JP2002257801A - Ultrasonic type gas analitical sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic type gas analytical sensor constructed so that the intensity of sound waves is maintained by avoiding effects of a gas flow rate and preventing ultrasonic waves from being attenuated by diffusion, and the measurement accuracy is improved by reducing interferences by external noises when a composition of the two-component based gas is analyzed with the utilization of an ultrasonic element. SOLUTION: The element 1a for emitting ultrasonic waves and the element 1b for receiving ultrasonic waves are arranged to both ends of a gas passage tube 3, and a tube 4 for reflecting ultrasonic waves which has an inner diameter almost equal to a diameter of an emitting part of the emitting element 1a is inserted via a buffer material 8 into the passage tube. Diffusion holes 5 are set to the reflecting tube 4 in a manner to avoid a gas inlet 7a and a gas outlet 7b and to be distributed uniformly. A temperature sensor is set to a central part of a measurement chamber. The measurement gas is introduced from the gas inlet 7a to flow a gap between the gas passage tube 3 and the ultrasonic reflecting tube 4. A part of the measurement gas is diffused through the diffusion holes 5 to the measurement chamber 6, so that the effects of the flow rate is avoided, ultrasonic waves are prevented from being attenuated, and external noises are prevented from interfering effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for analyzing the composition of a binary gas such as oxygen / nitrogen or hydrogen / nitrogen used for industrial or commercial purposes.

[0002]

2. Description of the Related Art An ultrasonic wave propagation velocity V in a gas is represented by the following equation (1): gas molecular weight M, specific heat ratio γ and absolute temperature T
Depends on The average molecular weight can be determined by measuring the speed of sound and the temperature. V ² = γ · RT · M (1) When the gas component is known, the average molecular weight M is obtained by measuring the gas temperature T and the propagation velocity V, and the gas concentration can be calculated from the average molecular weight. The concentration calculation equation is as shown in Equation 2 in the case of a mixture gas of a and b of two molecular gases. ma and mb represent the molecular weights of a gas and b gas, respectively.

[Problems to be Solved by the Invention] In an ultrasonic gas analysis sensor, when measuring a gas having a small difference in molecular weight,
Since the difference in sound speed is also small, a distance between transmission and reception is required to increase the measurement accuracy. Becomes In addition, errors often occur due to the influence of external noise. In addition, during fluid measurement, there is a problem that the flow velocity in the measurement chamber is directly affected, and there are very few practical examples.

[Means for solving the problems]
In order to solve the above-mentioned problem, an ultrasonic reflecting tube provided with a gas diffusion port is inserted in a gas flow pipe having a cylindrical gas flow path in which an ultrasonic transmitter and a receiver are arranged to face each other. It is characterized by the following.

[0005] The ultrasonic reflecting tube is made of a metal having a smooth surface,
It is characterized by using glass or hard plastic as a material.

The gas diffusion holes of the ultrasonic reflecting tube are arranged so as to avoid the entrance and exit at the time of gas inflow and outflow, and to be arranged uniformly over the entire length and the entire circumference.

[0007] It is characterized in that the inner diameter of the ultrasonic reflecting tube is substantially the same as the outer diameter of the ultrasonic transmitter.

The ultrasonic reflecting tube is inserted into and held in the gas flow tube main body via a buffer material.

[0009]

[Action] To accurately measure the concentration of a sample gas by inserting an ultrasonic reflection tube having a gas diffusion port in a gas flow tube and transmitting the ultrasonic wave inside the reflection tube to prevent attenuation of the sound wave. Can be done. Further, the influence of external noise can be reduced by the double tube structure.

The material of the ultrasonic reflecting tube is such that when the surface is rough, the ultrasonic wave is irregularly reflected and noise is increased, and when a soft material such as paper or cloth absorbs the ultrasonic wave, a hard material having a smooth surface is used. Must be used.

By providing diffusion holes uniformly distributed over the entire length of the ultrasonic reflecting tube and not providing holes near the inlet and outlet of the sample gas, the sample gas enters the measurement chamber only by diffusion. In addition, since there is no uneven diffusion, it is possible to prevent the influence of the flow velocity and perform accurate measurement.

[0010] When using a transmitter having an ultrasonic transmission surface of 9.6 mm and using a reflection tube having an inner diameter of 10 mm and a 14 mm inner diameter in the measurement chamber, the ultrasonic intensity differs by a factor of 10 or more. Therefore, the inner diameter of the reflector should be larger and smaller than the transmitter, and ideally the same diameter is better.

