JP4646107B2 - Ultrasonic flow meter - Google Patents

Description

The present invention relates to an ultrasonic flowmeter, and more particularly to an ultrasonic flowmeter that measures the flow velocity and flow rate of a fluid using ultrasonic waves. More specifically, the present invention relates to an ultrasonic flow meter used for management and control of fluid flow rate in the fields of a gas meter, a water meter, a gas flow meter, and the like.

2. Description of the Related Art Conventionally, as a flow meter that measures the flow rate of a fluid such as city gas, LPG, and water, an ultrasonic flow meter that measures flow velocity and flow rate using ultrasonic waves is known. As the measurement principle, the “propagation time difference method” is generally used. This is because a pair of ultrasonic transducers are provided on the upper and lower sides of the fluid flow direction of the flow path, and the ultrasonic waves emitted from the ultrasonic transducer on the upper side of the flow direction are switched by alternately switching the transmission and reception of ultrasonic waves. Time to reach the ultrasonic transducer on the lower side (hereinafter referred to as forward propagation time) and until the ultrasonic wave emitted from the ultrasonic transducer on the lower side in the flow direction reaches the ultrasonic transducer on the upper side in the flow direction This is a method of measuring the time (hereinafter referred to as the reverse propagation time) and obtaining the flow rate by multiplying the average flow velocity of the fluid flowing through the flow path by the difference between the two and the cross-sectional area of the flow velocity by the average flow speed. (For example, refer to Patent Document 1).

Now, T _{j is} the forward propagation time, T _g is the backward propagation time, C is the velocity of sound in the static fluid, V is the flow velocity of the measurement fluid, and L is the propagation distance of ultrasonic waves (distance between a pair of ultrasonic transducers). Then, the following formulas (1) and (2) are obtained.

T _j = L / (C + V) (1)
T _g = L / (C−V) (2)

From equations (1) and (2), the flow velocity V is obtained as in the following equation (3).

V = L {(1 / T _j ) − (1 / T _g )} / 2 (3)

Then, the flow rate Q1 is obtained by the following equation (4) using a correction coefficient H considering the cross-sectional area S of the flow path, the measurement time interval, and the like.

Q1 = V · S · H (4)

If the integrated flow rate Q0 up to the previous time is used, the integrated flow rate Q can be obtained by Q = Q0 + Q1.
Japanese Patent No. 2828615

Conventionally, this type of ultrasonic flowmeter measures the forward propagation time and the backward propagation time between a pair of ultrasonic transducers with the fluid shut-off valve closed (flow rate 0 state) at the time of factory shipment. Based on whether or not the same propagation time can be obtained, it is detected whether or not calibration (calibration) needs to be performed, and calibration is performed when necessary.

However, it is known that an ultrasonic transducer has a delay characteristic at the time of transmission / reception, that is, a delay characteristic fluctuation (drift) with time of an electro-mechanical / mechanical-electrical conversion characteristic. In other words, ultrasonic transducers are composed of piezoelectric ceramics, acoustic matching layers, supports, dampers, etc. joined with adhesives, so that the adhesives deteriorate over time, and piezoelectric ceramics and acoustic matching layers are used. When it deteriorates, the delay characteristic at the time of transmission / reception deteriorates.

For this reason, when the time has elapsed since the ultrasonic flowmeter was shipped from the factory and installed in the field, the delay characteristics of the pair of ultrasonic transducers fluctuated due to aging, and the delay characteristics of each pair deviated from the specified range. As a result, a delay characteristic fluctuation (drift) occurred over time. In particular, when the influence of the delay characteristic difference between a pair of ultrasonic transducers cannot be ignored, as in the case of measuring a minute flow rate, the amount of delay characteristic deviation between the pair of ultrasonic transducers must be corrected by some means. However, conventionally, there has been no good technique for sufficiently correcting the influence of the variation in delay characteristics over time, and therefore, correction for the variation in delay characteristics of the pair of ultrasonic transducers has not been performed. As a result, there has been a concern that the measurement accuracy is lowered and the reliability of the ultrasonic flowmeter is lowered.

Therefore, the problem of the present invention is that the change in the measurement frequency does not affect the flow velocity, but affects the propagation time of the ultrasonic wave, and the fluid flow is not completely stopped (there is a flow rate). Another object is to provide an ultrasonic flowmeter capable of correcting the aging delay characteristic fluctuation of an ultrasonic transducer by measuring the forward propagation time and the backward propagation time by changing the measurement frequency. .

Another object of the present invention is to provide an ultrasonic flowmeter that automatically performs a correction inspection every predetermined period after shipment from the factory, that is, on the field.

Furthermore, an object of the present invention is to change the measurement frequency, determine whether correction is necessary based on the forward propagation time difference and the reverse propagation time difference between the measurement frequencies, and perform correction when necessary. It is in providing an ultrasonic flowmeter.

Furthermore, an object of the present invention is to provide an ultrasonic flowmeter capable of performing high-precision correction, having extremely high measurement accuracy in the long term and capable of significantly improving the reliability in measurement. It is in.

Means for Solving the Problems and Effects of the Invention

The ultrasonic flowmeter of the present invention is provided with a pair of ultrasonic transducers on the upper and lower sides of the fluid flow direction of the flow path, and is alternately emitted and sent from the ultrasonic transducer on the upper side in the flow direction. Until the ultrasonic wave reaches the ultrasonic transducer on the lower side in the flow direction and until the ultrasonic wave emitted from the ultrasonic transducer on the lower side in the flow direction reaches the ultrasonic transducer on the upper side in the flow direction. In the ultrasonic flowmeter, the average flow velocity of the fluid flowing through the flow path is calculated from the difference between the two, and the flow rate is obtained by multiplying the average flow velocity by the cross-sectional area of the flow path . When an ultrasonic transducer is installed, a plurality of measurement frequencies are determined, and a forward propagation time and a reverse direction between the pair of ultrasonic transducers. The transport time is measured, the difference in forward propagation time between the plurality of measurement frequencies and the difference in reverse propagation time between the plurality of measurement frequencies are obtained, and the initial forward propagation time difference and the initial reverse direction are obtained. frequency storing transit time - the propagation time difference storage unit, at regular intervals, by the plurality of measurement frequencies, performs forward propagation time and the measurement of the backward propagation time between the ultrasonic transducers, said plurality of measurement frequencies the forward propagation time stored in the propagation time difference storage unit - the frequency difference of the forward propagation time, and obtains a difference between the backward propagation time between said plurality of measurement frequencies, and its forward propagation time difference between the initial forward transit time at temperatures were measured, and its backward propagation time difference between the frequency - the reverse Den stored in transit time storage unit Frequency comparing initial backward propagation time difference at the measured temperature time - transit time and a comparison unit, the frequency - Comparison of the propagation time difference comparison unit results based rather initial forward transit time and initial backward propagating By changing the normal measurement correction value to a negative value or a positive value according to the amount of deviation from the time difference, the normal measurement value by the ultrasonic transducer is changed according to the change in delay characteristics by the normal measurement correction value. was carried out, delay characteristics of the pair of ultrasonic transducers, regardless of the flow velocity of the fluid being measured, by utilizing the change by the measurement frequency, the flow rate correction for aging delay characteristic variation of the pair of ultrasonic transducers It is characterized by that. According to the ultrasonic flowmeter of the present invention , the initial forward propagation time difference and the initial reverse propagation time difference between the measurement frequencies are stored in advance, and the forward propagation time and the reverse propagation time at a plurality of measurement frequencies are set for each fixed period. The difference between the forward propagation time and the reverse propagation time between the measured frequencies is obtained and compared with the initial forward propagation time difference and the initial reverse propagation time difference between the same measurement frequencies stored in advance. Thus, the variation of the delay characteristics with time of the pair of ultrasonic transducers is corrected, so that it is possible to provide an ultrasonic flowmeter with less measurement errors by periodically correcting the delay characteristics fluctuation with time.

Ultrasonic flow meter of the present invention, prior Symbol ultrasonic transducer, with a low Q type, little unwanted spurious, be formed by ultrasonic transducer having a single resonance characteristic, using the frequency band of the ultrasonic transducer It is characterized by doing. According to the ultrasonic flowmeter of the present invention , the measurement fluid becomes a fluid with extremely low acoustic impedance such as air or gas (difference of 6 digits or more compared to the acoustic matching layer of the ultrasonic transducer) due to a somewhat low Q value. On the other hand, ultrasonic transmission / reception measurement with a relatively small current consumption is possible. Also, in order to cope with a wide flow range, since it has a single resonance characteristic with less unwanted spurious in the frequency band and the Q value is low to some extent, the frequency in the frequency band is used, and this frequency is As a result of transmitting the ultrasonic wave as the measurement frequency, the characteristic that becomes the reception frequency according to the measurement frequency can be secured (the wide flow rate range can be measured, and the reception wave becomes the frequency according to the measurement frequency, so the measurement accuracy is improved. ). Furthermore, the Q value is low to some extent, so that the reception characteristics corresponding to the measurement frequency can be obtained with as few drive pulses as possible, and the frequency tracking characteristics of the received waves are improved. As a result, the measurement accuracy is improved and the current consumption is compared. Less.

