JP2001091319A - Flow rate measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make stably obtainable the improvement of measurement accuracy and the reduction of consumption of power by controlling the oscillation intervals of ultrasonic wave signal to an optimum value according to the actual flowrate. SOLUTION: In the flow rate measurement device 1 calculating the flow rate of fluid such as gas based on the transmission time of ultrasonic wave signal transmitted and received by a pair of ultrasonic vibrators 3 and 4, a pressure judgment circuit 14 and a delay circuit 15 are provided as a measurement interval control means for controlling the function of a trigger circuit 6 based on the detected value so that the detected value of the pressure detector 13 for detecting the fluid pressure in the flow path 2 is monitored and the oscillation intervals of the ultrasonic signal are shortened according to the lowering of the fluid pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for measuring a flow rate of gas or the like using an ultrasonic signal, and more particularly, to a flow rate measuring device for improving measurement accuracy and reducing power consumption. Regarding improvement.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of a flow rate measuring device for measuring a flow rate of a gas or the like using an ultrasonic signal. This flow rate measuring device 51 has a single-around (Si
The flow rate of the fluid flowing in the flow path 52 is measured by the ng Around method. In principle, the sing-around method measures a flow velocity v on a measurement line in the flow path 52 as a difference Δf of a sing-around frequency which is a reciprocal of a change in a propagation velocity of the ultrasonic signal S in the fluid, The flow rate is calculated based on this value.

[0003] Specifically, as shown in the figure, a flow rate measuring device 51 includes a pair of ultrasonic vibrators 53 and 54 disposed in a flow path 52 so as to face each other with a fluid therebetween, and a pair of these ultrasonic vibrators 53 and 54. A transmitting circuit 55 for transmitting an ultrasonic signal from one of the ultrasonic vibrators 53 and 54, a trigger circuit 56 for driving the transmitting circuit 55 at predetermined intervals, and an amplifying signal received by the ultrasonic vibrators 53 and 54 Amplifying circuit 57 for outputting, and amplifying circuit 5
7 is compared with a prescribed signal to detect the reception of the ultrasonic signal, and the trigger circuit 56 is repeated based on the output signal of the comparison circuit 58 until the number of receptions of the ultrasonic signal reaches the prescribed number. A switching circuit 60 for switching and connecting one of the pair of ultrasonic transducers 53 and 54 to the transmitting circuit 55 and the other to the amplifier circuit 57;
A time counting circuit 61 for measuring the time required to repeatedly execute the transmission of the ultrasonic signal a prescribed number of times; a flow rate calculating circuit 62 for calculating a flow rate based on the propagation time of the ultrasonic signal measured by the time counting circuit 61; It is a configuration provided with.

According to the above configuration, first, an ultrasonic signal S is transmitted from one ultrasonic transducer 53, and when the ultrasonic signal S is received by the other ultrasonic transducer 54, the ultrasonic vibration The ultrasonic signal S is transmitted from the transducer 53 and received by the ultrasonic transducer 54, and the repetition is performed a specified number of times to measure the required time T1. Subsequently, the transmitting ultrasonic transducer is switched to the ultrasonic transducer 54, and similarly, the time T2 required to repeat the transmission and reception of the ultrasonic signal S by the specified number of times is measured, and the time difference between T1 and T2 is calculated. The flow velocity v of the fluid is calculated. Then, the flow rate is calculated from the obtained flow velocity v and the cross-sectional area of the flow path 52.

Incidentally, the flow rate measuring device 51 as described above
In the case of a large flow rate and a drastic change in the flow rate per unit time, it is difficult to improve the measurement accuracy unless the transmission interval of the ultrasonic signal is shortened to increase the number of measurements per unit time. On the other hand, when the flow rate is small and there is little change in the flow rate per unit time, even if the transmission interval of the ultrasonic signal is increased to reduce the number of times of measurement, almost no problem occurs in the measurement accuracy of the flow rate.

