JP2007017157A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the need for switching arithmetic coefficients when the temperature of a fluid is to be computed, reduce errors in the temperature of the fluid, eliminate adverse effects of individual distance differences between oscillators, reduce errors in flow velocity and quantity of flow, and eliminate dedicated temperature sensors and electronic circuit substrates for temperature correction. <P>SOLUTION: Ultrasonic waves are transmitted and received between transducers 2 and 3 in forward and backward directions. The gas species of a fluid to be measured is determined on the basis of the sum (inverse number sum) of inverse numbers f<SB>1</SB>and f<SB>2</SB>of propagation delay times in the forward and backward directions. The temperature of the fluid is determined on the basis of the relation between temperature and sound velocity or between temperature and the sum of the inverse numbers of the propagation delay times for every gas species. Fluid velocity, quantity of flow, or the quantity of passage at the temperature of the fluid is determined, and fluid velocity, quantity of flow, or the quantity of passage at a reference temperature is converted and computed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement in an ultrasonic flow meter.

  There has been proposed an ultrasonic flow velocity measurement method capable of obtaining the flow velocity at the reference temperature without being influenced by the fluid temperature, and thus capable of obtaining the fluid flow rate accurately (see, for example, Patent Document 1).

In this measurement method, ultrasonic transducers are arranged on the upstream side and the downstream side of the measurement fluid flowing in the ultrasonic flow velocity measurement tube, and the ultrasonic transducers generate and transmit ultrasonic waves to and from each ultrasonic transducer. Mutually receiving ultrasound,
Based on the sum of the propagation times of the ultrasonic waves, the fluid temperature T at the time of propagation time measurement is derived,
Based on the difference in propagation time of the ultrasonic wave, the flow velocity v at the fluid temperature T at the time of propagation time measurement is derived,
By substituting the fluid temperature T and the flow velocity v in the following equation (1), seeking the flow velocity v ₀ at the standard temperature T _0.

v ₀ = (T ₀ × v) / T (1)
v ₀ : Flow velocity at reference temperature T ₀ : Reference temperature (absolute temperature)
v: Flow velocity at fluid temperature during propagation time measurement T: Fluid temperature (absolute temperature) during propagation time measurement
In addition, transmission / reception means for transmitting / receiving sound waves to / from the fluid in the flow path, flow rate detection means for measuring propagation time of sound waves in the fluid, flow coefficient setting means for determining a flow coefficient, the flow coefficient and the propagation time. A flow rate calculation means for calculating a flow rate based on the temperature detection means for measuring the temperature of the fluid, and a coefficient correction means for changing the flow coefficient of the flow rate coefficient setting means based on the measured temperature and propagation time. An equipped flow meter side device has been proposed (see, for example, Patent Document 2).

In this flow meter side device, the flow coefficient determined by the flow coefficient setting means is set for each type of gas that is a fluid, and is changed by the coefficient correction means based on the gas type selection means that selects the type of gas to be applied. .
JP 2000-22108 (page 2, FIG. 1) JP 2001-255186 A (page 2, FIG. 1)

  In the ultrasonic flow velocity measuring method of Patent Document 1, it is necessary to determine the ultrasonic velocity according to the type of gas that is the fluid to be measured, and the calculation coefficient for calculating the fluid temperature is switched for each type of gas. There was a problem that it was necessary to change and was troublesome.

  In addition, if there is a fluctuation in flow velocity, the flow velocity at the measurement timing of the propagation time in the forward direction and in the reverse direction is different, so that there is a problem that the error in the derived fluid temperature increases.

  Further, if there is an individual difference in the distance between the ultrasonic transducers, there is a problem that the error of the derived fluid temperature becomes large.

  Furthermore, since the fluid temperature is derived based on the sum of the propagation times, there is a problem that an error in the derived fluid temperature increases.

When the error of the fluid temperature increases, naturally, the error of the flow velocity v _{0 at} the reference temperature T ₀ increases.

  In the flow rate measuring device of Patent Document 2, since a dedicated temperature sensor and an electronic circuit having a temperature correction function are required as temperature detecting means for detecting the temperature of the fluid, not only the cost is increased, but also the electronic circuit board However, there is a problem that the current consumption of the battery increases.

  Then, an object of this invention is to provide the ultrasonic flowmeter which can eliminate these problems.

