JPH0131573B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides, for example, a Karman vortex (Karman vortex).
The present invention relates to a device that detects the phase modulation of ultrasonic waves caused by a vortex, such as a vortex, and measures the flow rate or flow rate of a liquid in which a vortex is generated.

As a prior art in this field, JP-A-56-
No. 154669, and its structure is shown in Figure 1. In the figure, 10 indicates a flow path through which the fluid to be measured flows, and 1
is a vortex generator inserted and disposed in the center of the flow path 10. 2 is a transmitter, 3 is an oscillator, 4 is a receiver, 5 is a waveform shaping amplifier, 6 is a phase comparator, and 7 is a loop filter. In this case, the loop filter 7 is a low resistance 7
1, a capacitor 72, an operational amplifier 73, and resistors 74 and 75 for setting the voltage at one input terminal of the operational amplifier 73. 8 is a voltage controlled phase shift circuit, 815, 82
5 is a monostable multi-circuit whose output pulse width is controlled, and 835 is a duty ratio of the output pulse.
Monostable multi-circuit with fixed output pulse width for setting ratio), 811, 821, 831, 8
35, 836 are resistors, 812, 822, 832 are capacitors, 813, 823, 833 are diodes, and 814, 824, 834 are voltage comparators. 9 is a carrier filter, 70 is an output terminal of the loop filter 7, and 90 is an output terminal of the carrier filter 9. Also, V ₁ is the output voltage of oscillator 3,
V ₂ is the output voltage of the monostable multi-circuit 815, V ₃ is the output voltage of the monostable multi-circuit 825, V ₄ is the output voltage of the monostable multi-circuit 835, and V ₅ is the output voltage of the monostable multi-circuit 835.
The output voltage of V ₆ is the output voltage of the phase comparator 6.

FIG. 2 is a waveform diagram showing voltage waveforms at various parts of the circuit in FIG. ₁ , and _FIG.
The voltage waveforms of each are shown.

Next, the operation of the circuit shown in FIG. 1 will be explained. Oscillator 3
The electrical vibration V ₁ oscillated by the wave transmitter 2 is converted into an acoustic vibration and emitted into the flow path 10, but while propagating through the fluid, it undergoes phase modulation in the Karman vortex section and is transmitted to the wave receiver 4. It is converted into electric vibrations and amplified by amplifier 5 to become signal _V5 . Therefore, compared to the signal V ₁ , the signal V ₅ has an average phase delay due to propagation and a phase fluctuation caused by phase modulation due to the Karman vortex. Figure 2 a
This relationship is shown in V ₁ and V ₅ in Figure e. The arrow in the time axis direction in FIG. 2e indicates the width of the phase fluctuation. Figure f
The same applies to

In the embodiment shown in FIG. 1, the waveforms of V ₁ to _{V 6} are rectangular waves, and the phase comparator 6 is constituted by an exclusive OR circuit. Also the delay time between waveforms V ₁ and V ₂
TD ₁ (FIG. 2b) is controlled by the output of voltage comparator ₈₁₄ , and _{the delay time TD 2 (} second
Figure c) is controlled by the output of the voltage comparator 824, so the delay time TD ₁ + TD ₂ of the inverted waveform of the waveform V ₄ with respect to the waveform V ₁ is the output voltage of the loop filter 7.
Controlled by _V7 .

FIG. 3 is a characteristic diagram showing the characteristics of the phase comparator 6.
The horizontal axis shows the phase difference between _V5 and _V4 , and the vertical axis shows the average value of _V6 . One input voltage of the operational amplifier 73 of the loop filter 7 is adjusted by resistors 74 and 75 so that V ₇ becomes 0 when the average value of V ₆ becomes half of the peak value of V ₆ . Feedback loop of V ₇ → V ₄ → V ₆ → V ₇ makes V ₇ 0.
Since the phase difference between V ₅ and V ₄ is automatically adjusted, the average value of V ₆ is controlled to half of its peak value, and above that
Since the phase fluctuation of V ₅ is superimposed, the carrier of V ₆ is removed by a carrier filter, and the modulated signal due to the vortex is taken out from the terminal 90 to measure the flow velocity or flow rate.

By the way, the field back loop mentioned above is
When the phase difference between _V5 and _V4 increases, _V7 increases and _V5
It is designed as a negative feedback loop to reduce the phase difference between and _V4 . However, as shown in FIG. 3, when the phase difference is in the range of π to 2π and 3π to 4π, as the phase difference increases, V ₇ decreases and a positive feedback loop becomes unstable.
On the other hand, the monostable multicircuits 815 and 825 can each delay only up to a maximum of 2π.
Therefore, when a delay amount of 2π or more is required, several stages of monostable multicircuits are connected in series to obtain the required delay amount. In the embodiment shown in FIG.
5 is shown in two-stage cascade.

