JPH07167696A - Phase difference measuring method for flowing velocity in tube using ultrasonic current meter - Google Patents

Abstract

PURPOSE:To easily obtain a phase difference between a received wave in a flowing direction and a received wave in a reverse direction when a flowing velocity of fluid in a tube is measured from the difference. CONSTITUTION:A rectangular continuous wave is used as an ultrasonic wave. An exclusive OR W1 XOR W2 of a received wave W1 of a direction of a flow and a received wave W2 of a reverse direction to the flow is obtained and the exclusive OR is smoothed. An amplitude of the difference DELTAphi is obtained from a size of the smoothed result (DELTAphi/pi).Vo.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a phase difference of a flow velocity in a pipe using an ultrasonic velocity meter.

[0002]

2. Description of the Related Art It is known to use an ultrasonic flow meter to measure the flow velocity of a fluid, such as clean water, flowing in a pipe. This ultrasonic flowmeter utilizes that, when an ultrasonic wave propagates in a fluid, its propagation velocity is a vector sum of a sound velocity in a stationary fluid and a fluid flow velocity.

FIG. 3 shows the measuring principle. As shown in the figure, the first ultrasonic transmitter 11 is installed on the inner surface of the upstream pipe, and the first ultrasonic wave is installed on the inner surface of the downstream pipe at a distance L in the pipe axial direction. The receiver 12 is installed so that the ultrasonic waves 13 transmitted from the transmitter 11 are reflected by the inner surface of the tube on the opposite side in the radial direction and are received by the receiver 12. On the other hand, the second ultrasonic receiver 14 is installed at a position corresponding to the first ultrasonic transmitter 11.
A second ultrasonic transmitter 15 is installed at a position corresponding to the first ultrasonic receiver 12 so that ultrasonic waves can be sent in the opposite direction, that is, from the downstream side to the upstream side. There is. In other words, the two pairs of ultrasonic sensors are configured to simultaneously transmit and receive.

In this way, the flow velocity of the fluid in the pipe can be obtained from the difference between the propagation time in the flow direction and the propagation time in the opposite direction (double flow method, time difference method). When transmitting and receiving continuous waves, the flow velocity can be obtained by replacing the difference in propagation time with the phase difference (phase difference method).

The principle of the phase difference method will be described below. First, in FIG. 3, consider the propagation of ultrasonic waves from the upstream side to the downstream side. Then the propagation vector is

[0006]

[Equation 2]

[0007] If this is expressed as a scalar quantity, using angles θ and β,

[0008]

[Equation 3]

[0009] Here, since asin θ = vsin β,

[0010]

[Equation 4]

[0011] Substituting equation (3) into equation (2),

[0012]

[Equation 5]

[0013] Here, specifically, a = 1450
˜1500 m / s, v = 0 to 3 m / s, therefore a
>> Because it is v,

[0014]

[Equation 6]

Therefore, the equation (4) is

[0016]

[Equation 7]

[0017] Since the propagation distance ACB is L / cos β, the propagation time t is

[0018]

[Equation 8]

It becomes Next, let us consider the propagation of ultrasonic waves in the direction opposite to the flow direction, that is, from the downstream side to the upstream side. At this time, if the propagation velocity is V'and the propagation time is t ',

[0020]

[Equation 9]

[0021] From equations (7) and (9), the difference in propagation time Δt is

[0022]

[Equation 10]

However, since a ² >> v ² , after all,

[0024]

[Equation 11]

[0025] If this is represented by a phase difference: Δφ, the frequency of the ultrasonic wave is f,

[0026]

[Equation 12]

From the equation (11),

[0028]

[Equation 13]

It becomes

[0030]

However, in the prior art, there is no way to properly measure and quantify the above-mentioned phase difference, and it is difficult to measure the flow velocity of the fluid in the pipe using the above equation (12). There is a problem that

Therefore, an object of the present invention is to solve such a problem and to make it possible to easily obtain a phase difference representing a difference in propagation time of ultrasonic waves in the flow direction and the opposite direction. .

