducer electrically connected to
the input of said shaping amplifier, said first and second electroacoustical
transducers having a gap therebetween intended for passage of a
medium whose flow rate is to be measured, said electroacoustical
transducers being oriented in relation to each other so that one
of them is capable of transmitting and the other is capable of receiving
an acoustical signal traveling at an angle other than 90.degree.
to the flow direction;
an AND gate having a first input, a second input and an output
connected to the second input of said excitation pulse former;
a storage element having a first input connected to the output
of said inhibitor, a second input and an output connected to the
first input of said AND gate;
a search and automatic phase control circuit having a first input
connected to the output of said storage element, a second input
and an output;
a controlled master oscillator having an input connected to the
output of said search and automatic phase control circuit and an
output connected to the second input of said AND gate, to the second
input of said storage element and to the second input of said search
and automatic phase control circuit; and
a measuring unit having an input connected to the output of said
controlled master oscillator.
7. An ultrasonic flow meter as claimed in claim 6 wherein said
measuring unit has a second input, and further comprising a unit
for checking the correctness of measurements, said checking unit
having a first input connected to the output of said storage element,
a second input connected to the output of said controlled master
oscillator and an output connected to the second input of said measuring
unit.
8. An ultrasonic flow meter as claimed in claim 7 further comprising
a frequency divider connected in series between the output of said
controlled master oscillator and a common point of connection of
the second input of said AND gate, the second input of said storage
element and the second input of said search and automatic phase
control circuit.
9. An ultrasonic flow meter as claimed in claim 6 further comprising
a frequency divider connected in series between the output of said
controlled master oscillator and a common point of connection of
the second input of said AND gate, the second input of said storage
element and the second input of said search and automatic phase
control circuit.
Description FIELD OF THE INVENTION
The present invention relates to ultrasonic measurements and, more
specifically, to a method for triggering an ultrasonic flow meter
and an ultrasonic flow meter adapted for that method.
The invention is applicable to pulse-frequency ultrasonic flow
meters intended to automatically monitor the flow rate of oil and
chemical products, liquid foodstuffs, water, etc.
BACKGROUND OF THE INVENTION
In this specification, the term "flow meter" refers to
a flow velocity and flow rate measuring instrument, keeping in mind
that in the case of measurements based on the propagation of acoustical
waves flow rate is a function of flow velocity.
The growing need for highly accurate measurements of flow rates
of all kinds of fluids, including petroleum products, accounts for
increasingly stringent requirements imposed today on pulse-frequency
ultrasonic flow rate measuring techniques carried out with the aid
of ultrasonic flow meters of the type that comprises a synchronized
ring circuit, i.e. a pulse generating system with a delayed acoustic
feedback. Flow meters of this type are accurate only if the triggering
results in a continuous autocirculation of a pulse through the synchronized
ring circuit. This statement applies only to the pulse that carries
useful information. In actual measuring systems, however, the acoustical
channel, i.e. the spacing intended for passage of a medium to undergo
flow rate measurements and found between two electroacoustical transducers,
is subject to periodic disturbances which affect the accuracy of
measurements and are due to the scattering of the ultrasonic beam
by gas bubbles and foreign particles contained in the medium. With
foreign particles drawn away by the flow, one must restore the operating
state of the flow meter, i.e. the continuous autocirculation of
a pulse through the synchronizing ring circuit. A delayed triggering
of the flow meter or an autocirculation of two or more pulses through
the ring circuit distort the results of the measurements.
There is known a method for triggering a pulse-frequency ultrasonic
flow meter, consisting of simultaneously turning on the synchronizing
ring circuit and applying a trigger pulse thereto.
There is known an ultrasonic flow meter adapted for this method
and comprising two synchronized ring circuits, each incorporating,
in a series arrangement, an amplifier, an excitation pulse former
and two electroacoustical transducers separated by a gap intended
for passage of a medium to be subjected to flow rate measurements.
The electroacoustical transducers are so oriented in relation to
each other that one of them can transmit and the other receive an
acoustical signal traveling at an angle .alpha. other than 90.degree.
to the flow direction. The flow meter under consideration further
includes an auxiliary oscillator and a measuring unit which are
both connected to the synchronized ring circuits.
