JP2002310752A - Flow measurement device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a flow rate measuring device with reduced power consumption and high accuracy. SOLUTION: A delay means 19 for delaying a transmission signal when ultrasonic propagation is repeated a plurality of times, and a first counting means 20 for counting a first reference clock during the plurality of repetitions, and a second reference clock having a low frequency are provided. The second to count 19a
Counting means 19b and a third reference clock 19 having a high frequency
A third counting means 19d for counting c is provided. As a result, the second reference clock 19a having a low frequency is used for most of the delay time, and the third reference clock 19d having a high frequency is used for a fractional part. Therefore, it is possible to reduce power consumption while ensuring accuracy. Becomes possible.

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 a gas or the like using an ultrasonic wave.

[0002]

2. Description of the Related Art Conventionally, as this kind of flow rate measuring device,
For example, there is one described in JP-A-11-108718. FIG. 6 shows a conventional flow rate measuring device described in the above publication. In FIG.
The first vibrator 1 and the second vibrator 2 are both included in the fluid conduit 3. The transmission unit 4 drives the first transducer 1, and the ultrasonic wave propagates through the fluid conduit 3. The ultrasonic signal is received by the receiving unit 5 via the second transducer 2. When a signal is input from the receiving unit 5, the repetition unit 6 operates the delay unit 7, and after a predetermined delay time, ultrasonic waves are again emitted into the fluid pipeline 3 via the transmitting unit 4 and the first vibrator 1. Was something. In the delay means 7, the oscillation output of the asynchronous oscillation circuit is counted by a delay counter, and a predetermined delay time is set.

[0003]

However, in the above-mentioned conventional flow measuring device, it is necessary to increase the oscillation frequency of the asynchronous oscillation circuit in order to increase the resolution of the flow measurement, which is disadvantageous in terms of power consumption. there were. Further, since a delay element using L and R is used as an asynchronous oscillation circuit, there is a problem that the temperature characteristics are poor and it is difficult to ensure accuracy. An object of the present invention is to solve the above-mentioned conventional problems, and to provide a flow rate measuring device that reduces power consumption and ensures accuracy.

[0004]

In order to solve the above-mentioned conventional problems, a flow rate measuring apparatus according to the present invention comprises a first vibrator and a second vibrator provided in a fluid conduit for transmitting and receiving an ultrasonic signal; Transmitting means for driving the first vibrator or the second vibrator; receiving means for receiving a signal from the first vibrator or the second vibrator; and transmitting and receiving signals of the first vibrator or the second vibrator. Switching means for performing switching, repetition means for performing ultrasonic propagation between the first transducer or the second transducer a plurality of times, delay means for delaying a transmission signal at the time of the repetition, and a means for generating a predetermined frequency pulse. A first reference clock; and first counting means for counting the first reference clock during each of the plurality of repetition times. The delay means includes a second reference clock for generating a predetermined frequency pulse, and a second reference clock. K A second counting means for counting clocks of the clock, a third reference clock for generating a predetermined frequency pulse, and a third counting means for counting the clock of the third reference clock. The time calculated from the third counting means is set as a delay time.

By using the second reference clock having a low frequency for most of the delay time and using the third reference clock having a high frequency for the fractional part,
It is intended to reduce power consumption while ensuring accuracy.

[0006]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, there are provided a first vibrator and a second vibrator which are provided in a fluid conduit for transmitting and receiving an ultrasonic signal, and the first vibrator or the second vibrator. Transmitting means for driving; receiving means for receiving a signal from the first vibrator or the second vibrator; switching means for switching between transmission and reception of the first vibrator or the second vibrator;
Repetition means for performing ultrasonic propagation between the transducers or the second transducer a plurality of times, delay means for delaying a transmission signal during the repetition, and a first reference clock for generating a predetermined frequency pulse; A first counting means for counting the first reference clock for a time; a delay means for generating a predetermined frequency pulse; and a second counting means for counting an output pulse of the second reference clock. Counting means; and a third reference clock for generating a higher frequency pulse than the second reference clock.
A third counting unit for counting an output pulse of the reference clock, wherein a time calculated from the second counting unit and the third counting unit is set as a delay time; Most of the delay time uses the low-frequency second reference clock, and the fractional part uses the high-frequency third reference clock, thereby reducing power consumption while ensuring accuracy.

