JPS593314A - Ultrasonic wave detection type karman's vortex current meter - Google Patents

Abstract

PURPOSE:To improve the accuracy of detection by delaying electrically one or both phases of a reference wave after reception and controlling the average phase difference of the reference wave to a specified value except 180Xn deg.. CONSTITUTION:The ultrasonic wave generated from an MIC 3 for transmission by the oscillation of a square wave oscillator 5 is propagated in Karman's vortexes and is converted to an electric signal by an MIC 4 for reception. A delay circuit 7 which is fed with the reception signal inputs the pulse (i) obtained by delaying the reception pulse (a) by the time determined by a voltage (g) to the AND circuit 17 of an average phase difference circuit C. On the other hand, the output of the oscillator 5 is fed as a reference wave (c). A delay circuit 8 inputs the pulse (j) obtd. by delaying the reference wave pulse (c) by the time determined by a voltage (h) to the circuit 17. The pulses (i) and (j) are ANDed to a signal (f) by the circuit 17 and the phases of the (i) and the (j) are controlled in accordance with the voltage characteristic indicating the relation between the phase delay of the pulse (i) with respect to the pulse (j) and the signal (f).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a two-current velocity meter that detects the generation period of Karman vortices generated in accordance with the flow velocity of a fluid as the period of phase modulation of an ultrasonic beam.

When an ultrasonic wave is propagated in a Karman vortex, a phase difference occurs between the transmitted wave and the received wave, and the phase difference is ■ The phase difference that rapidly changes depending on the period and strength of the Karman vortex street; ■ This is a superposition with a phase difference (2) that changes gradually depending on the distance between transmitter and receiver, etc., which will be described later.

The above phase difference is detected by a phase detector using an exclusive OR circuit and a low-pass filter.
When the phase difference (■) is an integral multiple of 180°, the phase difference component cannot be demodulated, so the phase difference (■) is set to 180Xn.
It is necessary to control it to a constant value other than 0.

By the way, the main causes of the change in the above phase modulation (■) are: (1) the phase of the output voltage with respect to the transmitted sound pressure and human sound pressure to the input terminal of the ultrasonic ceramic microphone (hereinafter referred to as MIO), and the difference between the sound source and the receiving point. distance, ■ speed of sound in fluid,
■There is a transmission frequency.

Therefore, controlling the phase difference ■ by the element of ■ means that M
Regarding (2), which is difficult to manufacture the IC or makes the configuration of the detection part extremely complicated, the sound velocity changes due to temperature changes in the fluid to be measured, and it is impossible to control it without changing the flow velocity.

Regarding ■, when controlling by transmission frequency, MI
Since C has a sharp resonance point, the sensitivity changes rapidly, and the S/N ratio of phase modulation (2) due to the Karman vortex of the received wave deteriorates, making stable detection difficult.

In view of the above-mentioned points, the present invention electrically delays the phase of one or both of the received wave and the reference wave (usually the transmitted wave), thereby increasing the average phase difference between the received wave and the reference wave to a constant value other than 180Xn'. (For example, (9Q+18On)').

In other words, the ultrasonic detection type Karman vortex current meter according to the present invention removes phase modulation components of the received ultrasonic waves other than the Karman vortices in order to detect the generation period of the Karman vortices as phase modulation of the ultrasonic beam. In the Karman vortex current meter, which keeps the average phase difference between the received wave and the reference wave constant for comparison, the phase difference between the received wave and the reference wave is 0 to 180°.
Alternatively, a phase difference discrimination circuit for discriminating whether the wave is a positive or negative integral multiple of 180 to 360° is provided, and the phase of either the received wave or the reference wave, or both, is controlled by the output of this discrimination circuit. This is a characteristic configuration.

The present invention will be explained below with reference to the drawings.

FIG. 1 shows a circuit diagram of a current meter according to the present invention.

In FIG. 1, A is the main body of the current meter, and a Karman vortex generating column 2 is attached to a pipe-shaped case 1 placed in a fluid. 3 is the transmitting MX0 attached to the case, 4 is the receiving MC, C15 is the transmitting square wave oscillator, 6 is the receiving amplifier, 7 is the receiving wave pulse delay circuit, and 8 is the transmitting wave pulse delay circuit. be.

B shows a phase difference discrimination circuit, which includes an inverter 9, an integrating circuit resistor 10, an integrating circuit capacitor 11, AND
circuit 12, AND circuit 13, monostaple multivibrator 14, monostaple multivibrator time width setting resistor 15, and time width setting capacitor 16
It is composed of.

C indicates an average phase difference detection circuit, and the AND circuit 17
, an integrating circuit resistor 18, and a capacitor 19.

20 is an error amplifier, and 21 is an analog switch for switching. D is a Karman vortex detection filter.

In FIG. 1, ■ to ■ and ■ to ■ indicate voltage signals at each point.

In FIG. 1, the rectangular wave oscillator 5 oscillates at a constant frequency when the power is turned on, and the ultrasonic wave generated from the transmitting M unit 03 propagates through the Karman vortex and is converted into an electrical signal by the receiving M unit 04. The signal passes through the amplifier 6 and passes through the pulse delay circuit 7
will be sent to The delay circuit 7 delays the received pulse ■ by the time determined by the voltage @, and outputs the pulse ■ to the AND circuit r"7 of the average phase difference detection circuit 0. On the other hand, the output of the oscillator 5 is used as a reference wave ■ to the pulse delay circuit. 8, and this delay circuit 8 manually outputs the pulse (2), which is a delayed reference wave pulse (2) for a time determined by the voltage (2), to the average phase difference detection circuit 0 (7) AND circuit 17.
The pulses ■ and ■ are AND-processed in the ND circuit 17, and passed through a high-cut filter (consisting of a resistor 18 and a capacitor 19) to become a signal.