Ultrasonic flow meter of the present invention, compensation during inspection of the measurement frequency, the frequency of the resonance point frequency or near the frequency band of the ultrasonic transducer, the frequency away from the resonance point frequency within the frequency band And the ultrasonic transducer is driven by drive pulses of these frequencies, and the forward propagation time and the backward propagation time are measured. According to the ultrasonic flowmeter of the present invention , since the ultrasonic transducer has a low Q value, one of the measurement frequencies measured during the correction inspection is set to the resonance point frequency or a frequency near the resonance point frequency, so that The measurement frequency becomes a stable reference with little influence from the measurement frequency of the acoustic transducer and the environment, and the frequency tracking of the received wave can be obtained. In addition, by making the remaining measurement frequency near the boundary of the ultrasonic transducer frequency band away from the resonance point frequency, it becomes difficult to be affected by the resonance point frequency, and the received wave is a frequency according to the measurement frequency. can get.

Ultrasonic flow meter of the present invention, transmission in forced vibration by controlled burst drive signal wave drive pulse number N, the maximum N + 2 to 3 within the number of received pulses to the drive pulse number N of the transmission wave, if possible, A zero cross point of the number of received pulses within the maximum N is set as a detection point of a received wave. According to the ultrasonic flowmeter of the present invention, the ultrasonic transducer is corrected by giving a drive that can be a forced vibration depending on the number of drive pulses N of the transmission wave, and setting the reception area having a high dependency as a detection point. Measurement accuracy can be improved.

Ultrasonic flow meter of the present invention is characterized by changing the detection point of the driving pulse number and received wave of the transmission wave in accordance with the total measurement frequency. According to the ultrasonic flowmeter of the present invention , it is possible to prevent a decrease in measurement accuracy due to attenuation of the measurement frequency by changing the number of drive pulses of the transmission wave and the detection point of the reception wave according to the measurement frequency. Become.

Ultrasonic flow meter of the present invention, it is Ru is assumed to be adjusted and stored detection point of the driving pulse number and received wave of the transmission wave in accordance with the total measurement frequency. According to such an ultrasonic flow meter, since the flow rate correction is performed for the delay characteristic variation over time from the initial forward propagation time difference and the initial reverse propagation time difference, the initial state is maintained in the environment where the ultrasonic flow meter is installed. By performing learning (acquiring an initial forward propagation time difference and an initial reverse propagation time difference), it is possible to further improve the correction accuracy.

Ultrasonic flow meter of the present invention, the ultrasonic flow meter installed in the field, at a certain period, when it becomes a predetermined temperature, yet are sure to allow flow less time as possible measurement fluid, the measurement frequency it Ru is assumed to perform measurement of the forward propagation time and the backward propagation time for. According to the ultrasonic flowmeter of the present invention , it is possible to improve the correction accuracy by performing the correction inspection in a period in which the flow rate fluctuation is small.

Ultrasonic flow meter of the present invention, while made different measurement frequency measurement of the forward propagation time in the multiple measurement frequencies continuously performed, measures the measurement of the backward propagation time at a plurality of measurement frequencies thereafter It is characterized in that it is carried out continuously with different frequencies. According to the ultrasonic flowmeter of the present invention , forward / reverse propagation time measurement at the same measurement frequency and reverse propagation time measurement are performed in a forward / reverse manner compared to a case where measurement is performed continuously with different measurement frequencies. Since switching does not need to be repeated frequently, the measurement time interval is shortened accordingly, the influence of flow rate fluctuations can be reduced, and measurement correction can be performed with high accuracy.

Ultrasonic flow meter of the present invention applies a drive pulse for the forward propagation time or back propagation time measurement in Oh Ru measurement frequency, before the received pulse propagated through corresponding thereto, the following A drive pulse for measuring the forward propagation time or the backward propagation time at the measurement frequency is applied. According to the ultrasonic flowmeter of the present invention , a drive pulse of a certain measurement frequency is applied, and a drive pulse of the next measurement frequency is applied before the corresponding received pulse propagates. The measurement time interval between the measurement of forward propagation time or reverse propagation time at and the measurement of forward propagation time or reverse propagation time at the next measurement frequency is shortened, and a drive pulse of a certain measurement frequency is applied, Compared to applying the drive pulse of the next measurement frequency after waiting for the reception pulse corresponding to it to propagate, the measurement time interval becomes shorter, the influence of flow rate fluctuations can be further reduced, and higher Accurate measurement correction is possible.

The ultrasonic flowmeter related to the present invention is provided with a pair of ultrasonic transducers on the upper and lower sides of the fluid flow direction of the flow path, and alternately switching the transmission and reception of ultrasonic waves from the ultrasonic transducer on the upper side in the flow direction. The forward propagation time until the emitted ultrasonic wave reaches the ultrasonic transducer on the lower side in the flow direction, and the ultrasonic wave emitted from the ultrasonic transducer on the lower side in the flow direction reaches the ultrasonic transducer on the upper side in the flow direction. In an ultrasonic flowmeter that measures the reverse propagation time until the flow rate is obtained, finds the average flow velocity of the fluid flowing through the flow path from the difference between the two, and obtains the flow rate by multiplying the average flow velocity by the cross-sectional area of the flow passage. A frequency-propagation time difference storage unit that stores in advance an initial forward propagation time difference and an initial reverse propagation time difference between measurement frequencies at different temperatures, and a measurement at each measurement frequency. The forward propagation time difference and the backward propagation time difference between the measured frequencies calculated from the measured forward propagation time and backward propagation time are calculated between the measured frequencies at the current temperature stored in the frequency-propagation time difference storage unit. Frequency-propagation time difference comparison unit that compares initial forward propagation time difference and initial reverse propagation time difference, and drive pulse number management that variably controls the number of drive pulses applied to a pair of ultrasonic transducers according to the measurement frequency And the number of drive pulses of the transmission wave by the forced vibration by the burst driving in which the drive wave number N of the transmission wave is not measured in an area where the dependence by the forced vibration is low due to the inherent response of the ultrasonic transducer on the receiving side The number of received pulses within a maximum of N + 2 to 3 with respect to N, preferably the zero cross point of the maximum number of received pulses within N is detected. When the number of received pulse number management units and the ultrasonic flowmeter installed in the field reach a predetermined temperature at regular intervals, the timing of the measurement fluid flow rate is as low as possible. And an inspection period determination unit that determines whether or not it is an inspection period, and a characteristic variation determination / correction unit that determines a time-dependent delay characteristic variation of a pair of ultrasonic transducers and changes a normal measurement correction value. but Ru is assumed. According to such an ultrasonic flowmeter, the initial forward propagation time difference and the initial reverse propagation time difference between the measurement frequencies are stored in advance, and the forward propagation time and the reverse propagation time at a plurality of measurement frequencies are measured every predetermined period. Then, the forward propagation time difference and the reverse propagation time difference between the measurement frequencies are obtained and compared with the initial forward propagation time difference and the initial reverse propagation time difference between the measurement frequencies stored in advance, and based on the comparison result. Since the aging delay characteristic fluctuation of the pair of ultrasonic transducers is corrected, the aging delay characteristic fluctuation is periodically corrected, and an ultrasonic flowmeter with little measurement error can be provided.

By using the fact that the delay characteristics fluctuation (transmission delay characteristic fluctuation, reception delay characteristic fluctuation, etc.) of a pair of ultrasonic transducers changes with the measurement frequency regardless of the flow velocity of the measurement fluid, For example, every year, the forward propagation time and the backward propagation time between the ultrasonic transducers are measured at a plurality of temperatures at a plurality of measurement frequencies, and the forward propagation time difference and the backward propagation time difference between the measurement frequencies are measured. Is compared with the initial forward propagation time difference and the initial reverse propagation time difference between the measurement frequencies at the same temperature stored in advance, and the flow rate correction for the delay characteristic variation with time is performed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram illustrating the configuration of the ultrasonic flowmeter according to the first embodiment of the present invention. The ultrasonic flowmeter according to the first embodiment includes a pair of ultrasonic transducers 1a and 1b, a transmission / reception switching unit 2, a drive unit 3, a frequency variable unit 4, an amplification unit 5, a reception unit 6, and a propagation. The time measuring unit 7, the microcomputer 8, and the thermometer 9 constitute the main part.