In each synchronized ring circuit of such a flow meter, the oscillator
transmits a pulse to the excitation pulse former whose output signal
is applied to that electroacoustical transducer which sends a pulse
into the medium. This pulse is received by the second electroacoustical
transducer and again applied to the excitation pulse former, whereby
an autocirculation of pulses in the synchronized ring circuit is
effected. The difference .DELTA.f of the frequencies at which the
autocirculation of pulses takes place in the synchronized ring circuits
is indicative of the flow velocity V.
For example, with two electroacoustical transducers arranged on
the opposite sides of a pipeline whose diameter is D,
However, the method under review does not provide for an automatic
retriggering of the flow meter following a temporary disturbance
in the acoustic channel, because it does not include the operation
of resuming the autocirculation of a pulse through the synchronized
ring circuit. The autocirculation indicates that the flow meter
is in good working order and unless it takes place, one must bring
into play and auxiliary oscillator so as to apply a trigger pulse
to the synchronized ring circuit.
The above disadvantage is eliminated in another method for triggering
a pulse-frequency ultrasonic flow meter. The method is as follows.
At the start of the triggering, the pulse former of the synchronized
ring circuit operates in the self-oscillation mode, its natural
oscillation period being selected to be somewhat greater than the
maximum pulse propagation time in the synchronized ring circuit.
As in the foregoing case, the former transmits a pulse to an emitting
transducer whose signal is received by the receiving transducer.
This signal is received before the former of the synchronized ring
circuit produces a second pulse. The received pulse accounts for
a forced triggering of the former, whereby the latter operates in
the forced oscillation mode.
If there are disturbances in the acoustic channel, no pulses arrive
from the receiving transducer. The presence of detected voltage
indicates that the flow meter is back in its operating state and
that one may record the measurements.
There is known an ultrasonic flow meter adapted for the aforedescribed
case method and comprising two synchronized ring circuits connected
to a measuring unit and an amplitude discriminator. The trigger
pulse former of each synchronized ring circuit can operate in both
the self-oscillation and single-shot modes. At the instant the flow
meter is triggered into action, the pulse former of the synchronized
ring circuit is operating in the self-oscillation mode, its natural
oscillation period being selected to be somewhat greater than the
maximum pulse propagation time in the synchronized ring circuit.
Similarly to the aforedescribed case, the former transmits a pulse
to the emitting transducer, which is received by the receiving transducer.
The reception takes place before the former of the synchronized
ring circuit produces a second pulse. The received pulse brings
about a forced triggering of the former which operates in the forced
oscillation mode. If there are disturbances in the acoustic channel,
no pulses arrive from the receiving transducer, and the former operates
in the self-oscillation mode. As soon as the normal working condition
of the acoustic channel is re-established, the first received pulse
brings about a forced triggering of the former of the synchronized
ring circuit, whereby the flow meter is brought back to its operating
state. In order to ascertain the correctness of measurements, the
amplitude detection of the receiving transducer's output signal
is carried out, and the output voltage of the amplitude detector
indicates that the flow meter is in the working state.
The foregoing method is disadvantageous in that the operating condition
of the flow meter cannot be assessed correctly in the presence of
interference at its input.
All the aforedescribed types of flow meters have a low noise immunity
both in the course of triggering and during operation. This is due
to the fact that the synchronized ring circuit conducts current
throughout the operation. If the former of the synchronized ring
circuit is actuated by a spurious signal, two or more signals may
circulate through the ring circuit, distorting the measurements.
Also known is a method for triggering an ultrasonic flow meter
comprising a synchronized ring circuit, which method consists in
applying trigger pulses to the synchronized ring circuit, whereby
the latter is periodically turned on and off. According to the method,
the information on the presence of a pulse circulating through the
synchronized ring circuit is stored so as to restore the operating
condition of the flow meter following a temporary disturbance in
the acoustic channel. The noise immunity of the flow meter is improved
by turning the synchronized ring circuit off for a period of time
which is shorter than the estimated time of propagation of a signal
in the electroacoustic channel.