Figure 4 shows the relationship between the phase difference between V ₁ and V ₄ and the voltage at V _7. The required delay angle range is θ _nio (= π) to θ _nax (near 5π), so It is assumed that three stable multi-circuits are connected in series.
Let the values of V ₇ corresponding to θ _nio and θ _nax be V _nio and V _nax .
In Fig. 4, the delay amount at the point represented as synchronization point 1 is 2π+π/2, and the delay amount at the point represented as synchronization point 2 is 4π+π/2, then synchronization point 1 and synchronization point 2
In this case, the relationship between V ₁ and V ₄ is exactly the same, and therefore phase synchronization can be achieved in the same way in both. However, the delay amount of 2π+π/2 is (2π+π/2) per stage.
This means that a delay amount of π/2)/3=150° is given, and the delay amount of 4π+π/2 is (4π
+π/2)/3=270° of delay is given, so if the phase difference between V ₁ and V ₅ is actually 2π, the phase difference between V ₁ and V ₄ should be 2π + π/2. Regardless of this, the circuit shown in Figure 1 may be able to synchronize as 4π+π/2. In this case, if the phase difference between V ₁ and V ₅ increases to 3π, the phase difference between V ₁ and V ₄ must be set to 5π + π/2,
This puts the voltage at _V7 out of the adjustment range, which has been a drawback of conventional circuits.

The main cause of variation in the average phase difference due to propagation between the signals V ₁ and V ₅ is a temperature change in the fluid to be measured. For example, in the case of measuring the intake air amount of an automobile engine, etc., the temperature change of the fluid to be measured is large, so the fluctuation in the above-mentioned average phase difference is large.
For example, suppose that the temperature of the fluid to be measured is in the range of 0°C to 100°C, and when the temperature is 0°C, the device shown in Figure 1 starts operating and _V4 is phase-locked to a certain point. The control range of ₄ must be a range corresponding to -0℃ to +100℃, and conversely, if the above temperature is
If the device in Figure 1 starts operating at 100°C and V ₄ is phase-locked to a certain point, then the control range of V ₄ must be a range corresponding to -100°C to +0°C, and Therefore, the phase shift circuit 8 is -100℃
It is necessary to have a controlled range corresponding to ~+100°C, which has the disadvantage of unnecessarily increasing the circuit scale.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional ones, and is a flow rate or flow rate measuring device that can accurately measure even a wide range of temperature changes using a minimum necessary phase shift circuit. is intended to provide.

Embodiments of the invention will be described below with reference to the drawings. FIG. 5 is a block diagram showing one embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts, 76 is a reset switch, 85
0,851,852 are constant current sources, 85
3,854 is a diode constituting a heat sensitive element; 8
55 is an operational amplifier, 856, 857, 858, 8
Each of 59 is a resistance. 852,853,8
The circuit composed of 54, 855, 856, and 857 will be referred to as a temperature sensor circuit.

Next, the operation of the circuit shown in FIG. 5 will be explained. When the reset switch 76 is closed, a constant voltage is output to _V7 , and _V4 is not controlled by the feedback loop of _V7 → _V4 → _V6 → _V7 .
The forward voltage of diodes 853 and 854 biased by constant current source 852 is -
It varies with a slope of 2.3mV/°C. This voltage is amplified by a circuit including an operational amplifier 855 and resistors 856 and 857, and is applied to voltage comparators 814 and 824 via a resistor 858 to control TD1 and TD2 (see FIG. 2). On the other hand, the transmission time TD3 during which the ultrasonic wave is transmitted from the transmitter 2 to the receiver 4 is expressed as TD3=l/3.31+0.6T (1) when the fluid 10 to be measured is air. l is the effective propagation distance and T is the temperature. The solid line in Figure 6 is the equation (1) of temperature T and TD3.
This represents the relationship between On the other hand, the change in the value of TD1+TD2 due to the output voltage of the operational amplifier 855 can be adjusted as shown by the dotted line in FIG.
Therefore, with the reset switch 76 closed,
The phase difference between V ₅ and V ₄ is automatically set to a small value. In this state, reset switch 76
When V 4 is opened, the feedback loop through resistor 859 causes V ₄ to exactly match the average value of V ₅ .
As can be seen from FIG. 6, the amount of correction required by the above feedback loop is small.
Therefore, by closing the reset switch 76 for a predetermined period of time after turning on the power to the circuit shown in FIG. 5, and then opening it (the related circuits are not shown in FIG. 5), the necessary minimum delay circuit can be achieved. This makes it possible to measure flow velocity or flow rate over a wide temperature range.