  The present invention is an ultrasonic flowmeter in which ultrasonic transducers are arranged on the upstream side and the downstream side of a flow, and the flow velocity, flow rate, or passage amount is obtained from the reciprocal difference in propagation time between the forward direction and the reverse direction of the ultrasonic wave. The most important feature is that the fluid temperature is obtained from the reciprocal sum of the propagation times in the forward direction and the reverse direction, and the flow velocity, flow rate, or passage amount converted into the state of the separately determined reference temperature is obtained. The passing amount is a so-called integrated flow rate calculated by multiplying the flow rate by time.

  Therefore, in order to achieve the above object, the invention of claim 1 is characterized in that ultrasonic transducers are arranged on the upstream side and downstream side of the flow, and the flow velocity is determined by the reciprocal difference between the propagation times of the ultrasonic wave in the forward direction and in the reverse direction. An ultrasonic flow meter for obtaining a flow rate or a passing amount, wherein a fluid temperature is obtained from a reciprocal sum of forward and reverse propagation times, and a flow rate, a flow rate or a passing amount at a separately determined reference temperature is calculated. It is an ultrasonic flowmeter.

  The invention according to claim 2 is the ultrasonic flowmeter according to claim 1, from the arrival time until the received wave is detected after transmitting the ultrasonic wave, the time for propagating in the ultrasonic transducer, The propagation time is obtained by subtracting a delay time such as the time from the beginning of the received wave to the zero cross of the third wave.

  The invention according to claim 3 is the ultrasonic flowmeter according to claim 1 or 2, wherein the speed of sound is calculated from the reciprocal sum of propagation times, and the type of fluid is determined by comparing with a preset sound speed value, The temperature of the fluid is obtained.

  According to a fourth aspect of the invention, in the ultrasonic flowmeter according to the third aspect, the fluid temperature is obtained from the reciprocal sum of the propagation times using a preset temperature calculation table.

  According to a fifth aspect of the present invention, in the ultrasonic flowmeter according to the fourth aspect, the gas type determination value for determining the type of fluid and the data of the temperature calculation table are rewritten from the outside.

  According to a sixth aspect of the present invention, in the ultrasonic flowmeter according to the fifth aspect, an inter-sensor distance correction coefficient for correcting the distance between the ultrasonic transducers is set from the outside.

  The invention according to claim 7 is the ultrasonic flowmeter according to claim 6, wherein the measurement order in the forward direction and the reverse direction is changed for each measurement, and the reciprocal sum of the propagation times is averaged. is there.

  The invention described in claim 8 is characterized in that, in the ultrasonic flowmeter according to claim 7, the measurement interval is made random and the reciprocal sum of the propagation times is averaged.

  The invention according to claim 9 is characterized in that, in the ultrasonic flowmeter according to claim 8, when the flow velocity starts from zero, the number of data to be averaged is reduced.

  According to a tenth aspect of the present invention, in the ultrasonic flowmeter according to the ninth aspect, the fluid temperature is calculated only when the fluid flow rate is stable.

  The ultrasonic flowmeter of the present invention is configured as described above, and identifies the gas type of the corresponding fluid from the reciprocal sum of the propagation time. There is an advantage of not requiring the trouble of changing the temperature calculation coefficient by the switching operation.

  In addition, since a dedicated temperature sensor and temperature correction electronic circuit are not required, not only the cost can be reduced, but also the electronic circuit can be reduced in scale and power consumption can be reduced.

  In the invention of claim 5, it is possible to measure another fluid by rewriting from the outside.

In the invention of claim 6, individual differences in the distance between the transmitter and the receiver can be corrected.
In the invention of claim 7, the measurement error can be reduced corresponding to the monotonous flow rate change.

In the invention of claim 8, the measurement error can be reduced with respect to the periodic flow rate change.
According to the ninth aspect of the present invention, it is possible to improve the temperature measurement responsiveness on the assumption that the temperature of the fluid (gas) changes.

  In the invention of claim 10, the fluid temperature is calculated only when the flow rate is stable, and temperature mismeasurement when the flow rate changes can be prevented.

  Next, the best mode for carrying out the present invention will be described based on the embodiments shown in the drawings.

  In FIG. 1, ultrasonic waves are transmitted and received by the ultrasonic transducers 2 and 3 disposed on the upstream side and the downstream side of the fluid to be measured flowing in the flow path 1, and the flow indicated by the arrow A The propagation time of ultrasonic waves in the forward direction and in the opposite direction to the arrow A is measured.