A known ultrasonic flow meter is adapted for the foregoing triggering
technique and comprises at least one synchronized ring circuit composed,
in a series arrangement, of a shaping amplifier, an inhibitor, an
excitation pulse former and two electroacoustical converters separated
by a gap intended for passage of a medium to be subjected to flow
rate measurements. The transducers are oriented with respect to
each other so as to enable one of them to transmit and the other
receive an acoustical signal traveling at an angle other than 90.degree.
to the direction of the flow. The flow meter further includes a
trigger pulse unit and a measuring unit which are connected to the
synchronized ring circuit. Finally, the flow meter incorporates
a one-shot oscillator connected to the inhibitor. The trigger pulse
unit is a delayed feedback oscillator (cf. USSR Inventor's Certificate
No. 526827 C1. G01 P 5/00).
The latter flow meter operates as follows. The autocirculation
pulse actuates the delayed feedback oscillator which triggers the
flow meter back into action following a temporary disturbance in
the acoustic channel. In order to raise the noise immunity of the
flow meter, the synchronized ring circuit is turned on by the one-shot
oscillator which is actuated by a pulse received by the electroacoustical
transducer. This oscillator is actuated for a period of time which
is shorter than the estimated time of propagation of the signal
in the electroacoustical channel.
The aforedescribed method is disadvantageous in that it does not
provide for automatically triggering the flow meter. Besides, an
increase of the time of propagation of the signal in the medium
accounts for a prolongation of the period during which the synchronized
ring circuit conducts current, which means there is a possibility
of the synchronized ring circuit being turned on by a spurious signal.
The flow meter under consideration cannot be triggered automatically,
which is an important drawback if it is to be incorporated in an
automatic flow rate control system. An increased propagation time
of the signal in the acoustic channel means a longer time during
which the synchronized ring circuit conducts current. The resultant
possibility of the synchronized ring circuit being brought into
action by a spurious signal affects the accuracy of measurements.
Besides, with low flow velocities, the difference of the frequencies
in Equation (1) is quite small. Consider this example: .alpha.=45.degree.,
D=1 m, and V=0.1 m/sec; in this case, .DELTA.f=0.1 Hz, which means
that the measurement time is 10 seconds; clearly, this is too long.
The above considerations rule out the possibility of measuring
instantaneous flow rates, which also affects the overall accuracy
of measurements. On the whole, the flow meter under consideration
does not fit into automatic control systems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for
triggering an ultrasonic flow meter of the type that comprises a
synchronized ring circuit, which method would make the operation
of the flow meter fully automatic.
It is another object of the invention to improve the noise immunity
of the pulse autocirculation process in the synchronized ring circuits.
It is a further object of the invention to provide a criterion
which would make it possible to ascertain that the triggering is
over and the flow meter is in its operating state.
It is a further object of the invention to provide a simple, reliable,
noise-proof and fast-acting ultrasonic flow meter which would be
adapted for automatic triggering and which would ensure a high accuracy
of measurements.
The foregoing and other objects of the present invention are attained
by providing a method for triggering an ultrasonic flow meter comprising
a synchronized ring circuit, which method consists in applying trigger
pulses to the synchronized ring circuit and periodically turning
it on and off. In the method of the invention, the synchronized
ring circuit is turned on and off by trigger pulses whose repetition
period is varied within the range of possible changes of the repetition
period of autocirculation pulses of the synchronized ring circuit
until an autocirculation pulse is matched with a trigger pulse,
at which instant the application of trigger pulses to the synchronized
ring circuit is discontinued by matching the frequency of the trigger
pulses with that of the autocirculation pulses through the use of
automatic phase control of the trigger pulse frequency, the application
of trigger pulses to the synchronized ring circuit being resumed
when there are no autocirculation pulses in said synchronized ring
circuit.
In order to improve the noise immunity, it is expedient that the
synchronized ring circuit should be turned on for periods of time
which are not in excess of the trigger pulse duration. The noise
immunity can also be improved by limiting the trigger pulse duration
at a moment the autocirculation pulse is matched with the trigger
pulse.
The triggering time can be reduced by varying the trigger pulse
repetition period with a pitch not greater than the trigger pulse
duration.
The accuracy of measurements can be improved by recording the moment
the autocirculation pulse is matched with the trigger pulse, which
moment serves to indicate that the start-up is over and that the
flow meter is in operation.
