JP2011064517A - Flow measuring device of fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform power saving operation, while performing high-accuracy measurements. <P>SOLUTION: Each reception signal is amplified by a reception means 35, and a reception point storage means 38 sequentially stores the newest reception point data to a plurality of storage parts, until the maximum value of each reception signal falls between VH and VL. The mean value of a plurality of zero-cross points prior to its falling between VH and VL can be used as a reception point, and a propagation time having few errors, such as upper/lower offset can be measured, and power saving operation can be performed, with a shortened measurement time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fluid flow measuring apparatus that uses a vibrator or the like and measures the flow rate of gas or liquid using ultrasonic waves.

  A conventional fluid flow measuring device will be described with reference to FIG. 10. A pair of ultrasonic transducers 102 and 103 are arranged on the upstream side and the downstream side of a flow path 101 through which a fluid flows, and the ultrasonic waves are fluidized. Is crossed diagonally.

  Then, the flow velocity of the fluid is measured from the propagation time of the ultrasonic wave propagating between the pair of ultrasonic transducers 102 and 103, and the flow rate is calculated based on this. For example, the flow rate value can be calculated in consideration of the size of the pipeline and the flow state by obtaining the flow velocity from the time difference.

  In addition, the solid line arrow 104 in a figure shows the direction through which a fluid flows, and the broken line arrow 105 has shown the direction through which an ultrasonic wave propagates. The direction in which the fluid flows and the direction in which the ultrasonic waves propagate intersect at an angle θ (for example, see Patent Document 1).

JP 2002-13958 A

  However, in the conventional measuring apparatus, an ultrasonic wave is propagated from the upstream ultrasonic transducer 102 to the downstream ultrasonic transducer 103, and the ultrasonic propagation time Tud is determined. The ultrasonic wave is propagated from the ultrasonic wave to the ultrasonic transducer 102 on the upstream side, the ultrasonic wave propagation time Tdu is measured alternately, and the flow rate is calculated by calculating the time difference using the measured ultrasonic wave propagation times Tud and Tdu. It was. The amplitude is adjusted by an auto gain amplifier so that the received wave has a constant amplitude.

  At this time, a reference level is set to a received waveform portion where a predetermined amplitude can be obtained as a trigger level, and a propagation time is measured. Therefore, the propagation time of the ultrasonic wave cannot be measured using the zero cross point before the trigger level. In addition, a trigger level setting / determination circuit is required.

  For this reason, an uncertain time is included in the arrival time of the ultrasonic wave, which may cause an error, and there is a problem that high-precision flow measurement cannot be realized. That is, the ultrasonic reception waveform generally rises at a frequency driven by a drive circuit, and sequentially changes to a vibration frequency unique to the ultrasonic transducer.

  Alternatively, since the reception waveform of the ultrasonic wave is affected by the reflected wave from the side wall of the flow path or the like, the frequency at the rising portion near the reception point is stable, but the trigger level is relatively high. In the portion where the reception amplitude is large, a difference occurs in the waveform received between the upstream side and the downstream side, which is detected as an error in propagation time.

In addition, since the ultrasonic wave reflected by the side wall of the channel 101 arrives at the received wave with a slight delay and is received as the received wave, a zero cross point that passes through the zero point when the received waveform is subtracted from the offset is obtained. Sometimes it was uncertain. In addition, there is a problem that an extra circuit for setting the trigger level is necessary.

  The present invention solves the above-described conventional problem, and uses at least two arrival times of the zero cross point of the received ultrasonic wave before the trigger level, and calculates the average value to determine the ultrasonic wave arrival time. An object of the present invention is to realize a power saving operation while realizing high-accuracy measurement while reducing the error included in the propagation time of ultrasonic waves so that measurement can be performed.

  In order to solve the above-described conventional problems, a fluid flow measurement device according to the present invention includes a pair of transducers arranged in a flow path through which a fluid to be measured flows and transmits / receives ultrasonic waves, and a transmission unit that drives one transducer A receiving means for converting the output signal of the other receiving-side transducer into an electric signal, a received wave maximum value judging means for detecting a maximum value of the signal of the receiving means and outputting a signal, and a signal of the receiving means are predetermined. The reception point detection means for outputting a signal when the range is reached, at least two reception point storage means for storing the output of the reception point detection means, and the signals of the reception point storage means are used to propagate between the transducers. A time measuring means for measuring the propagation time of the ultrasonic signal, a flow rate calculating means for calculating a flow rate based on a time difference of the time measuring means, the transmitting means, a receiving means, a received wave maximum value determining means, a receiving point detecting means, Reception point storage means, timing means, And a control means for controlling at least one of the flow rate calculation means. The control means uses the output of the received wave maximum value determination means to convert the value of the reception point storage means that has been reversed by a predetermined number for propagation time calculation. Receiving point selecting means for selecting as above, and the receiving point storing means is overwritten and updated until there is an output signal of the received wave maximum value judging means.

  With this configuration, the propagation time of the ultrasonic wave propagating between the ultrasonic transducer on the upstream side and the ultrasonic transducer on the downstream side, that is, the arrival time of the ultrasonic wave is received before the maximum amplitude value of the received wave. Use at least two arrival times at the zero crossing point of the sound wave, obtain the average value and measure the arrival time of the ultrasonic wave, reduce the error included in the propagation time of the ultrasonic wave, high accuracy Power saving operation can be realized while realizing simple measurement.

