JP5467332B2 - Fluid flow measuring device - Google Patents

Description

  The present invention relates to a flow measuring device that measures the flow velocity and / or flow rate of a fluid by measuring the propagation time of an ultrasonic signal.

  Conventionally, this type of flow meter has been proposed that uses a technique called a sing-around method that increases measurement resolution by repeating transmission and reception between a pair of transducers a plurality of times. An example in which this type of measuring device is applied to a household gas meter will be described with reference to FIG.

  A pair of ultrasonic transmission / reception first and second transducers 42 and 43 are disposed in the middle of the fluid conduit 41 and on the upstream and downstream sides so that the ultrasonic waves flow through the fluid. It is set to propagate so as to cross diagonally.

  In addition, the measurement unit 44 that measures the propagation time of the ultrasonic wave, the control unit 45 that controls the measurement unit 44, and the calculation unit that calculates the flow velocity and / or flow rate of the fluid based on the measurement result of the measurement unit 44 46 is provided.

Now, the sound velocity is C, the flow velocity is v, the distance between the transducers is L, and the angle between the ultrasonic propagation direction and the flow direction is θ, and the ultrasonic waves are transmitted from the transducer 42 arranged on the upstream side. When the propagation time when received by the transducer 43 arranged on the downstream side is t ₁ and the propagation time in the reverse direction is t ₂ , t ₁ and t ₂ can be obtained by the following equations.

t ₁ = L / (C + v cos θ) (Formula 1)
t ₂ = L / (C−v cos θ) (Formula 2)
(Formula 1) and (Formula 2) are modified, and the flow velocity v is obtained by (Formula 3).

v = L · (1 / t ₁ −1 / t ₂ ) / ₂ cos θ (Formula 3)
If necessary, the fluid flow rate can be obtained by multiplying the value obtained in (Equation 3) by the cross-sectional area of the fluid conduit.

  By the way, in (Equation 3), the terms in parentheses can be modified as follows.

(T ₂ −t ₁ ) / t ₁ t ₂ (Formula 4)
Here, the denominator term in (Equation 4) has a substantially constant value regardless of the change in flow velocity, whereas the numerator term has a value that is substantially proportional to the flow velocity.

  Therefore, it is necessary to accurately measure the difference between the two propagation times. For this reason, as the flow rate becomes slower, it is necessary to obtain a minute time difference. To measure as a single phenomenon, the measurement unit 44 needs to have a very small time resolution, for example, in the order of ns.

  It is difficult to realize such a time resolution, and even if it can be realized, power consumption is increased by increasing the time resolution. Therefore, ultrasonic transmission is repeatedly performed many times, and the time required for the series of repeated measurements is measured by the measurement unit 44. The required time resolution is realized by obtaining the average value.

That is, if the time resolution of the measurement unit 44 is T _A and the number of repetitions is M, the measurement resolution of the propagation time is T _A / by operating the measurement unit 44 continuously during this repeated measurement.
M.

  This type of measuring device can achieve highly accurate measurement when the pressure in the fluid flow path is stable. For example, when applied to a gas meter that measures the flow rate of gas supplied to an ordinary household as an energy source. Face an inherent challenge called the pulsation phenomenon.

  This is a phenomenon that fluctuates the pressure in the surrounding gas supply piping in synchronization with the rotation of the gas engine, such as an air conditioner using a gas engine called GHP.

  When this pulsation occurs, even when the gas appliance is not used, the gas moves in the pipe in synchronization with the pressure fluctuation, and it is affected by the movement as if the gas is flowing. A measurement value is detected.

  As a method to suppress the effect of this phenomenon, the number of repeated measurements M is kept to the minimum number that can maintain the measurement accuracy, the measurement interval is shortened, and it is continuously executed for a relatively long time in small increments. There is one that performs flow rate calculation using the measured result.

  In particular, if the measurement interval is sufficiently shorter than the pressure fluctuation period, the phase state of the flow velocity fluctuation waveform can be captured evenly, and by averaging them, the true flow velocity with the fluctuation component removed The effect of detecting (flow rate) is aimed (see, for example, Patent Document 1).