The pair of ultrasonic transducers 1a and 1b has a low Q value (Q = 2 to 10, preferably Q = 2.5 to 5) indicating mechanical resonance sharpness, and has a single resonance characteristic with less unnecessary spurious. The frequency band of the ultrasonic transducer is used. As a result, stable measurement frequency and delay characteristics can be measured, and more accurate delay characteristic fluctuations can be corrected over time.

Hereinafter, as shown in FIG. 2, it is assumed that the measurement frequency f ₀ is the resonance frequency in the frequency band of the ultrasonic transducers 1a and 1b or a frequency in the vicinity thereof, and the measurement frequency f ₁ is the ultrasonic transducer 1a, within the frequency band 1b, the assumed to be a frequency that is displaced relative to the measuring frequency f _0. The correlation between delay characteristics due to unnecessary vibration modes is impaired in the ability to receive a received wave, which is a stable ultrasonic pulse proportional to the measurement frequencies f ₁ and f ₀ , and the responsiveness in the frequency band to be used. The ultrasonic transducers 1a and 1b having a single resonance characteristic with a low Q type and a small unnecessary spurious in the frequency band realize a stable measurement frequency and delay characteristic, and the measurement frequencies f ₁ and f ensuring the forward transit time between _{0 Δ j (f 1, f} 0) and reverse transit time _{Δ g (f 1, f 0} ).

The transmission / reception switching unit 2 includes a transmission unit 21 and a reception unit 22, and causes the ultrasonic transducers 1a and 1b to emit ultrasonic waves from the ultrasonic transducer 1a on the upper side in the flow direction to lower the flow direction. The control from the microcomputer 8 switches between reception by the ultrasonic transducer 1b on the side and emission of ultrasonic waves from the ultrasonic transducer 1b on the lower side in the flow direction and reception by the ultrasonic transducer 1a on the upper side in the flow direction. .

The drive unit 3 supervises the drive signal of the drive pulse number N controlled by the microcomputer 8 at the measurement frequency controlled by the frequency variable unit 4 via the transmission / reception switching unit 2 as an applied voltage for emitting ultrasonic waves. Applied to the sonic transducers 1a, 1b. In addition, the drive unit 3 transmits a propagation start signal to the propagation time measurement unit 7 to start measurement of the propagation time.

The frequency variable unit 4 changes the frequency of the drive signal applied to the ultrasonic transducers 1a and 1b to the determined measurement frequencies f ₁ and f ₀ when performing a correction inspection under the control of the microcomputer 8.

The amplifier 5 amplifies the voltage of the received waves received by the ultrasonic transducers 1a and 1b (an AGC (Automatic Gain Control) amplifier is desirable).

Under the control of the microcomputer 8, the reception unit 6 transmits the reception signal voltage amplified by the amplification unit 5 to the propagation time measurement unit 7 to measure the propagation time. Further, the receiving unit 6 controls the detection point of the received wave to be the optimum detection point by the control from the microcomputer 8.

The propagation time measuring unit 7 measures the time from the propagation start signal to the received signal and transmits it to the microcomputer 8 as the propagation time.

The microcomputer 8 includes a frequency-propagation time difference storage unit 81, a frequency-propagation time difference comparison unit 82, a drive pulse number management unit 83, a received pulse number management unit 84, an inspection period determination unit 85, a characteristic variation determination / And a correction unit 86.

The frequency-propagation time difference storage unit 81 has an initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and an initial inverse between the measurement frequencies f ₁ , f _{0 at} a plurality of temperatures t ₁ , t ₂ , t _{3 ,.} The direction propagation time difference Δ _g0 (f ₁ , f ₀ ) is stored in advance. Specifically, as shown in FIGS. 2 and 3, the initial forward propagation time by measuring the frequency _{f 1 T} j0 _{(f 1)} and the measurement frequency _f initial forward propagation time _T j0 _{(f 0)} at ₀ the initial forward transit time delta _j0 is the difference _(f 1, _{f 0),} the measurement frequency initial backward propagation time in the _{f 1 T} g0 _{(f 1)} and the initial back propagation time of the measurement frequency _{f 0 T g0} An initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ), which is a difference from (f ₀ ), is stored in advance for each of a plurality of temperatures t ₁ , t ₂ , t ₃ ,.

Δ _j0 (f ₁ , f ₀ ) = T _j0 (f ₁ ) −T _j0 (f ₀ ),
Δ _g0 (f ₁ , f ₀ ) = T _g0 (f ₁ ) −T _g0 (f ₀ )

Note that the initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and the initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ are, for example, factory shipment or field installation. Sometimes it is stored in the frequency-propagation time difference storage unit 81 by the microcomputer 8.

Now, ultrasonic transducers 1a, the reference forward propagation time between 1b and _{T j,} the frequency dependent forward propagation time term at the measurement frequency _{f 0 τ j0 (f 0)} , frequency-dependent order of the measurement frequencies _{f 1 Assuming} that the direction propagation time term is τ _j0 (f ₁ ), the forward propagation time T _j0 (f ₀ ) at the measurement frequency f ₀ is the reference forward propagation time T _j and the frequency-dependent forward propagation time term τ _j0 ( As the sum of f ₀ ), the forward propagation time T _j0 (f ₁ ) at the measurement frequency f ₁ is the sum of the reference forward propagation time T _j and the frequency-dependent forward propagation time term τ _j0 (f ₁ ). Represented as:

T _j0 (f ₀ ) = T _j + τ _j0 (f ₀ ),
T _j0 (f ₁ ) = T _j + τ _j0 (f ₁ )

The ultrasonic transducer 1a, the reference backward propagation time between 1b and _{T g, (0 f) τ} g0 frequency dependence backward propagation time section at the measurement frequency _{f 0,} a frequency-dependent reverse at the measurement frequency _{f 1} If the direction propagation time term is τ _g0 (f ₁ ), the backward propagation time T _g0 (f ₀ ) at the measurement frequency f ₀ is the reference backward propagation time T _g and the frequency dependent backward propagation time term τ _g0 ( As the sum of f ₀ ), the backward propagation time T _g0 (f ₁ ) at the measurement frequency f ₁ is the sum of the reference backward propagation time T _g and the frequency-dependent backward propagation time term τ _g0 (f ₁ ). Represented as:

T _g0 (f ₀ ) = T _g + τ _g0 (f ₀ ),
T _g0 (f ₁ ) = T _g + τ _g0 (f ₁ )

Therefore, the initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and the initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ stored in the frequency-propagation time difference storage unit 81. ) Is as follows.

Δ _j0 (f ₁ , f ₀ ) = T _j0 (f ₁ ) −T _j0 (f ₀ ) = τ _j0 (f ₁ ) _{−τ j0} (f ₀ ),
Δ _g0 (f ₁ , f ₀ ) = T _g0 (f ₁ ) −T _g0 (f ₀ ) = τ _g0 (f ₁ ) −τ _g0 (f ₀ )

The frequency-propagation time difference comparison unit 82 includes forward propagation times T _j0 (f ₁ ), T _j0 (f ₀ ) and backward propagation times T _g0 (f ₁ ), which are measured at the measurement frequencies f ₁ and f ₀ . A forward propagation time difference Δ _j (f ₁ , f ₀ ) and a backward propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ calculated from T _g0 (f ₀ ) are _expressed as frequency − Initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and initial reverse direction between the measured frequencies f ₁ and f ₀ at the current temperature (temperature when measured) t ₁ stored in the propagation time difference storage unit 81 Compared with the propagation time difference Δ _g0 (f ₁ , f ₀ ).

The drive pulse number management unit 83 performs change control on the drive pulse number N of the drive signal applied to the ultrasonic transducers 1a and 1b according to the measurement frequency. As a result, the reception frequency characteristics of the ultrasonic transducers 1a and 1b corresponding to the measurement frequency are ensured, and the propagation time can be measured with a small number of drive pulses N. Therefore, the power consumption can be reduced while improving the measurement accuracy. It becomes possible.

The reception pulse number management unit 84 does not perform measurement in the area where the dependence due to forced vibration is low due to the inherent responsiveness of the ultrasonic transducers 1a and 1b on the reception side, and the burst driving in which the drive pulse number N of the transmission wave is controlled. As a result of the forced vibration, the number of received pulses within a maximum of N + 2 to 3 with respect to the number of drive pulses N of the transmitted wave, and preferably the zero cross point of the number of received pulses within the maximum N is taken as the detection point of the received wave.

For example, in FIG. 4A, the number of drive pulses is 5 and the detection point is the seventh zero cross point. In FIG. 4B, the detection point is changed to 3 by changing the drive pulse number to 3. The seventh zero cross point is changed to the fifth zero cross point.

