JP3267942B2 - Phase-synchronized ultrasonic flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a phase-locked (phase-locked loop, hereinafter abbreviated as PLL) type ultrasonic flowmeter, and more particularly to an ultrasonic flowmeter suitable for a small-diameter type flowmeter. About.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional PLL type ultrasonic flow meter, and its outline will be described below. In the figure, reference numeral 1 denotes a flow tube having a fluid inlet 1a and an outlet 1b, 2a,
2b shows a pair of ultrasonic transducers provided at both ends of the tube.

A switch 3 has a function of alternately switching and connecting the excitation voltage source 4 and the amplifier 5 of the received signal to the vibrator 2a or 2b, but the switching signal will not be described here.

[0006] Reference numeral 6 denotes a phase comparator which supplies a low-pass filter 7 with a pulse output corresponding to a phase difference between an input signal 61 supplied from the amplifier 5 and a feedback signal 62 supplied from the frequency divider 9.

[0005] A voltage controlled oscillator (abbreviated as VCO) 8 receiving the output of the low-pass filter 7 supplies a high frequency variable frequency signal to a frequency divider 9 having a frequency division ratio of usually 1000 or more. Generate a signal. A description of the signal processing device will be omitted.

By virtue of such a configuration, the vibrator 2
A so-called sing-around oscillation occurs between a and 2b, and an output terminal 10 obtains an output frequency signal obtained by multiplying the sing-around frequency by a high frequency multiplication factor corresponding to the frequency division ratio of the frequency divider 9.

Therefore, the direction of the ultrasonic wave is reversed by operating the switch 3, and the flow velocity, that is, the flow rate, can be measured with high resolution from the difference between the two output frequencies obtained from the vibrators 2a, 2b.

[0008]

However, the above PL
When the L method is applied to a small-diameter flowmeter, the following technical problems occur.

In general, the inner diameter of the pipe of a flow meter for measuring a flow rate of several liters / minute or less needs to be about several millimeters. Therefore, the cross-sectional area of the ultrasonic wave propagation path is small, and the ultrasonic wave is remarkably attenuated.

For this reason, it is common to increase the output voltage of the excitation voltage source 4 or increase the amplification of the amplifier 5. However, in a so-called analog switch used as the switch 3, the excitation voltage leaks to the amplifier side as spike noise due to the capacitance of the switch in the off state, and in some cases, becomes larger than the received wave.

In the sing-around oscillation, when the amplifier 5 receives an ultrasonic signal, the oscillator 2a or 2b transmits the next ultrasonic wave from the excitation voltage source 4 at the same time.
Is excited, when viewed on the receiving side, the above-described excitation noise overlaps when a received wave is detected, and in some cases, normal operation becomes difficult.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and a phase-locked ultrasonic flowmeter according to the first invention of the present invention faces a flow tube. A pair of ultrasonic vibrators attached to each other, a switching device for switching between transmission and reception of the pair of vibrators, and an amplifier for amplifying a reception signal generated in a receiving-side vibrator by ultrasonic waves propagating in a fluid. A phase comparator that uses the output of the amplifier as an input signal, a low-pass filter that smoothes the output of the same phase comparator, a voltage-controlled oscillator that changes the oscillation frequency according to the output of the filter, and an output frequency of the oscillator. A frequency divider, and a delay circuit for delaying the output of the frequency divider.The output of the frequency divider is used as a feedback signal of a phase comparator. The excitation voltage is applied to the Certain delay time as those configured to be proportional to the oscillating period of the voltage controlled oscillator.

A phase-locked flow meter according to a second aspect of the present invention comprises a pair of ultrasonic vibrators mounted opposite to a flow path tube, and transmission / reception of the pair of vibrators. , An amplifier for amplifying a reception signal generated in the oscillator on the reception side by ultrasonic waves propagating in the fluid , a delay circuit for delaying the output of the amplifier, and a phase using the output of the delay circuit as an input signal. A comparator, a low-pass filter that smoothes the output of the in-phase comparator, a voltage-controlled oscillator that changes the oscillation frequency according to the output of the filter, and a frequency divider that divides the output frequency of the oscillator. The output of the frequency divider is used as the feedback signal of the phase comparator, and the output of the frequency divider applies an excitation voltage to the oscillator on the transmission side, and the delay time of the delay circuit is proportional to the oscillation cycle of the voltage controlled oscillator. One that is configured to And Aru.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a first embodiment of a PLL type ultrasonic flowmeter according to the present invention will be described with reference to FIG. 7, reference numerals 1 to 10 correspond to the reference numerals in FIG.

