JPS62185121A - Ultrasonic flowmeter - Google Patents

Abstract

PURPOSE:To enable measurement even when the ultrasonic wave propagation time is larger than the pulse width of the oscillation frequency, by providing two ultrasonic wave converters and a forward/backward switching circuit. CONSTITUTION:An output frequency (f) continuously oscillated form an oscillation circuit 10 is controlled intermittently through a counter circuit 20 and a gate circuit 30. Ultrasonic wave converters T and R convert an output of the circuit 30 into an ultrasonic wave signal and does the ultrasonic wave signal into an electrical signal respectively. A forward/backward switching circuit K changes over the propagation direction of the ultrasonic signal with respect to flow velocity V by switching the circuit 30 over to the converters T and R. Then, the ultrasonic wave signal is converted into an electrical signal, which is supplied to an up/down circuit 50 through a square wave converting circuit 41, a shift register 42 and an exclusive OR circuit 31 and respective outputs of the circuit 50 the one when the propagating direction of the ultrasonic wave signal is forward with respect to the flow velocity V and the other when it is backward are introduced into a addition circuit SIGMA and a subtraction circuit DELTArespective-to compute. At this point, once an output of the circuit SIGMA is feedback to a circuit 10 through a D/A converter 60 to keep an oscillation frequency output constant, an output of the circuit DELTA is outputted as flow velocity V.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to an ultrasonic anemometer, and particularly to a PLL circuit for an anemometer using continuous wave ultrasonic waves.

b. Conventional technology The ultrasonic transducer for transmitting and the ultrasonic transducer for receiving are arranged so that they do not face each other, and the dependence of the phase change of ultrasonic waves in the fluid on the flow velocity ■ and the ultrasonic transducer for both An ultrasonic current meter that measures the flow velocity from the distance between users was invented by the inventor of the present invention, and was filed in Japanese Patent Application No. 57-34979.
No., Japanese Patent Application No. 57-59126, Japanese Patent Application No. 57-9442
No. 58-137012, etc.

Since the sound speed C of ultrasound in a fluid depends on the temperature of the fluid,
Changes in the sound velocity of the fluid are a source of error in flow velocity measurements.

The invention according to Japanese Patent Application No. 58-137012 solves the above-mentioned problem in conventional ultrasonic current meters in which changes in the sound velocity of the fluid affect the flow velocity measurement, by solving the problem when the flow velocity and the direction of travel of the sound waves are in the forward direction and vice versa. This problem can be solved by keeping the sum φ and +φ2 of the phase differences φ1°φ2 in the direction constant.

FIG. 3 is a block diagram of an ultrasonic current meter disclosed in Japanese Patent Application No. 137012/1982.

The output of the transmitting oscillator VCO is applied to the transmitting ultrasonic transducer T, and the ultrasonic waves transmitted from the transducer T propagate through a fluid with a flow velocity of ■ to the receiving ultrasonic transducers R, , . Received at Rz. A part of the output of the transducer R is converted into a rectangular wave by an amplifier circuit, a delay circuit D1, and a rectangular wave converting circuit RW+.

Similarly, the output of the transducer R2 is also sent to the amplifier circuit 3. The signal passes through the delay circuit D3 to the rectangular wave converting circuit RW3, where it is converted into a rectangular wave. Furthermore, a part of the output of the transmission oscillator VCO is also converted into a rectangular wave in the rectangular wave converting circuit RW2.

The phase difference between the outputs of the rectangular wave conversion circuits 4 and 42 is detected by a phase difference detection circuit p (for example, an exclusive OR circuit), and the voltage conversion circuit C (for example, a CR smoothing circuit) is used to detect the phase difference proportional to the phase difference. A voltage signal φ1 is obtained. Similarly, a voltage signal φ2 proportional to the phase difference between the outputs of the rectangular wave conversion circuits 4 and 12 is obtained by the phase difference detection circuit P2 and the voltage conversion circuit C2.

