JP4797515B2 - Ultrasonic flow measuring device - Google Patents

Description

  The present invention relates to an ultrasonic flow measuring device that measures the propagation time of ultrasonic waves using at least a pair of ultrasonic transceivers and calculates the flow velocity and flow rate of a fluid to be measured.

  The conventional means for measuring the ultrasonic propagation time used in this type of measuring apparatus is to arrange a pair of ultrasonic transmitters / receivers facing each other and drive one ultrasonic transmitter / receiver with a burst signal to generate ultrasonic waves. And received and measured by the other ultrasonic transceiver.

  FIG. 5 shows a drive waveform A of the transmission-side ultrasonic transceiver and a reception waveform B received by the reception-side ultrasonic transceiver. The horizontal axis is time, and the vertical axis is voltage.

  In the figure, T0 indicates the start point of the drive waveform A, and T1 indicates the end point of the third wave after the start of drive. R0 indicates the reception start time, and R1 indicates the third wave end time after the start of reception.

Thus, the zero-cross point T1 of the m-th (m = 3) wave of the drive waveform is the starting point, and the m-th (m = 3) wave of the electrical signal received by the other ultrasonic transceiver is the end point R1. The time Tp between the start point T1 and the end point R1 is measured as the ultrasonic propagation time, and the flow rate of the fluid is measured using the propagation time to calculate the flow rate (see, for example, Patent Document 1).
JP-A-9-33308

  However, since the propagation speed of ultrasonic waves varies depending on the type of gas, the resolution that can be measured differs when measuring the flow rate and flow rate by changing the type of gas with a single ultrasonic flow measurement device. The problem is that the measurement accuracy differs for each fluid to be measured.

  The present invention solves the above-described conventional problems, and provides an ultrasonic flow measurement device that changes the resolution according to the sound velocity of the fluid to be measured so that there is no difference in measurement accuracy for each fluid. With the goal.

  In order to solve the above-described conventional problems, an ultrasonic flow measuring device according to the present invention includes at least a pair of ultrasonic transmitters / receivers arranged at intervals on the upstream and downstream sides of a fluid passage, and between these ultrasonic transmitters / receivers. A measurement unit that measures ultrasonic propagation time; and a calculation unit that calculates a flow velocity and / or a flow rate of a fluid based on a measurement result of the measurement unit. The measurement unit includes an oscillation circuit having a plurality of different frequencies. And a resolution switching means for switching the oscillation circuit used for the propagation time measurement according to the sound velocity of the measurement fluid.

  Thus, even when measuring fluids having different sound speeds, the measured values can be compared without worrying about the difference in measurement accuracy.

  Since the ultrasonic flowmeter of the present invention can measure with the same resolution even when measuring gases with different sound speeds, it can measure the flow velocity and flow rate of a plurality of fluids without worrying about the difference in accuracy.

The first invention is a measurement for measuring an ultrasonic propagation time between at least a pair of ultrasonic transmitters / receivers arranged at intervals on the upstream and downstream sides of a fluid passage through which a fluid to be measured flows, and the pair of ultrasonic transmitters / receivers. And an oscillation circuit for transmitting a frequency for driving the ultrasonic transceiver, and a calculation means for calculating the flow rate and / or flow rate of the fluid to be measured based on the measurement result of the measurement unit, wherein the measuring unit includes a plurality of oscillation circuits of frequencies different to be used for propagation time measurement, the in accordance with the sound speed of the fluid to be measured, by providing the resolution switching means for switching the plurality of oscillation circuits, a plurality It is possible to measure fluids with different sound speeds with the same accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
In FIG. 1, at least a pair of ultrasonic transmitters / receivers 2 and 3 are disposed in a fluid passage 1 through which a fluid to be measured flows, with an interval on the downstream side in the flow direction and as the ultrasonic waves obliquely cross the flow. It is. 4 is a drive circuit for the ultrasonic transmitters / receivers 2 and 3, 5 is a switching circuit for switching transmission / reception of the ultrasonic transmitters / receivers 2 and 3, 6 is an amplifier circuit, 7 is a reception detection circuit for detecting ultrasonic pulses, and 8 is an ultrasonic wave A measurement unit for measuring the propagation time of the pulse, 9 is a control unit for outputting a control signal to the drive circuit 4 and the measurement unit 7, and 10 is a flow velocity of the fluid flowing in the fluid passage 1 based on the propagation time measured by the measurement unit 8. And calculating the flow rate by multiplying it by the cross-sectional area of the fluid passage 1 and the correction coefficient as necessary.

  First, the operation and action of the measurement apparatus in the present embodiment will be described. For example, the non-measurement fluid is air, and the frequency used for the ultrasonic vibrators 2 and 3 is selected to be about 500 kHz.

  The oscillation circuit is composed of, for example, a capacitor and a resistor, and transmits a square wave of about 500 kHz. The drive circuit 4 drives the ultrasonic transmitter / receiver 2 from the signal of the oscillation circuit. Can be output. In addition, in order to improve the resolution of the measurement flow velocity, for example, a single-around method is used for the measurement means.

  The control unit 8 outputs a transmission start signal to the drive circuit 4 and simultaneously starts measuring the time set by the timer. When receiving the transmission start signal, the drive circuit 4 drives the ultrasonic transceiver 2 and transmits an ultrasonic pulse.