However, in the conventional flow measuring device 51, generally, a start signal for activating the trigger circuit 56 is
Measurement is performed at a fixed sampling frequency or a certain function including a random function. Even when the flow rate is very small or does not flow at all, measurement is performed at the determined sampling frequency. Therefore, even when the flow rate is small or when the flow is stopped, the power is frequently used,
When the apparatus is driven by a battery, there have been problems such as a need to replace the battery within a short period of time.

In view of such circumstances, the flow rate value or the flow velocity value calculated by the flow rate calculation circuit 62 is monitored.
When these values become smaller, there has been proposed a technique for increasing both the transmission interval of the ultrasonic signal and thereby improving the measurement accuracy and reducing the power consumption (Japanese Patent Laid-Open No. 8-122117). Gazette).

[0008]

However, the flow of the fluid in the flow path is in a flow state due to a pulsation caused by an output change of a fluid consuming device such as a gas device connected downstream of the flow measuring device. Is easily disturbed, and the disturbance of the flow in the flow path affects the above-described propagation speed of the ultrasonic signal, and causes a decrease in measurement accuracy of the flow velocity, the flow rate, and the like. For this reason, in the related art in which the transmission interval is adjusted based on the calculated flow rate value or flow velocity value, in a state of steady flow where the flow is not disturbed, the transmission interval of the ultrasonic signal is set to an optimum value corresponding to the flow rate. However, when the flow is disturbed due to pulsation or the like, the adjustment value of the transmission interval of the ultrasonic signal does not become the optimum value due to the error of the calculated flow rate value or the flow velocity value, and the transmission interval is not adjusted. The result of the adjustment may further cause an error in the next flow rate measurement process, and may cause deterioration in measurement accuracy.

The present invention has been made in view of the above circumstances, and adjusts the transmission interval of an ultrasonic signal to an optimum value according to an actual flow rate even if a flow in a flow path is disturbed due to pulsation or the like. It is an object of the present invention to provide a flow measurement device capable of stably obtaining both improvement in measurement accuracy of flow and reduction in power consumption.

[0010]

According to the present invention, there is provided a flow rate measuring apparatus comprising: a pair of ultrasonic vibrators disposed in a flow path so as to face each other with a fluid interposed therebetween; A transmitting unit that transmits an ultrasonic signal, a pressure detecting unit that detects a fluid pressure in the flow path, a measurement interval control unit that controls a transmission interval of the ultrasonic signal according to the fluid pressure, and the pair of the It is provided with time measuring means for detecting the propagation time of the ultrasonic signal between the ultrasonic transducers, and flow rate calculating means for calculating the flow rate of the fluid based on the detected propagation time.

Preferably, the measurement interval control means adjusts the transmission interval so that the transmission interval of the ultrasonic signal is shortened in accordance with the decrease in the fluid pressure. Further, the measurement interval control means adjusts the transmission interval of the ultrasonic signal for each transmission of the ultrasonic signal.
Alternatively, the measurement interval control means adjusts the transmission interval of the ultrasonic signal for each predetermined number of transmission units repeatedly performed by one ultrasonic transducer.

In the above configuration, since the fluid pressure fluctuates according to the actual flow rate change, the transmission interval of the ultrasonic signal is substantially adjusted according to the flow rate. Then, when compared with the conventional method of adjusting the transmission interval of the ultrasonic signal using the flow velocity value and the flow rate value of the measurement result, the pressure value is a direct detection value and includes a calculation error due to the influence of pulsation and the like. Therefore, it is possible to more accurately set the transmission interval of the ultrasonic signal according to the actual flow rate, and the measurement processing based on the optimum transmission interval of the ultrasonic signal improves the measurement accuracy of the flow rate.

At this time, when the fluid pressure decreases, for example, when the flow rate is large, the accuracy of measuring the flow rate can be further improved by shortening the transmission interval of the ultrasonic signal according to the fluid pressure. In addition, when the fluid pressure is high, such as when the flow rate is low or minute, the number of transmissions is reduced by increasing the transmission interval of the ultrasonic signal, thereby reducing the frequency of using the power of the flow measurement device and reducing the power consumption. When the device is driven by a battery, the battery life can be extended. In general, in a flow rate measuring device, since a pressure gauge is already provided, it is possible to use the existing pressure gauge without particularly adding a new sensor or the like as a pressure detecting means.
Optimization of the transmission interval of the ultrasonic signal can be realized at low cost.