  However, it is not a good idea in terms of power consumption to continue such a measurement method at all times.

  Therefore, in order to reduce unnecessary power consumption, the number of measurements is controlled according to the detected flow rate fluctuation amount. In a situation where it is determined that there is a large fluctuation and pulsation, the number of measurements is increased (see, for example, Patent Document 2).

JP 2002-350202 A JP 2003-222548 A

  However, in the conventional configuration, since the fluctuation is detected based on the fluctuation value of the flow rate measurement value of a plurality of times, a response delay occurs. As a result, at the time of starting the pressure fluctuation, the influence of the fluctuation causes the erroneous measurement. There were problems such as incurring unnecessary power consumption at the time of fluctuation stop.

  The present invention solves the above-mentioned conventional problems, and provides a fluid flow measurement device with high responsiveness that can instantaneously determine the presence or absence of pulsation and instantly switch to a measurement method according to the presence or absence of pulsation. It is aimed.

In order to solve the above-described conventional problems, a fluid flow rate measuring device according to the present invention is provided in a fluid flow path, and transmits and receives an ultrasonic signal. The first vibrator and the second vibrator, and the vibrator A time measuring means for measuring the propagation time of the ultrasonic signal between them, and a unit measuring step for measuring the propagation time of the forward and reverse ultrasonic signals by the time measuring means while switching the transmission / reception direction of the two transducers. And a time difference detecting means for calculating a flow time difference in both forward and reverse directions for each unit measurement step, and a calculation means for calculating a flow velocity and / or a flow rate based on a propagation time corresponding to the number of execution times. When the variation amount detecting means for determining the variation of transit time in the two unit measurement step of tandem which has been determined by the time difference detecting means, the pressure pulsation of the fluid flow path from the amount of variation which has been determined by the variation amount detecting means Which was provided with a pulsation detection means for determining free, and a measurement control means for controlling the number of times of execution of the unit measurement process based on the determination result of the pulse detecting means, and determining the presence or absence of pulsations instantaneously, pulsating presence It is possible to provide a fluid flow measuring device with high responsiveness that can be instantaneously switched to a measuring method according to the above.

  The flow rate measuring device of the present invention can determine the presence or absence of pulsation instantaneously and perform highly responsive measurement that can be instantaneously switched to a measurement method according to the presence or absence of pulsation.

1 is a block diagram of a fluid flow measurement device according to Embodiment 1 of the present invention. Time chart explaining the operation of the device Configuration diagram of timing means in the same device Time chart explaining operation of time measuring means in the same device Time chart explaining operation of time measuring means in the same device Time chart explaining operation of time measuring means in the same device Block diagram of a conventional fluid flow measurement device

1st invention is provided in the fluid flow path, the 1st vibrator and 2nd vibrator which transmit and receive an ultrasonic signal, The time measuring means which measures the propagation time of the ultrasonic signal between the vibrators, A unit measurement step for measuring the propagation time of forward and reverse ultrasonic signals by the time measuring means while switching the transmission / reception directions of the two vibrators is continuously executed a plurality of times at a predetermined interval, A flow rate calculating means for calculating a flow speed based on the propagation time of time, a time difference detecting means for obtaining a propagation time difference in both forward and reverse directions for each of the unit measurement steps, and two unit measurement steps in succession obtained by the time difference detection means . Based on the fluctuation amount detection means for obtaining the fluctuation amount of the propagation time difference, the pulsation detection means for judging the presence or absence of pressure pulsation in the fluid flow path from the fluctuation amount obtained by the fluctuation amount detection means, and the determination result of the pulsation detection means It said to It has a measurement control means that controls the number of executions of the position measurement process, and can quickly determine the presence or absence of pulsation and instantly switch to a measurement method according to the presence or absence of pulsation. A measuring device can be provided.

  In the second invention, in particular, in the first invention, the pulsation detecting means compares the output of the fluctuation amount detecting means with a predetermined threshold value, and when there is a pulsation when it is larger than the threshold value, Since it is determined that there is no pulsation, it is possible to determine the presence or absence of pulsation without performing complicated calculations.