The inspection period determination unit 85 causes the ultrasonic flowmeter installed in the field to reach a predetermined temperature every predetermined period (for example, every year by a calendar or clock function held in the microcomputer 8). In addition, it is determined whether or not it is the inspection period by measuring the timing at night when the flow rate of the measurement fluid is as low as possible.

The characteristic variation determination / correction unit 86 uses the frequency-propagation time difference comparison unit 82 to perform the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the backward propagation time difference Δ _g (f ₁ , f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ . f ₀ ), initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and initial reverse direction between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ stored in the frequency-propagation time difference storage unit 81 If the amount of deviation from the propagation time difference Δ _g0 (f ₁ , f ₀ ) is greater than or equal to a certain value, the normal measurement correction value is changed according to the amount of deviation. Specifically, the characteristic variation determination / correction unit 86 controls the frequency variable unit 4, the drive unit 3, and the reception unit 22 to perform a correction inspection, and sets a predetermined measurement frequency and drive pulse number N. is varied, to receive the detection point according its condition, the forward propagation time _T j _{(f 1)} and reverse transmission time at the measurement frequency _{f 1 T g (f 1)} , and the measurement frequency _{f 0} The forward propagation time T _j (f ₀ ) and the backward propagation time T _g (f ₀ ) are measured.

The thermometer 9 acquires a temperature (current temperature) t ₁ at the time of measurement. Incidentally, the current temperature t ₁ can also be obtained by calculating from the propagation time of the ultrasonic wave. For example, the current temperature t ₁ is obtained from the simple equation C = 331.68 + 0.61t _{1 by} obtaining the sound velocity C from the equations (1) and (2).

Next, the operation of the ultrasonic flowmeter according to the first embodiment configured as described above will be described with reference to the flowchart shown in FIG.

At the time of factory shipment or when the ultrasonic flowmeter is installed in the field, the microcomputer 8 has a plurality of measurement frequencies f ₁ , f ₃ at a plurality of temperatures t ₁ , t ₂ , t ₃ ,. initial forward propagation time at _{0 T j0 (f 1),} T j0 (f 0) and the initial backward propagation time _T g0 _{(f 1),} to measure the T g0 _{(f 0),} the measuring frequency _f 1, f seeking initial forward transit time between _{0 Δ j0 (f 1, f} 0) and the initial reverse transit time _{Δ g0 (f 1, f 0} ), the frequency - is stored in the transit time storage unit 81. Further, the microcomputer 8 adjusts and stores the drive pulse number N of the transmission wave according to the measurement frequencies f ₁ and f ₀ in the drive pulse number management unit 83 and the detection point of the reception wave in the reception pulse number management unit 84. To do.

After the field setting of the ultrasonic flowmeter, the microcomputer 8 periodically determines whether or not it is the inspection period by the inspection period determination unit 85 (step S101). The inspection period determination unit 85 is set to a predetermined temperature (for example, temperature t ₁ = 20 ° C. at any temperature measurable by the thermometer 9) every predetermined period (for example, every year), and as much as possible. It is determined that it is the inspection period by measuring the timing at night when the flow rate of the measurement fluid is low.

If it is not the inspection period, the microcomputer 8 performs normal flow rate measurement (step S102), and returns control to step S101.

If it is the inspection period, the microcomputer 8 measures the forward propagation time T _j (f ₀ ) at the measurement frequency f ₀ while the influence of the flow rate fluctuation is negligible (step S103).

Specifically, the microcomputer 8 first outputs a transmission / reception switching signal to the transmission / reception switching unit 2.

When the transmission / reception switching unit 2 receives the transmission / reception switching signal, the transmission / reception switching unit 2 switches the ultrasonic transducer 1a on the upper side in the flow direction to the transmission side and the ultrasonic transducer 1b on the lower side in the flow direction to the reception side. In other words, the ultrasonic transducer 1 a is connected to the transmission means 21, and the ultrasonic transducer 1 b is connected to the reception means 22.

Further, the microcomputer 8 outputs a measurement frequency switching signal for switching the measurement frequency to f ₀ to the frequency variable unit 4.

Frequency controller 4 receives the measurement frequency switching signal, switches the measurement frequency f _0.

Next, the microcomputer 8 outputs a drive start signal to the drive unit 3.

When the drive unit 3 receives the drive start signal, the drive unit 3 receives the drive signal of the measurement frequency f ₀ set by the frequency variable unit 4 by the drive pulse number N set by the drive pulse number management unit 83. A transmission wave is emitted by being applied to the ultrasonic transducer 1a on the transmission side via the transmission means 21. At the same time, the driving unit 3 outputs a propagation start signal to the propagation time measuring unit 7.

When the propagation time measuring unit 7 receives the propagation start signal from the driving unit 3, the propagation time measuring unit 7 starts measuring the forward propagation time T _j (f ₀ ) at the measurement frequency f ₀ .

When the transmission wave emitted from the ultrasonic transducer 1a on the upper side in the flow direction propagates through the measurement fluid and is received by the ultrasonic transducer 1b on the lower side in the flow direction, the amplifying unit 5 receives the receiving means 22 of the transmission / reception switching unit 2. The received wave input via the voltage is amplified and the received signal is input to the receiving unit 6.

When the reception unit 6 detects the zero cross point of the reception pulse number set by the reception pulse number management unit 84 as a detection point of the reception wave, it transmits a propagation detection signal to the propagation time measurement unit 7.

Propagation time measuring unit 7 receives the propagation detection signal from the receiving unit 6, and ends the measurement of the forward propagation time by measuring the frequency f ₀ T _{j (f 0),} the forward propagation in the measurement frequency f ₀ The time T _j (f ₀ ) is transmitted to the microcomputer 8.

When the measurement of the forward propagation time T _j (f ₀ ) at the measurement frequency f ₀ is completed, the microcomputer 8 outputs a measurement frequency switching signal for switching the measurement frequency from f ₀ to f ₁ to the frequency variable unit 4.

When receiving the measurement frequency switching signal, the frequency variable unit 4 switches the measurement frequency from f ₀ to f ₁ .

Thereafter, the microcomputer 8 measures the forward propagation time T _j (f ₁ ) at the measurement frequency f ₁ while the influence of the flow rate fluctuation is negligible in the same manner as in step S103 (step S104).

Note that step S103 and step S104 can also be executed simultaneously in parallel. That is, before applying the drive pulse for measuring the forward propagation time T _j (f ₀ ) and the reception pulse corresponding to it is propagated, the forward propagation time T _j (f ₁ ) is measured. And then receiving a reception pulse corresponding to the measurement of the forward propagation time T _j (f ₀ ), and subsequently receiving the measurement corresponding to the measurement of the forward propagation time T _j (f ₁ ). You may make it receive a pulse. In this way, the measurement time interval between the forward propagation time T _j (f ₀ ) and the forward propagation time T _j (f ₁ ) becomes shorter, the influence of the flow rate fluctuation can be further reduced, and higher accuracy is achieved. Measurement correction is possible.

When the measurement of the forward propagation time by measuring the frequency _{f 0 T} j _{(f 0)} and the forward propagation time by measuring the frequency _{f 1 T} j _{(f 1)} is completed, the microcomputer 8, duplexer transmission and reception switching signal Output to part 2.

When the transmission / reception switching unit 2 receives the transmission / reception switching signal, the transmission / reception switching unit 2 switches the ultrasonic transducer 1a on the upper side in the flow direction to the reception side and the ultrasonic transducer 1b on the lower side in the flow direction to the transmission side. In other words, the ultrasonic transducer 1 a is connected to the receiving means 22, and the ultrasonic transducer 1 b is connected to the transmitting means 21.

Further, the microcomputer 8 outputs a measurement frequency switching signal for switching the measurement frequency from f ₁ to f ₀ to the frequency variable unit 4.

When receiving the measurement frequency switching signal, the frequency variable unit 4 switches the measurement frequency from f ₁ to f ₀ .

Thereafter, the microcomputer 8 measures the backward propagation time T _g (f ₀ ) at the measurement frequency f ₀ while the influence of the flow rate fluctuation is negligible in the same manner as in step S103 (step S105).

Specifically, the microcomputer 8 outputs a drive start signal to the drive unit 3.

When the drive unit 3 receives the drive start signal, the drive unit 3 receives the drive signal of the measurement frequency f ₀ set by the frequency variable unit 4 by the drive pulse number N set by the drive pulse number management unit 83. A transmission wave is emitted by being applied to the ultrasonic transducer 1b on the transmission side via the transmission means 21. At the same time, the driving unit 3 outputs a propagation start signal to the propagation time measuring unit 7.

