JPH0196514A - Ultrasonic flow meter - Google Patents

Abstract

PURPOSE:To almost completely eliminate a zero point error and to measure a flow velocity with high accuracy by maintaining an output impedance of an originating circuit part at a prescribed value, and also, setting it to the same value as an input impedance of a receiving circuit part. CONSTITUTION:Probes 1, 2 are provided on the upstream and the downstream sides of a piping, and the probes 1, 2 are connected so as to be switchable separately to an originating circuit part 3 and a receiving circuit part 4 for which a burst pulser is used, through a transmission/reception switching part 7. In this state, a receiving signal of an incoming ultrasonic wave which is outputted from the probe 1 and received by the probe 2, and on the contrary, a receiving signal of an incoming ultrasonic wave which is outputted from the probe 2 and received by the probe 1 are sent to a signal processing display part 20, and various arithmetic operations and processings are performed and displayed on the display part 20. In this case, an output impedance is set so that an output impedance of the originating circuit part 3 and an input impedance of the receiving circuit part coincide with each other. In such a way, the respective receiving waveforms in case the probe 1 and the probe 2 have been used for transmission (reception) and reception (transmission), respectively become the same, and no zero point error is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic flowmeter that measures the flow velocity inside a pipe by attaching an ultrasonic transducer to the pipe.

[Conventional technology]

Conventional examples are shown in FIGS. 5 and 6. In the conventional example of FIG. 5, the ultrasonic transducer I of one ultrasonic transducer 1
The ultrasonic waves output from A toward the downstream side follow the propagation path: it, lx, la, 16. and Ab to the ultrasonic transducer 2A of the other ultrasonic transducer 2. The propagation time in this case is assumed to be 1.1.

Further, in FIG. 6, the ultrasonic waves outputted toward the upstream side from the ultrasonic transducer 2A of the other ultrasonic transducer 2 have propagation paths 1-b, ls, 14. l-3°f! + and! , to the ultrasonic transducer IA of one ultrasonic transducer l. The propagation time in this case is 1. shall be.

In this case, the flow velocity within the pipe 13 is determined by the following equation.

V=D・(t, ta)/2sin θ' cos θ(to −τ)2 ・・
(1) Here, D is the inner diameter of the pipe 13, and θ is the angle between a line perpendicular to the pipe wall and the propagation direction of the ultrasonic wave in the fluid to be measured.

t. Takes t6. The average value of τi, the route in FIGS. 5 and 6, 12. Is, and the time required for the ultrasonic wave to propagate through the 21st section.

Since the dimensions of the inner diameter of the pipe 13 are known in advance, the flow rate can be easily calculated.

These ultrasonic transducers (hereinafter referred to as "probes") 1
．． 2, the transmission circuit section 30 and the reception circuit section 4 are switched and connected via cables 5 and 6 by a transmission/reception switching section as necessary.

Arrow V indicates the flow velocity of the fluid to be measured.

In Fig. 5, upstream probe 1 (including cable 5)
Let the -F parameter of the downstream probe 2 (including the cable 6) be 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 shown in Figure 7 (1). can.

The transfer function T d ' of the circuit shown in FIG. 7(1) is T
d' = a / b c = (2
) Here, a=22L2.4 b =A Z M + B + Z S' (C
Z M + D >c=A'Z,+B' 10ZL
(C'Z, +D'). Further, Z,l is the output impedance of the transmitting circuit section 30 + ZM is the acoustic impedance in the fluid to be measured + ZL is the input impedance of the receiving circuit section 4 .

On the other hand, an equivalent circuit for measuring from the downstream side to the upstream side is shown in FIG. 7(2).

The transfer function T,l in this case is T,' = a / de −
=(3) Here, d=A' ZM +B'+Zs'(C'
ZM +D')+1! =AZM +B+ZL
(CZK +D).

By the way, in the above conventional example, a pulser (spike pulser) is used in the oscillation circuit section 30, which charges a capacitor with electric charge and discharges this electric charge using a switching element to generate a spike-like output pulse. ing. For this reason, the output impedance Z,' of the oscillation circuit section 30 largely depends on the operating impedance of the switching element, making it difficult to maintain a constant output impedance. For this reason, the transmitter circuit section 3
The value of the output impedance Z,' of 0 is different from the value of the input impedance ZL of the receiving circuit section 4, and therefore,
Transfer function T4'' between transmitting and receiving of the flowmeter when probe 1 is used for transmission and probe 2 is used for reception, and transfer function T, + when probe 2 is used for transmission and probe 1 is used for reception. It is different from that.