  In the third invention, in particular, in the second invention, when the pulsation detecting means determines that there is no pulsation, the measurement control means is configured to control to reduce the number of executions of the unit measurement process. Power consumption can be reduced under stable use conditions with no pulsation.

  In the fourth aspect of the invention, in particular, in the second aspect of the invention, when the pulsation detecting unit determines that there is no pulsation, the measurement control unit has a configuration in which the number of executions of the unit measurement step is cut off at a predetermined minimum value. The power consumption can be reduced under stable use conditions with no pulsation.

  In the fifth invention, in particular, in the second invention, when the pulsation detecting means determines that there is pulsation, the measurement control means is configured to control to increase the number of executions of the unit measurement process. Under the condition with pulsation, the influence of pulsation can be reduced.

In the sixth invention, in particular, in the second invention, when the pulsation detecting means determines that there is pulsation, the measurement control means has a configuration in which the number of executions of the unit measurement process is set to a predetermined maximum value. In the presence of pulsation, the influence of pulsation can be reduced.

  In a seventh aspect of the invention, in particular, in any one of the first to sixth aspects of the invention, the time measuring means includes a reference clock and a counter circuit that performs counting based on the clock, and the time difference detecting means is the counter circuit of the counter circuit. Since it is configured with a subtraction circuit using the count value and does not require multiplication / division in the process from the unit measurement process to pulsation determination, it is possible to determine the presence or absence of pulsation with a simple calculation method that only operates the subtraction circuit. The power consumption is small and a quick determination is possible.

  According to an eighth invention, in particular, in the time measuring means of the seventh invention, the time measuring means comprises at least two reference clocks having different frequencies and a counter circuit, and the time difference detecting means calculates a time difference for each counter circuit to generate pulsation. Since the detection means is configured to determine the presence or absence of pulsation from the combination of the count differences of all the counters obtained by the time difference detection means, quick determination is possible without impairing the measurement resolution.

  Embodiments of the present invention will be described below with reference to the drawings. The embodiment described below does not limit the present invention.

(Embodiment 1)
In FIG. 1, first and second transducers 2 and 3 for transmitting and receiving ultrasonic signals are arranged diagonally opposite to each other in the middle of the fluid flow path 1 and on the upstream and downstream sides in the flow direction. Propagates diagonally and crosses.

  For example, the transmission unit 4 outputs a drive signal to the first transducer 2, and as a result, the second transducer receives the ultrasonic signal output from the first transducer 2, and the received signal is received by the reception unit 5. Signal processed.

  The switching means 6 switches the transmission / reception roles of the first vibrator 2 and the second vibrator 3.

  The measurement control means 7 controls the overall transmission / reception operation executed between the two vibrators, and is composed of a trigger means 8, a repetition means 9, a delay means 10, and a measurement process control means 11.

  First, when a trigger output for starting measurement is made by the trigger means 8, the switching means 6 connects the first vibrator 2 and the transmission means 4, the second vibrator 3 and the reception means 5, and the first vibrator 2 is connected. Measurement with the transmitting side and the second vibrator 3 as the receiving side is started. For the following description, this will be referred to as forward flow measurement.

  When a drive signal is output from the transmission unit 4, an ultrasonic signal is output from the first transducer 2, and when this reaches the second transducer 3, reception processing is performed by the reception unit 5.

  Once the reception process is performed, the forward direction measurement is repeatedly executed by a predetermined number of times of sing-around by the action of the repeating unit 9. In the present embodiment, the number of sing-arounds is four, but the present invention is not limited to this.

  When the four repetitions are completed, after a predetermined delay time is generated from the delay means 10, the trigger means 8 outputs a transmission / reception switching signal to the switching means 6, and this time, transmission with the second vibrator 3 is performed. The means 4, the first vibrator 2 and the receiving means 5 are connected to each other, and measurement is started with the second vibrator 3 as the transmitting side and the first vibrator 2 as the receiving side. For the following explanation, this will be referred to as measurement in the reverse direction of the flow. At this time, a trigger signal for starting measurement is output from the trigger means 8.