When the propagation time measuring unit 7 receives the propagation start signal from the driving unit 3, the propagation time measuring unit 7 starts measuring the backward propagation time T _g (f ₀ ) at the measurement frequency f ₀ .

When the transmission wave emitted from the ultrasonic transducer 1b on the lower side in the flow direction propagates through the measurement fluid and is received by the ultrasonic transducer 1a on the upper side in the flow direction, the amplifying unit 5 receives the receiving means 22 of the transmission / reception switching unit 2. The received wave input via the signal is amplified and the received signal is input to the receiving unit 6.

When receiving the reception signal having the number of reception pulses set by the reception pulse number management unit 84 (detecting a zero cross point), the reception unit 6 transmits the propagation detection signal to the propagation time measurement unit 7.

Propagation time measuring unit 7 receives the propagation detection signal from the receiving unit 6, and ends the measurement of the backward propagation time of the measurement frequency f ₀ T _{g (f 0),} the backward-propagation at the measurement frequency f ₀ The time T _g (f ₀ ) is transmitted to the microcomputer 8.

When the measurement of the backward propagation time T _g (f ₀ ) at the measurement frequency f ₀ is completed, the microcomputer 8 outputs a measurement frequency switching signal for switching the measurement frequency from f ₀ to f ₁ to the frequency variable unit 4.

When receiving the measurement frequency switching signal, the frequency variable unit 4 switches the measurement frequency from f ₀ to f ₁ .

Thereafter, similarly to step S105, the microcomputer 8 measures the backward propagation time T _j (f ₁ ) at the measurement frequency f ₁ while the influence of the flow rate fluctuation is negligible (step S106).

Note that, similarly to step S103 and step S104, step S105 and step S106 can also be executed simultaneously in parallel. That is, before applying the driving pulse for measuring the backward propagation time T _g (f ₀ ) and receiving the corresponding reception pulse, the backward propagation time T _g (f ₁ ) is measured. And then receiving a reception pulse corresponding to the measurement of the reverse propagation time T _g (f ₀ ), and subsequently receiving the measurement corresponding to the measurement of the reverse propagation time T _g (f ₁ ). You may make it receive a pulse. In this way, the measurement time interval between the backward propagation time T _g (f ₀ ) and the backward propagation time T _g (f ₁ ) becomes shorter, the influence of flow rate fluctuation can be further reduced, and higher accuracy can be achieved. Measurement correction is possible.

Next, the microcomputer 8 subtracts the forward propagation time by measuring the frequency _{f 1 T} j _{(f 1)} forward propagation time by measuring the frequency _{f 0} from _T j _{(f 0),} the measuring frequency _f 1, forward propagation time difference between _{f 0 Δ j (f 1,} f 0) is calculated (step S107).

Δ _j (f ₁ , f ₀ ) = T _j (f ₁ ) −T _j (f ₀ ) = τ _j (f ₁ ) −τ _j (f ₀ )

Similarly, the microcomputer 8 subtracts the backward propagation time of the measurement frequency _{f 1 T} g _{(f 1)} back propagation time of the measurement frequency _{f 0} from _T g _{(f 0),} the measuring frequency _f 1, backward propagation time difference between _{f 0 Δ g (f 1,} f 0) is calculated (step S108).

_{Δ g (f 1, f 0} ) = T g (f 1) -T g (f 0) = τ g (f 1) -τ g (f 0)

Here, the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the reverse propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ are constant regardless of the flow velocity V. That is, under the specified temperature condition, the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the reverse propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ are It means the delay characteristics of the ultrasonic transducers 1a and 1b at the measurement frequencies f ₁ and f ₀ . In other words, the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the reverse propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ are determined by the medium and velocity V of the measurement fluid. The value does not change with the parameter.

Subsequently, in the microcomputer 8, the frequency-propagation time difference comparison unit 82 stores the forward-direction propagation time difference Δ _j (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ in the frequency-propagation time difference storage unit 81. Compared with the initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ (step S109).

Similarly, the microcomputer 8 stores the reverse propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ in the frequency-propagation time difference storage unit 81 by the frequency-propagation time difference comparison unit 82. Compared with the initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ) between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ (step S110).

As a result of the comparison, the measurement frequency _f 1, the forward propagation time difference between _{f 0 Δ j (f 1,} f 0) and the measurement frequency _f 1, the initial forward propagation time difference between _{f 0 Δ j0 (f 1,} f 0) If the amount of deviation is greater than or equal to a certain value (Yes in step S111), the microcomputer 8 causes the characteristic variation determination / correction unit 86 to use the correction value used during normal measurement so that the amount of deviation is less than the certain value. (Normal measurement correction value) is changed (step S112).

For more information,
If Δ _j (f ₁ , f ₀ )> Δ _j0 (f ₁ , f ₀ ), the normal measurement correction value is changed to minus,
If Δ _j (f ₁ , f ₀ ) _{≈Δ j0} (f ₁ , f ₀ ), the normal measurement correction value is not changed,
If Δ _j (f ₁ , f ₀ ) <Δ _j0 (f ₁ , f ₀ ), the normal measurement correction value is changed to plus.

Also,
If Δ _g (f ₁ , f ₀ )> Δ _{g 0} (f ₁ , f ₀ ), the normal measurement correction value is changed to minus,
If Δ _g (f ₁ , f ₀ ) _{≈Δ g 0} (f ₁ , f ₀ ), the normal measurement correction value is not changed,
If Δ _g (f ₁ , f ₀ ) <Δ _{g 0} (f ₁ , f ₀ ), the normal measurement correction value is changed to plus.

In this case, if Δ _j (f ₁ , f ₀ ) −Δ _j0 (f ₁ , f ₀ ) = α, the change is made when α <0 and α> 0, and the initial value of α is changed. This means that the magnitude of the change, that is, the change in the delay characteristic is taken into account during normal measurement, and is changed by adding or subtracting when calculating the flow rate. Specifically, the characteristic variation determination / correction unit 86 controls the frequency variable unit 4, the drive unit 3, the drive pulse number management unit 83, and the received pulse number management unit 84 in advance in order to perform a correction inspection. The determined measurement frequency, the drive pulse number N and the received pulse number are varied, and the forward propagation time T _j (f ₁ ) and the reverse propagation time T _g at the measurement frequency f ₁ are detected at a detection point that meets the conditions. (F ₁ ), and the forward propagation time T _j (f ₀ ) and the backward propagation time T _g (f ₀ ) at the measurement frequency f ₀ are measured.

By performing such correction, the ultrasonic flowmeter can measure the flow rate with high accuracy over a long period of time.

As described above, according to the first embodiment, the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the backward propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ are as follows. If the temperature is a specified temperature condition and the time during which the difference in propagation time is measured is the same flow velocity, the forward propagation time difference Δ _j between the measurement frequencies f ₁ and f ₀ is utilized by utilizing that the flow velocity is constant regardless of the flow velocity. It is possible to provide an ultrasonic flowmeter with less measurement error by correcting aged delay characteristic fluctuation (drift) based on (f ₁ , f ₀ ) and reverse propagation time difference Δ _g (f ₁ , f ₀ ). it can.

In the first embodiment, the ultrasonic transducers 1a and 1b have a relatively low Q value representing the mechanical resonance sharpness, about Q = 2 to 10 (more practically, Q = about 2.5 to 5). In order to obtain reception characteristics proportional to the measurement frequencies f ₁ and f ₀ within the frequency band, the ultrasonic transducers 1a and 1b have a delay characteristic close to a single resonance with unnecessary spurious being reduced within the frequency band. Corresponding to the two measurement frequencies f ₁ and f ₀ in the frequency band of the ultrasonic transducers 1a and 1b, the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the reverse propagation time difference Δ _g (f ₁ , f ₀ ) is obtained, and it is possible to correct the delay characteristics fluctuation (drift) over time with high accuracy.

Further, since the ultrasonic transducers 1a and 1b are not Q≈0 ultrasonic transducers having no resonance point even if they are low-Q type ultrasonic transducers f ₁ and f ₀ , the ultrasonic transducers 1a and 1b are not capable of receiving at the time of reception by a transmission wave of a measurement frequency. The responsiveness does not immediately become the measurement frequency due to the resonance effect of the ultrasonic transducers 1a and 1b. For this reason, high accuracy is achieved by applying forced vibration by burst driving of the ultrasonic transducers 1a and 1b and detecting at a zero cross point where a reception characteristic relatively proportional to the measurement frequency in the vicinity of the forced vibration is obtained. it can. At the same time, since it is a low Q type ultrasonic transducer, the number of drive pulses N can be reduced, so that the frequency can be varied with low power consumption and the battery life can be satisfied.

