JPH0999062A - Bubble detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect bubbles mixed into the sampling circuit of a blood circuit, etc. SOLUTION: This device is provided with an ultrasonic vibration driving circuit 1, ultrasonic vibrator 2 for transmission, ultrasonic vibrator 3 for reception, tube 4 consisting of the sampling circuit, amplifier circuit 5, 1st high-pass filter(HPF) 6, rectifier circuit 7, low-pass filter(LPF) 8, 2nd HPF 9 and comparator circuit 10. Then, the 1st HPF 6 passes only a high frequency component in the output signal of the amplifier circuit 5 and the 2nd HPF 9 passes a change component in the output signal of the LPF 8. Further, the comparator circuit 10 detects only a remarkable change component in the change component passed through the 2nd HPF 9. Then, since the influence of noises or small bubbles can be removed by amplifying a signal received by the ultrasonic vibrator 3 for reception and passing only its specified component through the various filters, bubbles can be surely detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bubble detector, and more particularly to a bubble detector suitable for use in a device for returning blood to a human body again from a blood circuit constructed outside the body (for example, an artificial dialysis device). is there.

[0002]

2. Description of the Related Art Conventionally, bubble detectors have been widely put to practical use in artificial dialysis machines and the like. That is, for example, in order to detect air bubbles mixed in blood flowing through a tube that is a blood return path to the human body, the ultrasonic transducer for transmission and the ultrasonic transducer for reception are opposed so as to sandwich the tube. The ultrasonic transducer for transmission transmits continuous ultrasonic waves, and the ultrasonic transducer for reception receives the ultrasonic waves through the blood flowing in the tube, and ultrasonic waves are generated in the air bubbles in the blood. The air bubble detector that detects the change in the received signal level that decreases as a result of passage is widely used.

[0003]

However, this type of bubble detector has the following drawbacks. That is, since the signal level from the receiving ultrasonic transducer is very low and the impedance of the signal line is high, it is easily affected by various electric noises such as the frequency of the AC100V power supply, and this noise is often generated. It will be a level that cannot be ignored.
In addition, there is a large difference in signal level due to variations in the characteristics of the ultrasonic transducer. Therefore, it is very difficult at what level to detect bubbles in the signal processing unit from the receiving ultrasonic transducer, and sometimes malfunctions occur.

The present invention has been invented in view of such drawbacks, and as a result of earnest studies to obtain a highly accurate bubble detector capable of reliably detecting bubbles, as will be described later, transmission is performed. Vibration driving circuit for driving the ultrasonic transducer for continuous rectangular waves, an amplifying circuit for amplifying the signal received by the receiving ultrasonic transducer, and passing only the high frequency component of the output signal of this amplifying circuit It has been found that such a purpose can be achieved by providing the first high-pass filter and the like.

[0005]

That is, a bubble detector according to the present invention is a bubble detector in which a transmitting ultrasonic transducer and a receiving ultrasonic transducer are mounted so as to sandwich a tube forming a sample circuit. In the detector, an ultrasonic vibration drive circuit that drives the transmitting ultrasonic vibrator with a continuous rectangular wave, an amplifier circuit that amplifies a signal received by the receiving ultrasonic vibrator, and an output signal of the amplifier circuit. A first high-pass filter that passes only high-frequency components, a rectifying circuit that rectifies the output signal of the first high-pass filter, and a low-pass filter that passes only low- and medium-frequency components that smoothes the output signal of the rectifying circuit, A second high-pass filter that passes the change component of the output signal of the low-pass filter and a large change component of the change components that pass the second high-pass filter It is characterized in that a comparison circuit to be detected. The sample circuit is preferably a blood circuit.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In an artificial dialysis device, a bubble detector for detecting bubbles in blood in order to prevent bubbles from being mixed into blood and carried into the body when returning to the human body. In FIG. 1, an embodiment of such a bubble detector is shown.

In the figure, this bubble detector comprises an ultrasonic vibration drive circuit 1, an ultrasonic oscillator 2 for transmission, an ultrasonic oscillator 3 for reception, and a blood circuit (sample circuit). Tube 4, amplifier circuit 5, first high-pass filter 6
A rectifier circuit 7, a low pass filter 8, a second high pass filter 9 and a comparison circuit 10.