[0007] The invention according to claim 2 of the present invention is based on claim 1.
The oscillation means starts oscillating the second reference clock at or before the receiving means receives the ultrasonic signal, and the third reference clock simultaneously outputs the second reference clock at the time when the receiving means receives the ultrasonic signal. According to this configuration, the second reference clock is oscillated stably at the time of receiving the ultrasonic signal, and the oscillation of the third reference clock is started at that time. By doing so, power consumption can be reduced while ensuring accuracy.

The third aspect of the present invention is the first aspect of the present invention.
Wherein the delay means includes: fourth counting means for counting output pulses of the first reference clock; and third reference clock for generating a frequency pulse higher than the first reference clock. A third counting means for counting the output pulses of the first and second counting means, wherein the time calculated from the third counting means and the fourth counting means is used as a delay time. By using the first clock for counting the number, the configuration is simplified, and low cost is realized while maintaining the measurement accuracy.

The invention according to claim 4 of the present invention is the invention according to claim 2.
Alternatively, one cycle of the output pulse of the first reference clock or the second reference clock according to claim 3 is measured by the third reference clock, and the entire delay time is corrected. A delay time can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram of a flow rate measuring apparatus according to Embodiment 1 of the present invention. FIG.
In FIG. 1, a first vibrator 11 and a second vibrator 12 for transmitting and receiving ultrasonic waves are arranged in the flow direction in the middle of the fluid pipeline 10. Reference numeral 13 denotes a transmitting unit that outputs ultrasonic waves to the first vibrator 11 or the second vibrator 12. Reference numeral 14 denotes a trigger unit, which transmits through the transmitting unit 13 to the first vibrator 11 or the second
The vibrator 12 is driven. Reference numeral 15 denotes a receiving unit that amplifies a signal received by the first vibrator 11 or the second vibrator 12. Reference numeral 16 denotes switching means for switching the connection between the first vibrator 11 or the second vibrator 12 and the transmitting means 13 or the receiving means 15. Reference numeral 17 denotes comparison means for comparing the built-in reference value with the output of the reception means 15 and outputting a signal when the received signal is equal to or more than the reference value. Reference numeral 18 denotes a repetition means,
When there is an output from 7, a repetitive signal is sent to the trigger means 14. Reference numeral 19 denotes a delay circuit. When a signal is received from the trigger unit 14, a built-in second reference clock 19a and a second counting unit 1
9b, the third reference clock 19c, and the third counting means 19d set a predetermined delay time. Reference numeral 20 denotes a first counting unit, which counts the output of the first reference clock 22 when the measurement start signal is output from the start unit 21. Reference numeral 23 denotes a flow rate calculating means for calculating a flow rate based on the count value of the first counting means 20 and the delay time of the delay means 19. The operation and operation of the flow rate measuring device configured as described above will be described below.

FIG. 2 is a flowchart showing the operation of the flow rate measuring device according to the first embodiment of the present invention, and FIG. 3 shows the same timing. First, when the start means 21 starts the measurement, the repetition means 18 operates the switching means 16 to transmit the first vibrator 11 and receive the second vibrator 12. That is, the first vibrator 11 is connected to the transmitting means 13 and the second vibrator 12 is connected to the receiving means 15, and the ultrasonic wave is propagated from the upstream side to the downstream side in the flow direction. (Step 1 in FIG. 2).

At the same time, the first counting means 20, the second counting means 19b and the third counting means 19d are initialized (step 2).

Then, the value of the repetition means 18 is set to an initial value, and the first counting means 20 starts counting output pulses of the first reference clock 22 (step 3). Further, the repetition unit 18 operates the trigger unit 14, and the transmission unit 13 drives the first vibrator 11 at a predetermined frequency according to the trigger signal of the trigger unit 14 to emit ultrasonic waves into the fluid pipeline 10 ( Step 4).