  Switching between the forward direction and the reverse direction is performed by switching the roles of the transmission side (transmission side) and reception side of the transducers 2 and 3 by the transmission / reception switching unit 4. The ultrasonic wave is transmitted from the transducer 2 in the direction of the arrow A by the drive signal from the transmitter 5 in the forward direction measurement, and the transducer 3 receives the ultrasonic wave and outputs the received signal. The received signal is amplified by the amplifying unit 6. The comparison unit 7 detects that the ratio of the n-th (for example, first) peak value and the (n + 2) -th peak value of the amplified received signal waveform exceeds a specified value, and the n + 2th satisfying this specified value The zero cross point of the (for example, third) wave is detected. This third zero cross point is hereinafter referred to as a third wave zero cross point.

  The time measuring unit 8 measures the arrival time from the transmission time of the transmitter / receiver 2 on the transmission side to the zero cross point of the third wave of the received signal, and the propagation time obtained by subtracting a delay time described later from this arrival time is the propagation time. Calculation is performed by the calculation unit 9. (Note that, in the case of the sing-around method (in the case of sing-around measurement), the time measuring unit 8 measures the time to the zero-cross point of the third wave of the received wave at the number of times of sing-around.)

  The propagation time includes a forward propagation time and a reverse propagation time, and the flow rate calculation unit 10 calculates the flow rate from the reciprocal difference between the two propagation times. Further, the temperature calculation unit 11 calculates the temperature from the reciprocal sum of the propagation times. Then, the temperature correction flow rate calculation unit 12 calculates the flow rate in the reference temperature state from the flow rate, the temperature, and the reference temperature.

  The arrival time and propagation time will be described below with reference to FIGS. FIG. 4A shows the relationship between the delay times a, b, c, d and e, the propagation time and the arrival time, and FIG. 5B shows the received waveform after amplification.

  The delay time a corresponds to a delay in the switching circuit 4a from the transmission to the PZT element of the transducer 2.

  The delay time b corresponds to the delay in the transducer 2, and the delay time c corresponds to the delay in the transducer 3. In general, the relationship b = c is established.

The delay time d corresponds to a delay in the receiving circuit 6a of the switching circuit 4b and the amplifying unit 6.
The delay time e corresponds to the delay in the reception wave detection 7a of the comparison unit 7, and is a third point that can be detected from the beginning of the reception wave as a point to be detected in the reception waveform in FIG. This corresponds to the delay time e until the zero cross point of the wave.

Since the total delay time is a + b + c + d + e, the relationship between the arrival time and the propagation time is expressed by the following equation.
Propagation time = arrival time-(a + b + c + d + e)
Propagation time = arrival time-total delay time

  It should be noted that there is a difference between the measured values due to the difference in the characteristics of the two transducers and the difference in the characteristics of the switching circuit between the forward measurement and the reverse measurement.

In order to reduce the measurement error by absorbing these characteristic differences, the arrival time at zero flow rate is measured a plurality of times at a stable temperature, and the average arrival time difference between the measurement values of the plurality of times is obtained.
Average arrival time difference = Forward average arrival time-Reverse average arrival time

The forward propagation time is calculated by subtracting the average arrival time difference thus calculated from the forward arrival time. That is, it is calculated for each measurement.
Forward propagation time = forward travel time - All delay time - average arrival time difference backward propagation time = reverse arrival time - All delay Incidentally, the arrival time was measured, forward arrival time t ₁ and reverse arrival time t ₂ The total delay time is a value that takes into account the time difference due to the characteristic difference between the forward direction and the reverse direction (that is, the average arrival time difference) in the total delay time for each of the forward direction measurement and the reverse direction measurement.

If the sum of the forward total delay time and the average arrival time difference is τ ₁ , and the reverse total delay time is τ ₂ ,
Forward propagation time = t ₁ −τ ₁ (1)
Reverse propagation time = t ₂ −τ ₂ (2)
It becomes.

When the reciprocal of the forward propagation time is expressed as f ₁ and the reciprocal of the reverse propagation time is expressed as f ₂ ,
f ₁ = 1 / (t ₁ −τ ₁ ) (3)
f ₂ = 1 / (t ₂ −τ ₂ ) (4)
The reciprocals f ₁ and f ₂ of the forward and reverse propagation times are expressed as follows: V is the flow velocity of the fluid, C is the sound velocity of the ultrasonic waves in the fluid, and L is the distance (interval) between the transducers 2 and 3.
f ₁ = (C + V) / L (5)
f ₂ = (C−V) / L (6)
Therefore, the reciprocal difference f ₁ −f ₂ of the propagation time is obtained from the equations (5) and (6):
f ₁ −f ₂ = 2V / L (7)
It becomes. Therefore, the flow velocity V at the measurement temperature can be obtained by the following equation (8).