  The flow velocity or flow rate measuring device of the present invention uses at least two arrival times of the received ultrasonic zero crossing point before the maximum amplitude value of the received wave, and calculates the average value to determine the ultrasonic arrival time. It can be measured. For this reason, the error included in the propagation time or arrival time of the measured ultrasonic wave can be reduced by using the average value of multiple zero cross points, and power saving operation is achieved while realizing highly accurate flow measurement. it can.

Whole block diagram of fluid flow measuring device of the present invention Enlarged view around the receiving means in the same measuring device Timing chart showing received wave and measurement of received wave in the same measuring device Timing chart showing received wave and measurement of received wave in the same measuring device Timing chart showing the operation of the measurement control means in the same measuring device Timing diagram showing operation of received point storage means and received wave in the measurement apparatus Timing diagram showing operation of received point storage means and received wave in the measurement apparatus Overall block diagram showing another example of the measurement apparatus Timing chart showing the operation of the measurement control means in the same measuring device Overall block diagram showing another example of the measurement apparatus Overall block diagram showing still another example of the measurement apparatus Sectional view of a conventional fluid flow measurement device

  According to a first aspect of the present invention, a pair of transducers arranged in a flow path through which a fluid to be measured flows transmits / receives ultrasonic waves, a transmission unit that drives one transducer, and an output signal of the other reception-side transducer as an electrical signal Receiving means for converting to, receiving wave maximum value judging means for detecting the maximum value of the signal of the receiving means and outputting the signal, receiving point detecting means for outputting the signal when the signal of the receiving means falls within a predetermined range, At least two or more reception point storage means for storing the output of the reception point detection means; time measuring means for measuring the propagation time of the ultrasonic signal propagated between the transducers using the signal of the reception point storage means; and At least one of a flow rate calculation means for calculating a flow rate based on a time difference of the time measurement means, the transmission means, a reception means, a received wave maximum value determination means, a reception point detection means, a reception point storage means, a time measurement means, and a flow rate calculation means Control that controls one And the control means includes a reception point selection means for selecting a value of the reception point storage means that has been reversed by a predetermined number for propagation time calculation, based on the output of the reception wave maximum value determination means, The reception point storage means is overwritten and updated until there is an output signal from the received wave maximum value determination means.

  Therefore, the propagation time of the ultrasonic wave propagating between the ultrasonic transducer on the upstream side and the ultrasonic transducer on the downstream side, that is, the arrival time of the ultrasonic wave is determined based on the received ultrasonic wave before the maximum amplitude value of the received wave. Using at least two arrival times at the zero crossing point, the average value can be obtained to measure the arrival time of the ultrasonic wave, reducing the error included in the propagation time of the ultrasonic wave, and highly accurate measurement The power saving operation can be realized while realizing the above.

  According to a second aspect of the invention, in particular, in the first aspect of the invention, the control means includes a power supply means for energizing the reception point storage means for storing the output of the reception point detection means for a long time only for the first time. At the time of measurement, it is possible to reliably catch the received wave by preparing to store the output of the received wave detecting means before the received wave originally arrives.

  According to a third aspect of the invention, in particular, in the first aspect of the first aspect of the invention, the control means energizes the reception point storage means for storing the output of the reception point detection means for the second and subsequent times, based on the previous value. By adjusting the timing of the power supply means so as to prepare for storing the output of the received wave detection means immediately before the received wave arrives, the received wave can be reliably captured and a power saving operation can be performed.

  According to a fourth aspect of the invention, in particular, in the first aspect of the invention, the control means has trigger means for outputting a signal when the output of the reception point detection means exceeds a predetermined number of times, and the power supply means receives the output of the trigger means. By starting energization to the reception point storage means for storing the output of the point detection means, it is possible to reliably confirm that the reception wave has arrived and to prepare for storing the output of the reception wave detection means. As a result, the power saving operation by the short time operation becomes possible.

  In a fifth aspect of the invention, in particular, in the first aspect of the invention, when the number of zero cross points to be written to the at least one reception point storage means is large, the control means adjusts so that the oldest data is sequentially overwritten. By having the control means, it is possible to reliably capture a plurality of zero cross points in the vicinity of the received wave maximum value judging means even in a state where the number of zero cross points increases, and sequentially reduce the number of reception point storage means. Power saving operation is possible by overwriting.

  According to a sixth aspect of the invention, in particular, in the first aspect of the invention, the control means determines the difference between the value of the reception point storage means and the output of the reception wave determination means that is reversed by a predetermined number based on the output of the reception wave maximum value determination means. A time verification means for calculating the value, and if the value of the time verification means is within a predetermined value, the measurement is validated to prevent erroneous detection of a zero cross point due to noise or the like. Reliability can be improved by selecting the zero cross point.

  According to a seventh invention, in particular, in the first invention, the control means receives the reception point storage means via the power supply means after elapse of a predetermined time after the output of the reception point detection means after the output of the received wave maximum value determination means. By stopping the power supply to the power supply, it is possible to stop the operation of measuring and storing an extra zero cross point, and to realize a power saving operation.