  The transmitted ultrasonic pulse propagates through the air flowing through the fluid passage 1 and is received by the other ultrasonic transceiver 3. The received ultrasonic pulse is amplified by the amplification circuit 6 and then output to the reception detection circuit 7.

  The reception detection circuit 7 determines the reception timing of the reception signal and outputs the reception detection signal to the control unit 9. When receiving the reception detection signal, the control unit 9 outputs a transmission start signal to the drive circuit 4 again after the elapse of a preset delay time td, and performs the second measurement. After repeating this operation N times, the timer is stopped. The calculation unit 10 calculates the propagation time t1 by dividing the time measured by the timer by the number of times N and subtracting the delay time td.

  Subsequently, the ultrasonic transmitter / receiver connected to the drive circuit 4 and the reception detection circuit 7 is switched by the switching circuit 5, and the control unit 9 again outputs a transmission start signal to the drive circuit 4 and simultaneously starts time measurement of the timer. Contrary to the measurement of the propagation time t1, an ultrasonic pulse is transmitted by the ultrasonic transmitter / receiver 3 and the measurement received by the ultrasonic transmitter / receiver 2 is repeated N times, and the calculation unit 10 calculates the propagation time t2.

Here, the distance connecting the centers of the ultrasonic transmitters / receivers 2 and 3 is L, the speed of sound in a windless state of air is C, the flow velocity in the fluid passage 1 is V, the flow direction of the non-measurement fluid and the ultrasonic transmitter / receiver If the angle with the line connecting the centers of 2 and 3 is θ, the propagation times t1 and t2 are
t1 = L / (C + V cos θ) (1)
t2 = L / (C−Vcos θ) (2)
Indicated by When the velocity of sound V is calculated by eliminating the sound velocity C from the equations (1) and (2), V = L / 2 cos θ (1 / t1-1 / t2) (3)
Is obtained.

Since L and θ are known in this way, the flow velocity V can be obtained by measuring t1 and t2. If the flow velocity V and the area of the flow rate measuring unit 1 are S and the correction coefficient is K, the flow rate Q is Q = KSV (4)
It can be calculated with.

The pair of ultrasonic transmitters / receivers 2 and 3 are arranged on the same side, so-called Z-path type, which is diagonally opposed as described above, and so-called I-path type, which is linearly opposed to the upstream and downstream sides. Thus, a so-called V-path, W-path type, etc., that receives the reflected light on the way can be considered, and if necessary, a plurality of pairs of ultrasonic transceivers can be used.

  By the way, the measurement unit 7 is provided with a resolution switching means 11. The resolution switching means 11 is provided with a plurality of oscillation circuits having different frequencies so that the oscillation circuit used for the propagation time measurement can be switched according to the sound velocity of the fluid to be measured.

  That is, as shown in FIG. 2, when measuring a fluid with a high speed of sound, an oscillation circuit having a high frequency is used as shown in (a), and when measuring a fluid with a low speed of sound, as shown in (b). Use a low-frequency oscillation circuit.

  Therefore, it is possible to measure with the same measurement accuracy with fluids having different sound speeds.

( Reference Example 1 )
In FIG. 3, the resolution is switched by changing the number of times of transmission and reception repeated in one measurement according to the sound velocity of the fluid. For example, the fluid is repeated N times as shown in (a) in the case of a fluid having a high sound velocity, and is repeated M times as shown in (b) in the case of a fluid having a slow sound velocity. Here, by setting N> M, the propagation time can be measured with a resolution suitable for the speed of sound.

( Reference Example 2 )
In FIG. 4, the resolution is switched by changing the measurement interval in accordance with the sound velocity of the fluid. For example, the fluid is measured at intervals of N seconds as shown in (a) for a fluid with a high sound speed, and at intervals of M seconds as shown in (b) for a fluid with a slow sound speed. Here, by setting N> M, the propagation time can be measured with a resolution suitable for the speed of sound.

  As described above, the flow measuring device according to the present invention is very high in measuring a plurality of types of fluids without being affected by the difference in sound velocity of the fluid to be measured, and always with the same measurement accuracy. Since it is possible to realize an ultrasonic flowmeter with high accuracy, it can also be applied to applications such as a measurement standard device, gas meter, and water meter.

Configuration diagram of ultrasonic flow measuring apparatus according to Embodiment 1 of the present invention Explanatory drawing of resolution switching of Embodiment 1 of the present invention Explanatory drawing of resolution switching of Reference Example 1 of the present invention Explanatory drawing of the resolution switching of the reference example 2 of this invention Transmission / reception waveform diagram of a conventional ultrasonic flow measurement device

DESCRIPTION OF SYMBOLS 1 Fluid path 2, 3 Ultrasonic transmitter / receiver 8 Measuring part 9 Control part 10 Calculation means 11 Resolution switching means

Claims (1)

At least a pair of ultrasonic transmitters / receivers arranged at intervals on the upstream and downstream sides of the fluid passage through which the fluid to be measured flows, a measuring unit for measuring an ultrasonic propagation time between the pair of ultrasonic transmitters / receivers, and the ultrasonic wave An oscillation circuit for transmitting a frequency for driving a transceiver, and a calculation means for calculating a flow rate and / or a flow rate of the fluid to be measured based on a measurement result of the measurement unit. comprising a plurality of oscillation circuits having different frequencies to be used for propagation time measurement, the in accordance with the sound speed of the fluid to be measured, the plurality of ultrasonic flow measuring device provided with resolution switching means for switching the oscillation circuit.

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