[Problem that the invention seeks to solve]

In the above conventional example, the transfer function is different when probe 1 is used for transmission and probe 2 is used for reception, and when probe 2 is used for transmission and probe 1 is used for reception (T4'≠ T,'), the received waveforms are also different from each other, especially the phases are slightly different. Therefore, even if the fluid to be measured is static water (flow rate = 0), the propagation time tu of the ultrasonic pulse from probe 1 to probe 2, and the propagation time tu of the ultrasonic pulse from probe 2 to probe 1 are slightly different. Therefore, ΔL = L ut a ≠0...
...(3) However, the calculation formula for the flow velocity V is: V=D-Δt/2stn θ" cos θ' (t
or) 2, so in the case of the conventional example described above, V-*O showed a certain value even though the fluid to be measured was static water. This is what is called a zero point error.

[Purpose of the invention]

An object of the present invention is to provide an ultrasonic flowmeter that can improve the disadvantages of the conventional example, eliminate zero point errors almost completely, and measure the flow velocity of a fluid to be measured with higher accuracy. shall be.

[Means for Solving the Problems] The present invention provides ultrasonic transducers disposed on the upstream and downstream sides of piping along the ultrasonic propagation line, and these two ultrasonic transducers. In an ultrasonic flowmeter having a transmitting/receiving switching section that alternately switches and connects a transmitting circuit section and a receiving circuit section as necessary, the output impedance of the transmitting circuit section is maintained at a constant value, and the output impedance is The above object is achieved by adopting a configuration in which the input impedance is set to the same value as the input impedance of the receiving circuit section.

[For production]

The output impedance of the oscillator circuit is maintained at a constant value,
Since the output impedance is set to the same value as the input impedance of the receiving circuit, the flowmeter can The transfer functions between transmitting and receiving are equal.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

Here, regarding the same components as the conventional example described above,
The same symbols will be used.

The embodiment shown in FIG. 1 has one probe 1 installed on the upstream side of the pipe 13 and the other probe 2 installed on the downstream side of the pipe 13.

Of these, one of the probes 1 transmits ultrasonic waves to the piping 13.
A wedge member IB and an oscillator IA are provided to allow oblique incidence to the oscillator. The wedge member IB is made of acrylic resin or the like, has a trapezoidal cross section, and has an ultrasonic transducer IA fixed to its slope 1a.

The other probe 2 also has substantially the same configuration.

In reality, each of these probes 1.2 is connected to the transmitting circuit section 3 and the receiving circuit section 4 through a transmitting/receiving switching section 7, respectively, 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. Note that the transmission/reception switching unit 7 is, for example, a third
As shown in the figure, switches St, St, Sz, S
It is composed of a quadruple switch consisting of a.

A reception signal of an incoming ultrasound outputted from the probe 1 and received by the probe 2, which will be described later, and a reception signal of an incoming ultrasound outputted from the probe 2 and received by the probe 1, which will be described later, are processed by the signal processing display section 20. The signal is sent to the computer, undergoes various calculations and processes, and is finally displayed on a display means (not shown) of the signal processing display section 20. This signal processing display section 20 has a signal selection function as a first function, a timekeeping function as a second function, a memory function as a third function, an arithmetic function as a fourth function, and a third function as a clock function. It has several functions such as a display function as the function of No. 5. Main control unit 10
has the function of controlling a series of operations of each component.

In this embodiment, the transmitting circuit section 3 uses a burst pulser. This burst pulser has the advantage that the output impedance of the pulser can be easily maintained at a constant value because its output impedance becomes the impedance of the final stage amplifier circuit due to the circuit configuration.

In this embodiment, the output impedance Z3 is set so that the output impedance Z3 of the transmitting circuit section 3 and the input impedance Zt of the receiving circuit section 4 match.

The other configurations are the same as the conventional example described above.