Furthermore, by reducing the number N of drive pulses of the transmission wave to reduce the reception accuracy due to the measurement frequency (for example, by increasing the number of drive pulses N of the transmission wave as measured at a high frequency), stable reception is achieved. By receiving a wave and further detecting by switching the detection point of the received wave to the zero cross point of the number of stable received pulses according to the drive pulse number N of the transmitted wave (high dependency of forced vibration), The accuracy of correction measurement is improved.

In addition, after being notified that the ultrasonic flowmeter is installed in the field, a plurality of measurement frequencies f ₁ , f at a plurality of temperatures t ₁ , t ₂ , t ₃ ,. initial forward propagation time at _{0 T j0 (f 1),} T j0 (f 0) and the initial backward propagation time _T g0 _{(f 1),} to measure the T g0 _{(f 0),} the measuring frequency _f 1, f _{By obtaining and storing} the initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and the initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ) between ₀ , the correction accuracy can be further improved. . As a method of knowing that the ultrasonic flowmeter is installed in the field, a method of detecting a constant flow rate, a method of receiving notification from the outside by communication or an external switch, etc. can be considered. For example, when the ultrasonic flow meter is installed in the flow path before the field installation, the flow characteristics are changed to gas, but the propagation characteristics (propagation time, received signal characteristics, attenuation characteristics, etc.) are different. Even if the propagation characteristics are stored in a gas environment such as the above, if there is a subtle component error with the gas used in the field, it can be a correction error, so that the correction error can also be reduced. It should be noted that when this function is used and an ultrasonic flowmeter that has not been used for a long time is used again, correction due to a difference in measurement fluid or the like can be easily considered.

In addition, it is possible to improve the correction accuracy by performing a correction inspection in a period where the flow rate is as low as possible and in which the flow rate fluctuation is small. (By performing the correction inspection in a period where the flow rate is as low as possible, there is no influence of noise. Therefore, measurement accuracy is improved).

In the ultrasonic flowmeter according to the second embodiment of the present invention, the measurement frequency in the ultrasonic flowmeter according to the first embodiment shown in FIGS. 1 to 5 is two frequencies of f ₀ and f ₁ . As illustrated in FIG. 6, the only difference is that the measurement frequency is set to three frequencies f ₀ , f _1, and f ₂ . Therefore, the other configuration is the same as that of the ultrasonic flowmeter according to the first embodiment. Therefore, FIG. 1 to FIG. 4 are also applied to the ultrasonic flowmeter according to the second embodiment, and are different. Excluding the detailed explanation is omitted.

The frequency-propagation time difference storage unit 81 has an initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and an initial inverse between the measurement frequencies f ₁ , f _{0 at} a plurality of temperatures t ₁ , t ₂ , t _{3 ,.} The direction propagation time difference Δ _g0 (f ₁ , f ₀ ), the initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) and the initial reverse propagation time difference Δ _g0 (f ₂ , f ₀ ) between the measurement frequencies f ₂ and f _{0. 0} ) is stored in advance. Specifically, as shown in FIGS. 6 and 3, the initial forward propagation time by measuring the frequency _{f 1 T} j0 _{(f 1)} and the measurement frequency _f initial forward propagation time _T j0 _{(f 0)} at ₀ the initial forward transit time delta _j0 is the difference _(f 1, _{f 0),} the measurement frequency initial backward propagation time in the _{f 1 T} g0 _{(f 1)} and the initial back propagation time of the measurement frequency _{f 0 T g0} early in the initial reverse transit time delta _g0 and _(f 1, _{f 0),} the initial forward propagation time by measuring the frequency _{f 2 T} j0 _{(f 2)} and the measuring frequency _{f 0} which is the difference between _{(f 0)} An initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) that is a difference from the forward propagation time T _j0 (f ₀ ), an initial reverse propagation time T _g0 (f ₂ ) at the measurement frequency f ₂ , and a measurement The initial _value which is the difference from the initial reverse propagation time T _g0 (f ₀ ) at the frequency f ₀ The reverse propagation time difference Δ _g0 (f ₂ , f ₀ ) is stored in advance for each of a plurality of temperatures t ₁ , t ₂ , t ₃ ,.

Δ _j0 (f ₁ , f ₀ ) = T _j0 (f ₁ ) −T _j0 (f ₀ ),
Δ _g0 (f ₁ , f ₀ ) = T _g0 (f ₁ ) −T _g0 (f ₀ ),
Δ _j0 (f ₂ , f ₀ ) = T _j0 (f ₂ ) −T _j0 (f ₀ ),
Δ _g0 (f ₂ , f ₀ ) = T _g0 (f ₂ ) −T _g0 (f ₀ )

The measurement frequency _f 1, the initial forward transit time delta _j0 between _{f 0 (f 1, f 0} ) and the initial reverse transit time _{Δ g0 (f 1, f 0} ), and the measurement frequency _f 2, _{f 0} between The initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) and the initial reverse propagation time difference Δ _g0 (f ₂ , f ₀ ) are stored in the frequency-propagation time difference by the microcomputer 8 at the time of factory shipment or field installation, for example. Stored in the unit 81.

Now, let T _j be the reference forward propagation time between the ultrasonic transducers 1a and 1b, and let the frequency-dependent forward propagation time terms at the measurement frequencies f ₂ , f ₁ , and f ₀ be τ _j0 (f ₂ ), τ _j0 ( If f ₁ ) and τ _j0 (f ₀ ), initial forward propagation times T _j0 (f ₂ ), T _j0 (f ₁ ), T _j0 (f ₀ ) at the measurement frequencies f ₂ , f ₁ , f ₀ Is represented by the sum of the reference forward propagation time T _j and the frequency-dependent forward propagation time terms τ _j0 (f ₂ ), τ _j0 (f ₁ ), τ _j0 (f ₀ ).

T _j0 (f ₂ ) = T _j + τ _j0 (f ₂ ),
T _j0 (f ₁ ) = T _j + τ _j0 (f ₁ ),
T _j0 (f ₀ ) = T _j + τ _j0 (f ₀ )

Further, the reference reverse propagation time between the ultrasonic transducers 1a and 1b is T _g, and the frequency dependent reverse propagation time terms at the measurement frequencies f ₂ , f ₁ and f ₀ are τ _g0 (f ₂ ) and τ _g0 ( _{Assuming that} f ₁ ) and τ _g0 (f ₀ ), initial forward propagation times T _g0 (f ₂ ), T _g0 (f ₁ ), T _g0 (f ₀ ) at the measurement frequencies f ₂ , f ₁ , f ₀ Is represented by the sum of the reference forward propagation time T _g and the frequency-dependent forward propagation time terms τ _g0 (f ₂ ), τ _g0 (f ₁ ), τ _g0 (f ₀ ).

T _g0 (f ₂ ) = T _g + τ _g0 (f ₂ ),
T _g0 (f ₁ ) = T _g + τ _g0 (f ₁ ),
T _g0 (f ₀ ) = T _g + τ _g0 (f ₀ )

Therefore, the frequency-propagation time difference storage unit 81 stores the initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) between the measurement frequencies f ₁ , f _{0 at} a plurality of temperatures t ₁ , t ₂ , t _{3 ,.} The initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ), the initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) between the measurement frequencies f ₂ and f ₀ , and the initial reverse propagation time difference Δ _g0 (f ₂ , F ₀ ) are stored in advance.

Δ _j0 (f ₂ , f ₀ ) = T _j0 (f ₂ ) −T _j0 (f ₀ ) = τ _j0 (f ₂ ) _{−τ j0} (f ₀ ),
Δ _j0 (f ₁ , f ₀ ) = T _j0 (f ₁ ) −T _j0 (f ₀ ) = τ _j0 (f ₁ ) _{−τ j0} (f ₀ ),
Δ _g0 (f ₂ , f ₀ ) = T _g0 (f ₂ ) −T _g0 (f ₀ ) = τ _g0 (f ₂ ) −τ _g0 (f ₀ ),
Δ _g0 (f ₁ , f ₀ ) = T _g0 (f ₁ ) −T _g0 (f ₀ ) = τ _g0 (f ₁ ) −τ _g0 (f ₀ )

The frequency-propagation time difference comparison unit 82 performs forward propagation times T _j0 (f ₂ ), T _j0 (f ₁ ), T _j0 (f ₀ ) and the inverse measured at the measurement frequencies f ₂ , f ₁ , f _0. direction propagation time _{T g0 (f 2), T} g0 (f 1), T g0 (f 0) measured frequency is calculated from _f 1, the forward propagation time difference between _{f 0 Δ j (f 1,} f 0) and backward propagation time difference _{Δ g (f 1, f 0} ), and the measurement frequency _f 2, the forward propagation time difference between _{f 0 Δ j (f 2,} f 0) and reverse transit time Δ _{g (f} 2, _{f 0} ), The initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and the initial reverse propagation time difference between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ stored in the frequency-propagation time difference storage unit 81. Δ _g0 (f ₁ , f ₀ ) and the measurement circumference at the current temperature t ₁ The initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) and the initial reverse propagation time difference Δ _g0 (f ₂ , f ₀ ) between the wave numbers f ₂ and f ₀ are compared.