(Embodiment 1)
In FIG. 1, the ultrasonic flowmeter of the present embodiment includes a flow path 31 through which a fluid to be measured flows, a first vibrator 32 that transmits and receives ultrasonic waves disposed in the flow path 31, and a second vibration. Receiving element 33, transmitting means 34 for driving the first vibrator 32 and the second vibrator 33, and receiving signals of the first vibrator 32 and the second vibrator 33 for amplifying the signal. Receiving means 35, a received wave determination means 36 that outputs a signal when the signal of the receiving means 35 reaches a predetermined value, a reception point detection means 37 that outputs a signal when the signal of the receiving means 35 falls within a predetermined range, Two reception point storage means 38 for storing the output of the reception point detection means 37; and a timing means 39 for measuring the propagation time of the ultrasonic signal propagated between the transducers using the signal of the reception point storage means 38; The flow rate is calculated based on the time difference of the time measuring means 39. Those having a flow rate computation means 40.

  FIG. 2 shows the periphery of the receiving means 35 and has a received wave maximum value judging means 43 for detecting the maximum signal of the receiving means 35.

  Further, a switching means 41 is provided between the transmission means 34 and the first vibrator 32, and between the second vibrator 33 and the reception means 35, and the first vibrator 32 and the second vibrator 33 are ultrasonic waves. It operates by switching between transmission and reception.

  The reception point storage means 38 has at least two or more storage units, and after the start of storage, it is overwritten and updated until there is an output signal of the reception wave maximum value determination means 43.

  The control means 42 includes the transmission means 34, the reception means 35, the reception wave determination means 36, the reception point detection means 37, the reception point storage means 38, the timing means 39, the flow rate calculation means 40, and the switching. At least one of the means 41 and the received wave maximum value judging means 43 is controlled.

  In addition, the control means 42 has a reception point selection means 44. When the reception wave maximum value determination means 43 detects that the ultrasonic wave has reached the receiving-side transducer, the control means 42 goes back to a time close to the original reception wave arrival point. At least two or more values are selected for propagation time calculation from the reception point data stored in the point storage means 38 and sent to the time measuring means 39 for measuring the propagation time.

  The time measuring means obtains the propagation time using the average value of the received reception point data and passes the value to the flow rate calculating means 40.

  The flow rate calculation means 40 obtains the flow rate based on the difference in propagation time, that is, the difference between the propagation time from the upstream side and the propagation time from the downstream side, and obtains the flow rate from the product of the cross-sectional area of the flow path.

  A normal flow rate or flow rate measurement operation will be described. Upon receipt of the start signal from the control means 42, the transmission means 34 pulse-drives the first vibrator 32 for a certain time, and at the same time, the time measuring means 39 starts measuring time. An ultrasonic wave is transmitted from the pulse-driven first vibrator 32.

  The ultrasonic wave transmitted from the first vibrator 32 propagates through the fluid to be measured and is received by the second vibrator 33. The reception output of the second vibrator 33 amplifies the signal by the receiving means 35 and then determines the reception of the ultrasonic wave at the signal level at a predetermined reception timing.

  For example, if the received wave reaches the next zero cross point ta after the received wave in FIG. 3A exceeds Vref, the time measuring means is determined at the time when the reception of the ultrasonic wave is determined (here, the ta point). The operation of 39 is stopped, and the flow velocity is obtained from the time information t by (Equation 1).

  Here, the measurement time obtained from the time measuring means 39 is t, the effective distance in the flow direction between the ultrasonic transducers is L, the accuracy is φ, the sound velocity is c, and the flow velocity of the fluid to be measured is v.

v = (1 / cosφ) * (L / t) −c (Formula 1)
The receiving means 35 is usually configured to compare the reference voltage and the received signal by a comparator.

  Further, the transmission and reception directions of the first ultrasonic transducer 32 and the second ultrasonic transducer 33 are switched, and the respective propagation times of the fluid under measurement from upstream to downstream and from downstream to upstream are measured. The speed v can be obtained from Equations 2, 3, and 4).

  Here, the measurement time from upstream to downstream is t1, and the measurement time from downstream to upstream is t2.

t1 = L / (c + v * cosφ) (Formula 2)
t2 = L / (c−v * cos φ) (Formula 3)
v = (L / 2 * cos φ) * [(1 / t1) − (1 / t2)] (Formula 4)
According to this method, the flow rate can be measured without being affected by the change in the sound speed, and thus it is widely used for measuring the flow velocity, the flow rate, the distance, and the like. When the flow velocity v is obtained, the flow rate can be derived by multiplying it by the cross-sectional area of the flow path 31.

  Usually, before performing the receiving operation from this series of transmissions, the auto gain operation is performed in order to make the magnitude of the received wave constant to some extent.

  This operation will be described including the receiving means 35 of FIG. The receiving means 35 includes an amplifying means 35-1 for amplifying the signal of the ultrasonic transducer on the receiving side, an output of the amplifying means, a received wave determining means 36 for outputting a signal when the received wave signal reaches a certain level, and an amplifying means. There is a reception point detection means 37 for determining the zero cross point by the output of, and a reception wave maximum value determination means 43 for detecting the maximum value of the reception wave by the output of the amplification means.