V = (f ₁ −f ₂ ) × L / 2 (8)
This flow velocity V is a flow velocity at the measurement temperature T [° C.]. The flow rate at the measurement temperature T [° C.] is calculated by multiplying the flow velocity V by the cross-sectional area of the flow path. Further, the flow rate is multiplied by time to calculate a passing amount, that is, an integrated flow rate. The flow rate V is calculated from the propagation times t ₁ −τ ₁ and t ₂ −τ _2, and the flow rate and passage amount are further calculated by the flow rate calculation unit 10 of FIG.

The temperature calculation unit 11 obtains the fluid temperature from the sum f ₁ + f ₂ of the reciprocals f ₁ and f ₂ of the forward and reverse propagation times.

Specifically, it is data indicating the relationship between the reciprocal sum corresponding to the gas type and the temperature, for example, a diagram illustrating the relationship between the reciprocal sum f ₁ + f ₂ [Hz] of air (AIR) propagation time and the temperature [° C.]. 3 is stored in the temperature calculation unit, and the temperature [° C.] corresponding to f ₁ + f ₂ is read from the data of FIG. 3 to be the fluid temperature T [° C.].

Based on the flow rate V obtained by the flow rate calculation unit 10 and the fluid temperature T [° C.] obtained by the temperature calculation unit, the flow rate V ₀ at the reference temperature T ₀ [° C.] is calculated as a temperature-corrected flow rate according to Charles' law. Calculation is performed by the unit 12.
V ₀ = (273 + T ₀ ) · V / (273 + T) (9)

The sum f ₁ + f ₂ of the reciprocals f ₁ and f ₂ of the forward and reverse propagation times calculated by the propagation time calculation unit 9 is:
f ₁ + f ₂ = 2C / L (10)
Thus, since there is a correlation with the sound speed C, the fluid temperature can be read from the data shown in FIG.

Next, the procedure of the temperature calculation unit of the second embodiment that calculates the temperature of the fluid based on the reciprocal sum of the propagation times t ₁ -τ ₁ and t ₂ -τ ₂ will be described with reference to the block diagram of FIG. This embodiment corresponds to the invention of claim 2.

Since the reciprocals f ₁ and f ₂ of the forward and reverse propagation times t ₁ -τ ₁ and t ₂ -τ ₂ are expressed by the equations (5) and (6), the propagation times t ₁ -τ ₁ and t ₂ The reciprocal sum of -τ ₂ is
f ₁ + f ₂ = 2C / L (10)
Since the interval L is a fixed known value, the reciprocal sum f ₁ + f ₂ is a value correlated with the sound speed C.

By the way, the unit of the reciprocal of the propagation time is [Hz]. Therefore, when the reciprocal sum of the propagation times in the forward direction and the reverse direction is taken on the vertical axis and the temperature [° C.] is taken on the horizontal axis, the relationship between the two is shown in FIG. ) And LPG, the three lines B, C, and D are used, and by using this relationship, the reciprocal number in the range of any line of B, C, and D based on the value of the reciprocal sum f ₁ + f ₂ Depending on whether there is a sum, it can be determined whether the gas type is 13A, AIR or LPG. 5 corresponds to the gas type 1 determination value 11c, the gas type 2 determination value 11d, and the gas type 3 determination value 11e in FIG. 4, and based on these determination values, the gas type determination of FIG. The part 11b functions. That is, in FIG. 5, since the reciprocal sum of the vertical axis is f ₁ + f ₂ , for example, if the reciprocal sum calculated by the reciprocal sum calculation unit 11 a is 8000 [Hz], the gas type determination unit based on FIG. 5. 11b determines that the gas type of the fluid is 13A of gas type 1.

In order to determine the gas type, the relationship between the speed of sound and temperature as shown in FIG. 6 can be used instead of FIG. In this case, the equation (10) is modified
C = (f ₁ + f ₂ ) L / 2 (11)
Then, the sound speed C is obtained based on the reciprocal sum f ₁ + f _2, and it is determined whether the gas type is 13A, AIR or LPG depending on which range of sound speed C is 13A, AIR or LPG in FIG.

