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DESCRIPTION JP2003014703

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DESCRIPTION JP2003014703
[0001]
【0001】 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
relates to a technology for improving detection accuracy in an ultrasonic bubble detection
apparatus for detecting bubbles in a liquid using ultrasonic waves.
【0003】
2. Description of the Related Art The technology for detecting air bubbles in liquid using
ultrasonic waves is to prevent air bubbles from being mixed in human blood with a artificial
dialysis device or a dripping device in the medical field, and to a developer in the field of
photography. Are widely used for the purpose of preventing air bubbles from being mixed, and
monitoring abnormalities in various plants.
【0005】
Conventionally, such bubble detection using ultrasonic waves is performed by detecting a change
in the transmission intensity of ultrasonic waves from the liquid or the reflection intensity from
the liquid due to the presence of bubbles, of the ultrasonic waves output toward the liquid. It will
be.
【0006】
FIG. 4 shows the configuration of a conventional typical ultrasonic bubble detector.
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【0007】
In the figure, reference numeral 501 is an oscillation circuit, 502 is a drive circuit, 503 is an
ultrasonic wave transmission element, 504 is a tube through which liquid flows, 505 is an
ultrasonic wave reception element, 506 is an amplification circuit, 507 is a rectification circuit,
and 508 is a comparison circuit. .
【0008】
In such a configuration, the ultrasound transmission element 503 is driven by the oscillation
signal of the oscillation circuit 501 via the drive circuit 502 to direct ultrasound into the tube
504. The ultrasound transmitted through the tube 504 and the liquid in the tube is received by
the ultrasound receiving element 505 and converted into an electrical signal, and is amplified by
the amplification circuit 506 with a predetermined gain. The amplified electrical signal is
rectified by the rectifying circuit 507, converted into a transmission intensity level signal, and
output to the comparing circuit 508. The comparison circuit 508 compares the input
transmission intensity level signal with the threshold value Th stored in advance, and outputs the
comparison result as a bubble detection signal.
【0009】
That is, in such an ultrasonic bubble detection device, when the transmission intensity level falls
below a predetermined threshold value based on the decrease in the transmission intensity level
of the ultrasonic wave when the bubble is present in the liquid It is assumed that air bubbles are
present inside.
【0010】
[0011] The strength of the ultrasonic waves transmitted through the tube and the liquid is not
only due to the presence of air bubbles, but also due to the fixed external factors such as the wall
thickness and dirt of the tube. It will differ due to differences and dynamic external factors such
as changes in the surrounding environment. For example, when considering application to a
hemodialysis apparatus, there are various types of tubes used.
【0012】
For this reason, according to the above-mentioned conventional typical ultrasonic bubble
detection apparatus, the influence of the difference of the fixed external factor is offset, and also
the false detection is made to the fluctuation of the external factor during the detection
operation. There is a problem that the operator must properly set the threshold used in the
comparison circuit by trial and error before the detection operation is started.
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【0013】
Also, if the threshold is set so as not to misdetect the air bubble against the fluctuation of the
dynamic external factor, the threshold is set to a value having a relatively large difference with
respect to the maximum value that the transmission intensity level signal should have There is a
problem that small bubbles can not be detected well because of the need.
【0014】
Then, this invention makes it a subject to provide the ultrasonic detection apparatus which can
detect a bubble appropriately irrespective of the change of an external factor. Another object of
the present invention is to provide an ultrasonic bubble detection apparatus capable of properly
detecting even small bubbles.
【0015】
In order to achieve the above object, the present invention is, for example, an ultrasonic bubble
detection apparatus for detecting bubbles in a liquid by using ultrasonic waves, which is provided
for a liquid Transmitting means for transmitting an ultrasonic signal, Receiving means for
receiving an ultrasonic signal that has been transmitted through a liquid or reflected from a
liquid flow path and converted into a received signal that is an electrical signal, Amplification
means for amplifying the received signal, Amplification Conversion means for converting the
received signal into a reception level signal representing the amplitude of the reception signal,
bubble detection means for detecting air bubbles in the liquid according to the change in the
reception level signal, and the level of the reception level signal And an automatic gain control
circuit for controlling the gain of the amplification means such that the value of the detection
means becomes constant.