  The received wave determining means 36 compares the trigger level setting means 36-1 for setting the trigger level for determining that the received wave has arrived, and the outputs of the trigger level determining means 36-1 and the amplifying means 35-1. Reception wave arrival comparison means 36-2 for sending a reception wave arrival signal.

  The reception point detecting means 37 compares the outputs of the zero reference means 37-1 for determining the zero cross point and the zero reference means 37-1 and the amplifying means 35-1 to send out a signal which becomes the zero cross point. Comparing means 37-2.

  The received wave determining means 43 is a first maximum value determining means 43-1 and a second maximum value determining means 43-2 for determining the maximum value of the received wave, and a determination value for switching the maximum value determining means. A switching means 43-3, and a received wave maximum value comparing means 43-4 for comparing the output signal from the judgment value switching means 43-3 with the output of the amplifying means 35-1 and sending out a received wave maximum value signal. .

  The operation of the auto gain is performed using the reception wave determination means 43. The control means 42 has an automatic gain adjustment means 42-1. First, the auto gain adjusting means 42-1 switches the determination switching means 43-3 to the second maximum value determining means 43-2 side.

  The second maximum value determination means 43-2 outputs VL in FIG. 3A as a voltage value. If the maximum value of the received wave is smaller than VL when the received wave is amplified by the amplifying unit 35-1 and reaches the received wave maximum value comparing unit 43-4, the output of the received wave maximum value comparing unit 43-4 does not change. For this reason, the auto gain adjusting means 42-1 outputs a signal so as to increase the amplification degree of the amplifying means 35-1. If the amplification is increased until the maximum value of the received wave becomes larger than VL, the signal of the output of the received wave maximum value comparing means 43-4 changes when the received wave reaches VL. As a result, the magnitude of the received wave can be made larger than a certain level.

  However, if the amplification degree of the received wave is too large, the waveform is distorted or the power of the receiving circuit is consumed excessively, which is inappropriate. For this reason, once the received signal exceeds VL, the automatic gain adjusting means 42-1 switches the determination switching means 43-3 to the first maximum value determining means 43-1 side. The first maximum value determining means outputs VH in FIG. 3A as a voltage value.

  If the maximum value of the received wave is smaller than VH when the received wave is amplified by the amplifying unit 35-1 and reaches the received wave maximum value comparing unit 43-4, the output of the received wave maximum value comparing unit 43-4 does not change. In this case, the maximum value of the received signal is adjusted between VH and VL.

  However, if the auto gain adjusting means 42-1 increases the amplification degree of the amplifying means 35-1 too much, the maximum value of the received wave becomes larger than VH, and when the received wave arrives, the received wave maximum value comparing means 43-4 The signal changes when the output exceeds VH. Since this indicates that the maximum value of the received wave has become too large, the auto gain adjusting means 42-1 reduces the amplification degree of the amplifying means 35-1.

  By performing this operation, the auto gain operation adjusts the amplitude of the received wave so that the maximum value of the received wave always falls between VL and VH.

  After the size of the received waveform becomes constant to some extent by the auto gain operation, the reception point is determined using the received wave determination means 36. The output of the trigger level setting means 36-1 is set to Vref.

  The conventional operation will be described with reference to the timing chart of FIG. 4 and the received waveform of FIG. Measurement is started from the start signal at time t 0 by the control means 42 and the first ultrasonic transducer 32 is driven via the transmission means 34.

  The ultrasonic signal generated there propagates through the flow path, and the ultrasonic wave emitted from the first ultrasonic transducer 32 reaches the second ultrasonic transducer 33 at time t1. The received signal is amplified by the receiving means 35, and when the signal level reaches a predetermined value (Vref), the received wave determining means 36 determines that the received wave has arrived and outputs a signal.

  Based on this signal, the reception point detection means 37 starts to operate, outputs a signal with the first zero cross point after Vref as the reception point, and the time until this point is obtained by the time measurement means 39. The switching means 41 switches between transmission and reception to perform the same operation, and the flow rate calculation means 40 calculates the flow rate based on the difference between the time obtained by the time measuring means 39 and the time previously obtained.

Here, the point ta in FIG. 3A is after Vref. This is because the value of Vref is used for reception wave determination, and the subsequent zero cross point ta is used as the reception point. For example, if the signal wave is 100 kHz and the propagation time is around 100 μs, a zero cross point such as ta occurs every 5 μs. As can be seen from FIG. 3, the received wave reaches before Vref. As the signal before Vref can be used, the arrival time of the ultrasonic wave is less likely to include an uncertain time.

  Furthermore, if a signal 5 μs prior to the zero crossing point of ta that has been used as a reception point can be used, the zero crossing point can be determined 5 μs earlier, which is a half cycle. For example, the propagation time to ta is 100 μs. Measurement time can be shortened by 5%, and current consumption can be reduced.