  Note that for city gas 13A, air (AIR), and LPG (LP gas), the speed of sound C and the reciprocal sum, as shown in FIGS. In, since the lines (curves) do not overlap each other, it is possible to reliably determine which gas type is.

  When the sound velocity curves (curves) such as other gas types or a wide operating temperature range may overlap each other as shown in FIG. 7, it is compared with the sound velocity C data set in advance when the overlapping region is removed. By doing so, the gas type is identified (determined), and the gas type information is switched to prevent erroneous determination.

  Next, a third embodiment corresponding to the configuration shown in claim 4 will be described. For example, as shown in FIG. 8, three-point reciprocal sum data (temperature point data, tp0, tp20, tp40) and four temperature calculation coefficient data km20, k0, kp20, kp40 at temperatures of 0 ° C., 20 ° C., and 40 ° C. Is stored in the temperature calculation table, and the temperature is calculated by the following equation. The overall block diagram is shown in FIG. 1, and the main part is shown in FIG.

A case where the reciprocal sum is in the range of tp20 to tp40 will be described.
T = (f ₁ + f ₂ −tp20) × kp20 + 20 [° C.]
Where T [° C]: Fluid temperature
f ₁ : reciprocal of forward propagation time
f ₂ : reciprocal of backward propagation time
tp20 [Hz]: Reciprocal sum in air (AIR) at 20 ° C.
kp20 [° C./Hz]: Temperature calculation coefficient The temperature calculation tables are shown in [Table 1] and [Table 2]. [Table 1] is the temperature point data, the unit is [Hz], and [Table 2] is the temperature calculation coefficient data, and the unit is [° C./Hz] for the inclination of the broken line in FIG.

この実施例３では、符号１１ｈで示す温度算出テーブル１は、前記［表１］のガス種がＡＩＲの欄のデータと、［表２］のガス種がＡＩＲのデータを電子回路のメモリに記憶したテーブルで構成される。また、符号１１ｉの温度算出テーブル２は同様に［表１］の１３Ａ欄のデータと［表２］の１３Ａ欄のデータとで、又、符合１１ｊの温度算出テーブルは同様に［表１］のＬＰＧの欄と［表２］のＬＰＧの欄のデータとで構成される。そして、１１ｈ、１１ｉ、１１ｊの各温度算出テーブル１、２、３のデータをテーブル選択部１１ｇで選択して、演算部１１ｆで温度Ｔ［℃］を算出する。

In Example 3, the temperature calculation table 1 indicated by reference numeral 11h stores the data in the column of “AIR” in [Table 1] and the data in “AIR” of [Table 2] in the memory of the electronic circuit. It consists of a table. Similarly, the temperature calculation table 2 of reference numeral 11i is the data in the column 13A of [Table 1] and the data of the column 13A of [Table 2], and the temperature calculation table of the reference numeral 11j is also similar to that in [Table 1]. It consists of the LPG column and the data in the LPG column of [Table 2]. And the data of each temperature calculation table 1, 2, 3 of 11h, 11i, and 11j are selected by the table selection part 11g, and temperature T [degreeC] is calculated by the calculating part 11f.

  Next, a fourth embodiment corresponding to the structure shown in claim 5 will be described. The overall block diagram is shown in FIG. 1, and the main part is shown in FIG. In the fourth embodiment, the gas type determination values 11c to 11e and the contents of the temperature calculation tables 1 to 3 (reference numerals 11h to 11j) can be rewritten from the outside by the setting device 13, and the measurement of the gas type is different from that before rewriting. Can be made to do.

  In general, the speed of sound varies depending on the gas type of the fluid to be measured, so the gas type determination value and the temperature calculation table of Example 4 need to be determined for each type of measurement fluid. By making these values externally settable by the setting device 13, it is possible to easily avoid the erroneous determination of the gas type and the occurrence of temperature measurement errors. In this way, the above-mentioned problem can be easily avoided even with unexpected different gas types.

  Next, a fifth embodiment corresponding to the structure of claim 6 will be described. The overall block diagram of this embodiment is the same as that in FIG.

  In the fifth embodiment, the transducers 2 and 3, that is, the correction coefficient of the sensor distance correction unit 11k can be set by an external setting device 13A.

  For example, when the distance between the transducers, that is, the distance L between sensors is 100 mm, the measurement error when the distance L is shifted by 0.2 mm due to the individual error is about 1 ° C. It becomes an error.