Furthermore, if temperature information is required for density correction of the fluid to be measured in the case of flow rate measurement, etc., it can be extracted from the output of the operational amplifier 855 in the embodiment shown in FIG. ₅ 's
Conversely, temperature information can be obtained from the amount of delay with respect to _V1 . That is, the temperature T can be obtained from the delay time of TD3 in FIG.

Furthermore, in the embodiment shown in FIG. 5, in order to extract the modulated signal due to the vortex, the time constant of the resistor 71 and capacitor 72 of the carrier filter 7 is made small so that the modulated signal due to the vortex can pass through the loop filter 7. The modulated signal may be extracted from the output of the filter 7.

As described above, according to the present invention, in a device that measures the phase modulation that an ultrasonic wave receives due to a Karman vortex and determines the flow velocity or flow rate of a fluid that generates the Karman vortex, Among the circuits that automatically compensate for changes in the phase of ultrasonic waves, changes due to temperature are compensated for by controlling a phase deviation circuit in an open loop using a signal from a temperature sensor that directly detects temperature. With a simple configuration in which only the remaining amount is corrected using feedback, even in the initial state when the device is turned on, most of the phase fluctuation due to temperature is corrected, and phase control using feedback is only possible within a small range. This has the effect of making it possible to measure the phase modulation of ultrasonic waves due to Karman vortices over a wide temperature range.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional device, Fig. 2 is a waveform diagram showing voltage waveforms at various parts of the circuit in Fig. 1,
Fig. 3 is a characteristic diagram showing the characteristics of the phase comparator, Fig. 4 is a characteristic diagram showing the characteristics of the voltage controlled phase shift circuit, Fig. 5 is a block diagram showing an embodiment of the present invention, and Fig. 6 is a characteristic diagram showing the characteristics of the voltage controlled phase shift circuit. FIG. 3 is a characteristic diagram showing the relationship between the temperature of the fluid to be measured and the delay time. 1... Vortex generator, 10... Fluid flow path to be measured,
2... Transmitter, 3... Oscillator, 4... Receiver, 6
...Phase comparator, 7...Loop filter, 76...
...Reset switch, 8...Voltage control phase shift circuit, 852, 853, 854, 855, 856,
857... Temperature sensor circuit, 9... Carrier filter. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A flow velocity or flow rate measuring device that determines the flow velocity or flow rate of the fluid to be measured by measuring the phase modulation of ultrasonic waves caused by vortices generated in the fluid to be measured, comprising: a transmitter that converts the output of the oscillator into acoustic vibrations and inputs them into the vortex; a receiver that converts the acoustic vibrations that have passed through the vortex into electrical vibrations; a phase shift circuit that shifts the phase; a phase comparator that detects the phase difference between the output of the phase shift circuit and the output of the receiver; and a long-term average value of the output of the phase comparator. a temperature sensor circuit that outputs a voltage that changes while maintaining a predetermined functional relationship with respect to the temperature of the fluid to be measured; and a temperature sensor circuit that combines the output of this temperature sensor circuit and the output of the loop filter. The present invention is characterized by comprising means for performing feedback control on the phase shift circuit, and means for maintaining the output of the loop filter at a predetermined voltage value within a predetermined time from the start of operation of the feedback control means. A device for measuring flow rate or flow rate. 2 The phase comparator is composed of an exclusive OR circuit, and the phase shift circuit is composed of one stage of monostable multicircuit or a cascade circuit of multiple stages, whose pulse width changes depending on the control voltage. The flow rate or flow rate measuring device according to claim 1, characterized in that it is constructed by cascading monostable multi-circuits. 3. The highest frequency that passes through the loop filter is set to be lower than the lowest frequency of the modulated signal due to the vortex, and the modulated signal is extracted from a carrier filter that receives the output of the phase comparator as input. The flow rate or flow rate measuring device according to item 1. 4. The flow rate or flow rate measuring device according to claim 1, wherein the frequency characteristics of the loop filter are set so that a signal modulated by the vortex passes through the loop filter. 5. The flow rate or flow rate measuring device according to claim 1, further comprising means for obtaining a signal related to the temperature of the fluid to be measured from the output of the loop filter and the output frequency of the oscillator.