  Let p be the zero reference that is the reference for the zero crossing point. If the offset occurs on the plus side, the zero reference becomes q and the zero crossing point arrives earlier than originally intended. On the contrary, when the offset occurs on the minus side, the zero reference becomes r and the zero cross point occurs later than originally intended. Similarly, when noise occurs and the received waveform shifts to the plus side, the zero cross point arrives later than the original ta point, and conversely, if the received waveform shifts to the minus side due to noise or the like, the zero cross point becomes less than the original ta point. It will arrive early. In this way, it is conceivable that the reception time accuracy deteriorates due to disturbances such as offset and noise in the reception point determination of only one point.

  Therefore, a method will be described in which a zero cross point before Vref is detected, and a reception point is obtained systematically even when a disturbance such as an offset occurs. It suffices to simply obtain the point at which the received wave reaches the zero cross point, for example, the point a in FIG. 3A, but in that case, Vref cannot be set. If the next b point close to it is a reception wave arrival point, Vref must be a broken line Vref-sub. In this case, since it is close to a zero signal, there is a possibility of erroneous detection by reacting with a change in waveform or a little noise when a flow rate flows.

  In order to avoid such a phenomenon and determine the arrival point of the received wave with higher accuracy than normal ta, two or more zero cross points are obtained continuously, and the average value is used to cancel the offset deviation. Can do.

  Therefore, a method of starting to detect the zero cross point before Vref will be described. It suffices to simply obtain the zero cross point from the point where the received wave arrives, for example, point a in FIG. 3A, but in that case, Vref cannot be set. If the next b point close to it is a reception wave arrival point, Vref must be a broken line Vref-sub.

  In this case, since it is close to a zero signal, there is a possibility of erroneous detection by reacting with a change in waveform or a little noise when a flow rate flows. In order to avoid such a phenomenon and determine the arrival point of the received wave in a shorter time than the normal ta, it is only necessary to detect at least two zero cross points before Vref and take the average value.

  Here, in detail, the zero crossing point before Vref is detected without using the reception wave determination means 36, and the average value is obtained as a method for obtaining the average value before the maximum value of the reception wave (reception wave falling between VH and VL). What is possible if the zero cross point is detected will be described below. By doing so, a configuration in which the reception wave determination means 36 is omitted can be realized.

  In order to realize this operation, measurement is started from the start signal at time t0 by the control means 42 and the first ultrasonic transducer 32 is driven via the transmission means 34. This will be described with reference to FIGS. The ultrasonic signal generated there propagates through the flow path, and the ultrasonic wave emitted from the first ultrasonic transducer 32 reaches the second ultrasonic transducer 33 at time t1.

  The received signal is amplified by the amplifying means 35-1 in the receiving means 35, and when the peak value of the signal reaches a predetermined value (between VH and VL), the received wave maximum value judging means 43 has reached the received wave. Is determined and a signal is output.

  For this reason, the reception point detection means 37 that outputs a signal when it falls within a predetermined range as a zero cross point, for example, within plus 1 mV or minus 1 mV, starts operation.

  If it does so, the reception point detection means 37 will output a signal when it will be the point a of FIG.3 (b), and the reception point memory | storage means 38-1 will memorize | store the output.

  If the value to be stored is the elapsed time from the time of transmission or the number of pulses having a specific fixed time width in which the elapsed time can be measured, the subsequent calculation is facilitated.

  Next, at the point b, the reception point storage means 37 outputs a signal and stores it in the reception point storage means 38-2. Similarly, the reception point data at the next point c is sequentially stored in the reception point storage means 38-3.

  In this case, when the reception point data is larger than the number of reception point storage means 38, the control unit 46 may control the order of writing so that the oldest reception points are overwritten sequentially.

  For example, as shown in FIG. 5 (a), after storing up to the reception point storage means 38-4, the next is to return to the reception point storage means 38-1 and overwrite.

  The peak value of the received wave enters between VH and VL, and the received wave maximum value determining means 43 determines that the received wave has arrived and outputs a signal. When this signal is received by the automatic gain adjusting means 42-2, the control means 42 prevents the reception point judging means 37 from outputting a signal at the subsequent zero cross point, or writes to the reception point storage means 38. Ban.

  By carrying out this operation, at least two zero cross points up to tx are stored, so that even two or more even numbers are used and the propagation time is obtained by the time measuring means 39 using the average value. .

  The offset will be described. For example, as shown in FIG. 3B, the occurrence of an offset may cause the conventional zero cross point to shift from the ta point to the tb and tc points.

  In that case, the Ta time as a reception wave arrival point becomes very unstable. When the average is obtained using two zero cross points, tl is obtained with respect to ta, tm with respect to tb, and tn with respect to tc. When an even number of zero cross points are used, it is possible to narrow down by averaging operation more than when two reception point fluctuations due to zero reference deviation are used.

  At that time, the control means 42 uses the reception point selection means 44, and when the reception wave maximum value determination means 43 detects that the ultrasonic wave has reached the receiving-side transducer, the time close to the original reception wave arrival point, for example, FIG. In order to go back to point a in (b), at least two values are selected as far back as possible from the reception point data stored last in the reception point data stored in the reception point storage means 38 for propagation time calculation. Then, it is sent to the time measuring means 39 for measuring the propagation time. The closer to point a in FIG. 5 (b), the more correctly received point can be detected without distortion of the received waveform, but it is susceptible to noise due to its small amplitude.