The ultrasonic wave propagates through the fluid conduit 10 and propagates to the second vibrator 12 after a predetermined propagation time (the temperature of the gas in the fluid conduit 10 and the distance between the first vibrator 11 and the second vibrator 12). Is determined). The receiving unit 15 amplifies the ultrasonic signal received by the second transducer 12 to a predetermined value and outputs the amplified signal to the comparing unit 17. The comparing means 17 compares the built-in reference value, and outputs a signal to the repetition means 18 when the amplified received signal is equal to or more than the reference value (step 5).

The repetition means 18 operates the trigger means 14 again, but simultaneously operates the delay means 19. This means that the trigger means 14 immediately activates the transmitting means 13,
When ultrasonic waves are emitted into the fluid conduit 10, the second vibrator 12
In, the multiple reflection component of the previously emitted ultrasonic wave and the received wave overlap, and the reception level is attenuated. Therefore, it is necessary to avoid multiple reflection components, and an ultrasonic wave must be emitted after a predetermined delay time.

The delay means 19 receiving the signal from the trigger means 14 operates the built-in third counting means 19d,
When the counting of the reference clock 19c is started, the built-in second counting means 19b is operated at the same time as the second reference clock 19c.
Start counting a. At this time, the second reference clock 1
Oscillation 9a is started, and stable oscillation is obtained when the delay unit 19 starts operating. The oscillation frequency of the second reference clock 19a is lower than the oscillation frequency of the third reference clock 19c, and it takes time until stable oscillation occurs. May not be stable. Second
From the viewpoint of power consumption, the timing for starting the oscillation of the reference clock 19a is desirably immediately before the receiving unit 15 receives the ultrasonic signal, and it is necessary to take sufficient time for stable transmission. However, since the second reference clock 19a operates asynchronously with the receiving means 15,
An error may occur in the counting of the delay time. The delay time is
Accuracy is required because it is one of the factors that determine the accuracy of the flow rate calculation.

FIG. 3 shows the timing of time measurement by the delay means 19. After the delay means 19 starts operating (A in FIG. 3)
3) until the rising edge of the output pulse of the second reference clock 19a (point B in FIG. 3).
Is counted by the third counting means 19d, and thereafter, the second reference clock 19a is counted by the second counting means 19b a predetermined number of times. (Point C in FIG. 3) For example, when the oscillation frequency of the second reference clock 19a is 1 MHz, the oscillation frequency of the third reference clock 19c is 20 MHz, and the delay time is set to 150 μs, the operation of the delay unit 19 in FIG. From the start time to the rise to the second reference clock 19a, it is a half cycle of the second reference clock 19a, that is,
When 0.5 μs is measured at 20 MHz, the third counting means 19 d
Are counted for 50 periods, and the second reference clock 19
When the remaining 149.5 μs is counted at the oscillation frequency of 1 MHz of “a”, it becomes 149 cycles, and the delay time is 149.5.
μs. Although a difference of 0.5 μs is obtained as compared with the set value of 150 μs, the difference of this degree is sufficient to avoid the above-mentioned multiple reflection components, and the counting of 149.5 μs is performed by two times.
The delay time can be set with an accuracy of 0 MHz, that is, an accuracy of 0.05 μs. Further, most of the delay time can be set by the second reference clock 19a having a lower frequency, and a fractional part of the second reference clock 19a can be set by the third reference clock 19c having a higher frequency, so that power consumption is reduced. (Steps 6, 7, 8).

Upon completion of the delay time setting of the delay means 19, the trigger means 14 operates the transmission means 13, drives the first vibrator 11 at a predetermined frequency, and emits an ultrasonic signal again into the fluid pipeline 10. Thereafter, the transmission-reception-delay is repeated until the number of repetitions of the repetition means 18 reaches the set value (steps 9 and 10).