【0017】
According to such an ultrasonic bubble detection apparatus, the gain in the amplification means
is automatically adjusted so that the reception level of the received ultrasonic signal does not
fluctuate due to the difference in fixed external factors such as the thickness of the tube and the
dirt. . Therefore, even if the operator does not adjust the threshold used in the comparison circuit
before the start of the detection operation, it is possible to automatically offset the influence of
the difference in the external factor. In addition, the influence can be similarly offset by the
automatic adjustment of the gain of the amplification means with respect to the fluctuation of the
external factor during the detection operation. Therefore, air bubbles can be properly detected
regardless of differences or fluctuations in external factors.
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【0018】
Further, in order to achieve the above object, according to the present invention, a transmitting
means for transmitting an ultrasonic signal to a liquid, and a received signal which is an electric
signal by receiving an ultrasonic signal transmitted through a liquid or reflected from a liquid
flow path Reception means for converting into a signal, conversion means for converting a
reception signal into a reception level signal representing the amplitude of the reception signal,
and a predetermined response to the magnitude of the reception level signal multiplied by a ratio
of less than 1 It has a reference signal generation means for generating a reference signal whose
magnitude follows with characteristics, and a bubble signal detection means for detecting
magnitude relationship or difference between the reference signal and the reception level signal,
and the predetermined response characteristic is An ultrasonic bubble detection device is
provided, which is a response characteristic that does not show a significant response to a
change appearing in a reception level signal due to the presence of a bubble at least smaller than
a predetermined level.
【0019】
According to such an ultrasonic bubble detection apparatus, the magnitude of the reference
signal does not show a significant response to the change appearing in the reception level signal
due to the presence of the bubble at least smaller than the predetermined level, but the reception
is generally performed. Since it follows the magnitude of the signal obtained by multiplying the
level signal by the ratio of less than 1, even if the ratio is set so that the distance between the
reference signal and the reception level signal becomes small, the reception level signal Changes
are not falsely detected as air bubbles. Then, by setting the difference between the reference
signal and the reception level signal small as described above, it becomes possible to reliably
detect small air bubbles which could not be detected conventionally. .
【0020】
DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be
described below.
【0022】
FIG. 1 shows the configuration of the ultrasonic bubble detection apparatus according to the
present embodiment.
【0023】
In the figure, 2 is an oscillation circuit, 3 is a drive circuit, 4 is an ultrasonic wave transmission
element, 6 is an ultrasonic wave reception element, 7 is an amplification circuit, 8 is a
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rectification circuit, 9 is an AGC circuit, 10 is a comparison circuit, 11 is a level A tracking type
comparison circuit, and 12 is a detection signal operation circuit. And, 20 is a tube through
which the liquid flows. Moreover, in such a configuration, the ultrasonic transmitting element 4
and the ultrasonic receiving element 6 are provided to face each other with the tube 20
interposed therebetween.
【0024】
Hereinafter, the operation of such an ultrasonic bubble detector will be described.
【0025】
The oscillation circuit 2 outputs an oscillation signal of several Mhz. The drive circuit 3 drives the
ultrasonic wave transmitting element 4 by the oscillation signal, and transmits ultrasonic waves
from the ultrasonic wave transmitting element 4 toward the liquid in the tube 20.
【0026】
The ultrasonic wave receiving element 6 receives the ultrasonic wave transmitted through the
tube 20 and the liquid and converts it into an electric signal, and the amplifying circuit 7
amplifies the converted electric signal and supplies it to the rectifying circuit 8. The rectifier
circuit 8 rectifies the supplied electric signal, generates a reception level signal sig representing
the reception intensity level of the reception ultrasonic wave in the ultrasonic wave reception
element 6 by the magnitude of the signal, and the AGC circuit 9, the comparison circuit 10 and
the level It is output to the tracking type comparison circuit 11. Here, the rectifier circuit 8 can
be replaced with a detection circuit.
