JPS582620B2 - Bubble detection method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting bubbles in a liquid, and more particularly to a method and apparatus for detecting bubbles contained in a liquid flowing in a conduit.

In general, in various industries, bubbles contained in liquids have an adverse effect on products, so it is extremely common to detect and remove them.

For example, in the photographic industry, if bubbles are present in a coating solution for photographic light-sensitive materials, small holes corresponding to the bubbles will be formed in the coating after coating and drying, causing the photographic material to lose its commercial value. It will lead to consequences.

Therefore, it is necessary to detect and remove the bubbles present in the coating solution prior to coating, no matter how minute or how many there may be.

Conventionally, methods disclosed in Japanese Patent Publication No. 33-6903, Japanese Patent Application Laid-Open No. 48-76591, and the like have been known as methods for detecting such bubbles in liquid.

In this method, a pair of ultrasonic transducers are installed at opposing positions on the wall of a conduit through which liquid containing bubbles generated by cavitation flows, and ultrasonic waves are emitted from one of the transducers and passed through the liquid. This is received by the other transducer, and bubbles in the liquid are detected from the change in the amount of attenuation of the ultrasonic energy upon reception.

However, in this method, if mechanical vibrations are applied to the conduit and vibrator from the outside, if fluid pressure fluctuations occur when pumping the liquid to be measured, or if fluctuations occur in the power supply voltage, etc. Fluctuations occur in the received output, which becomes noise and is detected at the same time as the output fluctuations due to bubbles, making it difficult to distinguish between the two, resulting in a problem in which the accuracy of bubble detection decreases and is slow.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic bubble detection method and apparatus that can eliminate the drawbacks of the conventional bubble detection methods and detect even minute bubbles with high accuracy.

This object of the present invention is achieved by providing at least two ultrasonic transmitting and receiving transducers with parallel transmitting and receiving axes on both sides of the conduit.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of an ultrasonic bubble detection device showing one embodiment of the present invention.

Here, 1 is an ultrasonic transmitter, 2a and 2b are transmitting transducers,
3a and 3b are receiving transducers.

The transmitting transducers 2a, 2b and the receiving transducers 3a, 3b are spaced apart by the same distance, and the transmitting transducer 2a and the receiving transducer 3a, and the transmitting transducer 2b and the receiving transducer 3
b are respectively provided on the outer wall of the conduit 4 so that the transmitting and receiving axes are parallel to each other.

In order to improve the transmission efficiency of ultrasonic waves, the portion of the conduit 4 where the transducers 2a, 2b, 3a, and 3b are attached is cut flat, as shown in the cross-sectional view of the conduit in FIG. , 2b, 3a, 3b are tightly fitted to the conduit 4 via the grease 5.

Furthermore, in order to prevent a decrease in the ratio of ultrasonic energy transmitted around the outer wall of the conduit 4 and received while transmitted through the liquid to be measured, grooves 6 are formed in this cut-out portion. is provided.

Further, 7a and 7b are amplifiers including a high frequency amplifier, an AC/DC converter, and a differential or bias circuit;
a, 8b are signal shapers including a rectangular pulse conversion circuit; 9a;
b is a comparator, and 10 is a recorder or other display device.

In this embodiment, the ultrasonic output emitted from the ultrasonic oscillator 1 excites the transmitting transducers 2a and 2b to emit a certain amount of ultrasonic energy into the liquid in the conduit 4, thereby creating an ultrasonic sound field. Form.

The frequency of the ultrasonic output to be used is selected so that the attenuation coefficient of ultrasonic energy is maximized for the bubble of interest.

Here, when there are no bubbles in the liquid, the transmitting vibrator 2
Since the energy transmitted from a, 2b to the receiving oscillators 3a, 3b is always constant, a constant voltage is always induced in the receiving oscillators 3a, 3b.

On the other hand, when there is even one bubble in the liquid, the ultrasonic energy emitted from the transmitting transducers 2a and 2b is scattered and absorbed by the bubbles, so the received energy is also attenuated by that amount. This causes fluctuations in the output voltage.