When the counting by the repetition means 18 is completed, the time counting by the first counting means 20 is stopped. The flow rate calculating means 23 reads the values of the first counting means 20, the second counting means 19b, and the third counting means 19d. Next, the second reference clock 19a
Is measured by the third reference clock 19c. It is assumed that the count value at this time is K2 and the count value of the third counting means 19d is K1. If K1 is normalized to one cycle of the second reference clock 19a, it becomes K1 / K2. Assuming that the count value of the second counting means 19b is L, if the delay time is adjusted to the oscillation frequency of the second reference clock 19a, L +
k1 / k2. Further, assuming that a correction value for adjusting the oscillation frequency of the second reference clock 19a to the oscillation frequency of the first reference clock 22 is α, and the count value of the first counting means 20 is T, the downstream side from the upstream side, that is, Time T1 required for propagation from the first transducer 11 to the second transducer 12
Is T1 = (T−α (L + k) where N is the number of repetitions.
1 / k2)) / N. This value is stored in the flow rate calculating means 23 (step 11).

Next, when the start means 21 starts the measurement again, the value of the repetition means 18 is set to the initial value and the first
The counting by the counting means 20 is started. Further, the second counting means 19b and the third counting means 19d are initialized. The first counting means 20 starts counting output pulses of the first reference clock 22. At the same time, the repetition means 18 operates the switching means 16 to place the first vibrator 11 on the receiving side and the second vibrator 1
2 is set on the transmission side. That is, the first vibrator 11 is connected to the receiving means 15, the second vibrator 12 is connected to the transmitting means 13, and the ultrasonic wave is transmitted from the downstream side to the upstream side with respect to the flow direction. . (Step 13)
Since this is the same as the case where the ultrasonic wave is propagated from upstream to downstream, the description is omitted. When the repetition is completed, the time required to propagate from the downstream side to the upstream side, that is, from the second vibrator 12 to the first vibrator 11, is T2. When the measurement in both directions is completed (step 12), the flow rate calculation is performed. At this time, if there is a flow in the fluid pipeline 10, the propagation time of the ultrasonic wave from downstream to upstream is delayed, so that T1> T2. T1 and T
The reciprocal difference of 2 is obtained by the flow rate calculating means 23, and further, the flow rate value is calculated in consideration of the cross-sectional area of the fluid pipeline 10 and the state of the flow (step 14).

(Embodiment 2) FIG. 4 is a block diagram of a flow rate measuring apparatus according to Embodiment 2 of the present invention. FIG.
In FIG. 1, a first vibrator 11 and a second vibrator 12 for transmitting and receiving ultrasonic waves are arranged in the flow direction in the middle of the fluid pipeline 10. Reference numeral 13 denotes a transmitting unit that outputs ultrasonic waves to the first vibrator 11 or the second vibrator 12. Reference numeral 14 denotes a trigger unit, which transmits through the transmitting unit 13 to the first vibrator 11 or the second
The vibrator 12 is driven. Reference numeral 15 denotes a receiving unit that amplifies a signal received by the first vibrator 11 or the second vibrator 12. Reference numeral 16 denotes switching means for switching the connection between the first vibrator 11 or the second vibrator 12 and the transmitting means 13 or the receiving means 15. Reference numeral 17 denotes comparison means for comparing the built-in reference value with the output of the reception means 15 and outputting a signal when the received signal is equal to or more than the reference value. Reference numeral 18 denotes a repetition means,
When there is an output from 7, a repetitive signal is sent to the trigger means 14. Reference numeral 19 denotes a delay circuit, which receives a signal from the trigger means 14 and a first reference clock 22 and a built-in fourth counting means 19.
e, a predetermined delay time is set by the third reference clock 19c and the third counting means 19d. 20 is a first counting means,
When a measurement start signal is output from the signal from the start means 21, the output of the first reference clock 22 is counted. 23 is a flow rate calculating means, which is a counter value of the first counting means 20 and a delay means 1
The flow rate calculation is performed based on the delay time of No. 9. The difference from the first embodiment is that the first reference clock 22 is used for setting the delay time.