The flow meter according to the present invention comprises a frequency divider 9 and an excitation voltage source 4.
An output signal from the voltage-controlled oscillator 8 or a signal obtained by appropriately dividing the output signal is supplied to the delay circuit 11 as a clock signal, and the delay time is determined by the oscillation of the voltage-controlled oscillator 8. It is characterized by being proportional to the period.

In a more specific example, as shown in FIG. 2, the frequency divider 9 is composed of a pre-frequency divider 91 and a programmable frequency divider 92. Ten
One having a division ratio of 0 and a programmable divider 92
The programmable frequency divider 92 is programmed so as to have an appropriate frequency dividing ratio according to the speed of sound in the fluid.

The frequency of the voltage controlled oscillator is set to
To multiply the output cycle to about several microseconds.
As the delay circuit 11, a counting timer is used.
Or L), the output signal 112 of the previous-stage frequency divider 91 provided as a clock signal starts to be counted, and when a predetermined wave number is counted, an output signal 113 is generated. This is used as an excitation signal. On the other hand, the output of the programmable frequency divider 92 is fed back to the phase comparator 6.

FIG. 3 shows a frequency divider 9 'having the function of the delay circuit 11 by utilizing the characteristics of the BCD programmable counter 92 of the frequency divider. The frequency divider 9' does not appear as an independent delay circuit. Is equivalent to Example 1.

FIG. 4 shows a second embodiment of the present invention. The point that a delay circuit 11 is interposed between the amplifier 5 and the input side of the phase comparator 6 differs from that of the first embodiment shown in FIG. Although different, the operation is substantially the same as that of the first embodiment.

In this case, the signal delayed by the amplifier and the PL
Since the L feedback signal is in phase in the lock-in state and the excitation voltage is the same, the excitation voltage is delayed from the reception signal by the delay time of the delay circuit 11.

[0021]

The operation of the PLL type ultrasonic flowmeter according to the present invention will be described. When the PLL is in a so-called lock-in state, the phases of the input signal and the feedback signal (to be precise, for example, H
(Transition point from L to L) coincides, so that the phases of the ultrasonic reception signal and the PLL feedback signal also coincide. On the other hand, the excitation phase is delayed by a predetermined time by the delay circuit 11.

Next, the details of the configuration of the amplifier 5 of the present invention and the waveforms of the signals in the amplifier will be described with reference to FIGS. 5 and 6. The received wave is amplified by an AC amplifier 51 as shown in FIG. A group of frequency AC peaks.

The amplified waveform is compared with a fixed reference voltage E by a comparator 52, and a point in time when the waveform exceeds the reference voltage E is detected to drive a one-shot circuit 53 for prohibiting a re-operation of the comparator for a fixed time.

In the lock-in state, the delay circuit 11 composed of a timer performs excitation after a predetermined delay time from the operation of the one-shot circuit. Therefore, as shown in FIG. 6, the excitation noise is delayed from the received signal, and adversely affects the operation. Has no effect.

Next, the effect on the measurement of the delay time will be described. In FIG. 1, L is the measurement line length between the transducers 2a and 2b, C is the sound velocity in the fluid, V is the average flow velocity of the fluid in the pipeline, Fd is the sing-around frequency when the ultrasonic wave goes downstream, and goes upstream. The single-around frequency when
u, if the delay time by the delay circuit 11, t _0, a 1 / Fd = L / (C + V) + t 0, 1 / Fu = L / (C-V) + t 0.

Here, if t ₀ = 0 as in the conventional case, Fd−Fu = 2V / L (1) Therefore, the output frequency of the voltage controlled oscillator 8 is
Assuming that fd and fu correspond to Fd and Fu and that the frequency multiplication factor by dividing the frequency of the frequency divider 9 is N, fd−fu = N · 2V / L , and V can be calculated from fd−fu.

