JPH0126008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas flow meter that utilizes Karman vortices, and is particularly applicable to medical anesthesia applications that require small flow rates and low pressure losses, using ultrasonic transceivers as detectors of Karman vortices. This relates to gas flow meters.

Hereinafter, a medical anesthetic gas flowmeter according to the present invention will be explained.

Medical anesthetic gas flowmeters are generally used to manage the amount of anesthetic gas required to produce an anesthetic effect when a patient inhales anesthetic gas. This is a flow meter that can be visually confirmed by measuring and displaying cumulative ventilation volume, minute respiratory rate, etc.

This type of medical anesthesia gas flowmeter is used to measure ventilation in all breathing conditions, from resting to vigorous breathing, and is intended for not only adults but also newborns. Mo5/
The flow rate ranges from a minute flow rate of about 80/min to about 80/min.
It is required to have low pressure loss and small instrumental error within the above measurement flow rate range. Further, as the anesthetic gas, oxygen, laughing gas, etc. are used alone or as a mixture of gases.

Conventionally, Karman vortex flowmeters such as those described above have been employed in many gas flowmeters commonly used for gas measurement, and as shown in FIG. The ultrasonic waves emitted by the ultrasonic transmitters 1, which are arranged facing each other on the same axis and driven by the oscillation circuit 3, are generated by the vortex generator 5 inserted into the detection pipe 4 through which the gas to be measured flows. The signal reaches the ultrasonic receiver 2 modulated by the Karman vortex, and the signal received by the ultrasonic receiver 2 is processed by the subsequent signal processing circuit 6 and displayed on the display section 7 as a flow rate.

However, when the ultrasonic transmitter 1 and the ultrasonic receiver 2 are placed facing each other on the same axis and the facing distance l is gradually changed, the magnitude of the signal received by the ultrasonic receiver 2 is determined by the standing wave. Due to the influence of

The situation is shown in Figure 2.

In the diagram of Fig. 2, the vertical axis represents the magnitude V _PP of the received signal of the ultrasonic receiver 2, and the horizontal axis represents the above-mentioned facing distance l.
represents.

In order to prevent fluctuations in the received signal V _PP as shown in Figure 2, at least the facing distance l should be set to a dimension that is not affected by standing waves, for example, l ₀ , l ₁ in the figure, and the facing distance l should be It is necessary to keep the dimensional accuracy to less than about half a wavelength, that is, about 1/4 wavelength.

However, keeping the dimensional accuracy to about 1/4 wavelength or less for short-wavelength sound waves such as ultra-wavelength waves is accompanied by manufacturing difficulties and reduces the degree of freedom in design.
In addition, since the wavelength changes depending on the density of the medium, in anesthesia gas flow meters where several types of gas are used alone or as a mixture, or where the same gas is used at different temperatures, the wavelength can be received by the ultrasonic receiver 2. It is quite difficult to prevent fluctuations in the received signal _VPP .
The present invention was made in view of the above-mentioned drawbacks, and its purpose is to provide an inexpensive anesthetic gas flow meter with high accuracy and capable of measuring even minute flow rates.

The gist of the present invention for achieving the above object is as described in the claims above.

Preferred embodiments of the present invention will be described below with reference to the drawings.

Note that the same parts as in the conventional one are given the same reference numerals.

In FIG. 3, the ultrasonic transmitter 1 and the ultrasonic receiver 2 are firmly fixed to the substrate 12 by adhesive or the like, and the facing angle θ is 160° to 170°, preferably θ, as shown in the figure.
= 167°, and the board 12 falls off.
It is bonded to a sound absorbing material 13 made of a material with a low modulus of elasticity, such as rubber or foamed plastic, by adhesive or slight compression bonding to prevent rotation.

The sound absorbing material 13 is inserted into the frame 14 and
It is compressed and fixed by a presser plate 15 fixed to 4 by adhesive or the like to an extent that does not impede the sound absorption effect.

The frame 14 is coupled to the detection tube 8 by adhesive or other means.