The process of adjusting the transmission interval of the ultrasonic signal by the measurement interval control means may be performed for each transmission of the ultrasonic signal, or may be performed repeatedly for a predetermined number of transmission units of the ultrasonic signal. It may be performed every time, and it is preferable to select appropriately according to the measurement method.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 to 3 show an embodiment of a flow measuring device according to the present invention. FIG. 1 is a block diagram showing a configuration of the flow measuring device. FIG. 2 is an ultrasonic signal in the flow measuring device of the present embodiment. FIG. 3 is an explanatory diagram showing a pressure change in the flow path of the flow rate measuring device in the present embodiment.

The flow rate measuring device 1 of the present embodiment measures a flow rate of a fluid such as a gas, and a pair of ultrasonic vibrators 3 and 3 disposed in the flow path 2 so as to face each other with the fluid interposed therebetween.
A transmitting circuit 5 as transmitting means for transmitting an ultrasonic signal from one of the pair of ultrasonic transducers 3 and 4;
A trigger circuit 6 for driving the transmission circuit 5 at a predetermined interval; an amplification circuit 7 for amplifying and outputting a signal received by the other of the ultrasonic transducers; and an ultrasonic circuit for comparing the output of the amplification circuit 7 with a prescribed signal. A comparison circuit 8 for detecting reception of a signal, a repetition circuit 9 for repeatedly operating the trigger circuit 6 based on the output signal of the comparison circuit 8 until the number of receptions of the ultrasonic signal reaches a specified number, and a pair of ultrasonic transducers Oscillator 5
Switching circuit 10 for switching and connecting the other to amplifying circuit 7
And a time-measuring circuit 1 as a time-measuring means for measuring a time required for repeatedly transmitting the ultrasonic signal a specified number of times.
1 and a flow rate calculating circuit 12 as a flow rate calculating means for calculating a flow rate based on the propagation time of the ultrasonic signal measured by the timing circuit 11.

Inside the flow path 2, there is provided a pressure detecting unit 13 such as a pressure gauge as pressure detecting means for detecting the pressure of the fluid in the flow path. In addition, as a measurement interval control unit that controls the transmission interval of the ultrasonic signal according to the fluid pressure, the detection value of the fluid pressure by the pressure detection unit 13 (for example, the magnitude or ratio of the detection value to the reference pressure value) is determined. The pressure determination circuit 14 and a delay circuit 15 that adjusts the transmission interval of the ultrasonic signal by adding an appropriate delay time to the transmission interval of the ultrasonic signal output from the trigger circuit 6 based on the determination result of the pressure determination circuit 14. Have. In the present embodiment, the existing pressure gauge generally provided in the flow rate measuring device is used for the pressure detection unit 13 to monitor the fluid pressure in the flow path, and an ultrasonic signal is generated in response to a decrease in the fluid pressure. The operation of the trigger circuit 6 is controlled based on the pressure detection value of the pressure detection unit 13 so as to shorten the transmission interval.

In the flow rate measuring apparatus 1 of the present embodiment configured as described above, the flow rate of gas or the like flowing in the flow path 2 is measured by the sing-around method. First, the trigger circuit 6 is started by a start signal from the start circuit 16, and
By driving one of the ultrasonic vibrators 3, an ultrasonic signal S is transmitted, and travels in the flow path 2 toward the other ultrasonic vibrator 4. When this ultrasonic signal S is received by the other ultrasonic transducer 4, the ultrasonic signal 3 is transmitted again from the ultrasonic transducer 3 and received by the ultrasonic transducer 4. The transmission and reception of the ultrasonic signal S are repeated a specified number of times, and the required time T1 is measured (see FIG. 2). Subsequently, the ultrasonic transducer to be transmitted is switched to the ultrasonic transducer 4, and transmission and reception of the ultrasonic signal S are similarly repeated a specified number of times.
The required time T2 is measured. Then, the flow velocity v of the fluid is calculated from the time difference between the required times T1 and T2, and the flow rate is calculated from the flow velocity v and the cross-sectional area of the flow path 2.