The characteristic variation determination / correction unit 86 uses the frequency-propagation time difference comparison unit 82 to perform the forward propagation time difference Δ _j (f ₁ , f ₀ ) and the backward propagation time difference Δ _g (f ₁ , f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ . f ₀ ), initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) and initial reverse direction between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ stored in the frequency-propagation time difference storage unit 81 If the amount of deviation from the propagation time difference Δ _g0 (f ₁ , f ₀ ) is greater than or equal to a certain value, the normal measurement correction value is changed according to the amount of deviation. Further, the characteristic variation determination / correction unit 86 uses the frequency-propagation time difference comparison unit 82 to perform the forward propagation time difference Δ _j (f ₂ , f ₀ ) and the reverse propagation time difference Δ _g (f (f) between the measurement frequencies f ₂ and f _{0. 2} , f ₀ ), the initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) between the measured frequencies f ₂ and f ₀ at the current temperature t ₁ stored in the frequency-propagation time difference storage unit 81, and the initial value If the amount of deviation from the backward propagation time difference Δ _g0 (f ₂ , f ₀ ) is equal to or greater than a certain value, the normal measurement correction value is changed according to the amount of deviation.

Next, the operation of the ultrasonic flowmeter according to the second embodiment configured as described above will be described with reference to the flowchart shown in FIG.

In addition, since the process to step S201-S204 is the same as the process (refer FIG. 5) to step S101-S104 of the ultrasonic flowmeter which concerns on Example 1, detailed description is abbreviate | omitted.

After step S _{< b} > 204, when the microcomputer 8 receives the forward propagation time T _j (f ₁ ) at the measurement frequency f ₁ , the microcomputer 8 sends a measurement frequency switching signal for switching the measurement frequency from f ₁ to f ₂ to the frequency variable unit 4. After outputting and switching the measurement frequency from f ₁ to f ₂ , the forward propagation time T _j (f ₂ ) at the measurement frequency f ₂ is similarly measured (step S 205).

Next, the microcomputer 8 outputs a transmission / reception switching signal to the transmission / reception switching unit 2 to switch transmission / reception of the pair of ultrasonic transducers 1a, 1b, and then outputs a measurement frequency switching signal to the frequency variable unit 4 to measure frequency. while switching and _{f 2} from _f 0, _{f 1,} backward propagation time _T g _(f 0) at the measurement frequency _{f 0,} the back propagation time of the measurement frequency _{f 1 T} g _{(f 1)} and the measurement frequency f backward propagation time _T g of the at _{2 (f 2)} are sequentially measured (step S206, S207, S208).

Next, the microcomputer 8 subtracts the forward propagation time by measuring the frequency _{f 1 T} j _{(f 1)} forward propagation time by measuring the frequency _{f 0} from _T j _{(f 0),} the measuring frequency _f 1, forward propagation time difference between _{f 0 Δ j (f 1,} f 0) is calculated (step S209).

Δ _j (f ₁ , f ₀ ) = T _j (f ₁ ) −T _j (f ₀ ) = τ _j (f ₁ ) −τ _j (f ₀ )

The microcomputer 8 subtracts the forward propagation time by measuring the frequency _{f 2 T} j _{(f 2)} forward propagation time by measuring the frequency _{f 0} from _T j _{(f 0),} the measurement frequency _f 2, f forward transit time between _{0 Δ j (f 2, f} 0) is calculated (step S210).

Δ _j (f ₂ , f ₀ ) = T _j (f ₂ ) −T _j (f ₀ ) = τ _j (f ₂ ) −τ _j (f ₀ )

Similarly, the microcomputer 8 subtracts the backward propagation time of the measurement frequency _{f 1 T} g _{(f 1)} back propagation time of the measurement frequency _{f 0} from _T g _{(f 0),} the measuring frequency _f 1, backward propagation time difference between _{f 0 Δ g (f 1,} f 0) is calculated (step S211).

_{Δ g (f 1, f 0} ) = T g (f 1) -T g (f 0) = τ g (f 1) -τ g (f 0)

The microcomputer 8 subtracts the backward propagation time of the measurement frequency _{f 2 T} g _{(f 2)} back propagation time of the measurement frequency _{f 0} from _T g _{(f 0),} the measurement frequency _f 2, f reverse transit time between _{0 Δ g (f 2, f} 0) is calculated (step S212).

_{Δ g (f 2, f 0} ) = T g (f 2) -T g (f 0) = τ g (f 2) -τ g (f 0)

The measurement frequency _f 1, the forward propagation time difference between _{f 0 Δ j (f 1,} f 0) and the measurement frequency _f 2, the forward propagation time difference between _{f 0 Δ j (f 2,} f 0), and backward propagation time difference between the measured frequency _{f 1, f 0 Δ g (} f 1, f 0) and the measurement frequency _f 2, backward propagation time difference between _{f 0 Δ g (f 2,} f 0) is the flow velocity V It is constant regardless. That is, when the temperature under defined conditions, the measurement frequency _f 1, _f forward transit time delta _{j (f} 1, _{f 0)} between ₀ and measurement frequency _f 2, the forward propagation time difference between _{f 0} delta _j ( _{f 2,} f 0), and measuring the frequency _f 1, backward propagation time difference between _{f 0 Δ g (f 1,} f 0) and the measurement frequency _f 2, _f backward propagation time difference between _{0 Δ g (f} 2, f ₀ ) means the delay characteristics of the ultrasonic transducers 1a and 1b at the respective measurement frequencies f ₂ , f ₁ and f ₀ . In other words, the forward propagation time difference between the measured frequency _{f 1, f 0 Δ j (} f 1, f 0) and the measurement frequency _f 2, the forward propagation time difference between _{f 0 Δ j (f 2,} f 0), and backward propagation time difference between the measured frequency _{f 1, f 0 Δ g (} f 1, f 0) and the measurement frequency _f 2, backward propagation time difference between _{f 0 Δ g (f 2,} f 0) , the measurement fluid It is a value which does not change with the parameters of the medium and the velocity V

Subsequently, in the microcomputer 8, the frequency-propagation time difference comparison unit 82 stores the forward-direction propagation time difference Δ _j (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ in the frequency-propagation time difference storage unit 81. Compared with the initial forward propagation time difference Δ _j0 (f ₁ , f ₀ ) between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ (step S213).

Further, in the microcomputer 8, the frequency-propagation time difference comparison unit 82 stores the forward-direction propagation time difference Δ _j (f ₂ , f ₀ ) between the measurement frequencies f ₂ and f ₀ in the frequency-propagation time difference storage unit 81. Further, the initial forward propagation time difference Δ _j0 (f ₂ , f ₀ ) between the measurement frequencies f ₂ and f ₀ at the current temperature t ₁ is compared (step S214).

Similarly, the microcomputer 8 stores the reverse propagation time difference Δ _g (f ₁ , f ₀ ) between the measurement frequencies f ₁ and f ₀ in the frequency-propagation time difference storage unit 81 by the frequency-propagation time difference comparison unit 82. Compared with the initial reverse propagation time difference Δ _g0 (f ₁ , f ₀ ) between the measured frequencies f ₁ and f ₀ at the current temperature t ₁ (step S215).

In the microcomputer 8, the reverse propagation time difference Δ _g (f ₂ , f ₀ ) between the measurement frequencies f ₂ and f ₀ is stored in the frequency-propagation time difference storage unit 81 by the frequency-propagation time difference comparison unit 82. and is compared with at the present temperature _{t 1,} the measurement frequency _f 2, the initial backward propagation time difference between _{f 0 Δ g0 (f 2,} f 0) ( step S216).

As a result of the comparison, the measurement frequency _f 1, the forward propagation time difference between _{f 0 Δ j (f 1,} f 0) and the measurement frequency _f 1, the initial forward propagation time difference between _{f 0 Δ j0 (f 1,} f 0) If the amount of deviation is greater than or equal to a certain value (Yes in step S217), the microcomputer 8 changes the normal measurement correction value by the characteristic variation determination / correction unit 86 so that the amount of deviation is less than the certain value. (Step S218).

For more information,
If Δ _j (f ₁ , f ₀ )> Δ _j0 (f ₁ , f ₀ ), the normal measurement correction value is changed to minus,
If Δ _j (f ₁ , f ₀ ) _{≈Δ j0} (f ₁ , f ₀ ), the normal measurement correction value is not changed,
If Δ _j (f ₁ , f ₀ ) <Δ _j0 (f ₁ , f ₀ ), the normal measurement correction value is changed to plus.