  Even in the measurement in the reverse direction in which the roles of transmission and reception are switched, four repeated measurements are executed. As described above, a series of operations in which measurement in the forward direction of the flow (four times around measurement) and measurement in the reverse direction (four times around) are alternately performed once are referred to as a unit measurement step.

  If the unit measurement process executed first is the first measurement process, when this is completed, a delay signal is output from the delay means 10 and the same operation as the first measurement process is repeated. This is the second measurement step. After the measurement process control means 11 executes the measurement process a prescribed number of times, the flow rate calculation is executed.

  The time measuring means 12 measures the time from the trigger signal output timing of the trigger means 8 to the end of sing-around, and the first addition means 13 integrates the measured values of the time measuring means 12 in the forward measurement of each unit measuring step. The second adding means 14 integrates the measurement values of the time measuring means 12 in the measurement in the reverse direction of each measurement process.

  When the predetermined N unit measurement steps are completed, the calculation means 15 calculates the flow velocity using the output values of the first addition means 13 and the second addition means 14, and adds fluid to this as necessary. The flow rate is calculated by multiplying the cross-sectional area of the channel 1 and the coefficient.

  On the other hand, the time difference detection means 16 obtains the difference between the measurement value of the time measurement means 12 in the forward direction measurement and the measurement value of the time measurement means 12 in the reverse direction measurement every time one unit measurement process is completed.

  The fluctuation amount detection means 17 obtains the fluctuation amount of the time difference between the two successive measurement steps obtained by the time difference detection means 16, and the pulsation detection means 18 compares the output of the fluctuation amount detection means 17 with the determination threshold value to pulsate. The determination result is output to the measurement process control means 11.

  The measurement process control means 11 sets how many times the unit measurement process is executed to obtain the flow velocity and / or flow rate according to the determination result of the pulsation detection means 18.

  Next, the flow of operation of each unit described above will be described with reference to FIG. FIG. 2 shows the elapsed time from the origin with the output timing of the trigger means 8 indicating the start of measurement in the forward direction of the flow in the first measurement step as the origin, and the vertical axis shows the operation of each part.

First, at time t ₁ , the forward measured value T _{d1 of} the first measurement process measured by the time measuring means 12 is output to the time difference detecting means 16 and at the same time T _d1 is added to the first adding means 13. .

Thereafter, a predetermined delay time T _int elapsed time t ₂ of the flow of the reverse direction measurement is started at time t3, the reverse direction of the measurement value T _u1 time difference detection of the first measurement step measured by the time measuring means 12 It is output to the means 16.

Here, the time difference detection means 16 _obtains the difference between the two measured values T _d1 and T _u1 , T _def1 using (Equation 5).

T _def1 = T _u1 −T _d1 (Formula 5)
At the same time, T _u1 is added to the second addition means 14.

  Similarly, after the second measurement step, the addition process is alternately executed by the first addition unit 13 and the second addition unit 14 every time the measurement in the forward direction and the reverse direction is completed, and the measurement in the reverse direction is completed. The time difference detection means 16 performs the subtraction process.

Thus, at time t _5, the forward direction of the measurement value T _d2 of the second measuring step, at time t _7, the reverse direction of the measurement value T _u2 of the second measurement step is output to the time difference detector 16.

Then, the time difference detection means 16 determines the difference between them, T _def2 . Thereafter, found using variation delta ₁ of variation amount detection means 17 is _{T def1} and _{T def2} (Formula 6).

Δ ₁ = T _def2 −T _def1 (Formula 6)
Here, if there is no fluctuation in the pressure in the flow path and there is no change in the flow velocity, T _d1 and T _d2 show almost the same value, and T _u1 and T _u2 show almost the same value. Therefore, since T _def1 and T _def2 are also approximately equal, Δ ₁ is considered to be approximately zero.

Conversely, when pressure fluctuations occur, flow velocity fluctuations occur in synchronization with the pressure fluctuations. In this case, the values of T _d1 and T _d2 do not become the same value, and similarly, the values of T _u1 and T _u2 do not become the same value.

Therefore, since T _def1 and T _def2 are considered to show different values, Δ ₁ does not become 0. In particular, if the pressure fluctuation is severe, it is considered that a larger value is generated.