When the ultrasonic reflecting tube is held in direct contact with the gas flow tube, the ultrasonic wave propagates through the solid, and the intensity of the wave is high, causing noise and a measurement error. By holding through a cushioning material such as rubber, propagation in a solid can be prevented and noise can be minimized.

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of the structure of the sensor of the present invention, in which the ultrasonic wave transmitting element 1a and the receiving element 2a
The ultrasonic reflecting tube 4 having substantially the same diameter as the transmitting portion of the transmitting element 1 a is inserted into the flow path tube 3 via the buffer material 8. A diffusion hole 5 is formed in the reflection tube 4 by a gas inlet 7a and an outlet 7b.
And a temperature sensor is mounted in the center of the measurement chamber 6. The sample gas is introduced from the gas inlet 7a, flows through the gap between the gas flow tube 3 and the ultrasonic reflecting tube 4, and partly diffuses through the diffusion hole 5 into the measuring chamber 6.

The ultrasonic wave transmitted in pulse form from the transmitter 1a propagates in the measuring chamber at a sound speed corresponding to the mixed gas, and is received by the receiver 1b after a predetermined time. If this time is measured and calculated by the microcomputer together with the temperature signal, Equations 1 and 2 are obtained.
, The gas concentration can be known. Continuous analysis can be performed by repeating pulse transmission. FIG. 3 is a block diagram showing the configuration of the measurement circuit.

The material of the ultrasonic reflecting tube 4 is required to be metal, glass or hard plastic, and paper or other fibrous or soft material is not preferable because ultrasonic waves are absorbed and detection becomes difficult.

FIG. 2 shows an example of the arrangement of diffusion holes in a reflecting tube. Gas turbulence in the measurement chamber causes fluctuations in the measured values, and uneven diffusion affects measurement accuracy and response speed. In order to eliminate these problems, it is necessary to uniformly distribute the diffusion holes over the entire length and circumference, and to avoid direct inflow or outflow from the gas inlet and outlet.

Although it is necessary to arrange a large number of diffusion holes with a small diameter in order to reduce uneven diffusion, it is desirable to reduce the number of holes as much as possible from the viewpoint of manufacturing cost. Depends on, but inner diameter 10mm
Flow rate 0.5-3 Lr / min. In case of
Arrangement at a pitch of 0 mm is sufficiently effective for response speed, measurement accuracy, and prevention of flow rate effects.

Ultrasonic waves propagate through a solid body at short distances with almost no attenuation, and give powerful sound waves to a receiver. Of course, since the sound speed is different from that in the gas, measurement can be performed separately, but the residual sound wave affects the pulse cycle.
This effect is significantly reduced by interposing a sponge material or a soft rubber material between the ultrasonic element and the reflecting tube.

[0016]

According to the sensor of the present invention, by inserting an ultrasonic reflecting tube in which diffusion holes are uniformly distributed in a gas flow tube, the sensor is at least 10 times as large as a sensor having no reflecting tube. Since ultrasonic waves can be received at a high intensity, it is possible to provide an ultrasonic gas analyzer that has a sufficiently improved practical use, has substantially improved measurement accuracy, has little influence on flow rate, and has little fluctuation in measured values.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a sensor structure of the present invention.

FIG. 2 is a structural view of a reflecting tube according to the present invention.

FIG. 3 is a block diagram of a measurement circuit according to the present invention.

[Explanation of symbols]

 1a Ultrasonic transmitter 1b Ultrasonic receiver 2 Temperature sensor 3 Gas flow pipe 4 Diffusion pipe 5 Diffusion hole 6 Measurement chamber 7a, 7b Gas inlet / outlet 8 Buffer material

Claims (5)

[The claims] 1. An ultrasonic transmitter and a receiver are arranged facing each other,
An ultrasonic gas analysis sensor having a cylindrical gas flow path having a gas temperature measuring means, wherein an ultrasonic reflection pipe provided with a diffusion hole in a gas flow path pipe is inserted. Sonic gas analysis sensor 2. The analytical sensor according to claim 1, wherein said ultrasonic reflecting tube is made of metal, glass or hard plastic having a smooth surface. 3. The analysis sensor according to claim 1, wherein the gas diffusion holes of the ultrasonic reflecting tube are arranged uniformly while avoiding a gas inlet / outlet. 4. The analysis sensor according to claim 1, wherein the inner diameter of the ultrasonic reflecting tube is substantially equal to the outer diameter of the ultrasonic transmitter. 5. The analysis sensor according to claim 1, wherein the ultrasonic reflecting tube is held between the reflecting tube and the flow tube via a buffer so that the gas flow tube does not directly contact.