The objects of the present invention are further attained by providing
an ultrasonic flow meter adapted for the foregoing triggering method
and comprising at least one synchronized ring circuit composed,
in a series arrangement, of a shaping amplifier, an inhibitor, an
excitation pulse former and two electroacoustical transducers separated
from each other by a gap intended for passage of a medium whose
flow rate is to be measured, which transducers are oriented in relation
to each other so as to enable one transducer to transmit and other
transducer to receive an acoustical signal traveling at an angle
other than 90.degree. to the flow direction, the flow meter further
including a trigger pulse unit and a measuring unit, both connected
to the synchronized ring circuit. In accordance with the invention,
the trigger pulse unit comprises a controlled master oscillator
whose output is connected to a first input of an AND gate, a first
input of a storage element, a first input of a search and automatic
phase control circuit and a first input of the measuring unit. An
output of the controlled master oscillator is connected to an output
of the search and automatic phase control circuit, whose second
input is connected to an output of the storage element connected,
in turn, to a second input of the AND gate. The output of the AND
gate is connected to a trigger input of the shaping amplifier and
a control input of the inhibitor whose output is connected to a
second input of the storage element.
The objects of the present invention are also attained by providing
the flow meter with a unit for checking the correctness of measurements,
whose inputs are connected to the output of the storage element
and that of the controlled master oscillator, respectively, whereas
its output is connected to an enable input of the measuring unit.
The objects of the invention are further attained by providing
the trigger pulse unit with a frequency divider interposed in series
between the output of the controlled master oscillator and a common
point of connection of the input of the storage element, the input
of the search and automatic phase control circuit and the input
of the AND gate.
The method for triggering an ultrasonic flow meter and the flow
meter adapted for this method make it possible to automate flow
rate measurements. The invention makes it possible to improve the
noise immunity and operating speed of flow meters and to raise the
accuracy of measurements.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other objects and advantages of the present invention will become
more apparent from a consideration of the following detailed description
of preferred embodiments thereof, taken in conjunction with the
accompanying drawings, wherein:
FIG. 1 is a block diagram of an embodiment of an ultrasonic flow
meter of the invention;
FIG. 2 is a block diagram of the ultrasonic flow meter of FIG.
1 including a unit for checking the correctness of measurements,
in accordance with the invention;
FIG. 3 is a block diagram of the ultrasonic flow meter of FIG.
1 including a frequency divider, in accordance with the invention;
FIGS. 4a, b, c, d, e are voltage diagrams which explain the operation
of the flow meter of FIG. 1;
FIGS. 5a, b, c, d, e, f are voltage diagrams which explain the
operation of the flow meter of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
The method according to the invention for triggering an ultrasonic
flow meter comprising a synchronized ring circuit is as follows.
Trigger pulses are applied to the synchronized ring circuit, their
repetition period varying within the range of possible changes of
the repetition period of autocirculation pulses of the synchronized
ring circuit. This means that the minimum trigger pulse period,
T.sub.min, must be less than the minimum time of propagation of
a signal in the acoustic channel:
where
L is the distance between the electroacoustical transducers, covered
by acoustical waves traversing the medium whereof the flow rate
is measured;
C.sub.max is the maximum speed of propagation of ultrasound in
the medium, which depends on the properties of the medium and external
conditions;
V'.sub.max is the projection of the maximum possible velocity of
the medium on the direction of the ultrasonic beam.
The maximum period, T.sub.max, of trigger pulses must be greater
than the maximum time of propagation of the signal in the acoustic
channel:
where C.sub.min is the minimum speed of propagation of ultrasound
in the medium, depending on the properties of the medium and external
conditions.
The pitch of the changes of the period is not to be greater than
the trigger pulse duration.
The trigger pulse repetition period is varied until an autocirculation
pulse coincides in time with a trigger pulse, whereupon the application
of trigger pulses to the synchronized ring circuit is stopped by
matching the frequency of trigger pulses with that of autocirculation
pulses, which is done by means of continuous phase adjustment of
the frequency of trigger pulses.
The phase adjustment goes on as long as the flow meter is in operation.