By inputting the above signals φ and φ2 to the adder circuit Σ, a sum signal (φ, +ψ2)/2 is created, and (φ, +φ2)/
The frequency of the transmitting oscillator is controlled via the negative feedback circuit Nr' so that 2 becomes a constant value. Note that the above-mentioned constant value is preferably π/2 in view of the measurement range. On the other hand, the signal φ,
and φ2 are also the inputs of the subtraction circuit N, and its output (
Since φ1-φ2) is proportional to the flow velocity, its output (φ1-φ
The flow rate is displayed by indicating 2) with the indicator. By controlling the frequency described above, the flow velocity determined from (φ, −φ2) does not depend on the sound velocity in the fluid.

C3 Problems to be Solved by the Invention In this type of ultrasonic current meter, because the flow velocity is high, it becomes impossible to measure when the phase shifts by one cycle or more.

d. Means for solving the problem An oscillation circuit that continuously oscillates, and the output frequency f of the oscillation circuit is set to a frequency f/N.
1 (N1+integer), a first gate circuit that intermittently controls the output signal of the oscillation circuit with the frequency division signal of the frequency f/N, and the output signal of the gate circuit an ultrasonic transducer that converts the ultrasonic signal into an ultrasonic signal; an ultrasonic transducer that converts the ultrasonic signal into an electrical signal; a forward/reverse switching circuit that connects the first gate circuit and the ultrasonic transducer; an amplifier circuit that is connected to the ultrasonic transducer that converts ultrasonic waves into electrical signals via the forward/reverse switching circuit; a rectangular wave converting circuit that shapes the output of the amplifier circuit into a rectangular wave; a shift register having a preset input terminal in which a signal corresponding to the output signal of the rectangular wave converting circuit is sent to an input terminal; and a shift register having a preset input terminal; an exclusive OR circuit having two inputs of the output signal and the output signal of the shift register, or a signal obtained by dividing them by the same 1M ratio; and an output of the exclusive OR circuit is connected to the first counter. A discrimination circuit that discriminates whether the output of the circuit or a signal obtained by dividing the frequency thereof precedes or follows the output of the circuit, and an up/down circuit that counts up or down the output of the exclusive OR circuit according to the output of the discrimination circuit. A counter circuit; converts the output of the up-down counter circuit into a pulse train, sends the output to the preset terminal of the shift register circuit, and connects a negative feedback circuit so that the output of the first up-down counter circuit becomes zero. calculate the sum and difference of the output of the up-down counter circuit when the ultrasonic propagation direction is in the forward direction with respect to the flow velocity, and the output of the up-down counter circuit when the ultrasonic propagation direction is in the opposite direction to the flow velocity, respectively. an addition circuit and a subtraction circuit; a phase-locked feedback circuit that feeds back the output of the addition circuit to the oscillation circuit in order to change the oscillation frequency of the oscillation circuit so that the output of the addition circuit is constant; and the subtraction circuit. The above problems have been solved by an ultrasonic current meter equipped with an output circuit that outputs the output of , or an equivalent ultrasonic current meter.

e. Effect: The output of the first gate circuit is the oscillation frequency f of the oscillation circuit.
is controlled intermittently using the output (frequency F/N l ) of the first counter circuit. The signal sent to the exclusive OR circuit via the shift register is basically the first signal sent to the exclusive OR circuit.
It has the same waveform as the output of the gate circuit.

On the other hand, the signal sent from the first counter circuit to the exclusive OR circuit basically has the same waveform as the output of the first counter circuit.

If the preset in the shift register circuit is zero, the ultrasound propagation time between both ultrasound transducers is T
When the pulse width of the high frequency Br is T, /2 = (1/2f), the above exclusive OR circuit calculates the output pulse from the first counter circuit (frequency f /N, :pulse width N,
After Tl)/2), two pulses NIT+/To (frequency r: pulse width = 1/f2) are output.

After the output pulse is determined by the discrimination circuit to be later than the output pulse from the first counter circuit, it is counted by the up/down counter circuit.

The output of the up/down counter circuit is converted into a pulse train by a feedback circuit.