[0032]

In order to achieve the above object, the present invention uses a rectangular continuous wave as an ultrasonic wave, and excludes a received wave in the direction of flow and a received wave in the direction opposite to the flow. The logical OR is calculated, the exclusive OR is smoothed, and the magnitude of the phase difference is calculated from the magnitude of the smoothed result.

[0033]

In this way, the exclusive OR of the received wave in the flow direction and the received wave in the opposite direction to the flow includes information on the phase difference between the two received waves. Therefore, the magnitude of the phase difference is obtained by smoothing this exclusive OR, and as a result, the flow velocity of the fluid in the pipe is obtained by using the above equation (12).

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a concrete method for obtaining a phase difference according to the present invention. The received wave W1 in the direction of flow and the received wave W2 in the direction opposite to the flow are both rectangular waves having the same frequency f, and have a duty ratio of 50, and a predetermined output Vo (volt ) Occurs or it does not occur and becomes 0. As described above, the phase difference Δφ based on the flow velocity of the fluid in the pipe exists between the received wave W1 and the received wave W2.

Exclusive OR W1 of both received waves W1 and W2
XOR W2 is as shown. Therefore, when the signal for the exclusive OR is smoothed by a known means, its value becomes (Δφ / π) · Vo, and the phase difference can be converted into a voltage, and the magnitude thereof can be obtained. it can.

FIG. 2 shows the relationship between this phase difference Δφ and the voltage obtained by smoothing W1 XOR W2. As shown,
When the phase difference Δφ is in the range of 0 to π radians, the voltage changes simply and incrementally. Therefore, the difference Δt in propagation time is 1 / 2f
Within the range (-1 / 2f to 1 / 2f), the flow velocity v can be obtained from the phase difference Δφ. Therefore, the distance L and the frequency f may be appropriately selected according to the measurement target so that the propagation time difference Δt falls within this range. However, since the flow direction cannot be determined, it is applied when the flow direction is known.

Next, a specific example of the measurable flow velocity range will be described. Distance L = 0.15 m, sound velocity in fluid a =
Substituting the maximum phase difference Δφ = π radian into the equation (12) with 1450 m / s and the ultrasonic frequency f = 1 × 10 ⁶ Hz,

[0038]

[Numerical equation 14]

It becomes Thus, the phase difference Δφ is 0 to π
By keeping it within the range of radians, the flow velocity v can be uniquely obtained from the value of the signal regarding the exclusive OR,
The signal processing circuit for that purpose becomes simple.

[0040]

As described above, according to the present invention, when the flow velocity in a pipe is measured using ultrasonic waves, the exclusive OR of the received wave in the flow direction and the received wave in the opposite direction to the flow is obtained. Since the smoothed phase difference between the two waves is measured, the magnitude of this phase difference can be easily obtained, and the flow velocity of the fluid in the pipe can be easily measured.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of obtaining a magnitude of a phase difference in a method of measuring a phase difference of a flow velocity in a pipe according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a phase difference and a voltage obtained by smoothing an exclusive OR of both received waves.

FIG. 3 is a principle diagram of a conventional ultrasonic velocity meter.

[Explanation of symbols]

 W1 Received wave in the flow direction W2 Received wave in the opposite direction

Claims (1)

[Claims] 1. A first ultrasonic transmitter and a second ultrasonic receiver are installed on the upstream side in the pipe, and a second ultrasonic transmitter and a first ultrasonic receiver are installed on the downstream side in the pipe. And the ultrasonic waves transmitted from the first and second ultrasonic transmitters are respectively received by the first and second ultrasonic receivers, and the flow of the flow received by both receivers is received. When measuring the flow velocity of the fluid in the pipe based on the following equation (i) from the phase difference between the received wave in the direction and the received wave in the opposite direction, A rectangular continuous wave is used as the ultrasonic wave, the exclusive OR of the received wave in the direction of the flow and the received wave in the direction opposite to the flow is obtained, and this exclusive OR is smoothed and smoothed. A method for measuring the phase difference of the flow velocity in a pipe using an ultrasonic velocity meter, which is characterized in that the magnitude of the phase difference is obtained from the size of the result.