  Therefore, the pulsation detecting means 18 compares the fluctuation amount of the output of the time difference detection means 16 output from the fluctuation amount detection means 17 with a predetermined threshold every time the unit measurement process is completed, and if it is smaller than the threshold value. If there is no pulsation and it is larger than the threshold value, it is determined that there is pulsation.

  In addition, rather than determining the presence or absence of pulsation by only one comparison determination, more determination is made by using the idea of coincidence many times, such as determining that there is no pulsation several times or more consecutively based on a plurality of results. Needless to say, the main point of the present embodiment is to determine the presence or absence of pulsation based on the amount of fluctuation, so the same type of determination method may be used as long as it does not violate this point. .

  In this embodiment, when it is determined that there is no pulsation for five consecutive times, that is, if the output of the time difference detection means 16 is stable for six consecutive times, the subsequent measurement process is aborted assuming that there is no pulsation. The flow rate calculation means 15 performs the flow rate calculation.

  Conversely, if the determination of no pulsation does not continue for 5 consecutive times, the subsequent measurement process is extended until it is determined that there is no pulsation for 5 consecutive times, and the measurement is performed for the predetermined maximum measurement process. Shall be carried out continuously.

  When there is pulsation, the number of executions of the measurement process increases, so even if there is a flow velocity fluctuation accompanying pressure fluctuation, the fluctuation is averaged to some extent, so that a value closer to the true value can be obtained.

  Therefore, even when the pulsation is continuously generated, even if the measurement is stopped at the predetermined maximum number of execution times of the unit measurement process, the influence of the fluctuation is reduced.

  Next, the structure of the time measuring means 12 is demonstrated using FIG. 3 and FIG.

  The clock means 12 includes an oscillation circuit 19 that generates a clock signal (a), a gate circuit 20 that is configured by an AND circuit that switches supply / stop of the clock signal output from the oscillation circuit 19, and the gate circuit 20. The counter circuit 21 counts the output reference clock (b), and the latch circuit 22 reads the count value of the counter circuit 21 at an appropriate timing.

Further, (a) to (d) show digital signals transmitted between the time measuring means 12 and each component.

  When a trigger signal for starting measurement is output from the trigger means 8, the signal (b) becomes “L” and the counter circuit 21 is cleared.

  At the same time, since the signal (c) becomes “H” and the gate circuit 20 becomes active, the clock (a) output from the oscillation circuit 19 is supplied to the counter circuit 21 as the reference clock (d) through the gate circuit 20. Is done.

  The counter circuit 21 is an up counter that is incremented by one count every time the reference clock is supplied. (E) shows the count value of the counter circuit 21.

  When the predetermined number of times of sing-around is completed, a control signal is output from the repeating means 9, the signal (c) becomes "L", the gate circuit 20 becomes inactive, and thereafter the reference clock (d) to the counter circuit 21 Is stopped.

  At the same time, since the signal (f) becomes “H”, the count value of the counter circuit 21 is output to the latch circuit 22 at this timing.

  The value read by the latch circuit 22 is output as a signal (g) to the time difference detection means 16, the first addition means 13, and the second addition means 14.

  For the sake of simplicity, FIG. 4 shows the operation of each signal when the period in which the gate signal (c) is “H” is set to a short period of 3 clock cycles + α. The measured value of the time measuring means 12 is 3.

  FIG. 5 shows the operation of the time measuring means 12 in more detail, with the horizontal axis indicating the elapsed time and the vertical axis indicating the voltage levels of the signals (a) to (c). The signal (a) is an ultrasonic drive signal output from the transmission unit 4, and a rectangular AC signal having a frequency of about 500 kHz is output.

(B) is an ultrasonic wave reception waveform signal-processed by the receiving means 5. The reception means 5 forms a waveform shaping circuit (not shown) that is regarded as reception completion after the point (zero cross point) that first reaches 0 V after exceeding the threshold voltage _Vref , and when reception completion is detected. Again, an ultrasonic drive signal is output from the transmission means 4.

