JPH0739964B2 - Ultrasonic flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic flowmeter, and more particularly to an ultrasonic flowmeter of a type in which an ultrasonic wave transmitter / receiver is attached to a pipe to measure a flow velocity inside the pipe. Regarding

[Conventional technology]

A conventional example is shown in FIGS. In the conventional example of FIG. 5, the ultrasonic transducer 1A of one ultrasonic transducer 1 is used.
Ultrasonic output toward the downstream side from the propagation path l _1, l
_{2, l 3, l 4,} l 5, and via the l ₆ reaches the other ultrasonic transducer 2A of the ultrasonic transducer 2. The propagation time in this case is t _d
And

Further, in FIG. 6, the ultrasonic waves output from the ultrasonic transducer 2A of the other ultrasonic transducer 2 toward the upstream side are the propagation paths l ₆ , l ₅ , l ₄ , l ₃ , l ₂ , And l ₁ to reach the ultrasonic transducer 1A of one ultrasonic transducer 1. The propagation time in this case is t _u .

In this case, the flow velocity in the pipe 13 is calculated by the following equation.

V = D · (t _u −t _d ) / 2sinθ · cos θ (t _o −τ) ² ...... where D is the inner diameter of the pipe 13, θ is the line perpendicular to the pipe wall and ultrasonic waves in the fluid to be measured. Angle with respect to the propagation direction of, t _o is the average value of t _d and t _u , τ is the path l ₁ , l ₂ , l ₅ , and of FIGS.
l The time required for ultrasonic waves to propagate through the _6th part.

Since the dimension of the inner diameter D of the pipe 13 is known in advance, the flow rate can be easily calculated by this.

These ultrasonic transducers (hereinafter referred to as "probes") 1,
The transmitting / receiving switching unit 2 includes a transmitting circuit unit 30 and a receiving circuit unit 4.
Are connected to each other via cables 5 and 6 as required. The arrow V indicates the flow velocity of the fluid to be measured.

In FIG. 5, the upstream probe 1 (including the cable 5)
F parameter of Set the F parameter of the downstream probe 2 (including the cable 6) Then, the equivalent circuit when measuring from the upstream side to the downstream side can be shown as in FIG.

The transfer function T _d ′ of the circuit of FIG. 7 is T _d ′ = a / bc ... where a, b, and c are each expressed by the following equation.

a = 2Z _L Z _M b = AZ _M + B + Z _S ′ (CZ _M + D) c = A′Z _M + B ′ + Z _L (C′Z _M + D ′) Further, Z _S ′ is the output impedance of the transmitting circuit section 30, Z _M is the acoustic impedance in the fluid to be measured, Z _L is the receiving circuit section 4
Is the input impedance of.

On the contrary, FIG. 7 shows an equivalent circuit for measurement from the downstream side to the upstream side.

The transfer function T _u ′ in this case is T _u ′ = a / de, where d and e are respectively expressed by the following equations.

d = A'Z _M + B '+ Z _S '(C'Z _M + D ') e = AZ _M + B + Z _L (CZ _M + D).

By the way, in the above-mentioned conventional example,
A spike pulsar of a type in which a capacitor is charged with electric charges and a switching element discharges the electric charges to generate a spike-shaped output pulse is used. For this reason, the output impedance Z _S ′ of the transmission circuit section 30 largely depends on the operating impedance of the switching element, and it is difficult to maintain a constant output impedance.

Therefore, the value of the output impedance Z _S ′ of the transmitter circuit section 30 is different from the value of the input impedance Z _L of the receiver circuit section 4, and therefore, when the probe 1 is used for transmission and the probe 2 is used for reception. The transfer function T _d ′ between the transmitter and the receiver of the flowmeter in FIG. 2 is different from the transfer function T _u ′ when the probe 2 is used for transmission and the probe 1 is used for reception.

[Problems to be solved by the invention]

In the above conventional example, the transfer function is different when the probe 1 is used for transmission and the probe 2 is used for reception, and when the probe 2 is used for transmission and the probe 1 is used for reception (T _d ′). ≠ T _u ′), the received waveforms are different from each other, especially the phase is slightly different.

