JPS6125289B2 - - Google Patents

Description

Detailed Description of the Invention This invention provides a vortex generating column in the measurement fluid flowing in a conduit, and detects the number of Karman vortices (generated vortex frequency) downstream of the column using ultrasonic waves to measure the flow velocity or flow rate. The purpose is to detect eddy signals using a phase-locked loop circuit using a voltage-controlled phase-shift circuit. This invention provides a method that allows self-recovery even when the phase-locked loop becomes out of synchronization, and allows the normal vortex signal detection operation to be performed again.

Japanese Utility Model Publication No. 17010/1973 proposes a method in which a vortex generating column is provided in a conduit and the generation frequency of the Karman vortex generated downstream of the column is detected using ultrasonic waves to measure the flow velocity or flow rate of fluid flowing within the tube. When detecting the Karman vortex using this method, the ultrasound transmitted from the ultrasound transmitter propagates through the fluid, is modulated by the Karman vortex, and is received by the receiver. The modulation that ultrasonic waves undergo is amplitude modulation, frequency modulation, phase modulation, etc., and the vortex signal can be demodulated by each demodulation method. One of these demodulation methods is a phase demodulation circuit method. FIG. 1 shows an example of a conventional phase demodulation circuit system. In the figure, 1 is a vortex generating column, 11 is a conduit, 2 is an ultrasonic transmitter, 3 is an oscillator for exciting the ultrasonic transmitter 2 at the optimal oscillation frequency, 4 is an ultrasonic receiver, and 5 is a waveform of the received signal. 7 is an active low-pass filter circuit that constitutes a loop filter; 71, 74, and 75 are resistors;
72 is a capacitor, 73 is an operational amplifier, 8 is a voltage controlled phase shift circuit, and 81 and 82 are monostable multi-circuits with variable time width for shifting the phase of the input signal according to the control voltage _V7 . Phase shift circuit, 8
3 is a monostable multi-circuit with a fixed time width for adjusting the duty ratio of output pulses, 811, 821,
831, 835, 836 are resistors, 812, 82
2,832 is a capacitor, 813,823,83
3 is a diode, 814, 824, 834 are voltage comparators, and 815, 825, 835 are D flip-flop circuits.

The ultrasonic transmitter 2 is driven by an oscillator 3 to oscillate ultrasonic waves. The sound wave is phase modulated by a Karman vortex street, a modulated signal is received by a receiver 4, and the waveform is shaped by an amplifier 5 to become a voltage _V5 , which is applied as one input of a phase comparator 6 comprised of an exclusive OR circuit. The voltage controlled phase shift circuit 8 is a circuit that generates a phase shift signal whose phase shift angle from the output signal V ₁ of the oscillator 3 is controlled in response to the output voltage V ₇ of the loop filter 7, and is connected in series with each other. The pulse width can be controlled by the output voltage of the loop filter 7.
It consists of phase shift circuits 81 and 82 (two) and a monostable multi-circuit 83 with a fixed time width that sets the output pulse width to substantially match the oscillation frequency signal pulse width. Phase shift circuits 81 and 82 in each stage above
are resistors 811 and 821 and capacitor 81, respectively.
2, 822, a voltage comparator 814, 824 that compares this capacitor voltage with the voltage V ₇ of the loop filter 7, and a signal V ₁ of the oscillator 3.
D-type flip-flop circuits 815 and 825 are sequentially triggered using the first stage trigger signal and are reset by the outputs of the comparators 814 and 824, respectively.
and diodes 813, 823 which control charging and discharging of the capacitors 812, 822 by the output of the flip-flop circuit. The output signal V ₄ of the voltage controlled phase shift circuit 8 is input to the other input of the phase comparator 6, and the phase comparator 6, the loop filter 7, and the voltage controlled phase shift circuit 8 are input to the other input of the phase comparator 6.
Together, they form a phase-locked loop. Figure 2
V ₁ to _{V 6} represent voltage signal waveform diagrams of respective parts indicated by the same reference numerals V ₁ to _{V 6} in FIG. 1.