  Therefore, the point a is estimated by subtracting a predetermined fixed value from the average value as the propagation time using, for example, points b and c several points before the maximum amplitude value of the received wave. Is also possible.

  Since the receiving point storage means 38 is overwritten sequentially from the oldest one, the data next to the overwritten value is the oldest.

  The number of traces going back is determined in advance by experiments or the like, or if the data near the point a in FIG. It may be set to a predetermined value several points before.

  Further, the reception point data (propagation time) used by the time measuring means 39 is useful because it is possible to cancel the offset when two continuous points or even numbers are used. However, it is also possible to use an odd number from the rising edge or an odd number from the falling edge depending on the characteristics of the flow path and the characteristics of the vibrator.

  With this configuration, the propagation time of the ultrasonic wave propagating between the ultrasonic transducer on the upstream side and the ultrasonic transducer on the downstream side, that is, the arrival time of the ultrasonic wave is set to zero of the received ultrasonic wave before the trigger level. By using at least two cross point arrival times in succession, the average value can be obtained and measured.

  For this reason, even if an offset or the like is superimposed, it is possible to cancel the rising zero point and the falling zero point.

  The switching means 41 switches between transmission and reception to perform the same operation, and the flow rate calculation means 40 calculates the flow rate based on the difference between the time obtained by the time measuring means 39 and the time previously obtained. As a result, the circuit constituting Vref can be omitted.

  Up to now, the propagation time has been determined at ta in FIG. 5B, but the influence of offset or the like cannot be avoided. In this method, by using the average value of a plurality of zero cross points, an error included in the propagation time or arrival time of the measured ultrasonic wave can be reduced, and highly accurate flow measurement can be realized.

  Further, even in a state where the number of zero cross points increases, a plurality of zero cross points in the vicinity of the received wave maximum value judging means 43 can be reliably captured, and the number of receiving point storage means 38 is appropriately reduced to sequentially overwrite. By doing so, power saving operation becomes possible.

  In addition, the reception point storage unit 38 that stores the output of the reception point detection unit 37 consumes electric power to perform the storage operation, but it is often not known in advance from which point in time it may be energized.

  If it is turned on too early, power is wasted, and there is no point in energizing after passing the reception point.

  Therefore, as shown in FIG. 6, the power supply means 45 is provided in the control means 42 to perform power control. The timing will be described with reference to FIG.

  When measurement is started first, Ta is unknown. Although the approximate time can be estimated from the physical distance between the ultrasonic transducers 32 and 33, it is not certain.

  Therefore, the control unit 42 uses the power supply unit 45 to adjust the energization timing to the reception point storage unit 38. First, measurement is started from a start signal at time t 0 and the first ultrasonic transducer 32 is driven via the transmission unit 34. The ultrasonic signal generated there propagates through the flow path, and the ultrasonic wave emitted from the first ultrasonic transducer 32 reaches the second ultrasonic transducer 33 at time t1.

At the previous time t2, energization to the reception point storage means 38 is started using the power supply means 45.
t2 is a time sufficiently shorter than t1.

  Thus, the control means 42 has the power supply means 45 for energizing the reception point storage means 38 for storing the output of the reception point detection means 37 for a long time only for the first time. By preparing to store the output of the received wave detection means before the wave arrives, it is possible to reliably receive the received wave.

  In addition, the reception point is determined by the first time and the propagation time is obtained. In that case, it becomes easy to adjust the energization time after the second time.

  For example, in FIG. 7, at first, energization of the reception point storage unit 38 is started at t2, but it is at t1 that the ultrasonic wave has actually propagated and received. In the next measurement, since the propagation time does not change significantly, the power supply means 45 in the control means 42 can wait to be energized until t2 where the received signal has not reached yet near t1. . The third time uses the second propagation time, or uses the first and second moving averages to predict the propagation time, thereby making it possible to shorten the energization time as much as possible.

  In this way, the control means 42 adjusts the timing of the power supply means 45 so that the reception point storage means 38 for storing the output of the reception point detection means 37 is energized for the second time and thereafter, based on the previous value. Thus, by preparing for storing the output of the reception wave detection means immediately before the reception wave arrives, the reception wave can be reliably captured and a power saving operation can be performed.

  In this description, only the energization time of the reception point storage means 38 is adjusted. However, if the operation downstream from the reception means 35 for amplifying the reception signal does not continue to be unstable for a long time when the power is turned on, a set of them or particularly If the power supply means 45 adjusts the energization of the part that requires power, further power saving can be achieved.

  Further, it is assumed that the state from the zero cross point a to d in FIG. 5B is the same as that in the vicinity of t3 to t1 in FIG. In this case, the reception unit 35 operates before the reception signal arrives, and the reception point determination unit 37 also operates to send a signal for each of a, b, c, and d.

  In FIG. 8, the control means 42 counts the output signal of the reception point determination means 37, and when the number of times reaches a predetermined number of times, for example, twice, the trigger means 46 receives via the power supply means 45 when the reception point reaches the point b. Energization of the point storage means 38 is started. The energization time until tx when reception is confirmed can be further shortened.

