Abstrict An ultrasonic wave blood flow meter comprises a probe which sends
to and receives an ultrasonic wave reflected with Doppler effect
from the blood flow, a detecting circuit for converting a frequency
variation of the received reflected wave into a first signal whose
amplitude varies with frequency and a second signal whose amplitude
is kept constant, and first and second effective-value detecting
circuits for obtaining d.c. components of the first and second signals.
A level discrimination circuit is further provided for discriminating
the level of the d.c. component detected by the second effective-value
detecting circuit. First and second sensitivity-variable amplifiers
are also provided for varying their sensitivities in accordance
with the result of the level discrimination circuit. A dividing
circuit divides the d.c. component amplified by the first sensitivity-variable
amplifier by the d.c. component amplified by the second sensitivity-variable
amplifier, and a voltage hold circuit holds the output of the dividing
circuit in accordance with the discrimination result of the level
discrimination circuit.
Claims We claim:
1. An ultrasonic flow meter for measuring the rate of flow of a
fluid comprising
probe means for sending and receiving an ultrasonic signal which
impinges on said fluid and is reflected therefrom;
detecting means coupled to said probe means for converting frequency
variations in said reflected ultrasonic signal due to the Doppler
effect into a first signal having an amplitude which varies with
frequency and a second signal having an amplitude which is constant
and independent of frequency, each of said first and second signals
having a d.c. component;
first and second effective-value detecting means coupled to said
detecting means, said first and second effective-value detecting
means detecting the d.c. components of said first and second signals
respectively;
level discrimination means coupled to the output of said second
effective-value detecting means, said level discrimination means
determining the magnitude of the d.c. component of said second signal;
first and second sensitivity-variable amplification means coupled
to the outputs of said first and second effective-value detecting
means respectively and to the output of said level discrimination
means, the sensitivity of said first and second amplification means
being varied in accordance with the output of said level discrimination
means;
dividing means coupled to the outputs of said first and second
sensitivity-variable amplification means, said dividing means dividing
the d.c. component detected by said first effective-value detecting
means and amplified by said first sensitivity-variable amplification
means by the d.c. component detected by said second effective-value
detecting means and amplified by said second sensitivity-variable
amplification means; and
hold means coupled to the outputs of said dividing means and said
level discrimination means for holding the output of said divider
means in accordance with the output of said level discrimination
means.
2. An ultrasonic flow meter according to claim 1 wherein said
detecting means comprises an orthogonal phase detection circuit
having first and second outputs and an input coupled to said probe
means, the signals generated at said first and second outputs having
a 90.degree. phase difference; a differentiation circuit coupled
to the first output of said orthogonal phase detection circuit;
a multiplication circuit coupled to the second output of said phase
detection circuit and to the output of said differentiation circuit,
said multiplication circuit multiplying the output of said second
orthogonal phase detection circuit and the output of said differentiation
circuit to form the product of the two signals; and a squaring circuit
for squaring the second output of said orthogonal phase detection
circuit.
3. An ultrasonic flow meter for measuring the rate of flow of a
fluid comprising
probe means for sending and receiving an ultrasonic signal which
impinges on said fluid and is reflected therefrom;
detecting means coupled to said probe means for converting frequency
variations in reflected ultrasonic signal due to the Doppler effect
into a first signal having an amplitude which varies with frequency
and a second signal having an amplitude which is constant and independent
of frequency, each of said first and second signals having a d.c.
component, said detecting means comprising
an orthogonal phase detection circuit having first and second outputs
and an input coupled to said probe means, the signals generated
at said first and second outputs having a 90.degree. phase difference;
a differentiation circuit coupled to the first output of said orthogonal
phase detection circuit; and
first and second squaring circuits, said first squaring circuit
being coupled to the output of said differentiation circuit and
said second squaring circuit being coupled to the second output
of said orthogonal phase detection circuit;
first and second effective-value detecting means coupled to said
detecting means, said first and second effective-value detecting
means detecting the d.c. components of said first and second signals
respectively;
level discrimination means coupled to the output of said second
effective-value detecting means, said level discrimination means
determining the magnitude of the d.c. component of said second signal;
first and second sensitivity-variable amplification means coupled
to the outputs of said first and second effective-value detecting
means respectively and to the output of said level discrimination
means, the sensitivity of said first and second amplification means
being varied in accordance with the output of said level discrimination
means;
dividing means coupled to the outputs of said first and second
sensitivity-variable amplification means, said dividing means dividing
the d.c. component detected by said first effective-value detecting
means and amplified by said first sensitivity-variable amplification
means by the d.c. component detected by said second effective-value
detecting means and amplified by said second sensitivity-variable
amplification means; and
hold means coupled to the outputs of said dividing means and said
level discrimination means for holding the output of said divider
means in accordance with the output of said level discrimination
means.