It should be noted that although the ultrasonic transducer 2 for transmission and the ultrasonic transducer 3 for reception are mounted so as to face each other so as to sandwich the tube 4 constituting the blood circuit (sample circuit), Ultrasonic transducer 2 is equal to the resonance frequency of transmitting ultrasonic transducer 3, that is, specifically, 1 MHz.
Is driven by the ultrasonic vibration drive circuit 1 which is driven by a continuous rectangular wave.

On the other hand, the receiving ultrasonic transducer 3 receives the ultrasonic waves that have passed through the blood in the tube 4, and the electric signal output from the receiving ultrasonic transducer 3 is amplified by the amplifying circuit 5. Then, a predetermined detection signal can be obtained through the first high-pass filter 6, the rectifier circuit 7, the low-pass filter 8, the second high-pass filter 9, and the comparison circuit 10.

At this time, the impedance between the receiving ultrasonic transducer 3 and the amplifying circuit 5 is high and noise is likely to be generated, but at the resonance frequency of the receiving ultrasonic transducer 3, the receiving ultrasonic transducer 3 has a resonance frequency. Since the output impedance is very small, it is difficult for noise to ride. However, with a frequency component larger than the resonance frequency, the amplification circuit 5 does not have sufficient amplification characteristics, and therefore, noise at a frequency lower than the signal frequency, particularly noise at the power supply frequency, becomes a problem. Therefore, the first high-pass filter 6 that passes only the high-frequency component that is the signal component of the output signal of the amplifier circuit 5 is provided to remove the noise component.

A rectifier circuit 7 for rectifying the output signal of the first high-pass filter 6 and a low-pass filter 8 for passing only the low and medium frequency components for smoothing the output signal of the rectifier circuit 7.
And the signal component is changed to a DC signal, and the low-pass filter 8 attenuates the noise component and bubbles, which are small bubbles that are dissolved in the blood again without harm to the human body.

The level of the output signal of the low-pass filter 8 fluctuates greatly due to variations in the characteristics of the transmitting ultrasonic transducer 2 or the receiving ultrasonic transducer 3, so that only the signal change component is passed. By providing the 2 high-pass filter 9, the influence of the fluctuation of the signal level due to the variation of the characteristics of the transmitting ultrasonic transducer 2 or the receiving ultrasonic transducer 3 is avoided.

Further, in order to avoid the influence of noise and small air bubbles, a comparator circuit 10 is provided which detects a certain amount of change without detecting a small change, thereby making it possible to surely detect the air bubble.

Therefore, according to the bubble detector of the present invention, the signal received by the ultrasonic transducer for reception is amplified,
Since the influence of noise and small bubbles can be removed by allowing only the specific component to pass through various filters, it is possible to reliably detect the bubbles.

Although one embodiment of the bubble detector according to the present invention has been described above, in the present invention, a sample other than blood may be used. In that case, the tube 4 is used.
The predetermined sample circuit may be configured with.

[0016]

As described above, according to the first and second aspects of the present invention, it is possible to reliably detect air bubbles while avoiding the influence of noise and small air bubbles, and especially in medical devices such as artificial dialysis machines. A high-precision bubble detector suitable for use can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a bubble detector according to an embodiment of the present invention.

[Explanation of symbols]

 1 ultrasonic vibration drive circuit 2 ultrasonic transducer for transmission 3 ultrasonic transducer for reception 4 tube constituting blood circuit (sample circuit) 5 amplification circuit 6 first high-pass filter 7 rectification circuit 8 low-pass filter 9 second High-pass filter 10 Comparison circuit

Claims (2)

[Claims] 1. A bubble detector in which an ultrasonic transducer for transmission and an ultrasonic transducer for reception are mounted so as to sandwich a tube constituting a sample circuit, and the ultrasonic transducer for transmission has a continuous rectangular shape. An ultrasonic vibration drive circuit driven by waves, an amplifier circuit that amplifies a signal received by the receiving ultrasonic vibrator, a first high-pass filter that passes only a high frequency component of an output signal of the amplifier circuit, and A rectifier circuit that rectifies the output signal of the first high-pass filter, a low-pass filter that smoothes the output signal of the rectifier circuit, and that passes only low- and medium-frequency components, and a second high-pass filter that passes the change component of the output signal of the low-pass filter. Bubble detection comprising a filter and a comparator circuit that detects only a large change component of the change components that have passed through the second high-pass filter. vessel. 2. The bubble detector according to claim 1, wherein the sample circuit is a blood circuit.