The operation and operation of the flow rate measuring device configured as described above will be described below. Except for the setting of the delay time, the configuration is the same as that of the first embodiment, and the description is omitted here. The delay unit 19 which has received the signal from the trigger unit 14 operates the built-in third counting unit 19d to start counting the third reference clock 19c, and simultaneously operates the built-in fourth counting unit 19e to start the first reference clock. Start counting 22. Although the first reference clock 22 is input to the first counting means 20 which has started counting after the start means 21 has started measurement, the same clock is also counted by the fourth counting means 19e. FIG. 5 shows the timing of the time measurement by the delay means 19. From the start of the operation of the delay means 19 (point D in FIG. 5) to the time when the output pulse of the first reference clock 22 rises (point E in FIG. 5), the third reference clock 19c is counted by the third counting means 19d. Time with
Thereafter, the first reference clock 22 is counted by the fourth counting means 19e (point F in FIG. 5). Since the first reference clock 22 is also used to count the entire propagation time for setting the delay time, the configuration can be simplified and the cost can be reduced without losing accuracy.

[0024]

As described above, according to the first, second, and fourth aspects of the present invention, since two clocks, a high frequency clock and a low frequency clock, are used for setting the delay time, the accuracy of the delay time can be improved. It can be obtained with a high frequency clock, and most of the delay time is counted with a low frequency clock, so that low power saving can be realized. Further, since L and R are not used for realizing the asynchronous oscillation means, the influence of temperature characteristics and variation can be reduced.

According to the third aspect of the present invention, since the clock used for setting the delay time is also used as the clock used for counting the propagation time, the configuration can be simplified and the cost can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing the operation of the apparatus.

FIG. 3 is a diagram showing timing of counting by a delay unit of the apparatus.

FIG. 4 is a block diagram illustrating a configuration of a flow rate measuring device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing the timing of counting by a delay unit of the apparatus.

FIG. 6 is a block diagram showing a configuration of a conventional flow measurement device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fluid pipeline 11 1st oscillator 12 2nd oscillator 13 Transmitting means 14 Trigger means 15 Receiving means 16 Switching means 17 Comparison means 18 Repeating means 19 Delay means 19a Second reference clock 19b Second counting means 19c Third reference clock 19d Third counting means 19e Fourth counting means 20 First counting means 21 Starting means 22 First reference clock 23 Flow rate calculating means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Osamu Eguchi 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Term (reference) 2F035 DA16

Claims (4)

[Claims] 1. A first vibrator and a second vibrator provided in a fluid conduit for transmitting and receiving an ultrasonic signal, a transmitting unit for driving the first vibrator or the second vibrator, and the first vibration Receiving means for receiving a signal from the transducer or the second transducer; switching means for switching between transmission and reception of the first transducer or the second transducer; and ultrasonic propagation between the first transducer and the second transducer. A plurality of times, a delay means for delaying a transmission signal at the time of the repetition, a first reference clock for generating a predetermined frequency pulse, and a second reference clock for counting the first reference clock during each of the plurality of repetition times. A second counting clock for generating a predetermined frequency pulse; a second counting means for counting an output pulse of the second reference clock; and a second counting clock. Third to generate high frequency pulse
A flow rate measuring device, comprising: a reference clock; and third counting means for counting output pulses of the third reference clock, wherein a time calculated from the second counting means and the third counting means is a delay time. 2. The second reference clock starts transmitting at or before the receiving means receives the ultrasonic signal, and the third reference clock starts operation at the same time as the receiving means receives the ultrasonic signal. The flow measurement device according to claim 1, wherein the flow measurement is performed. 3. The delay means includes: fourth counting means for counting output pulses of the first reference clock; and third reference clock for generating a frequency pulse higher than the first reference clock. The third counting the output pulse of
The flow rate measuring device according to claim 1, further comprising a counting means, wherein a time calculated from the third counting means and the fourth counting means is set as a delay time. 4. The flow rate measurement according to claim 2, wherein one cycle of the output pulse of the first reference clock or the second reference clock is measured by the third reference clock to correct the entire delay time. apparatus.