In this way, bubbles in the liquid can be detected, but even when noise due to mechanical vibration, pressure fluctuation, voltage fluctuation, etc. occurs during transmission, the signal from the transmitting transducer 2a+2b to the receiving transducer 3 is detected.
The energy transmitted to a and 3b is affected by instantaneous poor adhesion between the vibrator and the tube wall due to mechanical vibration, fluctuations in transmission efficiency due to fluid pressure fluctuations, fluctuations in power supply voltage, etc., and the output is affected in the same way as in the case of foam. cause fluctuations.

However, signals due to variations in ultrasonic energy transmission efficiency and output voltage caused by the presence of bubbles are received by the receiving transducers 3a and 3b with a time difference;
In the case of noise due to mechanical vibrations, pressure fluctuations, voltage fluctuations, etc., the receiving transducers 3a and 3b receive the noise almost simultaneously without any time delay, so according to this embodiment, it is possible to clearly distinguish between the two. becomes possible.

In other words, the amount of time delay in reception by the receiving transducers 3a and 3b that occurs when bubbles exist in the liquid is determined by the flow velocity of the liquid and the floating of the bubbles when the liquid flows from the bottom to the top in FIG. It is inversely proportional to the speed and proportional to the distance between the receiving transducers 3a and 3b.

Therefore, by appropriately selecting the distance between the receiving transducers 3a and 3b, it is possible to distinguish between the bubble detection signal and noise.

By the way, if the distance between the two oscillators is too narrow, there is a possibility that bubbles detected by the first oscillator will be trapped by the time they reach the second oscillator, or it will be difficult to distinguish them from other bubbles. Therefore, it is not appropriate to provide the vibrators too far apart.

The signals received by the receiving transducers 3a and 3b are sent to amplifiers 7a and 3b.
After being high-frequency amplified at 7b, it is converted into a rectangular wave by signal shapers 8a and 8b, and then enters a comparator 9ab.

The comparator 9ab compares both signals input from the signal shapers 8a+8b, and if both signals are input at the same time, it does not output an output, and if there is a time delay, it outputs an output.Noise is output. The bubble detection signal is not taken out as an output, but only the bubble detection signal is taken out as an output.

In this way, the noise signal is completely eliminated by the comparator 9ab, and only the bubble detection signal is displayed on the recorder 10 as the output of the comparator 9ab.

The signal conversion method will be explained in more detail.

FIG. 3 shows an example of changes in the attenuated signal due to bubbles and noise after being converted into rectangular pulses by the signal shapers 8a and 8b.

In FIG. 3, S is a rectangular pulse due to bubbles, and N is a rectangular pulse due to noise.

FIG. 3a shows an example of the bubble and noise signal patterns converted into rectangular pulses by the signal shaper 8a and FIG. 3b by the signal shaper 8b, respectively.

Here, the X axis represents time, and the Y axis represents the voltage scale of the recorder.

Comparing the graphs in Figures 3a and b at the same time, the pulse S indicating the bubble detection signal has a slight time lag in Figures 3a and b, while the pulse N indicating the noise signal has a slight time lag in both figures. It can be seen that they are at exactly the same position with respect to the X-axis.

The pulses representing the noise signal in FIGS. 3a and 3b are eliminated by the comparator 9ab, and only the pulses representing the bubble detection signal as shown in FIG. 3C are displayed by the recorder.

Therefore, since the number of pulses corresponds to the number of bubbles, the number of bubbles that have passed through the conduit 4 can be easily determined by using a counter.

FIG. 4 shows another embodiment of the invention.

In the embodiment described above, two pairs of ultrasonic transducers are provided whose transmitting and receiving axes are parallel to each other, but as shown in FIG. Na2
A pair of transmitting transducers 2c, 2d and receiving transducers 3c, 3d may be provided on the conduit wall.

In the case of two pairs of transmitting and receiving transducers as in the embodiment described above,
Bubbles passing within the area connecting opposing transducer pieces, as shown by diagonal lines in Figure 2, can be detected accurately, but bubbles passing outside this area have poor detection accuracy due to the directivity of the ultrasonic waves. It will be inferior.

However, by providing two new pairs of vibrators in this way, the area in which bubbles can be detected accurately increases, resulting in the effect of improving accuracy.