  The slope of the reciprocal sum in the vicinity of 20 ° C. of air is about 12 Hz / ° C. from the sound velocity curve shown in FIG.

  From the above equation (9), the reciprocal sum of L = 100 mm and L = 100.2 mm is as follows when the sound velocity at air 23 ° C. is 345 m / s.

In the case of L = 100 mm f ₁ + f ₂ = 2C / L = 2 × 345 / 0.1 = 6900 [Hz]
When L = 100.2 mm f ₁ + f ₂ = 2C / L = 2 × 345 / 0.1002 = 6886 [Hz]
The difference between them is 14 [Hz], which corresponds to an error of about 1 ° C.
Therefore, for a flowmeter of L = 100.2 mm, the individual difference of the inter-sensor distance is corrected by multiplying the inter-sensor distance correction coefficient of 100.2 / 100 by 6 ₁ [Hz] of f ₁ + f _2. Therefore, the correct value f ₁ + f ₂ = 6900 can be obtained.

The procedure for setting the inter-sensor distance correction coefficient is shown below.
(1) Under a constant temperature environment condition, the propagation time in the state of zero flow rate is measured a plurality of times, and the average propagation time in each of the forward direction and the reverse direction is calculated.
(2) The reciprocal of the average propagation time in the forward direction and the reverse direction is taken, and the average value of the reciprocal numbers in the forward and reverse directions is taken.
(3) Calculate the sum of the average values of the reciprocals of forward and reverse.
(4) The inter-sensor distance correction coefficient is calculated from the theoretical reciprocal sum at the fluid temperature when measuring the propagation time and the average value of the measured reciprocal sums. (Sensor distance correction coefficient = theoretical reciprocal sum ÷ (sum of average values of reciprocals)). The theoretical reciprocal sum means the reciprocal sum of the propagation time calculated from the target value (set value) of the sound velocity at the fluid temperature at the time of propagation time measurement and the distance between the sensors.
(5) The calculated inter-sensor distance correction coefficient is set in the flow meter and stored.

The sixth embodiment corresponds to the structure of the seventh aspect. When the flow rate fluctuates, as shown in FIG. 12, the flow rates captured by the forward measurement and the reverse measurement become different values of V ₁ and V ₂ . That is, it becomes V ₁ in the n-th forward measurement and V _{2 in the} backward measurement. At the (n + 1) th time, the forward direction measurement value and the reverse direction measurement value become V ₁ ′ and V ₂ ′. Therefore, in the nth measurement,
f ₁ = (C + V ₁ ) / L (5 ′)
f ₂ = (C−V ₂ ) / L (6 ′)
f ₁ + f ₂ = (2C + V ₁ −V ₂ ) / L (7 ′)
Therefore, in the sixth embodiment, the measurement error can be reduced by changing the order of the propagation time measurement for each measurement and averaging the reciprocal sum. Since V ₁ −V _{2 in} the equation (7 ′) is substantially zero as an average of the n-th and n + 1-th measurements in FIG. 13, the measurement error is reduced.

  FIG. 14A shows an overall block diagram of the sixth embodiment, and FIG. 14B shows details of the temperature calculation unit. A measurement order control unit 14 shown in FIG. 10A and an averaging unit 11m shown in FIG. 10B are added as compared with the other embodiments. The measurement order measurement unit 14 switches the measurement order between the forward direction and the reverse direction.

The seventh embodiment corresponds to the configuration of the eighth aspect. In the case of a flow rate change that fluctuates periodically, by making the measurement interval random, V ₁ -V ₂ in the above equation (7 ′) becomes substantially zero on average, so that the measurement error can be reduced.

  FIG. 15 is an explanatory diagram when the measurement interval is randomized. When the flow velocity V periodically fluctuates in a sine wave shape, the measurement interval is randomized so that the average value of the measurement error is brought close to zero. Indicates.

  When the flow is stopped and the flow velocity starts from zero, the temperature measurement response can be improved by reducing the number of data to be averaged.

  The block diagram of FIG. 16 is a block diagram showing the entirety of the seventh and eighth embodiments. When the flow rate change determination unit 16 is provided and the fluid flows out from a zero state, the number of data to be averaged handled by the averaging unit 11m Reduce. Further, the measurement interval control unit 17 is provided to perform control such as randomization of the measurement interval described in the seventh embodiment.