A characteristic curve (a) of FIG. 2 shows a time chart of transmission and reception of an ultrasonic signal in the ultrasonic transducer 3 located on the upstream side in the flow path 2, and a characteristic curve (b).
4 shows a time chart of transmission and reception of an ultrasonic signal in the ultrasonic transducer 4 located on the downstream side in the flow path 2. Further, T1 shown on the characteristic curve (a) is a predetermined number of times that the ultrasonic signal transmitted from the ultrasonic transducer 3 is received by the ultrasonic transducer 4 based on the sing-around method. T2 shown on the characteristic curve (b) is a time required when the ultrasonic signal is transmitted from the ultrasonic transducer 4 and received by the ultrasonic transducer 3 in the same manner. This is the required time when the processing to be performed is repeated a predetermined number of times (for example, 100 to 1000 times).

Further, Δt is a delay time from when an ultrasonic signal transmitted from one ultrasonic transducer is received by the other ultrasonic transducer to when the next transmission is made. By increasing or decreasing the delay time Δt according to the fluid pressure by the delay circuit 15, the transmission interval of the ultrasonic signal (that is, the sampling interval at the time of the flow rate measurement) is adjusted. In the case of this embodiment, since the flow rate is measured by the sing-around method,
The process of adjusting the transmission interval of the ultrasonic signal by the pressure determination circuit 14 and the delay circuit 15 is performed by a predetermined number of transmission units when the transmission and reception of the ultrasonic signal are repeated a predetermined number of times (100 to 1000 times) as described above. It is done every time.

As described above, in the present embodiment, the transmission interval of the ultrasonic signal is adjusted in accordance with the fluid pressure, but as shown in FIG. 3, the fluid pressure in the flow path 2 is adjusted in accordance with the actual flow rate change. Fluctuate. Accordingly, the transmission interval of the ultrasonic signal is substantially adjusted according to the flow rate. In this case, since the fluid pressure is a directly detected value and does not include a calculation error due to the influence of pulsation or the like at the time of flow rate measurement, the transmission interval of the ultrasonic signal is determined using the flow velocity value or the flow rate value of the measurement result. Compared with the conventional method of adjusting, it is possible to more accurately calculate an appropriate ultrasonic signal transmission interval according to the actual flow rate. For this reason, it is possible to always perform the measurement process based on the optimum transmission interval of the ultrasonic signal, and it is possible to improve the measurement accuracy of the flow rate.

At this time, when the fluid pressure decreases, for example, when the flow rate is large, the accuracy of measuring the flow rate can be further improved by shortening the transmission interval of the ultrasonic signal according to the fluid pressure. Also, when the fluid pressure is high such as at low flow rate or minute flow rate, the transmission interval of the ultrasonic signal is extended to reduce the number of transmissions, thereby reducing the frequency of using the power of the flow measurement device and reducing power consumption. When the device is driven by a battery, the battery life can be extended. In addition, since a pressure gauge for detecting the pressure in the flow path is generally provided in the flow rate measuring device, an existing pressure gauge can be used without particularly adding a new sensor or the like as a pressure detecting means. By doing so, optimization of the transmission interval of the ultrasonic signal can be realized at low cost.

Referring to FIG. 3, a specific example of the adjustment of the transmission interval of the ultrasonic signal will be described. In the period L1 during which the fluid pressure drops from the reference pressure P0 to the reference pressure P1 (a period during which there is a certain flow rate when gas is used). , The decrease rate of the fluid pressure (reference pressure P
(The ratio of the fluid pressure P1 to 0: P1 / P0), the above-mentioned delay time Δt is set short, and the measurement interval (sampling interval) is shortened.
Try to improve.