Disturbances in the acoustic channel normally lead to a disappearance
of the autocirculation pulses. In such cases, phase-adjusted pulses
are applied to the synchronized ring circuit. With the synchronized
ring circuit in operation, it is periodically turned on and off
by trigger pulses. The synchronized ring circuit may be turned on
for specified periods of time. However, it is strongly recommended
that it should be turned on for periods of time which are not in
excess of the trigger pulse duration which should be limited at
an instant an autocirculation pulse is matched with a trigger pulse.
Double-frequency circulation of pulses through the synchronized
ring circuit is avoided by meeting this condition:
The foregoing may be easily complied with, keeping in mind that
normally
The flow meter according to the invention, whereof a block diagram
is presented in FIG. 1 is intended for measuring the flow rates
of liquid media transported through pipelines and is adapted for
the method of this invention.
This flow meter comprises at least one synchronized ring circuit
1 (FIG. 1) incorporating a shaping amplifier 2 connected to an input
3 of an inhibitor 4 connected to an input 5 of an excitation pulse
former 6. The flow meter further includes two electroacoustical
transducers, 7 and 8 separated by a gap 9 intended for passage
of a medium whose flow rate is to be measured.
The transducers 7 and 8 are arranged on the opposite sides of a
pipeline and oriented in relation to each other so as to enable
one of them to transmit an acoustical signal and the other to receive
that signal. The acoustical signal travels at an angle .alpha. other
than 90.degree. to the direction of the flow through the pipeline.
The ultrasonic flow meter according to the invention further includes
a trigger pulse unit 10 and a measuring unit 11 which are both connected
to the synchronized ring circuit 1.
The trigger pulse unit 10 comprises a controlled master oscillator
12 whose output 13 is connected to an input 14 of an AND gate 15
an input 16 of a storage element 17 an input 18 of a search and
automatic phase control circuit 19 and an input 20 of the measuring
unit 11. An input 21 of the controlled master oscillator 12 is connected
to an output 22 of the search and automatic phase control circuit
19. An input 23 of the search and automatic phase control circuit
19 is connected to an output 24 of the storage element 17 which,
in turn, is connected to an input 25 of the AND gate 15 whose output
26 is connected to a trigger input 27 of the former 6 and a control
input 28 of the inhibitor 4 whose output 29 is connected to an input
30 of the storage element 17.
Unlike the embodiment of FIG. 1 the ultrasonic flow meter of FIG.
2 additionally includes a unit 31 for checking the correctness of
measurements. Inputs 32 and 33 of the unit 31 are connected to the
output 24 of the storage element 17 and the output 13 of the controlled
master oscillator 12 respectively. An output 34 of the unit 31
for checking the correctness of measurements is connected to an
enable input 35 of the measuring unit 11.
Unlike the trigger pulse unit 10 of FIG. 1 its version 10' of
FIG. 3 is provided with a frequency divider 36 connected in series
between the output 13 of the controlled master oscillator 12 and
a common point 37 of connection of the input 16 of the storage element
17 the input 18 of the search and automatic phase control circuit
19 and the input 14 of the AND gate 15.
The function of the inhibitor 4 may be performed by an EXCEPT gate.
The function of the storage element 17 may be performed by an RS
flip-flop. The function of the unit 31 (FIG. 2) for checking the
correctness of measurements may be performed by a D flip-flop.
The search and automatic phase control circuit 19 is a potential-accumulating
element, such as a capacitor, complete with a discharger.
The triggering method of the present invention is applicable to
the ultrasonic flow meter according to the invention and is carried
out as follows.
From the output 22 (FIG. 1) of the search and control circuit 19
voltage is applied to the input 21 of the controlled master oscillator
12 readjusting its frequency. At a moment supply voltages are applied,
voltage across the output 22 of the search and phase control circuit
19 is zero. The pulse period of the controlled master oscillator
12 is at its minimum, i.e. T.sub.min (FIG. 4a), and less than the
minimum time of propagation of a signal through the acoustic channel.
The period of the controlled master oscillator 12 is selected so
that the maximum pulse period, T.sub.max, at its output should be
greater than the maximum time of propagation of a signal through
the acoustic channel. This means that the conditions of Equations
(2) and (3) must be complied with.