  In this way, the control means 42 has the trigger means 46 that outputs a signal when the output of the reception point detection means 37 exceeds a predetermined number of times, and the power supply means 45 outputs the output of the reception point detection means 37 according to the output of the trigger means 46. By starting energization to the reception point storage means 38 for storing the number of zero cross points from there until a plurality of zero cross points are between VH and VL or a plurality of reception point storage means 38 prepared in advance. Remember only the number.

  Then, the propagation time is obtained using two consecutive zero cross point data. Thus, by confirming that the received wave has arrived reliably, and preparing to store the output of the received wave detecting means 37, the reliability is improved and a power saving operation by a shorter time operation becomes possible.

The control means 42 stops the power supply to the reception point storage means 38 via the power supply means 45 after the elapse of a predetermined time after the output of the reception point detection means 37 after the output of the reception wave maximum value determination means 43. Thus, the operation of measuring and storing the extra zero cross point can be stopped, and the power saving operation can be realized.

  Further, the zero cross point in FIG. 5B has been generated with a period of almost half of the transmission frequency if noise is not superimposed on the received wave.

  However, when a fluid actually flows in the flow path, something is operating downstream by the fluid. A spike-like signal may be superimposed on the received wave due to this operation or other external noise. In this case, if the point where the noise crosses zero is taken as the reception point, the calculation of the propagation time will be greatly shifted.

  In order to prevent this, as shown in FIG. 9, the control means 42 is provided with a time verification means 47.

  The operation when the time verification means 47 is used will be described. First, similarly to FIG. 5B, when reception of the zero cross point starts, the reception point detection means 37 outputs a signal, and the reception point storage means 38-1 stores the output.

  If the value to be stored is the elapsed time from the time of transmission or the number of pulses having a specific fixed time width in which the elapsed time can be measured, the subsequent calculation is facilitated. Next, when the point b is reached, the reception point storage means 37 outputs a signal, and the reception point storage means 38-2 stores the reception point data. After storing the points c and d and the point tx, the received signal enters between VH and VL.

  At this time, the received wave maximum value judging means 43 outputs a signal for the first time. When a signal is output from the received wave maximum value determining means 43, the control means prevents the receiving point judging means 37 from outputting a signal at the subsequent zero cross point, or writes to the receiving point storage means 38. Is prohibited.

  Then, the time of the next zero cross point ta is sent directly to the time verification means 47 of the control means without going through the reception point storage means 38. The time verification unit 47 sequentially obtains the difference between the value of the reception point data in the reception point storage unit 38 and the value of ta.

  If this difference is within a predetermined range, it is determined that the data at points a, b, c, and tx are not due to noise, and it is determined that the data can be adopted as a flow rate calculation. Then, the flow rate is calculated using two or more zero cross points among them.

  For example, if the transmission frequency is 100 kHz, the half of the period is 5 μs. Therefore, if tx-ta is within a predetermined vicinity of 5 μs, it is determined that tx is an effective reception point. Similarly, if a-ta is within the vicinity of an integer multiple of 5 μs, it is determined as an effective reception point. The same determination is made for points b, c, and d.

  As described above, the control means 42 has the time verification means 47 for calculating the difference between the output of the reception point detection means 37 after the output of the reception wave maximum value determination means 43 and the value of the reception point storage means 38, and the time verification. If the value of the means 47 is within a predetermined value, it is possible to prevent erroneous detection of the zero cross point due to noise or the like by enabling the measurement, and to improve reliability by selecting an accurate zero cross point. Is possible.

  If the flow path and transmission method are known in advance, the wave number that becomes the maximum value point of the received wave is known in advance, so the zero crossing point immediately before that is used as having transmitted the same propagation distance even if switched upstream and downstream It is possible.

  Further, after the received signal enters between VH and VL before the zero crossing point tx in FIG. 3B, the circuit subsequent to the receiving means 35 does not need to operate other than the time measuring means 39 and the flow rate calculating means 40.

  Therefore, when the received wave maximum value determining means 43 detects that the received wave has entered between VH and VL, the control means 42 stops energization to the receiving point storage means 38 and performs a power saving operation. It is possible to stop the energization operation of the receiver circuit that is not present.

  The time of stopping may be immediately after entering between VH and VL, or noise may be generated by the signal at the time of energization stop, and the operation of the timing means 39 and the like may not be adversely affected. The energization may be stopped after detecting ta.

  In this way, the control means 42 supplies power to the reception point storage means 38 via the power supply means 45 after the elapse of a predetermined time after the output of the reception point detection means 37 after the output of the reception wave maximum value determination means 43. By stopping, it is possible to stop the operation of measuring and storing an extra zero cross point, and to realize a power saving operation.

  Although it has been described in FIG. 3B that the average value Ta ′ of the tx and ta2 points can be determined as the reception arrival point, it will be described because it may seem different from the conventional arrival point Ta.

  The original reception arrival point is point a in FIG. As described above, it is very difficult to detect only this point.

  Therefore, the time Ta to ta is obtained, and the time to point a is obtained by subtracting a predetermined constant.

  Therefore, when tx and ta are used, the time to the reception arrival point a can be calculated by adjusting a predetermined constant by a value of a quarter period (ta-tx) / 2 of the received wave. is there. Since Ta 'has less error than Ta, the time to a can be obtained stably. This explanation uses two zero cross points, but the case of an even number of zero cross points is similarly stable.

