JPH11271117A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the S/N of the detecting signal of an ultrasonic flowmeter by suppressing ghost signal components directly received by means of receivers from transmitters with a simple constitution. SOLUTION: Detector attaching sections 2 and 2 are respectively welded to the upstream and downstream sides of a flow tube 1 at a prescribed inclined angle and detectors 4 and 4 are respectively put in the attaching sections 2 and 2. An ultrasonic pulse is propagated between the detectors 4 and 4 by a reflecting method and the time required for propagating the pulse is alternately measured by alternately using the detectors 4 and 4 as transmitters and receivers. An ultrasonic flowmeter measures the flow rate of a fluid from the difference in propagating time. When the pulse is propagated, ghost signals are directly received by the receivers from the transmitters without passing through normal routes produced by the reflection. In order to improve the S/N of the detecting signal of the flowmeter by suppressing the generation of the ghost signals, the upstream detector 4 facing the flow passage is installed in such a position that the detecting end 6 of the detector 4 is separated from the flow passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter, and more particularly, to an ultrasonic flowmeter that suppresses a signal component traveling along an inner wall of a flow tube to improve an SN ratio of a detection signal.

[0002]

2. Description of the Related Art A propagation time reciprocal difference method (frequency difference method) is well known as a measurement principle widely used in an ultrasonic flowmeter.
The transit time reciprocal difference method is to measure a measured flow velocity V of a fluid as a change in the propagation velocity of ultrasonic waves in the fluid, that is, a difference Δf in frequency, which is the reciprocal of the transit time, and multiply the measured flow velocity V by a known cross section A of flowing water. Is a method of measuring the flow rate Q by

As an example of ultrasonic flow measurement to which the time difference method is applied, there is known a V method (reflection method) in which an ultrasonic pulse is reflected once on the inner surface of a measurement tube.

FIG. 6 is a system diagram of an ultrasonic flowmeter for explaining the principle of flow measurement by the V method. A detection end (ie, an end of a device for transmitting and receiving ultrasonic waves) is provided upstream of a measuring tube.
A detection end Pd is attached to the downstream side of Pu, and a transmission pulse oscillated from the transmission circuit of the converter T excites a vibrator (not shown) installed at the detection end Pu via the dedicated cable C. The transducer converts a transmission pulse (electric signal) into an ultrasonic pulse (acoustic signal) and emits it into a fluid.

The ultrasonic pulse propagated in the fluid is reflected by the tube material, reaches the detection end Pd, and excites the transducer at the detection end Pd. The transducer receives the ultrasonic pulse, converts it into a received pulse (electric signal), and returns to the receiving circuit of the converter T via a dedicated cable. In a cycle in which the electric signal and the acoustic signal make a round, the transmission circuit → dedicated cable → detection end Pu → fluid → tubing (reflection) → fluid → detection end Pd → dedicated cable → receiving circuit, Pu along the flow → Pd direction ( The forward propagation time td can be measured. As soon as the measurement of the propagation time td is completed, Pd against the flow, which is the next measurement operation, →
The propagation time tu in the Pu direction (reverse direction) is measured. That is, the propagation time tu in the direction opposite to the flow can be measured by the transmission circuit → the dedicated cable → the detection end Pd → the fluid → the tubing (reflection) → the fluid → the detection end Pu → the dedicated cable → the reception circuit.

In the propagation path length of the ultrasonic pulse in the fluid, if the path length from the detection end Pd to the reflection surface of the tube is L, the path length from the reflection surface to the detection end Pu is L.
The propagation path length from the detection end Pd to the detection end Pu is 2L. Assuming that the sound velocity inherent to the fluid is C and the angle between the ultrasonic wave propagation path and the tube axis is θ, the sound velocity C _{0 of the} ultrasonic pulse traveling between the detection ends Pu and Pd is affected by the flow velocity V. ₀ = C ± Vcos θ

Here, the propagation time of the ultrasonic pulse in the fluid is represented by tdL for the forward direction (Pu → Pd), and
Assuming that the case of d → Pu is tuL, tdL and tuL are respectively tdL = 2L / C ₀ = 2L / (C + Vcos θ) tuL = 2L / C ₀ = 2L / (C−Vcos θ).

Here, considering the frequencies fd and fu on the measuring circuit proportional to the reciprocals of the propagation times tdL and tuL, fd = N / tdL fu = N / tuL where N is a constant (multiple number) on the measuring circuit. ), And taking these frequency differences Δf,

[0009]

(Equation 1)

## EQU1 ## Therefore, the measured flow velocity V is

[0011]

(Equation 2)

Accordingly, the flow rate can be obtained by calculating the flow rate correction coefficient and the flow tube cross-sectional area for converting the measured flow rate into the average flow rate.

