JPS5994015A - Ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To measure accurate measurement of a flow rate with a stable ultrasonic wave by driving an ultrasonic vibrator with a multiple driving pulses of frequencies almost equal to the resonance frequency thereof. CONSTITUTION:In response to a start signal, an excitation signal generator 7 for variable division is enabled through no. of waves control circuit 8 to divide a pulse of frequency in an inverse proportion to the time of transmitting or receiving ultrasonic waves outputted from a voltage control oscillator 1 so that the generator 7 generates a driving pulse of the frequency almost equal to the resonance frequency of an ultrasonic vibrator. When this pulse is counted with a counter 3 to reach a specified value, an enable signal vanishes from the circuit 8 and an ultrasonic pulse generation circuit 4 is driven by a specified number of drive pulses of a specified frequency to transmit a specified number of stable ultrasonic pulses. Thus, an accurate measurement of a flow rate is done by an ultrasonic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flow meter used in iC1 for measuring the flow rate of large-diameter water pipes and the like.

FIG. 1 is a block diagram showing the configuration of an ultrasonic pulse generation circuit and its peripheral circuits in a conventional ultrasonic flowmeter.
In the figure, 1 is a voltage open side 1 oscillator (hereinafter referred to as VCO). vcoi is a control voltage V (! VC) supplied from a time difference voltage conversion circuit (not shown), so that its oscillation frequency f is equal to the reciprocal 1/T of the ultrasound propagation time T from when the ultrasound is transmitted to when it is received. The oscillation frequency f is inversely proportional to the propagation time T#L.The oscillation frequency f is inversely proportional to the propagation time T#L.The oscillation frequency f1 of the VCOI when emitting the Q wave is The flow rate is measured from the difference between the oscillation frequency f2 of the VCOI and the oscillation frequency f2 when the VC ultrasound is emitted in the opposite direction of the flow.The pulse signal 81 (
Frequency f) is supplied to the synchronization circuit 2 and the counter 3. The synchronous circuit 2 starts the KVC immediately after the start signal S '1' RT applied at a constant cycle reaches the 1H'' level.
It is triggered by the pulse signal Slam supplied from the OI and outputs an excitation signal EXc synchronized with the pulse signal Sla. This excitation signal 1xcFi is supplied to the counter 3 and the ultrasonic pulse generation circuit 4. When the counter 3 receives the excitation signal EXC, it immediately starts counting the pulse signals S1, and when it counts N pulse signals, it outputs %i, which is
Me is supplied to the time difference voltage conversion circuit. This time difference subpressure converter circuit outputs a control voltage Vc based on the difference between the ultrasonic propagation time T and the time N/f that elapses while counting eight pulse signals S1, and thereby 'r=N /f, that is, f=N/T. Also,
As shown in FIG. 1, the ultrasonic pulse generation circuit 4 generates an ultrasonic transducer drive pulse (
(hereinafter referred to as drive pulse) is generated. The waveform of this driving pulse V is a unit impulse waveform as shown in FIG. 1 (b). This driving pulse drives an ultrasonic probe (hereinafter referred to as a transducer), which is not shown, to generate ultrasonic waves.

By the way, the above-described unit impulse-like drive pulse C has some disadvantages other than the resonant frequency fr of the vibrator.

(1) In ultra-VR wave current tht' resistance, it is common to use vibration in the thickness direction of the vibrator (the frequency of this vibration is the resonance frequency frvr of the vibrator mentioned above) as a sound source. When the vibrator is driven by a drive pulse with a wide frequency band, radial vibration of the vibrator also occurs at the same time.
This becomes a noise wave and becomes an obstacle to stable measurement.

(2) Exciting a vibrator having a sharp resonance characteristic at a certain frequency with a signal having a wide frequency band causes a decrease in the efficiency of Vi excitation.

(3) When the vibrator is driven with a unit pulse-like drive pulse, the duration of the undesired linking is long.

In order to eliminate these inconveniences, it is sufficient for the VC to drive the vibrator with several (several waves) drive pulses having a frequency equal to (or almost exclusively) the resonant frequency fr of the vibrator. known (Reference: Fukukita et al.
“Ultrasonic probe with multi-layer matching layer” Confucian Connection US
75-28 (1975-11)). By the way, in an ultrasonic flowmeter, it is essential that the flow be performed in synchronization with the . However, if a signal from an external oscillator were to be used as an excitation signal or drive pulse, there was a problem in that it was difficult to achieve synchronization. For example, if you start an external oscillator in synchronization with the start signal and try to use that signal, the signal that is actually needed is several pulses (or waves) immediately after synchronization (that is, immediately after the start signal is generated). However, the initial vibration of No. 16 (startup of vibration) supplied from this external oscillator is not sufficiently stable and cannot be used as an excitation signal.