The output of the feedback circuit is sent to the preset terminal of the shift register. In this case, the amount of brisé throat is −N+
Corresponds to T+/To2.

When −N+”+/To2 is preset in the shift register circuit, when the ultrasonic propagation time between both ultrasonic transducers corresponding to the next pulse of the first counter circuit is T2, the above exclusive The OR circuit performs l Tt TI l /To after (T2-TI>0) or before (Tz-TI<O) the output pulse from the first counter circuit.
Outputs pulses. If TzT+=O, the above first
The output of the exclusive OR circuit is zero, so the output of the up/down counter circuit that integrates its own outputs does not change. That is, when the ultrasonic propagation time between the ultrasonic transducers corresponds to the output of the shift register circuit, the output of the exclusive OR circuit becomes zero and the output of the up/down counter circuit does not change.

If T2-TI<O, the exclusive OR circuit outputs a pulse before the output pulse from the first counter circuit, and this is detected by the discrimination circuit. The first up/down counter circuit is wired so that when T2-TI>0, the amplifier counts, and when T2-TI<O, it counts down (the reverse is also possible).

The output of the exclusive OR circuit, including its sign, is integrated by an up/down counter circuit. Therefore, the output of the up-down counter circuit quickly converges to a specific value, and the converged value corresponds to the ultrasound propagation time.

The ultrasonic propagation time t, L2 between the ultrasonic transducers when the ultrasonic propagation direction is in the forward direction and in the opposite direction with respect to the flow velocity is expressed by Equation (11) and Equation (2), respectively. expressed.

t, = L/(C+V) -----
(i) Lz=L/ (C-V) ・
-・(2) Here, L: Distance between ultrasonic transducers C: Speed of sound in fluid V: Flow velocity In the present invention, the above propagation time is expressed as the output of the knob down counter circuit, that is, the preset input number of the shift register. Desired.

When V/C<1, 1. , 12 can be approximated by equations (3) and (4), respectively.

t, = (L/C) (1-V/C) -43
) h= (L/C) (1+V/C) −(4
) Therefore, the respective outputs El of the above-mentioned addition circuit and subtraction circuit
``jZ+t, t2 is given by equations (5) and (6).

t z + t + = 2L / C-(5) Mz
−−L+ = LV/C”
...-(6)(tl +t2
) is fed back to the oscillation circuit by the phase lock feedback circuit, and is maintained at t, +t2=K (K is a constant value). Therefore, equation (6) is transformed into the following equation.

tz −tl = (K”/4L) V
-(71 Comparing equations (6) and (7), equation (6) includes the sound speed C, which has a large temperature dependence, as a parameter, whereas equation (7) has a large temperature dependence. Let the ultrasonic transducer open circuit #L with a small value be a parameter.

Therefore, when the phase-locked feedback circuit is used and the flow velocity is measured from the output of the subtraction circuit based on equation (7), the measurement error due to temperature is extremely small.

Pulse width N of t, tz in equation (11, (2))
, ratio 2t+/N4o, 2jz/N+ to TO/2
To corresponds to the preset convergence value of the shift register. That is, measurement can be performed even when the ultrasonic propagation time is longer than the period T0. This point is in contrast to the prior art, which required the ultrasonic propagation time to be shorter than the period T0. The limit in the case of the present invention is given by the following inequality.

To < t I < N IT+ / 2
−(81To < Lx < N4a/ 2
-19) f, Embodiment FIG. 1 is a block diagram of the electric circuit section of a preferred embodiment of the ultrasonic current meter according to the present invention, and FIG. 2 is a conceptual diagram of signals at its main points.

The output frequency f (pulse width T, = t
/2f) is divided into the frequency f/N1 (Nl: integer) (pulse width: JTo) in the first counter circuit CNTl (FIG. 2(b)).

The output signal of the oscillation circuit OSC is controlled intermittently by the first gate circuit G using a frequency-divided signal having the frequency f/N (FIG. 2(C)).