At a moment of the arrival of supply voltages, there is no pulse
at the output 13 of the controlled master oscillator and a low level
is observed at said output 13. This level is stored by the storage
element 17 with a high level at its output 24. In the initial state,
there is a high level at the output 26 of the AND gate 15. The output
24 of the storage element 17 is connected to the input 25 of the
AND gate, so the first positive pulse 38 (FIG. 4a) is applied from
the output 13 of the controlled master oscillator 12 to the AND
gate 15. As this takes placed, a pulse 39 (FIG. 4b) is applied to
the input 28 (FIG. 1) of the inhibitor 4 and drives the latter into
conduction. The pulse 39 is also applied to the input 27 of the
former 6 and drives it into conduction. The former 6 is actuated
by the trailing edge of the positive pulse 39 (FIG. 4b).
A pulse 40 (FIG. 4c) is applied from the former 6 (FIG. 1) to the
transducer 7 to be converted to an ultrasonic signal which traverses
the medium whose flow rate is to be measured. The acoustic signal
is then received by the transducer 8 which converts it to an electric
signal. The electric signal is applied to the shaping amplifier
2 which amplifies it and transforms it into a square pulse 41 (FIG.
4d). The pulse 41 is applied to the inhibitor 4 (FIG. 1). The pulse
produced by the shaping amplifier 2 is delayed with respect to the
pulse arriving from the output of the former 6 by a time t. The
period of the controlled master oscillator 12 is kept at a minimum
and less than t. As a result, the next pulse 42 (FIG. 4b) is applied
from the output 26 of the AND gate 15 to the input 28 of the inhibitor
4 before the arrival of the pulse from the output of the shaping
amplifier 2. Thus, the inhibitor 4 is cut off by the moment of arrival
of the pulse from the shaping amplifier 2. Nevertheless, the pulse
42 (FIG. 4b) from the output of the AND gate 15 passes through the
acoustic channel as the first pulse, etc. At the same time positive
pulses are applied from the output 13 of the controlled master oscillator
12 to the input 18 of the search and automatic phase control circuit
19 whereby its output voltage is increased (FIG. 4e). The period
of the controlled master oscillator 12 increases until by the time
a pulse 43 (FIG. 4d) from the shaping amplifier 2 is applied to
the inhibitor 4 the latter is driven into conduction by a pulse
44 (FIG. 4a) arriving from the master oscillator 12. The pulse 43
(FIG. 4d) is applied from the shaping amplifier 2 to the input 5
(FIG. 1) of the former 6 which is actuated by the leading edge of
the negative pulse. The synchronizing ring circuit is turned on
per a synchropulse 45 of FIG. 4c. At the same time the negative
pulse is applied from the output 29 of the inhibitor 4 to the input
30 (FIG. 1) of the storage element 17. As a result, there is a low
level at the output 24 of the storage element 17 and an inhibit
signal is applied to the AND gate 15 whereby the duration of a
pulse 46 (FIG. 4b) at the output of the AND gate 15 is reduced per
a time t.sub.1 (FIGS. 4a to 4e). The trailing edge of the positive
pulse at the output 26 of the AND gate 15 is matched with the leading
edge of the negative pulse at the output 29 of the inhibitor 4
which means that further operation of the controlled master oscillator
12 has no effect upon the synchronized ring circuit 1. The controlled
master oscillator 12 is thus automatically switched off.
At this point, the search and automatic phase control circuit 19
stops operating in the search mode and starts matching the phase
of the pulses produced by the master oscillator 12 with that of
the autocirculation pulses of the synchronized ring circuit 1. The
trailing edge of the positive pulse arriving from the controlled
master oscillator 12 again establishes a high level at the output
of the storage element 17. The trigger pulse from the master oscillator
12 is applied to the input 18 of the search and automatic phase
control circuit 19. Pulses from the output 24 of the storage element
17 are applied to the input 23 of the circuit 19. The leading edge
of these pulses is matched with that of the ring circuit pulse passed
through the inhibitor 4. The search and automatic phase control
circuit 19 determines the time difference between the trigger pulse
and the leading edge of the autocirculation pulse of the synchronized
ring circuit. The difference is converted to a control signal which
is used to control the phase and frequency of the controlled master
oscillator 12. These parameters are controlled so that the leading
edge of the autocirculation pulse of the synchronized ring circuit
should be found within the trigger pulse, preferably, in its middle.