Therefore, even when the fluid to be measured is still water (flow velocity V = 0), the propagation time t _d of the ultrasonic pulse from the probe 1 to the probe 2 and the propagation time t of the ultrasonic pulse from the probe 2 to the probe 1 _u is slightly different. Therefore, Δt = t _u −t _d ≠ 0 ... However, the calculation formula of the flow velocity V is V = D · Δt / 2sin θ · cos θ · (t _o −τ) ² ; Despite the fact that the fluid to be measured is still water, there was the inconvenience that V ≠ 0, indicating a certain value. This is the so-called zero point error.

[Object of the Invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrasonic flowmeter capable of measuring the flow velocity of a fluid to be measured with higher accuracy by improving the disadvantages of the conventional example and eliminating the zero point error almost completely. And

[Means for solving problems]

In the present invention, ultrasonic wave transmitters / receivers respectively arranged on the upstream side and the downstream side of the pipe corresponding to the propagation direction of the ultrasonic waves, and an oscillation circuit unit and a reception circuit unit in these two ultrasonic wave transmitters / receivers. And a transmission / reception switching unit for alternately switching and connecting.

The oscillator circuit section is configured by a burst pulser, the output impedance of the burst pulser is maintained at a constant value, and the output impedance of the burst pulser is set to the same value as the input impedance of the receiving circuit section. It adopts the configuration of setting. This aims to achieve the above-mentioned object.

[Action]

Maintaining a constant value for the output impedance of the oscillator circuit,
Since the output impedance is set to the same value as the input impedance of the receiving circuit section, the flowmeter is used when the upstream probe is used for transmission and the downstream probe is used for reception, and vice versa. The transfer functions for transmission and reception are equal, and the conditions for signal propagation are the same.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.

Here, regarding the same components as the above-mentioned conventional example,
The same code will be used.

The embodiment shown in FIG. 1 has one probe 1 installed upstream of the pipe 13 and the other probe 2 installed downstream of the pipe 13. Of these, one probe 1 is provided with a wedge member 1B and an oscillator 1A for causing ultrasonic waves to obliquely enter the pipe 13. The wedge member 1B is made of acrylic resin or the like, has a trapezoidal cross section, and the ultrasonic transducer 1A is fixed to the inclined surface 1a thereof.

The other probe 2 has substantially the same configuration.

Each of these probes 1 and 2 is actually switched and connected separately to the transmitting circuit section 3 and the receiving circuit section 4 via the transmission / reception switching section 7 as shown in FIG. .
FIG. 1 shows a state in which the upstream probe 1 is connected to the transmitting circuit section 3 and the downstream probe 2 is connected to the receiving circuit section 4. Here, the transmission / reception switching unit 7 is specifically configured by a quadruple switch including switches S ₁ , S ₂ , S ₃ , and S ₄ as shown in FIG. 3, for example.

The received signal of the incoming ultrasonic wave output from the probe 1 and received by the probe 2 and the received signal of the incoming ultrasonic wave output from the probe 2 and received by the probe 1, which will be described later, are displayed on the signal processing display unit 20. Sent, various operations,
Then, the signal is processed and finally displayed on a display unit (not shown) of the signal processing display unit 20. This signal processing display section 20
Is a signal selection function as a first function, a clock function as a second function, a memory function as a third function,
It has several functions such as a calculation function as a fourth function and a display function as a fifth function. The main controller 10 has a function of controlling a series of operations of each component.

In this embodiment, a burst pulser is used in the transmission circuit section 3. This burst pulsar has an advantage that the output impedance of the pulsar can be easily maintained at a constant value because the output impedance of the burst pulsar becomes the impedance of the final stage amplifier circuit.

In the present embodiment, as the output impedance Z _S of the oscillator circuit portion 3 and the input impedance Z _L of the reception circuit unit 4 matches the output impedance Z _S is set.

Other configurations are the same as those of the conventional example described above.

In FIG. 1, as in the case of the conventional example described above, the ultrasonic waves output from the ultrasonic transducer 1A of the one probe 1 toward the downstream side are the propagation paths l ₁ , l ₂ , l ₃ , l ₄ , l ₅ and l ₆ to reach the ultrasonic transducer 2A of the other probe 2. The propagation time in this case is t _d .