When four-elbow transducers are provided in this manner, the output voltages received by the receiving transducers 3a, 3b, 3c, and 3d are applied to amplifiers 7a+zb and 7c+7, respectively, as in the previous embodiment.
ds signal shaper 8a+8b+gc, 8ds comparator 9ab
, 9cd to the newly provided OR circuit 11 for signal selection, and then displayed on the recorder 10.

The present invention is not limited to the embodiments described above, but can be modified in various ways.

For example, in the embodiment described above, the signal converted into a rectangular pulse is processed using a comparator to eliminate the signal due to noise. By providing at least two pairs of transmitting and receiving transducers, it is possible to distinguish between a bubble detection signal and a noise signal, and comparators, counters, etc. are not necessarily required.

As the material of the conduit used in the present invention, metals such as stainless steel, plastics, etc. can be used.
Ultrasonic energy passes through the conduit wall and wraps around to the receiving side.
Plastic is more preferable in order to prevent detection accuracy from deteriorating.

Plastics include hard polyvinyl chloride, acrylic resin, tetrafluoroethylene, Delrin (US E.
I. Du Pont (trade name, polyacetal resin), etc. can be used, but tetrafluoroethylene and Delrin are particularly superior in terms of hardness and workability.

Further, although the diameter of the conduit is not particularly limited, if it is too small compared to the vibrator, the amount of ultrasonic energy reaching the receiving side through the conduit wall becomes excessive, which may reduce the S/N ratio.

Furthermore, if the transmitting voltage used in the present invention is too large, the ultrasonic energy will be too high, and the mounting screw of the transducer will likely come loose.On the other hand, if the transmitting voltage is too small, the receiving voltage will be small and the signal processing equipment Stability deteriorates, so
Appropriate values must be selected.

Usually 0.5-5V. Preferably 1 to 3V, more preferably around 2V would be appropriate.

In addition, the frequency of the ultrasonic waves used in the present invention varies depending on the size of the bubbles to be detected, and a frequency that is as small as the size of the bubbles is suitable, so it is not possible to determine an appropriate value in general. , 30~ for bubbles with a diameter of 30~200μ
A frequency of 150 KHz, preferably 50-100 KHz is suitable.

Furthermore, in the present invention, the appropriate distance between two or more transmitting transducers or receiving transducers varies depending on the flow rate and required accuracy, and it is not possible to say in general what the appropriate distance is.

That is, in general, the smaller the distance between the transducers, the higher the accuracy, but when the flow rate is a dog, on the other hand, if the distance is too small, the accuracy decreases.

Normally, when the flow rate is about 1 to 5/min, 4 to 60 Cm,
Preferably 5-15cm, more preferably 5-15C
m would be appropriate.

According to the present invention, it is possible to completely eliminate noise such as mechanical vibration, fluid pressure vibration, voltage vibration, etc., and to detect bubbles in liquid with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a bubble detection device showing one embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of an ultrasonic bubble detection section. FIG. 3 is a graph showing an example of signal processing. FIG. 4 is a block diagram of a bubble detection device showing another embodiment of the present invention. 1... Ultrasonic transmitter, 2a, 2b, 2c, 2d
...... Transmission vibrator, 3a, 3b, 3c, 3d...
...Receiving transducer, 4... Conduit, 7a, 7b
, 7c, 7d...Amplifier, 8a, 8b, 8c,
8d...Signal shaper, 9ab, 9cd...
... Comparator, 10 ... Recorder, 11 ...
・OR circuit.

Claims (1)

[Claims] 1. A method for detecting bubbles in a liquid by transmitting ultrasonic waves from one side of a conduit through which liquid flows, receiving the ultrasonic waves at the other side, and further amplifying and shaping the received signal. A bubble detection method characterized in that at least two pairs of an ultrasonic transmitting transducer and a receiving transducer are provided, the transmitting and receiving axes of which are parallel to each other. 2. In an ultrasonic bubble detection device equipped with an ultrasonic transmitting transducer and a receiving transducer on both sides of a conduit through which liquid flows, an amplifier for amplifying the received signal, and a signal shaper for shaping the received signal, 1. A bubble detection device comprising at least two pairs of ultrasonic transmitting and receiving transducers whose transmitting and receiving axes are parallel to each other.