In the phase-locked loop configured as described above, a modulated signal V _{5 is phase-modulated by a Karman vortex using the signal V 1} of the oscillation circuit 3 as a reference, and is further accompanied by a phase delay from the transmitter 2 to the receiver ₄ .
is given as one input of the phase comparator 6.
In Figure 2, the signal V ₁ of oscillator 3 and the modulation signal
V ₅ happens to be in the same phase, but if the density of the fluid to be measured changes and the speed of sound changes, a wide angle phase difference will occur in the phase difference between these two signals.

The signal V ₁ from the one-way oscillator 3 is applied to a voltage controlled phase shift circuit 8 . In the voltage controlled phase shift circuit 8, the first stage D-type flip-flop 815 is triggered by the rising of the signal _V1 of the oscillator 3 to the "H" level, performs an inverting operation, and starts charging the capacitor 812. When the charging voltage of this capacitor reaches the output voltage _V7 of the loop filter 7, the D-type flip-flop 815 connects the comparator 814.
It is reset by the output of , and outputs a pulse output V ₂ with a time width TD ₁ corresponding to the output voltage V ₇ . Second
The D-type flip-flop 825 in the first stage is triggered by the rise of the first stage pulse output V ₂ to the "H" level, and outputs a pulse output V ₃ with a time width TD ₂ corresponding to the output voltage V ₇ of the loop filter 7. This pulse output V ₃ rises to the “H” level, causing the third
The flip-flop circuit 835 in the second stage is triggered and generates a pulse output V ₄ with a predetermined time width determined by the voltage divided by the resistors 835 and 836.
is given as the other input. That is, the output V ₄ of the voltage controlled phase shift circuit 8 is the composite time of the pulse time widths TD ₁ and TD 2 of the first and second stage phase shift circuits 81 and 82 corresponding to the output voltage V ₇ of the loop filter ₇ . The signal is shifted in phase from the signal V ₁ of the oscillator 3 by the phase of .

The phase comparator 6 generates a voltage V ₆ corresponding to the phase difference between the above-mentioned modulation signal V ₅ and the output signal V ₄ of the voltage controlled phase shift circuit 8, and the loop filter 7 generates a harmonic component of the voltage output V ₆ . The phase shift angle of the voltage controlled phase shift circuit 8 is controlled so that the phase error of the two inputs V ₄ and V ₅ of the phase comparator 6 becomes small by removing unnecessary components such as noise and noise. It is composed of

FIG. 3 shows the voltage characteristics of the average value of the output voltage corresponding to the phase difference of the input of the phase comparator 6. As is clear from FIG. 3, the set voltage of the positive phase input terminal of the operational amplifier 73 of the loop filter 7 in FIG.
If you set it to 1/2 with a dividing ratio of 4,75, the signal will be
It can be seen that the phase difference between V ₄ and V ₅ is π/2, forming a phase locked loop.

With the phase-locked loop configured in this way, a signal V ₄ that follows the phase modulation of the phase modulation signal V ₅ due to the Karman vortex is obtained, so by setting the loop response of the loop filter 7, the phase modulation signal of the Karman vortex is In other words, the vortex signal appears at the output V ₇ of the loop filter or the output V ₆ of the phase comparator 6,
The carrier filter 9 provides vortex signals 1 and 2 from which unnecessary frequency components have been removed. Detect the frequency of this vortex signal and determine the flow velocity (or flow rate) of the fluid to be measured.
can be measured.

By the way, the phase shift angle that can be shifted per stage of the above-mentioned phase shift circuits 81 and 82 is from 0 to 2π at the maximum.
In this embodiment, the phase angle that can be synchronized by the phase-locked loop is limited from π to a maximum of 5π, as shown in FIG. For this purpose, the phase modulation signal
If V ₅ is phase modulated at a wide angle beyond the synchronizable phase shift angle range of π to 5π, loss of synchronization occurs. Due to their characteristics, the phase shift circuits 81 and 82 cannot maintain the input frequency below 0 and above 2π, and there is no continuity and reversibility between the phase shift angle of the control voltage V ₇ and the output V ₄ . There was a drawback that once synchronization occurred, resynchronization was no longer possible.