As the material for the frame body 14 and the pressing plate 15, it is preferable to use a material that has a large attenuation of sound waves, such as rubber or foamed plastic.

The shielded wire 16 inserted into the frame 14 is soldered to the ultrasonic transmitter 1 and the ultrasonic receiver 2 inside the frame 14, and is connected to the oscillation circuit 3 and the signal processing circuit 6, respectively.

In the anesthesia gas flow meter having the above configuration, the case where the opposing angle θ between the ultrasonic transmitter 1 and the ultrasonic receiver 2 is changed and the opposing distance l is gradually changed is shown in Fig. 4 a to i. show.

In the diagram in the figure, the vertical axis represents the magnitude V _PP of the received signal of the ultrasonic receiver 2, and the horizontal axis represents the facing distance l.
represents.

According to Figure 4, when θ=172° to 180°, the received signal V _PP
is strongly influenced by standing waves and fluctuates sharply every half wavelength as the facing distance l changes, but when θ = 166° to 170°, the received signal V _PP fluctuates only slightly, and θ = 166° or less, it can be seen that the fluctuation of the received signal V _PP becomes slightly larger again.

Therefore, by setting the facing angle θ in the range of 160° to 170°, preferably θ = 167°, even if the facing distance l changes, the influence of standing waves can be removed, and the facing distance l
can be certified to any size, and it also makes it easy to adjust the oscillation circuit 3 that drives the ultrasonic transmitter 1, and allows the ultrasonic receiver to receive a stable reception signal even with slight fluctuations in the oscillation frequency. It can be obtained from 2.

Here, as shown in FIG. 3, if the angles between the center lines of the ultrasonic transmitter 1 and the ultrasonic receiver 2 and the center line of the detection pipe 5 are θ ₁ and θ ₂ , respectively, then the ultrasonic transmitter 1 And the ultrasonic receiver 2 does not necessarily need to be installed so that θ ₁ = θ ₂ .If θ ₁ + θ ₂ = θ, θ ₁ > θ ₂
Alternatively, it may be installed such that θ ₁ < θ ₂ , and the detection tube 4
It may also be attached at a symmetrical position with the axis of symmetry being a line perpendicular to the center line of.

As described in detail above, according to the present invention, the facing angle θ between the ultrasonic transmitter 1 and the ultrasonic receiver 2 is set to 160° to 160°.
By setting θ=170° and preferably 167°, the influence of standing waves can be removed, making it easier to adjust the oscillation circuit 3 and ensuring a stable received signal even with slight fluctuations in the oscillation frequency. can be obtained from an ultrasonic receiver and the facing distance l
Since it can be set to any size, the degree of freedom in design increases, and since there is no need to strictly control its dimensional accuracy, manufacturing costs are reduced.

Furthermore, according to the present invention, since it is not affected by wavelength changes due to the medium, there is no need to change the facing distance l even when several types of gases with different densities are used alone or as a mixture. It is.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main part of the detection part of the Karman vortex flowmeter, Fig. 2 is a diagram showing the relationship between the magnitude of the received signal of the ultrasonic receiver and the facing distance, and Fig. 3 is an embodiment of the present invention. A cross-sectional view of the main part of the detection unit according to Fig. 4 a to i
is a diagram showing the relationship between each received signal and facing distance when the facing angle is changed. 1... Ultrasonic transmitter, 2... Ultrasonic receiver, 3
... Oscillator circuit, 4 ... Detection pipe, 5 ... Vortex generator, 6 ... Signal processing circuit, 7 ... Display section, 8 ...
Detection tube, 9... Screw, 10... Sound wave, 11... Sound wave, 12... Board, 13... Sound absorbing material, 14... Frame, 15... Pressing plate, 16... Shield wire.

Claims (1)

[Claims] 1. By detecting the number of Karman vortices generated by a vortex generator inserted into the gas to be measured from changes in sound waves by ultrasonic transmitters and receivers disposed at opposite positions in the flow path, 1. An ultrasonic flowmeter for detecting the flow rate of gas, characterized in that the ultrasonic transmitter/receiver is disposed at a facing angle of 160° to 170°.