4. An ultrasonic flow meter for measuring the rate of flow of a
fluid comprising
probe means for sending and receiving an ultrasonic signal which
impinges on said fluid and is reflected therefrom;
detecting means coupled to said probe means for converting frequency
variations in said reflected ultrasonic signal due to the Doppler
effect into a first signal having an amplitude which varies with
frequency and a second signal having an amplitude which is constant
and independent of frequency, each of said first and second signals
having a d.c. component, said detecting means comprising
a phase detection circuit having an input coupled to said probe
means;
a differentiation circuit coupled to the output of said phase detection
circuit; and
first and second squaring circuits, said first squaring circuit
being coupled to the output of said differentiation circuit and
said second squaring circuit being coupled to the output of second
phase detection circuit;
first and second effective-value detecting means coupled to said
detecting means, said first and second effective-value detecting
means detecting the d.c. components of said first and second signals
respectively;
level discrimination means coupled to the output of said second
effective-value detecting means, said level discrimination means
determining the magnitude of the d.c. component of said second signal;
first and second sensitivity-variable amplification means coupled
to the outputs of said first and second effective-value detecting
means respectively and to the output of said level discrimination
means, the sensitivity of said first and second amplification means
being varied in accordance with the output of said level discrimination
means;
dividing means coupled to the outputs of said first and second
sensitivity-variable amplification means, said dividing means dividing
the d.c. component detected by said first effective-value detecting
means and amplified by said first sensitivity-variable amplification
means by the d.c. component detected by said second effective-value
detecting means and amplified by said second sensitivity-variable
amplification means; and
hold means coupled to the outputs of said dividing means and said
level discrimination means for holding the output of said divider
means in accordance with the output of said level discrimination
means.
Description BACKGROUND OF THE INVENTION
This invention relates to an ultrasonic wave blood flow meter for
measuring the flow rate and the flow speed, etc. of blood by depending
upon the Doppler effect of the ultrasonic wave signal reflected
from the blood flow.
It is well known that, if an ultrasonic wave is radiated and the
Doppler effect of the reflected wave is measured, a signal proportional
to the flow rate can be obtained. Furthermore, various methods for
obtaining the flow speed from a signal proportional to the flow
rate have been proposed. A typical example is the so-called arithmetic
method. According to this method, the Doppler signal reflected from
the fluid is orthogonally or quadrature-phase detected to obtain
two signals V.sub.A and V.sub.B with their phases different by 90.degree.
from each other. The signal V.sub.A is differentiated and multiplied
with the signal V.sub.B. The d.c. component of this signal is divided
by the d.c. component of V.sub.B.sup.2. Then, we obtain a voltage
proportional to the flow speed.
However, this method has the following defect. The operation accuracy
of the currently available divider is expressed as
where V.sub.I is the denominator voltage and e is the standard
error. Therefore, if we perform division by using such a divider,
the dividing operation error increases in inverse proportion to
the voltage V.sub.B. Hence, no accurate flow speed is obtained.
When V.sub.B is zero, the output of the divider remains undefined.
Due to noise of the input signal, a similar result as in the case
of a rapid flow may be obtained. Another defect is that the output
in the case without flow or the zero level is not defined well.
This invention is intended to solve the abovementioned problems
of the prior art. The objective is to provide an ultrasonic blood
flow meter which can keep the operating precision of the divider
at a value as constant as possible for such various flow rates and
yet can give a zero-frequency output in the absence of flow.