【0027】
Next, the AGC circuit 9 which has received the reception level signal sig has a predetermined
time constant so that the overall level of the reception level signal sig (the size of the amplitude
in the absence of a bubble) becomes a predetermined size, The gain of the amplifier circuit 7 is
controlled. However, the AGC circuit 9 limits the maximum value of the gain to be controlled so
that the gain of the amplifier circuit 7 is not excessive when there is no signal.
【0028】
As described above, in the present embodiment, the gain of the amplifier circuit 7 is set by the
AGC circuit 9 so that the overall level (the magnitude of the amplitude in the absence of air
bubbles) of the reception level signal sig becomes a predetermined size. Since the control is
performed, it is possible to automatically keep the magnitude of the overall level of the reception
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level signal used for detecting the air bubble later in the comparison circuit 10 or the level
tracking comparison circuit 11. Therefore, in accordance with the change in external factors such
as the environment, the air bubbles can be favorably detected without the operator performing
adjustment operations one by one before the start of the detection operation so that this is offset.
【0029】
The comparison circuit 10 that receives the reception level signal sig compares the magnitude
relation between the reception level signal sig and the threshold value Th set in advance, outputs
the comparison result as the first detection signal Det1, and The detection signal Det1 is also
output to the detection signal calculation circuit 12. Here, the comparison circuit 10 plays the
same role as the comparison circuit 507 in the conventional ultrasonic bubble detection
apparatus (see FIG. 4) described above, and can detect relatively large bubbles as described
above. .
【0030】
Further, the level tracking type comparison circuit 11 which has received the reception level
signal sig generates a reference signal ref that follows the magnitude of the reception level signal
sig with a predetermined response characteristic, and the magnitude of the reference signal ref
and the reception level signal sig The relationship is compared, and the comparison result is
output as a second detection signal Det2, and the second detection signal Det2 is also output to
the detection signal operation circuit 12. Here, the response characteristic of the reference signal
ref generated by the level tracking comparison circuit 11 to the reception level signal sig is
significant at least against a relatively quick response small amplitude change appearing in the
reception level signal sig due to the presence of a small bubble. It is set to show no response.
Further, the small air bubbles referred to here include at least those smaller than the minimum
air bubble size detectable by the comparison circuit 10.
【0031】
FIG. 2a shows an example of the configuration of the level tracking comparison circuit 11.
【0032】
The illustrated example is an example in which the level tracking comparison circuit 11 is
configured by the peak hold circuit 111, the voltage dividing circuit 112, and the comparator
113. The time constant of the peak hold circuit 111 is set so that the peak of the reception level
signal sig before that can be held against the change of the reception level signal sig due to the
small air bubble, at least for the time corresponding to the period when the small air bubble is
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detected. It is done. The signal held peak by the peak hold circuit 111 is then divided by the
voltage divider circuit 112, and is made the reference signal ref obtained by multiplying the peak
held signal by a predetermined ratio less than one. Then, the magnitude relationship between the
reference signal ref and the reception level signal sig is compared in the comparator 113, and
the comparison result is output as the second detection signal Det2.
【0033】
Here, the level tracking type comparison circuit 11 using the peak hold circuit as described
above can be realized more specifically by the circuit using the operational amplifier 115 and the
comparator 119 shown in FIG. 2b. In this circuit, the operational amplifier 115, the diode 116,
the capacitor 117 and the resistor 118 constitute a peak hold circuit, the time constant of which
is determined by the capacitance of the capacitor 117 and the resistance of the resistor 118, and
the resistor 118 also constitutes a voltage divider circuit. By taking out the signal from the
middle of the resistor 118, a divided voltage signal of the peak-held signal is generated.
【0034】
By generating the reference signal ref using the peaked hold circuit 111 in this manner, only a
temporary variation in the negative direction corresponding to a bubble having a size smaller
than or equal to the desired size appearing in the reception level signal sig can be satisfactorily
masked. It becomes possible.
【0035】
However, here, the level tracking type comparison circuit 11 using the peak hold circuit is taken
as an example, but according to the required detection accuracy etc., the peak level hold circuit is
replaced and the reception level signal sig The level tracking type comparison circuit 11 can be
configured by using any sample hold circuit or low pass filter having a response characteristic
that does not show a significant response to a relatively quick response small amplitude change
appearing in FIG.