When the pressure drop further increases as in the period L3 and the fluid pressure becomes P2, the pressure ratio P2 / P
According to 0, the delay time Δt is set to be shorter than in the period L1. Alternatively, until the predetermined measurement accuracy is obtained,
The delay time Δt is shortened, and the measurement interval is shortened. For example,
Pressure ratio P1 / P0 or P2 / P for obtaining a predetermined measurement accuracy
The relationship between 0 and the delay time Δt is obtained in advance, and the delay time is set. The delay time for pressure and the value of the measurement interval are calculated by learning for a predetermined period at the time of initial operation after installation of the flow rate measuring device, and the values are set and stored in a storage unit (not shown) in a form such as a table.

Further, period L4 (fluid pressure P0) → period L5
When the fluid pressure decreases stepwise as in (fluid pressure P3) → period L6 (fluid pressure P4), the delay time is set short in accordance with the pressure ratio P4 / P0, and the measurement interval is shortened.
Alternatively, a delay time corresponding to the pressure ratio (P3 / P0) + (P4 / P0) is set to shorten the measurement interval.

The fluid pressure becomes P as in periods L2 and L4.
When the value is 0, fluid such as gas is not used, or the flow rate is extremely small. Therefore, by setting the delay time Δt to a maximum value, the transmission interval of the ultrasonic signal is maximized. By reducing the number of transmissions of ultrasonic signals per unit time, power consumption can be reduced.

The method of measuring the flow rate of a fluid conforming to the present invention is not limited to the above-described sing-around method. For example, the present invention can be applied to measurement methods such as a so-called propagation time difference method and a frequency difference method. If the method is not the sing-around method, the process of adjusting the transmission interval of the ultrasonic signal by the measurement interval control means may be performed for each transmission of the ultrasonic signal, or may be appropriately selected according to the measurement method.

[0028]

As described above, according to the present invention, even if the flow in the flow path is disturbed due to pulsation or the like, the transmission interval of the ultrasonic signal is adjusted to the optimum value according to the actual flow rate. Thus, there is an effect that it is possible to provide a flow measurement device capable of stably obtaining both the improvement of the flow measurement accuracy and the reduction of power consumption.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a flow measurement device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing transmission / reception intervals of an ultrasonic signal in the flow rate measuring device of the present embodiment.

FIG. 3 is an explanatory diagram showing a pressure change in a flow path of the flow measurement device according to the embodiment.

FIG. 4 is a block diagram illustrating a configuration example of a conventional flow measurement device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow rate measuring device 2 Flow path 3, 4 Ultrasonic vibrator 5 Oscillation circuit 6 Trigger circuit 7 Amplification circuit 8 Comparison circuit 9 Repetition circuit 10 Switching circuit 11 Timing circuit 12 Flow rate calculation circuit 13 Pressure detection circuit 14 Pressure judgment circuit 15 Delay circuit

Claims (4)

[Claims] A pair of ultrasonic vibrators disposed in a flow path so as to face each other with a fluid interposed therebetween; a transmitting unit configured to transmit an ultrasonic signal from one of the pair of ultrasonic vibrators; Pressure detecting means for detecting a fluid pressure in a road; measuring interval control means for controlling a transmission interval of the ultrasonic signal according to the fluid pressure; and a propagation time of the ultrasonic signal between the pair of ultrasonic transducers. And a flow rate calculation means for calculating a flow rate of the fluid based on the detected propagation time. 2. The flow rate measuring device according to claim 1, wherein the measurement interval control means adjusts the transmission interval so that the transmission interval of the ultrasonic signal is shortened in accordance with the decrease in the fluid pressure. . 3. The flow rate measuring device according to claim 1, wherein the measurement interval control means adjusts the transmission interval of the ultrasonic signal for each transmission of the ultrasonic signal. 4. The apparatus according to claim 1, wherein the measurement interval control means adjusts the transmission interval of the ultrasonic signal for each predetermined number of transmission units repeatedly performed by one of the ultrasonic transducers. Flow measurement device.