FIG. 2 is a voltage characteristic showing the relationship between the phase delay of the pulse (2) with respect to the pulse (2) and the signal (2).

The output of the AND circuit 17 of the average phase difference detection circuit C is power! Since the Lemann vortex detection filter D is also used as a human power, the phase delay of the received pulse with respect to the reference wave is 180
Therefore, if the above average voltage is taken as a constant value, for example, 180 ×n -1-9Q
By setting the phase difference to -VDD, the influence of the phase modulation (2) mentioned above can be removed and stable measurement can be performed. In this case, there are infinite points where the voltage is -VDD, and the phase delay of the voltage ■ or ■ is adjusted depending on whether it is at a positive or negative integral multiple of 0-180' or 180-360°. Therefore, the change in the voltage manually applied to the pulse delay circuit 7 or 8 must be reversed to the direction of change in the error voltage. In Fig. 2, for example, if the voltage in the range of 0 to 180° is -VDD, then the voltage ■ is -VDD at the stable point 1.
To obtain D, either advance the phase of the voltage ■ or increase the voltage ■
It is necessary to delay the phase of 180 to 360
Assuming that the voltage in the range of 0 is -g VaD, in order to reach the stable point 2, the phase of the voltage (2) must be delayed or the phase of the voltage (2) must be advanced.

The error amplifier 20 is equipped with two output terminals having positive and negative intensification degrees with respect to the voltage. The phase control of (1) or (2) is performed as follows.

FIG. 3 shows a timing chart corresponding to the voltages ■ to ■ and ■ to ■ in FIG. The received wave (2) is inverted by an inverter 9, delayed by a delay circuit consisting of a resistor 10 and a capacitor 11, and then enters an AND circuit 12, where the delayed signal and the received wave (2) are AND-processed to become a signal (2). This signal (■) indicates the rising position of the received wave (■).

(2) is a reference wave, and the AND circuit 13 performs AND processing on the reference wave (2) and the signal (2) to obtain a signal (2). If the received wave (2) is delayed by 0 to 180 degrees with respect to the reference wave (2), a trigger signal (2) is generated and enters the mono-staple multipipelator 14. At this time, vibrator 14
outputs a pulse (1) for a period of time determined by the resistor 15 and capacitor 16, but since this time width is longer than the period of the signal (2), it is retriggered, and the output (2) maintains a high level H. The time width of the output ■ is 180° of the phase modulation ■ mentioned above.
The switching frequency of the changeover switch 21 is determined in response to the above fluctuations, and in this way, the voltage @ is controlled, the pulse delay circuit 7 advances the phase of the received wave ■, and the pulse delay circuit 8 advances the phase of the reference wave ■. is delayed.

On the other hand, when the output of the AND circuit 130 is ■, that is, when the received wave ■ is delayed by 180 to 36o0 with respect to the reference wave, the signal ■ becomes ■ compared to the above ■, and the pipe rake output ■ becomes a low level ■. Then, phase control is performed in the opposite direction to that described above.

Note that in the above, one of the pulse delay circuits 7 and 8 may be omitted.

The present invention has the configuration as described above, and includes changes in the temperature of the fluid,
Even if there are mechanical errors such as the distance between MICs, the appearance of these as phase modulation is removed, so stable Karman vortex detection over a long period of time is possible. Therefore, the transmission frequency with the optimum S/N value of M/C can be selected, and highly accurate detection is possible.

[Brief Description of the Drawings] Fig. 1 is an electric circuit diagram showing the ultrasonic detection type Karman vortex current meter according to the present invention, and Fig. 2 is an explanatory diagram showing the output voltage characteristics of the average phase difference detection circuit in Fig. 1. , FIG. 3 is an explanatory diagram showing signal voltages at each point in FIG. 1. In the figure, A is the current meter body, 3 is the transmitting MIO 14, the receiving MIO 0, B is the phase difference discrimination circuit, ■ is the received wave signal,
(2) is a reference wave signal, and 7 and 8 are pulse delay circuits.

Claims (2)

[Claims] (1) In order to detect the generation period of the Karman vortex as a phase modulation of the ultrasound beam, phase modulation components other than the Karman vortex of the received ultrasound are removed, and the difference between the received ultrasound and the reference wave for comparison is removed. In a Karman vortex current meter that keeps the average phase difference constant, the phase difference between the received wave and the reference wave is 0 to 18.
A phase difference discrimination circuit is provided to discriminate whether it is 0° or a positive or negative integral multiple of 180 to 360°, and the phase of either the received wave or the reference wave or both is controlled by the output of this discrimination circuit. An ultrasonic detection type Karman vortex current meter characterized by: (2) The phase difference discrimination circuit consists of an integrating circuit and an inverter, A N
The ultrasonic detection type Karman vortex current meter according to claim 1, wherein the ultrasonic detection type Karman vortex current meter is comprised of a D circuit and a monosdapple multibiflator. □