Thus the leading edge of the trigger pulse actuates the inhibitor
4 and the synchronized ring circuit. On the other hand, the inhibitor
4 and ring circuit 1 are cut off by the leading edge of the autocirculation
pulse. Thus, the time during which the synchronized ring circuit
conducts current amounts to half the trigger pulse duration. From
the viewpoint of noise immunity, the duration of the trigger pulse
should be 1 to 2 per cent of the autocirculation pulse repetition
period.
Thus, the output pulses of the controlled master oscillator 12
are related in phase and frequency to the pulses of the synchronized
ring circuit. The repetition frequency of the synchronized ring
circuit pulses can be determined by applying pulses from the output
of the controlled master oscillator 12 to the input 20 of the measuring
unit 11.
In case of a disturbance in the acoustic channel, output pulses
of the controlled master oscillator 12 continue to arrive at the
input of the search and automatic phase control circuit 19 increasing
voltage at its output. This is accompanied by an increase of the
trigger pulse period.
This period is at its maximum with a maximum voltage at the output
of the search and automatic phase control circuit 19. A discharge
follows to reduce that voltage to zero, whereupon the flow meter
operates as hereinbefore described.
The ultrasonic flow meter of FIG. 2 is similar to that of FIG.
1 but operates to permit the checking of the correctness of measurements.
The idea is to find out if each pulse of the synchronized ring circuit
1 is matched with the trigger pulse. For this purpose, pulses are
applied from the output 24 of the storage element 17 to the information
input 32 of the unit 31 for checking the correctness of measurements.
The unit 31 is also referred to as the storage element 31. Meanwhile,
pulses are aplied from the output 13 of the controlled master oscillator
12 to the input 33 of the storage element 31 which is a synchroinput.
The present of voltage at the output 34 of the storage element 31
indicates that the flow meter is in good working condition. This
voltage is applied to the enable input 35 of the measuring unit
11.
In case of a disturbance in the acoustic channel, i.e., the gap
9 filled with the medium whose flow rate is being measured, a high
level is observed at the information input 32 of the storage element
31 at the time of arrival of the trailing edge of the pulse applied
from the controlled master oscillator 12 to the input 33 of the
storage element 31. The high level indicates that the synchronized
ring conduit 1 is off. The trailing edge of the trigger pulse erases
the information on the matching of the trigger pulses and those
of the synchronized ring circuit. An inhibit signal is applied from
the output 34 of the storage element 31 to the enable input 35 of
the measuring unit 11. From the output 13 of the controlled master
oscillator 12 pulses continue to arrive at the input 18 of the
search and automatic phase control circuit 19 increasing the voltage
at its output 22. As this takes place, the trigger pulse period
increases. When the voltage at the output 22 of the search and automatic
phase control circuit 19 reaches a maximum, a discharge follows
to reduce that voltage to zero, whereupon the flow meter operates
as hereinbefore described.
To actuate the flow meter during the very first cycle of variation
of the trigger pulse period, it is necessary that each next trigger
pulse period should be changed by not more than the trigger pulse
duration.
The only difference between the ultrasonic flow meter of FIG. 3
and that of FIG. 1 is that the former includes the frequency divider
36 incorporated in the triggering unit 10'. The divider 36 makes
it possible to divide the frequency of pulses (FIG. 5a) at the output
of the controlled master oscillator 12 (FIG. 3) by K. The output
pulses of the master oscillator 12 are related in phase and frequency
to the pulses of the synchronized ring circuit 1 but the frequency
of the former pulses is K times higher than that of the latter pulses.
If a flow meter according to the invention comprises two synchronized
ring circuits, the measuring unit will find the following difference
.DELTA.F between the frequencies of the controlled master oscillators:
With K=100 the measurement time is 0.1 sec. Thus, the flow meter
of FIG. 3 is fit for instantaneous flow rate measurements and for
actual operation as part of an automatic control system.
The voltage diagrams of FIGS. 5b, c, d, e and f, which illustrate
the operation of the ultrasonic flow meter of FIG. 3 are similar
to the voltage diagrams of FIGS. 4a, b, c, d, e. The only difference
is that FIG. 5b, which corresponds to FIG. 4a, shows a train of
pulses at the output of the frequency divider 36.
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