The flow rate can also be obtained by the propagation time difference method in addition to the above-described propagation time reciprocal difference method.

FIG. 7 is a sectional view of a detector mounting portion of the ultrasonic flowmeter to which the above-described measurement principle is applied. In the drawing, reference numeral 1 denotes a flow tube, and 2 denotes a detector mounting portion installed on the flow tube 1. Department. The detector mounting portion 2 has a cylindrical shape, one end of which has an opening 2a into which a detector to be described later is inserted and a flange 2b connected to the opening 2a, and the other end of which is connected to the flow tube 1. The hole 3 communicates with the inside of the flow channel through the hole 3 and is fixed to the flow tube 1 by welding at a predetermined angle θ.

FIG. 8 is a side view of the detector, in which 4 is a detector, 5 is a bottomed cylindrical portion, 6 is a detection end of the detector 4, and 7 is the cylindrical portion 5 attached to the flange 2b. The fastening flange 8 is a cable connector provided on the cylindrical portion 5. A vibrator (not shown) is provided in the cylindrical portion 5, and is connected to the cable connector 8 by a lead wire (not shown). Reference numeral 9 denotes a dedicated cable connected to a converter (not shown). l ₁ (ell) represents the length of the cylindrical portion 5.

FIG. 9 is a view showing a state in which the detector 4 is installed on the detector mounting portion 2. The cylindrical portion 5 of the detector 4 is inserted into the hollow portion of the detector mounting portion 2 through the opening 2 a of the detector mounting portion 2. The flange 7 is installed so as to stay on the flange 2b, and is fixed by screws 10. The fluid flows from the right side (upstream side) to the left side (downstream side) according to the arrow. l ₂ represents the length of the detector mounting portion 2, and S is an imaginary line extending from the inner wall surface of the flow tube 1 set in the hole 3. In addition, reference numerals are assigned only to the upstream detector, and the downstream detector is the same as the upstream detector, and thus the description is omitted.

[0017]

Relationship of the invention It is an object of the length l ₂ of the detector mounting portion 2 and the length l ₁ of the cylindrical portion 5 of the detector 4, not being standardized, freedom manufacturer I have decided. For this reason, in reality, the mounting position is usually such that the center line in the length direction of the cylindrical portion 5 coincides with the center of the detection end 6 at the virtual line S. FIG. 9 shows a state in which the detector 4 is mounted on the detector mounting part 2 due to such a dimensional relationship. That is, the detection end 6 faces the flow path, and its corner is exposed in the flow path. As a result,
It is known that the emission signal of the ultrasonic wave follows the above-described path length 2L, and there is a signal G which travels along the inner wall of the flow tube 1.

This signal is a so-called ghost signal, and is a factor that deteriorates the SN ratio of the detection signal. As a technique for improving this, there is a technique disclosed in Japanese Patent Application Laid-Open No. 9-287990. However, various processes must be performed in a narrow pipeline, and there is a practical difficulty.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a simple configuration to suppress a signal component traveling along the inner wall of a flow tube and improve an SN ratio of a detection signal. Is provided.

[0020]

According to a first aspect of the present invention, there is provided a detector mounting portion having a mounting space for a detector installed at a predetermined inclination angle in a flow pipe through which a fluid to be measured flows, and a detector. In an ultrasonic flowmeter having a detector installed in the space so that an end comes out of a flow path in the flow tube, a position at which a detection end of the detector is separated from the flow path on the upstream side. The present invention is characterized in that the signal component received by the receiver directly from the transmitter along the inner wall of the flow tube is suppressed, and the SN ratio of the detection signal is improved.

According to a second aspect of the present invention, in the first aspect of the present invention, the position at which the detection end of the detector is separated from the flow path is adjusted by the spacer mounted between the detector mounting portion and the detector. Thus, the position of the detector can be easily adjusted corresponding to the detector mounting portions having various dimensions.

[0022]

FIG. 1 is a sectional structural view of a detector mounting portion of an ultrasonic flow meter to which the present invention is applied. In the drawing, the same reference numerals are given to the same components as those in FIG. And the description is omitted.

In the present invention, the position is adjusted by shortening the size of the cylindrical portion 5 of the upstream detector 4 or changing the mounting position, and the detection end 6 of the detector 4 is not exposed in the flow path. And separated from the flow channel.