【0036】
FIG. 3 schematically shows how air bubbles are detected in the comparison circuit 10 and the
level tracking comparison circuit 11 described above.
【0037】
In the figure, a represents a received ultrasound signal. In this example, the overall level of the
received ultrasound signal (the magnitude of the amplitude in the absence of air bubbles) varies
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with time.
【0038】
Next, b is a schematic diagram showing bubble detection in the comparison circuit 10, Sig
represents a reception level signal obtained by rectifying the received ultrasonic signal, Th
represents a threshold value, and Det1 represents a second detection signal. 1 represents a
detection signal.
【0039】
As shown, the threshold Th is a fixed distance relative to the maximum possible level of the
reception level signal sig so that the fluctuation of the overall level of the reception ultrasonic
signal is not erroneously detected as a bubble (the reception ultrasonic wave A distance larger
than the fluctuation range of the overall level of the signal) is set. Then, while the reception level
signal sig becomes less than the threshold value Th due to the presence of the bubble A, the
comparison circuit 10 outputs a low level detection pulse to the first detection signal Det1.
【0040】
Here, since the threshold value Th is set at a fixed distance to the maximum possible level of the
reception level signal sig in this way, the reception level signal sig has a threshold depending on
the presence of the small bubble B shown in the figure. It does not become less than the value
Th. Therefore, the comparison circuit 10 can not detect small air bubbles.
【0041】
Next, c schematically indicates how air bubbles are detected in the level tracking type
comparison circuit 11, Sig represents a reception level signal sig obtained by rectifying the
received ultrasonic signal, and ref represents a reference signal Det2 represents a second
detection signal.
【0042】
As shown, the reference signal ref follows the overall level of the received ultrasound signal and
is a signal that takes on a magnitude proportional to the overall level of this received ultrasound
signal. Then, while the reception level signal sig becomes less than the reference signal ref due to
the presence of the bubbles A and B, the level tracking comparison circuit 11 outputs a low level
detection pulse to the second detection signal Det2.
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【0043】
Here, as described above, since the reference signal ref follows the entire level of the received
ultrasonic signal, even if the distance between the reference signal ref and the received level
signal sig is set small, the entire received ultrasonic signal Level fluctuation is not falsely detected
as a bubble. Then, by setting the distance between the reference signal ref and the reception level
signal sig small as described above, it becomes possible to reliably detect a small air bubble B
which could not be detected by the comparison circuit 10.
【0044】
By the way, a signal that follows the overall level of the received ultrasonic signal is directly used
as a reference signal ref, a positive constant bias is applied to the received level signal sig, and
then both are compared to detect a small bubble. Although it is conceivable that such a method is
considered, detection of small bubbles as compared with the method of the present embodiment
in which the reference signal ref is a signal having a constant ratio of the signal that follows the
overall level of the received ultrasonic signal. Accuracy is poor. This is because, according to the
method of providing a constant bias, the difference in the overall levels of the reference signal ref
and the received ultrasound signal is always kept constant, but the magnitude of the signal
change for the small bubble to be detected is It is because it changes with the same external
factor as the change of the overall level of the received ultrasonic signal. That is, even for the
same bubble, it is expected that the signal change for the bubble will be smaller when the overall
level of the received ultrasound signal is smaller and greater when the overall level of the
received ultrasound signal is larger. Be done. Thus, by making the reference signal ref a signal
having a constant ratio of the signal following the overall level of the received ultrasound signal,
the overall level of the received ultrasound signal is small when the overall level of the received
ultrasound signal is small. It is appropriate to make the difference between the overall level of
the received ultrasound signal and the reference signal ref large when the difference between the
dynamic level and the reference signal ref is small and the overall level of the received
ultrasound signal is large. is there.