FIG. 5 shows the point of completion of reception of the last sing-around, omitting the repeated part in the middle. In FIG. 5, assuming that the start time of sing-around is τ ₀ and the end time is τ ₁ , the exact time required value is T _x = τ ₁ −τ ₀ (Equation 7)
As shown in FIG. 5, the time measuring means 12 counts the time until the rising timing τs of the clock before τ ₁ , and the measured value in this case is expressed as T _y = τ _s −τ ₀ (formula 8)
It can be expressed.

At this time, since the difference between τ ₁ and τ _s is within one cycle of the reference clock, it goes without saying that the measurement error is within one clock. For simplicity, the period of the ultrasonic reception waveform and the period of the reference clock are shown to be approximately the same. However, in actual measurement, the reference clock is sufficiently smaller than the period of the ultrasonic reception waveform, and one clock is used. It is possible to set the minute error to a range where there is no problem.

If the period of the reference clock is T _sc , T _y is T _y = N × T _sc (Equation 9)
It can be expressed as

  Here, N is a count value of the counter circuit 21.

  Therefore, the calculation in the time difference detecting means 16 can be constituted only by a subtracting circuit that obtains the difference between the count values of the counter circuit 21.

  Not only that, the calculation of the fluctuation amount in the fluctuation detection means 17 and the threshold value determination of the pulsation detection means 18 can be configured with only a simple subtraction circuit.

  As described above, if the configuration of the time measuring means 12 is made simple with only the reference clock and the counter circuit that is counted in synchronization with this, the time difference calculation in the time difference detection means 16 and the fluctuation amount in the fluctuation detection means 17 are calculated. Up to the threshold determination of the pulsation detecting means 18 can be configured with only a simple subtraction circuit.

  Therefore, it is possible to determine pulsation without performing multiplication and division as well as complicated calculation of procedures such as standard deviation, and it is possible to obtain a result in a short time after each unit measurement process is completed. Pulsation can be determined without delay.

  On the other hand, in order to reduce the measurement error, the reference clock frequency of the counter circuit 21 may be increased. However, it is not a good idea from the viewpoint of power saving to increase the frequency too much, so two counters with different frequencies are used. Although a method of configuring the time measuring means 12 has been conventionally used, even in this case, the pulsation determination can be realized with a simple configuration using only a subtracting circuit.

  This will be described with reference to FIG. In FIG. 6, the clock used in FIG. 5 is a low-speed clock, a low-speed counter circuit (not shown) using this clock as a reference clock, and a high-speed clock of a much higher frequency (for example, several hundred times). It is assumed that the time measuring means is composed of two high-speed counter circuits (not shown) having the reference clock as a reference clock.

  Here, since the operation on the low-speed clock side is the same as that of FIG. 5, the description is omitted, and the operation on the high-speed clock side will be described.

The high-speed clock starts operation from the reception point τ ₁ and operates until τ ₂ which is the rising timing of the next low-speed clock after τ ₁ , and the high-speed counter circuit counts the time from τ ₁ to τ ₂ . At this time, assuming that the obtained value is T _z , the required time T _y2 of the sing-around can be obtained by the following arithmetic expression.

T _y2 = (τ ₂ −τ ₀ ) −T _z = (τ _s + T _sc −τ ₀ ) −T _z (Expression 10)
However, T _sc is the period of the low-speed clock. Here, when (Equation 8) is used, T _y2 = T _y + T _sc −T _z (Equation 11)
It can be expressed. Further, if the count value of the low-speed counter circuit is N, the count value of the high-speed counter circuit is M, and the cycle of the high-speed clock is T _fc (Equation 11) can be further modified as follows.

T _y2 = (N + 1) × T _sc −M × T _fc (Formula 12)
The measurement error in this case is one clock of the cycle _{Tfc of the} high-speed counter, and the time accuracy is significantly improved as compared with FIG. Moreover, since the operation time of the high-speed clock with large current consumption is extremely short, the power consumption is not increased unnecessarily.

  Here, for each of the two counter circuits, the time difference detection means 16 obtains the time difference between the forward measurement value and the reverse measurement value, and the fluctuation amount detection means 17 obtains the fluctuation amount of the time difference. For example, the presence or absence of pulsation can be determined by the following determination.