On the contrary, the ultrasonic waves output from the ultrasonic transducer 2A of the other probe 2 toward the upstream side are transmitted through the propagation paths l ₆ , l ₅ ,
Ultrasonic transducer of one probe 1 through l ₄ , l ₃ , l ₂ and l ₁
Up to 1A. The propagation time in this case is t _u .

In this case, the flow velocity in the pipe 13 is obtained by the above-mentioned formula.

The equivalent circuit of FIG. 1 can be shown as in FIG.

The transfer function T _d of the circuit of FIG. 4 is T _d = a / b'c ... where b '= AZ _M + B + Z _S (CZ _M + D), and a and c are the same as in the case of the conventional example described above. It is the same.

Further, Z _S is the output impedance of the transmission circuit section 3.
Contrary to FIG. 1, an equivalent circuit when measured from the downstream side to the upstream side can be shown as in FIG.

The transfer function T _U of the circuit of FIG. 3 is T _u = a / d'e ... Here, d'is represented by the following equation.

d '= A'Z _M + B' + Z _S (C'Z _M + D) a, e is the same as in the conventional example.

However, in the case of the present embodiment, since Z _S = Z _L holds, T _d = T _u holds from the equations and expressions (∵b′c =
d'e). Therefore, in the present embodiment, the reception waveforms are the same when one probe 1 is used for transmission and the other probe 2 is used for reception, and vice versa.

Therefore, when the fluid to be measured is stationary, the probe 1
The propagation time t _{d of the} ultrasonic pulse from the probe 2 to the probe 2 and the propagation time t _{u of the} ultrasonic pulse from the probe 2 to the probe 1 match. In other words, since Δt = t _u −t _d = 0,
From the formula, V = 0.

Therefore, according to the present embodiment, unlike the conventional example, there is an advantage that a flow velocity measurement error (zero point error) due to a difference in waveform shape does not occur.

〔The invention's effect〕

Since the present invention is configured and functions as described above, according to this, the oscillator circuit section is configured by a burst pulser, the output impedance of the burst pulser is maintained at a constant value, and the burst pulser is maintained. Since the output impedance of is set to the same value as the input impedance of the receiving circuit section, the transfer function between transmission and reception when one probe is used for transmission and the other probe is used for reception is the same. Since it is possible to eliminate the zero-point error due to the difference in the shape of the received waveform, it is not necessary to select a probe with similar characteristics to reduce the zero-point error, which reduces the manufacturing cost. It is possible to reduce the flow rate and to measure the flow velocity of the fluid to be measured with higher accuracy than before. It is possible to provide an amount meter.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of the ultrasonic flowmeter according to the present invention in the state of measuring from the upstream side to the downstream side, and FIG. 2 is a block showing the overall configuration of the flowmeter of FIG. Figure, third
FIG. 4 is a diagram showing a specific configuration example of the transmission / reception switching unit in FIG. 2, and FIG. 4 is a diagram showing an equivalent circuit in the case where measurement is performed from the upstream side to the downstream side and the opposite case,
FIG. 5 is a diagram showing a configuration in which measurement is performed from the upstream side to the downstream side with an ultrasonic flowmeter of a conventional example, and FIG. 6 is opposite to FIG. 5 from the downstream side to the upstream side. The figure showing the configuration in the state of measurement, FIG. 7, is FIG. 5, respectively.
It is a figure which shows the equivalent circuit of FIG. 1,2 ... Ultrasonic transmitter / receiver, 3 ... Transmission circuit, 4 ... Reception circuit, 7 ... Transmission / reception switching unit, Z _S ... Output impedance of transmission circuit, Z _L ... Reception circuit Input impedance of.

Claims (1)

[Claims] 1. An ultrasonic wave transmitter / receiver arranged on the upstream side and the downstream side of a pipe corresponding to the direction of propagation of ultrasonic waves, and an oscillator circuit section and a receiver circuit section on the two ultrasonic wave transmitters / receivers. In an ultrasonic flowmeter having a transmission / reception switching unit for alternately switching and connecting and, the transmission circuit unit is configured by a burst pulser, and the output impedance of the burst pulser is maintained at a constant value, and the burst An ultrasonic flowmeter in which the output impedance of the pulsar is set to the same value as the input impedance of the receiving circuit section.