SUMMARY OF THE INVENTION
According to the ultrasonic wave blood flow meter provided by this
invention, the frequency variation in the Doppler signal received
by a probe is converted into a first signal whose amplitude varies
with frequency and a second signal whose amplitude is kept constant
without regard to frequency. D.c. components of the first and second
signals are amplified by two sensitivity-variable amplifiers which
switch their sensitivities in accordance with the level of d.c.
component of the second signal. Thereafter, the amplified d.c. component
of the first signal is divided by that of the second signal. The
divided output is held for a prescribed period.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be made apparent from the following
detailed description taken in conjunction with the accompanying
drawings, in which:
FIG. 1 is a rough block diagram showing a prior-art ultrasonic
wave blood flow meter;
FIG. 2 is a block diagram of an ultrasonic wave blood flow meter
according to one embodiment of this invention;
FIG. 3 and FIG. 4 are block diagrams showing another constitution
of a detecting means of this invention. In these figures, the same
reference numerals are used to denote like parts.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before the explanation of this invention, one example of a prior
art ultrasonic wave blood flow meter will be described. In FIG.
1 the ultrasonic wave radiated from a probe 1 is reflected and
received by the probe after being subjected to the Doppler effect
by the flow of a fluid such as a blood. The wave received by the
probe 1 is amplified by a receiving circuit 2 and introduced into
an orthogonal-phase detection circuit 3 where signals V.sub.A and
V.sub.B with their phases shifted by 90.degree. from each other
are obtained. These signals V.sub.A and V.sub.B are related to the
blood flow and expressed as follows.
where A is the amplitude and w is the angular deviation frequency.
The signal V.sub.A is supplied to a differentiator 4 and the frequency
variation is converted into a voltage variation V.sub.A ' as
ps V.sub.A ' and V.sub.B are supplied to a multiplication circuit
5 and then to an effective-value detecting circuit (RMS detector)
6. The output of the effective value detecting circuit 6 becomes
A.sup.2 .omega., which is a d.c. voltage proportional to the flow
rate. V.sub.B is also supplied to another effective value detecting
circuit 6' through a squaring circuit 7. The output of this effective
value detecting circuit 6' becomes A.sup.2. If the output A.sup.2
.omega. is divided by the output A.sup.2 by a divider 8 we obtain
a d.c. output voltage which is proportional to .omega. or to the
flow speed.
However, since this arrangement has the aforementioned operation
error of the divider 8 no accurate flow speed is obtained. When
V.sub.B becomes zero, a large error appears.
FIG. 2 shows a block diagram showing one embodiment of this invention
which solves these defects.
In this figure, 1 denotes a probe, 2 a receiving circuit, 3 an
orthogonal-phase detection circuit, 4 a differentiation circuit,
5 a multiplication circuit, 6 and 6' effective-value detecting circuits,
and 7 a squaring circuit. The circuit configuration containing these
circuits is the same as that of the prior art in FIG. 1. A reflected
wave received by the probe 1 is signal-processed (amplification,
etc.) by the receiving circuit 2 and converted into signals V.sub.A
and V.sub.B with their phases different by 90.degree. in the orthogonal-phase
detector 3.
The one signal V.sub.A is differentiated by the differentiator
4 and supplied to the multiplication circuit 5 where it is multiplied
with the other signal V.sub.B. The output is supplied to an effective-value
detecting circuit 6 to obtain an output A.sup.2 .omega.. Signal
V.sub.B is passed through a squaring circuit 7 and another effective
value detecting circuit 6' to obtain an output A.sup.2.
Here, the detecting means comprising the orthogonal-phase detection
circuit 3 the differentiation circuit 4 the multiplication circuit
5 and the squaring circuit 7 has a function of separating the signal
from the receiving circuit 2 into a signal whose amplitude varies
with frequency and a signal whose amplitude is kept constant without
regard to the frequency.