This invention attempts to eliminate the above-mentioned drawbacks, and provides a flow velocity measuring device that can be quickly resynchronized if the phase of the modulated signal returns to the phase synchronizable range even if synchronization occurs. It is.

An embodiment of the present invention shown in FIG. 5 will be described below.

That is, in FIG. 5, the resistors 501, 502, 50
3. The diode 504 and the reference voltage circuit are for level converting and voltage clamping the output voltage V ₇ of the loop filter 7 to become the control voltage V ₈ of the voltage control phase shift circuit 8, and constitute the clamp circuit 51. ing. The output of the ordinary operational amplifier 73 can take any value from the lowest voltage V _OL to the highest voltage V _OH , and V _nio and V _nax shown in FIG.
The following relationship holds true between .

V _OL < V _nio < 1/2 reference voltage < V _nax < V _OH When V ₇ reaches the maximum value V _OH , the control voltage V ₈ is V ₈ = Reference voltage + (V _OH - Reference voltage) R ₅₀₂ / R ₅₀₁ + R ₅₀₂ , and depending on the settings of resistors 501 and 502, V ₈ <
It can be set as V _nax . Similarly, V ₇ is the minimum value V _OL
Even when V _nio <
It can be made into _V8 .

In this way, no matter what value the output V ₇ of the loop filter 7 takes, the control voltage V 8 of the voltage controlled phase shift circuit ₈ satisfies the relationship V _nio < V ₈ < V _nax , so the phase Even if synchronization occurs, the output V ₄ of the voltage controlled phase shift circuit 8 outputs a signal that maintains the frequency of the output V ₁ of the oscillator 3, and the phase of the modulation signal V ₅ is within the range where phase synchronization is possible again. If it returns to , it is quickly resynchronized and normal phase-locked loop operation and flow velocity detection operation can be performed again.

Note that in this embodiment, the output V ₇ of the loop filter 7
The clamp circuit was constructed by converting the level of the integrator capacitor 7 that constitutes the loop filter 7.
It goes without saying that the same effect can be obtained by bidirectionally connecting a Zener diode for level clamping in parallel to 2.

As explained above, according to the present invention, there is provided a flow velocity measuring device that uses a phase locked loop circuit using a voltage controlled phase shift circuit to demodulate the phase modulation signal received by an ultrasonic wave due to a Karman vortex. The output abnormality of the phase shift circuit caused by the finite amount of phase shift of the shift circuit is resolved by clamping its control voltage within a predetermined voltage value range. To provide a flow rate measuring device in which the circuit can always operate in a state where resynchronization is possible even if such occurrence occurs.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing a conventional flow velocity measuring device using a phase demodulation circuit system, Figure 2 is an operating waveform diagram of each part in Figure 1, and Figure 3 is the input/output characteristics of the phase comparator in Figure 1. 4 is an input/output characteristic diagram of the voltage controlled phase shift circuit shown in FIG. 1, and FIG. 5 is a configuration diagram showing an embodiment of the present invention. In the figure, 1 is a vortex generating column, 2 is an ultrasonic transmitter, 3 is an oscillator, 4 is an ultrasonic receiver, 6 is a phase comparator, and 7
is a loop filter, 8 is a voltage controlled phase shift circuit,
51 is a clamp circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A vortex generating column arranged substantially perpendicular to the fluid flow, and an ultrasonic transmitter installed to propagate ultrasonic waves across the flow of the Karman vortex street generated downstream of this vortex generating column. , an oscillator that excites this ultrasonic transmitter, an ultrasonic receiver that receives the ultrasonic wave phase-modulated by the Karman vortex, a phase comparator that receives the received phase-modulated signal as one input, and this phase comparison. a loop filter that removes unnecessary frequency components from the output of the oscillator, and generates an output signal whose phase deviation angle from the output signal of the oscillator is controlled in accordance with the output voltage of the loop filter; A flow velocity measuring device comprising: a voltage controlled phase shift circuit as an input; and a clamp circuit for preventing the output of the loop filter from exceeding a specified maximum value and not exceeding a specified minimum value.