(Embodiment 2)
The difference from the first embodiment is that the signals of the received wave maximum value determining means 43 and the receiving means 35 that output signals when the signals of the vibrators 32 and 33, the transmitting means 34, the receiving means 35, and the receiving means 35 reach the maximum values are obtained. Receiving point detecting means 37 that outputs a signal when it falls within a predetermined range, receiving point storing means 38 that stores the output of the receiving point detecting means 37, and the signal transmitted from the receiving point storing means 38 that has propagated between the transducers. At least one of a time measuring means 39 for measuring the propagation time of the sound wave signal, a flow rate calculating means 40 for calculating a flow rate based on the time difference of the time measuring means 39, a switching means 41 for switching between transmission and reception, and a receiving point selecting means 44. That is, a storage medium 48 having a program for causing a computer to function to ensure the operation of the control means 42 to be controlled is used.

  In order to perform the operation of the control means 42 shown in the first embodiment, the operation of the reception point storage means for obtaining tx and the energization method are obtained in advance by experiments or the like, the secular change, the temperature change, the stability of the system Correlation such as operation timing with respect to the degree is obtained, and software is stored in the storage medium 48 as a program.

  Usually, it is convenient to use an electrically writable memory such as a microcomputer memory or a flash memory. Since the direction of transmission / reception changes due to the operation of the switching means 41, the number of condition settings and the like increases, but this can be easily realized by adjusting this by operation by a computer.

As described above, when the operation of the control means 42 can be performed by a program, it is possible to easily set, change and adjust the measurement interval of the correction coefficient for the flow rate calculation, and to flexibly cope with aging. Therefore, the accuracy of flow velocity or flow rate measurement can be improved more flexibly.

  In the present embodiment, operations other than the control means 42 may be performed by a program such as a microcomputer.

  As a result, it has a configuration that has a program for causing the computer to function as a control means, and can easily set and change the operation of the measurement method, and can flexibly cope with aging, etc. Improvements can be made.

  The flow velocity or flow rate measuring device of the present invention overwrites and stores two or more zero cross points, and stops the operation when there is an output signal in the received wave maximum value judging means indicating that the received wave has surely arrived. To do.

  As a result, the trigger point by the received wave determining means is set at a portion where the amplitude of the received waveform is relatively large, and the trigger is stably operated, and the average of two or more optimum zero cross points before that is averaged. Since the value can be used for the propagation time measurement, it is possible to measure the propagation time with few errors and to realize the power saving operation by shortening the measurement time.

31 flow path 32 first vibrator 33 second vibrator 34 transmission means 35 reception means 36 reception wave determination means 37 reception point detection means 38 reception point storage means 39 timing means 40 flow rate calculation means 42 control means 43 maximum received wave Value determination means 44 Reception point selection means 47 Time verification means

Claims (7)

A pair of transducers arranged in a flow path through which the fluid to be measured flows and that transmits and receives ultrasonic waves; a transmission unit that drives one transducer; and a reception unit that converts an output signal of the other reception-side transducer into an electrical signal; Receiving wave maximum value determining means for detecting the maximum value of the signal of the receiving means and outputting the signal, receiving point detecting means for outputting the signal when the signal of the receiving means falls within a predetermined range, and output of the receiving point detecting means At least two or more reception point storage means for storing, a time measurement means for measuring the propagation time of an ultrasonic signal propagated between the transducers using a signal of the reception point storage means, and a time difference between the time measurement means Control for controlling at least one of flow rate calculation means for calculating a flow rate based on the transmission means, reception means, received wave maximum value determination means, reception point detection means, reception point storage means, timing means, and flow rate calculation means Means and The control means has a reception point selection means for selecting a value of the reception point storage means that has been reversed by a predetermined number based on the output of the reception wave maximum value determination means, for calculating the propagation time, and the reception point storage means A fluid flow measuring device for overwriting and updating until there is an output signal of the received wave maximum value judging means. 2. The fluid flow measuring device according to claim 1, wherein the control means has power supply means for energizing the reception point storage means for storing the output of the reception point detection means for a long time only for the first time. 2. The fluid flow according to claim 1, wherein the control means adjusts the timing of the power supply means so that the reception point storage means for storing the output of the reception point detection means is energized for the second time and thereafter, based on the previous value. Measuring device. The control means includes trigger means for outputting a signal when the output of the reception point detection means exceeds a predetermined number of times, and the power supply means supplies the reception point storage means for storing the output of the reception point detection means by the output of the trigger means. The fluid flow measuring device according to claim 1, wherein energization is started. 2. The fluid flow measuring device according to claim 1, wherein the control means has accumulation control means for adjusting the reception point storage means so that the oldest data is sequentially overwritten. The control means has time verification means for calculating a difference between the value of the reception point storage means and the output of the reception wave determination means which is reversed by a predetermined number based on the output of the reception wave maximum value determination means, and the time verification means The fluid flow measuring device according to claim 1, wherein the measurement is valid if the value of is within a predetermined value. The control means stops the power supply to the reception point storage means via the power supply means after the elapse of a predetermined time after the output of the reception point detection means after the output of the reception wave maximum value determination means. Flow measuring device.

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