FIG. 2 is a view showing a situation where the mounting position of the detector is adjusted by the spacer. Reference numeral 11 denotes a spacer which is held between the flange 2b and the flange 7 of the detector 4. The mounting position of the detector 4 is adjusted by the spacer 11 so that the detection end 6 of the detector 4 is separated from the flow path.

FIG. 3 shows that the detector 4 is mounted so that the corner at the tip of the cylindrical portion 5 of the upstream detector is set back by 10 mm from the line S, and the mounting position of the downstream detector remains unchanged. It is a waveform diagram of the ultrasonic reception wave when the
The left waveform shows a waveform received as a ghost wave, and the right waveform shows a waveform received via a normal path. By the way,
FIG. 5 shows a waveform of a reception wave in the related art.
A comparison of these shows that the effect of the ghost wave is clearly improved.

The reason for the improvement is that, of the space having a substantially triangular cross section formed by the bottom surface of the cylindrical portion 5, the virtual line S, and the wall of the detector mounting portion 2, the wall portion of the detector mounting portion 2 It is thought to serve as a shield for signal components traveling along the inner wall of the flow tube directly from the transmitter to the receiver.

The waveform is a received wave at a flow rate of 125% of the full scale.
³ / h, flow rate: 37.5 m / s. 3 to 5, the voltage value represents the median value of the maximum wave in the ghost waveform and the median value of the third signal wave in the signal wave.

As is apparent from FIG. 3, the position of the detector on the downstream side detector does not substantially contribute to the improvement of the influence of the ghost wave.

Therefore, the inventors conducted further experiments, retreated the mounting positions of the upstream and downstream detectors, and measured the change state of the ghost wave. FIG. 4 shows the result, and the improvement is almost the same as that of FIG. 3, but it has also been found that the waveform received via the regular path becomes smaller.

As described above, in the ultrasonic flow meter,
Since the upstream and downstream detectors alternately repeat transmission and reception, it is desirable that they have the same structure. If the structures are different, two sets of detectors must be provided for transmission and reception. Therefore, instead of using the detector 4 in which the length of the cylindrical portion 5 is changed between the upstream side and the downstream side, it is preferable to make the same configuration by the spacer.

[0031]

According to the first aspect of the present invention, a detector mounting portion having a mounting space portion for a detector installed at a predetermined inclination angle in a flow pipe through which a fluid to be measured flows, and a detection end. In an ultrasonic flowmeter having a detector installed in the space so as to exit a flow path in the flow tube, the upstream detector is installed at a position where a detection end of the detector is separated from the flow path. Therefore, it is possible to suppress a signal component that reaches the receiver directly from the transmitter along the inner wall of the flow tube, thereby improving the SN ratio of the detection signal.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, a position where the detection end of the detector is separated from the flow path is sandwiched between the detector mounting portion and the detector. Since the adjustment is performed by the spacers, the position of the detector can be easily adjusted corresponding to the detector mounting portions having various dimensions.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a detector mounting portion of an ultrasonic flowmeter to which the present invention is applied.

FIG. 2 is a diagram showing a situation where a mounting position of a detector is adjusted by a spacer.

FIG. 3 is a waveform diagram of a received wave when a detection end of an upstream detector is separated from a flow path.

FIG. 4 is a waveform diagram of a received wave when a detection end is separated from a flow path for both an upstream side detector and a downstream side detector.

FIG. 5 is a waveform diagram of a received wave in the related art.

FIG. 6 is an apparatus system diagram of an ultrasonic flow meter for explaining the principle of flow measurement by a reflection method.

FIG. 7 is a sectional configuration diagram of a detector mounting portion of the ultrasonic flowmeter.

FIG. 8 is a side view of the detector.

FIG. 9 is a diagram showing an attached state of a detector according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flow pipe, 2 ... Detector attachment part, 2a ... Opening part, 2b ... Flange, 3 ... Hole part, 4 ... Detector, 5 ... Cylindrical part, 6 ... Detection end, 7 ... Flange part, 8 ... Cable connector , 9: dedicated cable, 10: screw, l ₁ : length of cylindrical portion, l ₂ : length of detector mounting portion, S: virtual line.

Claims (2)

[Claims] 1. A detector mounting part having a mounting space for a detector installed at a predetermined inclination angle in a flow pipe through which a fluid to be measured flows, and a detection end of the detector mounting part exits a flow path in the flow pipe. An ultrasonic flowmeter having a detector installed in the space, wherein the upstream detector is installed at a position where a detection end of the detector is separated from the flow path. Total. 2. The apparatus according to claim 1, wherein the position at which the detection end of the detector is separated from the flow path is adjusted by the detector mounting portion and a spacer sandwiched by the detector. Sound flow meter.