  The block diagram of FIG. 17 is a diagram of the ninth embodiment, and a flow rate variation determination unit 18 is provided to determine the presence or absence of flow rate variation. When there is a flow rate variation, in order to prevent erroneous temperature measurement, the flow rate is stabilized. The temperature was not calculated (claim 10).

1 is a block diagram of Embodiment 1 of the present invention. It is a figure which sets the arrival time and propagation time in Example 2 of this invention, (a) is a figure which shows the correspondence of both time, (b) is a figure which shows a received waveform. The figure which shows the relationship between the reciprocal sum and fluid temperature in the Example of this invention. The block diagram which shows the detail of the temperature calculating part 11 of the block diagram of FIG. The figure which shows the relationship between the fluid temperature and the reciprocal sum in the Example of this invention. The figure which shows the relationship between the fluid temperature and sound speed in the Example of this invention. The figure which shows the relationship between the fluid temperature and sound speed in the Example of this invention. The figure which shows the relationship between the reciprocal sum and fluid temperature in the Example of this invention. The block diagram of the temperature calculating part in this invention. The block diagram of the temperature calculating part in this invention. The block diagram of the temperature calculating part in this invention. The figure explaining the flow-velocity change for every measurement in this invention. The figure explaining the flow-velocity change for every measurement in this invention. The block diagram (a) of the whole Example of this invention, and the block diagram (b) of a temperature calculating part. The figure explaining the measurement timing when a flow velocity fluctuates to a sine wave shape. The block diagram of the Example of this invention. The block diagram of the Example of this invention.

Explanation of symbols

1 channel 2, 3 transducer (sensor)
T fluid temperature T ₀ reference temperature V, V ₀ flow velocity 8 time measurement unit 9 propagation time calculation unit 10 flow rate calculation unit 11 temperature calculation unit 12 temperature correction flow rate calculation unit t ₁ forward arrival time t ₂ reverse arrival time f ₁ forward Reciprocal of direction propagation time f ₂ reciprocal of reverse propagation time f ₁ + f ₂ reciprocal sum 11 temperature calculating unit 11a reciprocal sum calculating unit 11b gas type determining unit 11f calculating unit 11g table selecting unit 11h, 11i, 11j temperature calculating table 13, 13A Setter 11k Sensor-to-sensor distance correction unit 14 Measurement sequence control unit 11m Averaging unit 17 Measurement interval control unit 16 Flow rate change determination unit 18 Flow rate fluctuation determination unit

Claims (10)

  An ultrasonic flowmeter in which ultrasonic transducers are arranged on the upstream and downstream sides of the flow, and the flow rate, flow rate, or passage amount is obtained from the reciprocal difference between the propagation times of the ultrasonic forward and reverse directions. An ultrasonic flowmeter characterized by calculating a fluid temperature from a reciprocal sum of propagation times in the opposite direction and calculating a flow velocity, a flow rate, or a passing amount at a separately determined reference temperature.   Subtract delay times such as the time to propagate through the ultrasonic transducer and the time from the head of the received wave to the zero cross of the third wave from the arrival time from when the ultrasonic wave is transmitted until the received wave is detected. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is a propagation time.   The ultrasonic flowmeter according to claim 1 or 2, wherein a sound velocity is calculated from a reciprocal sum of propagation times, a type of fluid is determined by comparison with a preset sound velocity value, and a temperature of the fluid is obtained. .   4. The ultrasonic flowmeter according to claim 3, wherein a fluid temperature is obtained from a reciprocal sum of propagation times using a preset temperature calculation table.   The ultrasonic flowmeter according to claim 4, wherein the gas type determination value for determining the type of fluid and the data of the temperature calculation table are rewritten from the outside.   6. The ultrasonic flowmeter according to claim 5, wherein a distance correction coefficient between sensors for correcting the distance between the ultrasonic transducers is set from the outside.   7. The ultrasonic flowmeter according to claim 6, wherein the measurement order in the forward direction and the reverse direction is changed for each measurement, and the reciprocal sum of the propagation times is averaged.   The ultrasonic flowmeter according to claim 7, wherein the measurement interval is made random and the reciprocal sum of propagation times is averaged.   9. The ultrasonic flowmeter according to claim 8, wherein the number of data to be averaged is reduced when the flow velocity starts from a zero state.   10. The ultrasonic flowmeter according to claim 9, wherein the fluid temperature is calculated only when the fluid flow rate is stable.

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