However, if t ₀ = 0, Fd = (C + V) / {L + (C + V) t ₀ } Fu = (C−V) / {L + (C−V) t ₀ } ∴fd−fu = {N (C + V) / L + (C + V) t ₀ } − {N (C−V) / L + (C
−V) t ₀ }, and it is generally difficult to accurately measure the average flow velocity V.

However, in the present invention, t ₀ is not constant, but is exactly proportional to the reciprocal of Fd and Fu in accordance with the cycle of the voltage controlled oscillator 8.

Therefore, the delay time t ₀ is changed again to Fd and Fu.
Let td and tu be respectively the delay times td and tu, where M is a proportionality constant and td = M / Fd, tu = M / Fu Fd−Fu = {(1-M) / L} 2V∴fd −fu = N {(1-M) / L} 2V (2) where td and tu may be a few percent of the single-around period 1 / Fd and 1 / Fu, so that the coefficient is slightly increased as shown in equation (2). The average flow velocity V of the fluid can be calculated from fd-fu in the same manner as in the equation (1) except that the value becomes smaller.

[0030]

As described above, according to the present invention, even if the excitation voltage is increased or the amplification degree in the amplifier is increased, the excitation noise is not affected.
P suitable for flow rate measurement for small flow rate where the flow path pipe has a small diameter
An LL type ultrasonic flow meter can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a phase-locked ultrasonic flowmeter according to the present invention.

FIG. 2 is a configuration diagram illustrating an example of a frequency divider and a delay circuit.

FIG. 3 is a configuration diagram showing another example of a frequency divider and a delay circuit.

FIG. 4 is a configuration diagram showing a second embodiment of the phase-locked ultrasonic flowmeter according to the present invention.

FIG. 5 is a configuration diagram showing details of an amplifier.

FIG. 6 is a diagram showing a waveform of a reception signal in the amplifier.

FIG. 7 is a configuration diagram showing a second embodiment of a conventional phase-locked ultrasonic flowmeter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow path tube 2a, 2b Ultrasonic transducer 3 Switch 4 Excitation voltage source 5 Amplifier 6 Phase comparator 7 Low pass filter 8 Voltage controlled oscillator 9 Divider 10 Output terminal 11 Delay circuit

Claims (2)

(57) [Claims] (A) A pair of ultrasonic vibrators mounted opposite to a flow path tube, a switch for switching transmission / reception of the pair of vibrators, and a supersonic wave propagating in a fluid. An amplifier that amplifies a received signal generated in a transducer on the receiving side due to sound waves, a phase comparator that uses the output of the amplifier as an input signal, a low-pass filter that smoothes the output of the in-phase comparator, and an output of the filter. A voltage-controlled oscillator that changes the oscillation frequency in accordance with the frequency divider, a frequency divider that divides the output frequency of the oscillator, and a delay circuit that delays the output of the frequency divider. As a feedback signal of the comparator, and while applying an excitation voltage to the oscillator on the transmission side by the output of the delay circuit,
(c) A phase-locked ultrasonic flowmeter configured to make the delay time of the delay circuit proportional to the oscillation cycle of the voltage controlled oscillator. (A) a pair of ultrasonic vibrators mounted opposite to the flow path tube, a switch for switching between transmission and reception of the pair of vibrators, and a supersonic wave propagating in the fluid; an amplifier for amplifying a reception signal generated on the reception side of the transducer by waves, and delay circuit allowed to delay the output of the amplifier, the delay circuit output
A phase comparator for the input signal, and a low pass filter for smoothing the output of the phase comparator, a voltage controlled oscillator for changing an oscillation frequency according to the output of the filter to divide the output frequency of the oscillator min (B) using the output of the frequency divider as a feedback signal of the phase comparator, and applying an excitation voltage to the oscillator on the transmission side by the output of the frequency divider; A phase-locked ultrasonic flowmeter configured to make a delay time proportional to an oscillation cycle of a voltage-controlled transmitter.