In view of the above circumstances, the present invention provides an ultrasonic flowmeter that can perform stable copper measurement using ultrasonic waves with low noise. The percentage indicates that the drive is driven by a drive pulse. More specifically, the present invention divides the frequency of a pulse signal output from a VCO to generate an excitation signal (which is amplified and driven to operate or stop it) having a frequency equal to or approximately equal to the resonant frequency of the vibrator. It is also characterized by comprising a wave number limiting path 1i1 for controlling the number of pulses (wave number) of the excitation signal.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 3 is a block diagram showing the configuration of the mounting section of the seventh embodiment of the present invention, and in the figure, VCol, counter 3,
The ultrasonic pulse generation circuit 4 has the same configuration and function as shown in FIG. Also, 7 is an excitation signal generator! Then, the pulse signal Sl, which is the output of the VCOI, is
The frequency is divided by π to generate an excitation signal EXC with a duty ratio jO%, which is supplied to the counter 3, the ultrasonic pulse generation circuit 4, and the wave number limiting circuit 8. The wave number limiting circuit 8 is cleared by the start signal 4STRTVc, and supplies an enable signal ENB of 'L# level to the excitation signal generator 7 to operate the excitation signal generator 7, while counting the wave number of the excitation signal EXC, It is a constant number (in this example, l
When the wave J) is reached, turn the enable signal ENB into ゞH“
The operation of the excitation signal generator 7 is stopped at this level.

In such a configuration, the time t1rc wave number limiting circuit 8π start code 5TRT shown in the time chart of FIG.
When ((b) in the same figure) is applied, the wave number limiting circuit 8 is cleared, and its output, the enable signal ENB (in the same figure)) becomes the 'LI level. This enables the excitation signal generator 7, and the excitation signal generator 7 The output signal of , that is, the excitation signal EXC ((c) in the same figure) goes to 'L'' level.Thereafter, every time j pulse signals S1 are applied, the excitation signal generator 7 goes to 1L.
Excitation whose level changes from ``→1H''→'L'' (i1f E
Output XC (see Figure V (c)). The frequency fe of this excitation signal EXC is made to match the resonant frequency fr of the vibrator (this will be described later).
. The excitation signal EXCVi thus formed, the counter 3
and is supplied to the wave number limiting circuit 8. The counter 3 sequentially counts the pulse signal S1 starting from the pulse signal Sla, stops counting when the count value reaches N (constant) vc, and supplies the output signal to a time difference voltage conversion circuit (not shown). Further, the wave number limiting circuit 8 is connected to the excitation signal EXC
is counted, and the excitation signal EXC is 9L"→ゝH"→ゝL
At time t2) shown in FIG. 11, the enable signal E NB
level. In other words, the wave number limiting circuit 8
is the excitation (when the N generator 7 outputs the excitation signal EXC in lj waves, the enable signal ENB is set to the H level and the frequency division operation of the excitation signal generator 7 is stopped.The excitation signal EXC obtained in this way is It is amplified by the sound wave pulse generation circuit 4, and is supplied as a driving pulse V (FIG. Since the ultrasonic flowmeter according to the present embodiment is driven by a driving pulse (2) with a wave number of /j, it emits ultrasonic waves with less noise and ringing, and thereby the ultrasonic flowmeter according to this embodiment can measure stable iR.

Next, FIG. 5 is a block diagram showing the configuration of main parts of a second embodiment of the present invention. This λth embodiment differs from the lth embodiment shown in FIG. 3 in the configuration of the wave number limiting circuit 9. In FIG.
Flip-flop (hereinafter referred to as FF) 9 bN to J-
It consists of FF9c and 251. Here, the inverter 9a inverts the excitation signal EXC and supplies it to the clock terminal CKK of i,'F9b, and the FF9b is inverted every time the inverted excitation No. 16 EXC falls, and its J-K input terminal is 1
The Q1 output is set to the H'' level, and the Q1 output is supplied to the clock terminal CK of E'F9 (!.
, the input terminals are set at low levels such as 1H'' level, etc.), and when the Q1 output falls, the Q2 output, that is, the enable signal ENB, is at the The frequency dividing operation of the generator 7 is stopped.Furthermore, the clear terminal CLRvc of f"F9bN9(! is supplied with a start signal STRRT.

In such a configuration, the time t I K shown in FIG.
When it comes to 5iゝH rubel, F F 9 b % 9 C
As a result, the Q2 output, that is, the enable signal BNB, goes to the 1L# level, enabling the excitation signal generator 8 and the excitation signal generator 7.The excitation signal generator 67 then outputs the pulse signal S1 as described above. Divide the frequency,
An excitation signal EXC whose level changes every j pulses is output (FIG. 6 (c)), and the excitation signal EXC is sent to the counter 3 and the ultrasonic pulse generation circuit 4 as in the case of the first embodiment shown in FIG. is supplied and performs a similar function. On the other hand, Fp
In 9b and 9e, the start signal 5TRT is at the '■I' level V.
r, is kept in a reset state for a certain period of time. Then, at time t2 shown in FIG.
When the level is reached, 1i'' F 9 b is inverted by the falling edge JIK of the inverted excitation signal EXC that occurs at time t3 shown in FIG. gives 1 and falls,
Q1 output is inverted again and becomes 'L' level, but this Q1 output
The Q2 output of Ii'F9c, that is, enable No. 46 END, is set to 'H level by the fall of the l output.
This causes the excitation signal generator 7 to stop the frequency dividing operation.