The first counter circuit CNTl also outputs a second frequency-divided signal of frequency f/KN (Fig. 2(d)), and the forward/reverse switching circuit K controlled by this signal changes the ultrasonic propagation direction to the flow velocity. On the other hand, the first gate circuit and the ultrasonic transducer are connected to alternately switch between forward and reverse directions. The value of K is chosen to be, for example, 4.8°16.

In this embodiment, two ultrasonic transducers are provided, and the transmitting function and receiving function are alternately switched using the switching circuit K. Note that it is also possible to provide receiving ultrasonic transducers upstream and downstream of the transmitting ultrasonic transducer, respectively.

In any case, it includes an ultrasonic transducer T that converts the output signal of the gate circuit into an ultrasonic signal, and an ultrasonic transducer R that converts the ultrasonic signal into an electrical signal.

An amplifier circuit AMP is connected via the forward/reverse switching circuit K to an ultrasonic transducer R that converts ultrasonic waves into electrical signals.

In a rectangular wave converting circuit including a comparator circuit COMP, the output of the amplifier circuit is shaped into a rectangular wave.

In this embodiment, the output of the rectangular wave converting circuit is further frequency-divided by a second counter, and the pulse width is expanded by N2 times (N, ≧1). Note that Nz=1 means that the second frequency dividing circuit is not used.

The output signal of the second counter circuit CNT2 is sent to the input terminal of the shift register SFT. Figure 2(e) shows N2=1
Shift 1-register input signal in case of . The shift register SFT operates as a serial-in/serial-out shift register using the output of the second counter circuit CNT2 as a clock pulse.

On the other hand, a part of the signal sent from the first counter circuit CNTl to the first gate circuit G1 is branched and divided by the third counter CNT3 at the same frequency dividing ratio as the second counter. The first output has a pulse width N3 times the input signal (1'h=Nz), and the second output has a frequency division ratio of N2/2.
The pulse width is N3/2 times that of the input signal.

The output of the shift register is counted by a fourth counter, N
When one pulse is counted, the shift register is cleared.

The first output signal of the third counter circuit CNT3 and the output of the shift register SFT are connected to the exclusive OR circuit G.
Sent to 2. The output of the exclusive OR circuit G2 appears before or after the first output of the third counter circuit CNT3 (FIG. 2(r)).

When the second output of the third counter circuit is "I" before the first output, it is "L" after the first output (the reverse is also possible). The second output is further branched, and one is sent via an inversion circuit IV to one input terminal of the first AND circuit ANDI, and the other is sent directly to one input terminal of the second AND circuit AND2. NDI to both AND circuits, 8N
The other input signal of D2 is the output of the exclusive OR circuit G2. Depending on whether the output of the exclusive OR circuit is before or after the first output of the third counter circuit CNT3, both the AND circuits A1. One of ^2 generates an output.

The outputs of the AND circuit 8N and AND2 are counted in opposite directions by an up/down counter circuit UDCI.

That is, when one output is counted up, the other output is counted down.

For example, the output of the up/down counter circuit uoct, which is expressed in binary notation, is converted into a pulse train in the feedback circuit NF and sent to the preset input terminal of the shift register 5IiT.

When one cycle is defined as the period of one pulse sent from the first counter circuit to the first gate circuit, in the next cycle, the shift register is delayed or advanced by the time corresponding to the above preset value, and the second pulse is sent from the first counter circuit to the first gate circuit. Counter circuit C
The output of NT2 is sent to exclusive OR circuit G2. When the preset value corresponds to the ultrasound propagation time between the ultrasound transducers, the output of the exclusive OR circuit G2 is zero. When they do not correspond, a pulse corresponding to the difference is output from the circuit G2, which is counted up or down in the up/down counter circuit tlDcI. The up/down count circuit is not cleared every cycle, but the output is integrated within the period defined by the second output (f/KNI) of the first counter circuit CNTl. Therefore, its output converges to a quantity corresponding to the propagation time. In the up-down counter circuit UDCI, by switching the ultrasonic transducer using the switch K at the frequency (f/KNI),
The propagation time LI+L2 is determined when the ultrasonic wave and flow velocity are in the forward direction and in the reverse direction.