In FIG. 1, similarly to the conventional example described above, the ultrasonic waves output toward the downstream side from the ultrasonic transducer IA of one probe 1 follow propagation paths 11, 2* * 7! !
＋j! 4 + j! It reaches the ultrasonic transducer 2A of the other probe 2 via S and 16. The propagation time in this case is assumed to be t.

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 path 11h.
,ls,I! a, 1-s, lx, and 2° to reach the ultrasonic transducer IA of one probe 1. The propagation time in this case is assumed to be tu.

In this case, the flow velocity within the pipe 13 is determined by the above-mentioned equation (1).

The equivalent circuit of FIG. 1 can be shown as shown in FIG. 4 (1).

The transfer function T of the circuit shown in FIG. 4 (1) is T 4 =
a, / b' c ”・”
・(4) Here, b”=AZi+B+Zs (CZM 10D), a, c
is the same as in the conventional example described above.

Further, Z is the output impedance of the oscillation circuit section 3. The equivalent circuit when measured from the downstream side to the upstream side, contrary to FIG. 1, can be shown as shown in FIG. 3 (2).

The transfer function Tu of the circuit shown in FIG. 3 (2) is T, =
a/d' e・・・・・・
・(5) Here, d' = A' 2M + B' + ZS (C
' ZM +D) a and e are the same as in the conventional example.

However, in the case of this embodiment, since Zs=Zt holds, T,=T holds from equation (4) 1 and equation (5) (because ', 'b'c=d' e) . Therefore, in this embodiment, the received waveform is 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 t4 of the ultrasonic pulse from the probe 2 to the probe 2, and the propagation time t of the ultrasonic pulse from the probe 2 to the probe 1
u matches. In other words, Δt =tu ta
'O, so from the formula (]), ■=0. According to this embodiment, unlike the conventional example, there is an advantage that no flow velocity measurement error (zero point error) occurs due to a difference in waveform shape.

〔Effect of the invention〕

Since the present invention is configured and functions as described above, the output impedance value of the transmitting circuit section is set to the same value as the input impedance of the receiving circuit section, so that one probe is used for transmitting. , it is possible to match the transmission and reception transfer functions when the other probe is used for reception and vice versa. Therefore, zero point errors due to differences in the shape of received waveforms can be almost eliminated.

This eliminates the need to select probes with similar characteristics in order to reduce zero point errors, reducing manufacturing costs and making it possible to measure the flow velocity of the fluid being measured with higher precision than before. We can provide an excellent ultrasonic flow meter.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of an ultrasonic flowmeter according to the present invention in a state where measurement is performed from the upstream side to the downstream side, and Fig. 2 is a block diagram showing the overall configuration of the flowmeter of Fig. 1. Figure, 3rd
The figure shows a specific example of the configuration of the transmission/reception switching section in Figure 2, and Figures (1) and (2) show the case where measurements are taken from the upstream side to the downstream side, respectively. A diagram showing an equivalent circuit in the opposite case, FIG. 5 is a diagram showing the configuration of a conventional ultrasonic flowmeter measuring from the upstream side to the downstream side, and FIG. Figures 7 (1) and (2) are diagrams showing the configuration in which measurements are taken from the downstream side to the upstream side, contrary to the figure, and Figures 5 and 6 respectively.
It is a figure which shows the equivalent circuit of a figure. 1.2... Ultrasonic transducer, 3... Transmitting circuit section, 4... Receiving circuit section, 7......
Transmission/reception switching section, Z... Output impedance of the transmitting circuit section, ZL... Input impedance of the receiving circuit section. Patent applicant: Tokyo Co., Ltd. Meter Figure 2, 4F! A Figure 7

Claims (2)

[Claims] (1) An ultrasonic transducer is installed on the upstream and downstream sides of the piping along the ultrasonic propagation line, and a transmitting circuit and a receiving circuit are installed in these two ultrasonic transducers. In an ultrasonic flowmeter having a transmitting/receiving switching section that is alternately connected as necessary, the output impedance of the transmitting circuit section is maintained at a constant value, and the output impedance is the same as the input impedance of the receiving circuit section. An ultrasonic flowmeter characterized in that the value is set to . (2) The ultrasonic flowmeter according to claim 1, characterized in that a burst pulser is used as the transmitting circuit section.