In this way, the excitation signal generator 7 continues frequency division from time t1 to time t4! 1, 2! Outputs an excitation signal EXC consisting of waves.

In this way, by changing the length of the start signal 5TRT at %i■#level rC during a certain period of time (times t1 to t2 in FIG. 6), the excitation (wave number of No. 8) can be changed.

In addition, in the above-mentioned λ embodiments, the excitation signal EXC
In order to match the frequency fe of the sensor with the resonance frequency f1 of the sensor, the frequency f of the pulse signal s1 and the division ratio of the excitation signal generator 70 must be appropriately selected, or the frequency f that can be realized must be
It is sufficient to use a vibrator with a resonant frequency fr that matches eVc0.Also, ■The frequency f of the pulse signal s1 output from c01 changes depending on the flow velocity VC, but this rate of change t'i is extremely small, so it can be ignored. be able to. For example, set the center value of frequency A (the value of f when M speed is 0) to 1
0MHz, and the span proportionality constant (the change in the value of f when the flow velocity changes by 1 mm/S) is jllz/(/ mm/
S), even if the flow velocity becomes 2tOmlSf, the value of f shows only a change of 25of(IlzN degrees (change rate θI'11.). Therefore, this pulse No. 716 81 is divided by //1oyc. The number of cycles f of the excitation signal EXC
, is / M Hz f j K Ilz and the force 1. Considering the resonance characteristic Q of the vibrator being moved, it can be said that this excitation signal EXCii has a certain degree of stability.

Further, the ultrasonic pulse generation circuit 4 includes, for example, a FET II driven by an excitation signal EXCr, as shown in FIG.
and p″E 1′ 11 output 1ill VC-connected LC resonant circuit 12 (the resonant frequency of this resonant circuit 12 is set to 11?: to match the resonant frequency fr of the camera). By configuring this structure, efficient energy transmission to the vibrator becomes possible.

After the oscillation, the excitation (N-number generator 7 and wave number limiting circuit 8) do not necessarily have to be configured as in the above embodiment, and for example, a microprocessor may be used.

In addition, the excitation (K generator 70 frequency division ratio (l/lθ in the above embodiment) and the wave number count value of the wave number limiting circuit 8 (
In the seventh embodiment yr, lJ$, ) can be set to any arbitrary value (iM).

As explained above, the present invention generates several waves of excitation signals having a frequency equal to (and almost equal to) the resonant frequency of one radial element from the output pulse signal of the VCO, and based on this excitation, Since the vibrator is driven, it is possible to efficiently generate ultrasonic waves with little noise in synchronization with the start signal. Furthermore, this provides the advantage of enabling stable 6Ie measurements.

[Brief explanation of the drawing]

Fig. 7 is a block diagram showing the configuration of the ultrasonic pulse generation circuit and its peripheral circuits in a conventional ultrasonic flowmeter, and Fig. 1 shows the waveforms of the input and output of the ultrasonic pulse generation circuit 40 shown in Fig. 7. The figure (a) shows the waveform of the excitation Tsukuda Nishiki EXC that is input to the ultrasonic pulse generation circuit 4, and the figure (b) shows the waveform of the ultrasonic pulse generation circuit 4. FIG. 6 is a diagram showing the waveform of the Ruru drive pulse (■) at the output No. 1; Further, FIG. 3 is a block diagram showing the configuration of the ABE of the first embodiment of the present invention, FIG. q is a time chart for explaining the operation of the same embodiment, and FIG. FIG. 6 is a block diagram showing the configuration of essential parts of the embodiment, FIG. 6 is a time chart for explaining the operation of the embodiment, and FIG. 7 is a circuit diagram showing an example of the configuration of the ultrasonic pulse generation circuit 4. 1...VCO (voltage controlled oscillator), 7...
...Excitation signal generator, 8... Wave number limiting circuit.

Claims (1)

[Claims] Ultrasonic wave driven by excitation signal and emits ultrasonic waves
and a voltage-controlled oscillator that outputs a pulse signal with a frequency that is inversely proportional to the ultrasonic propagation time from when the ultrasonic wave is emitted until it is received, and the flow rate is controlled based on the frequency of the pulse signal. In the ultrasonic flowmeter to be measured: 1. an excitation signal generator that divides the frequency of the pulse signal to generate an excitation number equal to or approximately equal to the resonant frequency of the ultrasonic transducer; , and a wave number limiting circuit for stopping the generation of the FIiI excitation signal.