The difference in propagation time between the two is 1. -1. and sum 1. +1. is calculated.

The output of the adder circuit Σ is fed back to the voltage controlled oscillation circuit via a digital-to-analog conversion circuit D/A, which is a phase rotor feedback circuit.

The output of the subtraction circuit Δ is proportional to the flow velocity and is sent to an output circuit (not shown) where it is displayed or recorded as appropriate.

The present invention is applicable not only to an ultrasonic current meter in which ultrasonic transducers are arranged so as not to face each other, but also to any type of ultrasonic current meter in which the flow velocity is determined from the difference in ultrasonic propagation time in the forward and reverse directions with respect to the flow velocity. It can be applied to the type of ultrasonic current meter.

It is also possible to use a second shift register, which is a bidirectional shift register, instead of the up/down counter, and to preset the shift register 5IFT using a feedback circuit based on its parallel output signal.

g6 Effect of the invention ■) When the ultrasonic propagation time is longer than the pulse time width,
Flow velocity can be measured. 4] The 11 constant accuracy improves as the pulse width becomes smaller.

2) The range of measurable flow velocities is very wide.

3) can be applied to almost all types of ultrasonic current meters.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the electric circuit section of a preferred embodiment of the ultrasonic anemometer according to the present invention, Fig. 2 is a conceptual diagram of signals at its main points, and Fig. 3 is a block diagram of the ultrasonic anemometer according to the prior art. This is a diagram. AMr'...Amplification circuit, ANDI, AND2・
-AND circuit, CNTl, CNT2. CNT3.
CNT4... Counter circuit COMP... Rectangular wave conversion circuit, D/A... Digital-to-analog conversion circuit, G1...
First gate, G2...exclusive OR circuit, IV
...Inversion circuit, K...Forward/reverse switching circuit, O
SC...voltage controlled oscillation circuit, SFT...shift register, UDCI...up/down counter circuit, Δ...subtraction circuit, Σ...addition circuit, NF...feedback circuit. Figure 2 Figure 3

Claims (1)

[Claims] An oscillation circuit that continuously oscillates, and an output frequency f of the oscillation circuit that is set to a frequency f/N_1(N_
1: an integer), a first gate circuit that intermittently controls the output signal of the oscillation circuit with the frequency division signal of the frequency f/N_1, and an ultrasonic wave generator that converts the output signal of the gate circuit into an ultrasonic transducer that converts the ultrasonic signal into a signal; an ultrasonic transducer that converts the ultrasonic signal into an electric signal; a forward/reverse switching circuit connecting the gate circuit of No. 1 and the ultrasonic transducer; an amplifier circuit connected to the ultrasonic transducer for converting ultrasound into an electrical signal via the forward/reverse switching circuit; A signal corresponding to the output signal of the rectangular wave converting circuit is sent to an input terminal, a shift register having a preset input terminal, and a shift register when the number of output pulses of the shift register reaches a predetermined value. a counting means for clearing, and an exclusive OR circuit having two inputs: the output signal of the first counter circuit and the output signal of the shift register, or a signal obtained by dividing them by the same frequency division ratio; a determination circuit that determines whether the output of the exclusive OR circuit is before or after the output of the first counter circuit or a signal obtained by frequency-dividing the first counter circuit; an up/down counter circuit that counts up or down according to the output of the circuit; converts the output of the up/down counter circuit into a pulse train; sends the output to the preset terminal of the shift register circuit; a feedback circuit forming a negative feedback circuit so that the output of the counter circuit becomes zero; and the above when the output of the up-down counter circuit is in the opposite direction to the output of the up-down counter circuit when the ultrasonic propagation direction is in the forward direction with respect to the flow velocity. An adder circuit and a subtracter circuit calculate the sum and difference of the outputs of the up/down counter circuits, respectively, and the output of the adder circuit is connected to the An ultrasonic current meter comprising: a phase-locked feedback circuit that feeds back to the oscillation circuit; and an output circuit that outputs the output of the subtraction circuit as a flow velocity.