When Δ _sn = 0 and | Δ _fn | ≦ 5, there is no pulsation. When ΔΔ _sn | ≧ 1, there is pulsation. However, here, Δ _sn and Δ _fn are the low-speed counter circuit side obtained by the fluctuation amount detection means 17. And the fluctuation value on the high-speed counter circuit side are shown.

  That is, if there is no pulsation, the fluctuation value on the low-speed counter circuit side is 0, and only the value obtained on the high-speed counter circuit side changes slightly.

  Therefore, even if the time measuring means 12 is composed of two counter circuits having different frequencies, it is still possible to determine the presence or absence of pulsation using only the subtracting circuit.

  Here, an example in which the time measuring means 12 is configured using two counter circuits having different frequencies has been shown, but the time measuring means 12 is configured by combining three or more counter circuits having different frequencies in order to further improve time accuracy. It goes without saying that even if it is a case, the same effect can be obtained.

  The fluid flow measuring device of the present invention can provide a highly responsive measuring device that can instantaneously determine the presence or absence of pulsation and instantly switch to a measurement method according to the presence or absence of pulsation. It can also be applied to meters and liquid flow meters.

DESCRIPTION OF SYMBOLS 1 Fluid flow path 2 1st vibrator 3 2nd vibrator 7 Measurement control means 12 Time measuring means 15 Calculation means 16 Time difference detection means 17 Fluctuation amount detection means 18 Pulsation detection means 21 Counter circuit

Claims (8)

A first vibrator and a second vibrator which are provided in the fluid flow path and transmit and receive ultrasonic signals;
Time measuring means for measuring the propagation time of the ultrasonic signal between the vibrators;
A unit measurement step for measuring the propagation time of forward and reverse ultrasonic signals by the time measuring means while switching the transmission / reception directions of the two vibrators is continuously executed a plurality of times at a predetermined interval, Computing means for computing the flow velocity and / or flow rate based on the propagation time of
A time difference detecting means for obtaining a difference in propagation time in both forward and reverse directions for each unit measurement step;
Fluctuation amount detection means for obtaining a fluctuation amount of the propagation time difference in the two unit measurement steps preceding and following obtained by the time difference detection means,
Pulsation detection means for determining the presence or absence of pressure pulsation in the fluid flow path from the fluctuation amount obtained by the fluctuation amount detection means;
A measurement control means for controlling the number of times of execution of the unit measurement process based on the determination result of the pulse detecting means,
A fluid flow measuring device comprising: 2. The fluid flow according to claim 1, wherein the pulsation detecting means compares the output of the fluctuation amount detecting means with a predetermined threshold value, and determines that there is pulsation when it is larger than the threshold value and that there is no pulsation when smaller than the threshold value. Measuring device. 3. The fluid flow measuring device according to claim 2, wherein when the pulsation detecting unit determines that there is no pulsation, the measurement control unit performs control so as to reduce the number of executions of the unit measuring step. 3. The fluid flow measuring device according to claim 2, wherein when the pulsation detecting means determines that there is no pulsation, the measurement control means terminates the number of executions of the unit measuring step with a predetermined minimum value. 3. The fluid flow measuring device according to claim 2, wherein when the pulsation detecting means determines that there is pulsation, the measurement control means controls to increase the number of executions of the unit measuring step. 3. The fluid flow measuring device according to claim 2, wherein, when the pulsation detecting means determines that there is pulsation, the measurement control means sets the number of executions of the unit measurement step to a predetermined maximum value. The time measuring means is composed of a reference clock and a counter circuit that counts based on the clock, and the time difference detecting means is composed of a subtracting circuit using the count value of the counter circuit, from the unit measuring step to the pulsation determination. The fluid flow measuring device according to any one of claims 1 to 6, wherein multiplication / division in the process is unnecessary. The time measuring means is composed of at least two reference clocks having different frequencies and a counter circuit, the time difference detecting means calculates a count difference for each counter circuit, and the pulsation detecting means is all obtained by the time difference detecting means. The fluid flow measuring device according to claim 7, wherein the presence or absence of pulsation is determined from a combination of count differences of the counter circuit.

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