Next, the output from the effective-value detecting circuit 6'
is introduced into a level discriminator 9 to discriminate the output
level of the effective-value detecting circuit 6' and indicate a
sensitivity to sensitivity-variable amplifiers 10 and 10' such that
the operation error of the following divider 8 can be small. The
output A.sup.2 .omega. of the effective-value detecting circuit
6 and the output A.sup.2 of the effective-value detecting circuit
6' are sent to the divider 8 after the sensitivities of the sensitivity-variable
amplifiers 10 and 10' are adjusted according to the indication of
the level discriminator 9. Through division of the output A.sup.2
.omega. by the output A.sup.2 a d.c. voltage proportional to .omega.
is obtained. This output is supplied to a voltage hold circuit 11
where an output is generated in accordance with the discrimination
result of the level discriminator 9. Thus, the speed of the direction
of flow are measured. The voltage hold circuit 11 is of such a type
that holds the voltage for a prescribed time and thereafter the
output decays gradually to zero. The circuit is constituted with
a condenser and a switch and is called a sample-hold circuit.
In the above embodiment, when the level discriminator 9 discriminates
that the magnitude of the signal from the effective-value detecting
circuit 6' is finite (not null), the switch which constitutes the
voltage hold circuit 11 is always turned on so that the divided
result of the divider 8 is given as an output.
On the other hand, if the level discriminator 9 discriminates that
the signal from the effective-value detecting circuit 6' assumes
a zero voltage, the switch which constitutes the voltage hold circuit
11 is turned off and a voltage stored in the condenser just before
the zero voltage has been detected is given as an output.
In the circuit configuration of this invention, even if the measuring
point deviates from the blood vessel and the flow speed drops to
zero suddenly, the abnormally large voltage which would appear in
the conventional circuit is not obtained, since the output can be
compensated by a voltage at a time just before it has dropped to
zero.
When the flow speed becomes zero for a long period, zero value
is given to the output after a predetermined time. Therefore, no
large errors happen even in the absence of flow.
Although in the above embodiment an orthogonal-phase detection
circuit 3 is used in the detecting means 12 where the one signal
is processed by the differentiator 4 and the multiplication circuit
5 while the other signal is processed by the squaring circuit 7
any detecting means will do as long as it performs the function
of separating the output supplied from the receiving circuit 2 into
a first signal whose amplitude varies with frequency and a second
signal whose amplitude is kept constant without regard to frequency.
For example, arrangements as shown in FIGS. 3 and 4 work as the
detecting means 12.
In FIG. 3 the output from the preceding receiving circuit is supplied
to an orthogonal-phase detecting circuit 3 where signals V.sub.A
and V.sub.B with the phases different by 90.degree. from each other
are generated. The one signal is differentiated by a differentiator
circuit 4 and multiplied by itself in a squaring circuit 13 to become
a signal whose amplitude varies with frequency. The other signal
V.sub.B is multiplied by itself in a squaring circuit 7 to become
a signal with a constant amplitude. Thereafter, the same signal
processing as in the embodiment of FIG. 2 is performed to obtain
the flow speed.
In FIG. 4 the output from the preceding circuit is introduced
into a phase detection circuit 14. The output V is passed through
a differentiation circuit 4 and a squaring circuit 13 to obtain
a signal whose amplitude varies with frequency. The output V is
passed to another squaring circuit 7 to obtain a signal with a constant
amplitude. Thereafter, the same signal processing as in the embodiment
of FIG. 2 is performed to obtain the flow speed.
Both embodiments of FIGS. 3 and 4 have the same effect as that
of FIG. 2.
As described above, the present invention provides an ultrasonic
wave blood flow meter characterized by comprising a probe which
sends and receives an ultrasonic wave at a suitable angle with respect
to the blood flow; detecting means for converting a frequency variation
of the reflected wave due to the Doppler effect which is received
by said probe into a first signal whose amplitude varies with the
frequency and a second signal whose amplitude is constant without
regard to the frequency; first and second effective-value detecting
means for detecting d.c. components of said first and second signals
obtained by said detecting means; level discrimination means for
discriminating level of the d.c. component detected by said second
effective-value detecting means; first and second sensitivity-variable
amplification means for varying their sensitivities in accordance
with the result of said level discrimination means; dividing means
for dividing the d.c. component detected by said first-effective
value detecting means and amplified by said first sensitivity-variable
amplification means, by the d.c. component detected and amplified
by said second sensitivity-variable amplification means; and hold
means for holding the output of said dividing means in accordance
with the discrimination result of said level discrimination means.
The flow speed of blood can be measured always accurately without
regard to the level of the reflected ultrasonic wave. Even in the
case without flow, the measured result does not become indeterminate
and no large errors appear. |