【0045】
In addition, as a method of canceling the fluctuation of the overall level of the received ultrasonic
signal, a method may be considered in which only the AC component of the received ultrasonic
signal is taken out by a capacitor or the like to be processed. There is a problem that it becomes a
differentiating circuit, is relatively weak to noise, responds excessively to sharp signal changes, or
is subject to large signal changes and subsequent small signal changes due to air bubbles will be
buried, so accuracy is high. Less desirable from the point of view of air bubble detection.
【0046】
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Referring back to FIG. 1, the detection signal operation circuit 12 performs a predetermined
operation on the first detection signal Det1 and the second detection signal Det2 which are
output as described above, and outputs a third detection signal Det3. The content of this
calculation is appropriately set according to the content of the required third detection signal
Det3. For example, if it is only necessary to detect the presence of air bubbles as an output and it
is not necessary to distinguish between the air bubbles, the detection signal operation circuit 12
performs an OR operation on the first detection signal Det1 and the second detection signal Det2.
To output the result. On the other hand, if it is necessary to completely separate the detection
results of the large bubble and the small bubble in the ultrasonic bubble detector, on the other
hand, the second detection is performed using the timing of the detection pulse for the large
bubble appearing in the first detection signal Det1. The detection pulse for the large bubble
appearing in the signal Det2 is masked, and a signal including only the detection pulse for the
small bubble is output.
【0047】
The ultrasonic bubble detection device according to the present embodiment has been described
above.
【0048】
In the above embodiment, the comparison circuit 106 detects the magnitude relation between
the threshold value Th and the reception level signal and outputs this. However, in the
comparison circuit 106, the threshold value is detected. The difference between Th and the
reception level signal sig may be calculated and output. In the above embodiment, the level
tracking comparison circuit 1111 detects the magnitude relationship between the reference
signal Ref and the reception level signal and outputs the same. However, similarly, the level
tracking comparison is performed. The circuit 11 may calculate and output the difference
between the reference signal Ref and the reception level signal. By outputting the difference in
this manner, the size of the bubble can be more finely calculated from the size of the difference
output from the comparison circuit 106 and the level tracking comparison circuit 11. In order to
output the difference in this manner, for example, the comparator circuit 106 and the
comparator 119 of the level tracking type comparator circuit 11 of FIG. 2 may be replaced with a
subtraction circuit.
【0049】
Further, in the above embodiment, the ultrasonic wave transmitted through the liquid is received
and the air bubbles are detected from this, but the configuration of the air bubble detection in
this embodiment receives the ultrasonic wave reflected from the liquid and detects the air
bubbles from this The same applies to the case of Moreover, the above embodiment is applicable
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not only to detection of air bubbles in liquid, but also to detection of foreign matter in other
subjects.
【0050】
Further, the ultrasonic bubble detection apparatus according to the above embodiments prevents
bubble mixing in human blood by a artificial dialysis device or drip device in the medical field,
prevents bubble mixing in a developer in the photographic field, It can be widely applied to
abnormality monitoring in various plants.
【0051】
As described above, according to the present invention, in the ultrasonic bubble detection
apparatus, air bubbles can be properly detected regardless of changes in external factors.
Moreover, in the ultrasonic bubble detection apparatus, even small bubbles can be properly
detected.
[0002] Brief description of the drawings
[0003] 1 is a block diagram showing a configuration of an ultrasonic bubble detection device
according to an embodiment of the present invention.
[0004] 2 is a block diagram showing a configuration example of a level tracking type comparison
circuit according to an embodiment of the present invention.
[0005] 3 is a view schematically showing the mechanism of ultrasonic bubble detection
according to the embodiment of the present invention.
[0006] 4 is a block diagram showing a configuration of a conventional ultrasonic detection
apparatus.
[0007] Explanation of sign
[0008] 2: Oscillator circuit 3: Drive circuit 4: Ultrasonic transmitting element 6: Ultrasonic
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receiving element 7: Amplifier circuit 8: Rectifying circuit 9: AGC circuit 10: Comparison circuit
11: Level tracking type comparison Circuit 12: detection signal arithmetic circuit 20: tube 111:
peak hold circuit 112: voltage divider circuit 113: comparator 115: operational amplifier 116:
diode 117: capacitor 118: resistance 119: comparator
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