Also,
If Δ _g (f ₁ , f ₀ )> Δ _{g 0} (f ₁ , f ₀ ), the normal measurement correction value is changed to minus,
If Δ _g (f ₁ , f ₀ ) _{≈Δ g 0} (f ₁ , f ₀ ), the normal measurement correction value is not changed,
If Δ _g (f ₁ , f ₀ ) <Δ _{g 0} (f ₁ , f ₀ ), the normal measurement correction value is changed to plus.

Specifically, the characteristic variation determination / correction unit 86 controls the frequency variable unit 4, the drive unit 3, the drive pulse number management unit 83, and the received pulse number management unit 84 in advance in order to perform a correction inspection. The determined measurement frequency, the drive pulse number N and the received pulse number are varied, and the forward propagation time T _j (f ₁ ) and the reverse propagation time T _g at the measurement frequency f ₁ are detected at a detection point that meets the conditions. (F ₁ ), and the forward propagation time T _j (f ₀ ) and the backward propagation time T _g (f ₀ ) at the measurement frequency f ₀ are measured.

Further, the measurement frequency _f 2, _{f 0} between the backward propagation time difference _{Δ g (f 2, f 0} ) and the measurement frequency _f 2, _f initial reverse transit time between _{0 Δ g0 (f 2, f} 0) If the amount of deviation is greater than or equal to a certain value (Yes in step S217), the microcomputer 8 changes the normal measurement correction value by the characteristic variation determination / correction unit 86 so that the amount of deviation is less than the certain value ( Step S218).

For more information,
If Δ _j (f ₂ , f ₀ )> Δ _j0 (f ₂ , f ₀ ), the normal measurement correction value is changed to minus,
If Δ _j (f ₂ , f ₀ ) _{≈Δ j0} (f ₂ , f ₀ ), the normal measurement correction value is not changed,
If _{Δ j (f 2, f 0} ) <Δ j0 (f 2, f 0), plus change the normal measurement correction value.

Also,
If Δ _g (f ₂ , f ₀ )> Δ _{g 0} (f ₂ , f ₀ ), the normal measurement correction value is changed to minus,
If Δ _g (f ₂ , f ₀ ) _{≈Δ g 0} (f ₂ , f ₀ ), the normal measurement correction value is not changed,
If Δ _g (f ₂ , f ₀ ) <Δ _{g 0} (f ₂ , f ₀ ), the normal measurement correction value is changed to a plus value.

Specifically, the characteristic variation determination / correction unit 86 controls the frequency variable unit 4, the drive unit 3, and the reception unit 22 to perform a correction inspection, and sets a predetermined measurement frequency and drive pulse number N. is varied, to receive the detection point according its condition, measuring frequency _{f 2} in the forward propagation time _T j _{(f 2)} and reverse propagation time _T g _(f 2), and the measurement frequency _{f 0} The forward propagation time T _j (f ₀ ) and the backward propagation time T _g (f ₀ ) are measured.

As described above, according to the ultrasonic flow meter according to the second embodiment, the same effect as that of the ultrasonic flow meter according to the first embodiment can be obtained. However, since the measurement frequency is changed from two frequencies to three frequencies, finer details are obtained. The normal measurement correction value can be corrected, and more accurate measurement can be realized.

1 is a block diagram showing the configuration of an ultrasonic flow meter according to Embodiment 1 of the present invention. 3 is a graph showing a relationship between a measurement frequency, a forward propagation time, and a backward propagation time in the ultrasonic flowmeter according to the first embodiment. 3 is a graph showing a relationship between a measurement frequency and an initial forward propagation time difference and an initial reverse propagation time difference in the ultrasonic flowmeter according to the first embodiment. FIG. 4 is a waveform diagram for explaining the relationship between the number of drive pulses and detection points in the ultrasonic flowmeter according to the first embodiment. 3 is a flowchart illustrating a correction operation of the ultrasonic flowmeter according to the first embodiment. The graph which shows concretely the relationship between the measurement frequency in the ultrasonic flowmeter which concerns on Example 2 of this invention, and forward direction propagation time and reverse direction propagation time. 10 is a flowchart illustrating a correction operation of the ultrasonic flowmeter according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Ultrasonic transducer 2 Transmission / reception switching part 3 Drive part 4 Frequency variable part 5 Amplifying part 6 Receiving part 7 Propagation time measuring part 8 Microcomputer 9 Thermometer 21 Transmitting means 16 Receiving means 81 Frequency-propagation time difference storage part 82 Frequency- Propagation time difference comparison unit 83 Drive pulse number management unit 84 Received pulse number management unit 85 Inspection period determination unit 86 Characteristic variation determination / correction unit

Claims (9)

A pair of ultrasonic transducers is provided on the upper and lower sides of the fluid flow direction of the flow path, and ultrasonic transmission / reception is alternately switched, so that the ultrasonic waves emitted from the ultrasonic transducer on the upper side of the flow direction are on the lower side of the flow direction. Measure the forward propagation time to reach the ultrasonic transducer and the reverse propagation time for the ultrasonic wave emitted from the ultrasonic transducer on the lower flow direction to reach the ultrasonic transducer on the upper flow direction. Then, in the ultrasonic flowmeter that obtains the average flow velocity of the fluid flowing through the flow path from the difference between them and obtains the flow rate by multiplying the average flow velocity by the cross-sectional area of the flow path
When the pair of ultrasonic transducers is installed, a plurality of measurement frequencies are determined, a forward propagation time and a reverse propagation time between the pair of ultrasonic transducers are measured, A frequency-propagation time difference storage unit that obtains a difference in forward propagation time in, and a difference in backward propagation time between the plurality of measurement frequencies, and stores the initial forward propagation time difference and the initial backward propagation time difference;
At regular intervals, by the plurality of measurement frequencies, the carried forward propagation time and the measurement of the backward propagation time between the ultrasonic transducers, the difference between the forward propagation time between said plurality of measurement frequencies, and the plurality of obtaining a difference of the backward propagation time between the measurement frequency, the forward transit time and the frequency - initial forward propagation time difference at the measured temperature of the forward propagation time stored in the transit time storage unit, and A frequency-propagation time difference comparison unit that compares the reverse propagation time difference and an initial reverse propagation time difference at a temperature at which the backward propagation time stored in the frequency-propagation time difference storage unit is measured ;
The frequency - changing a negative value or a positive value normal measurement correction value in accordance with the amount of deviation between the initial forward propagation time difference and the initial reverse transit time rather based on a comparison result of the propagation time difference comparison unit Then, the normal measurement value by the ultrasonic transducer is changed according to the change of the delay characteristic by the normal measurement correction value,
Characterized in that the delay characteristics of the pair of ultrasonic transducers, regardless of the flow velocity of the fluid being measured, by utilizing the change by the measurement frequency, the flow rate correction for aging delay characteristic variation of the pair of ultrasonic transducers Ultrasonic flow meter. 2. The ultrasonic transducer according to claim 1, wherein the ultrasonic transducer is formed of an ultrasonic transducer having a single resonance characteristic, having a low Q-type, less unnecessary spurious, and using a frequency band of the ultrasonic transducer. The described ultrasonic flowmeter. The measurement frequency at the time of the correction inspection uses a resonance point frequency in the frequency band of the ultrasonic transducer or a frequency near the resonance point frequency and a frequency away from the resonance point frequency in the frequency band, and drive pulses of these frequencies. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic transducer is driven to measure a forward propagation time and a backward propagation time. Zero-crossing point of the maximum number of received pulses within N + 2 to 3 with respect to the number of drive pulses N of the transmission wave, preferably, the maximum number of received pulses within the maximum N with the forced oscillation by the controlled burst driving of the drive pulse number N of the transmitted wave ultrasonic flowmeter according to any one of claims 1 to 3, characterized in that the detection point of the reception wave. Ultrasonic flowmeter according to any one of claims 1 to 4, characterized in that to change the detection point of the driving pulse number and received wave of the transmission wave in accordance with the measured frequency. Ultrasonic flowmeter according to any one of claims 1 to 5, characterized in that adjusting and storing the detection point of the driving pulse number and received wave of the transmission wave in accordance with the measured frequency. When the ultrasonic flowmeter installed in the field reaches a predetermined temperature for a certain period of time, and ascertains the timing when the flow rate of the measurement fluid is as low as possible, the forward propagation time and the reverse propagation time with respect to the measurement frequency ultrasonic flowmeter according to any one of claims 1 to 6, characterized in that for performing the measurement. Wherein the plurality of forward propagation time of the measurement frequency measured continuously performed while made different measurement frequency, the plurality of back propagation time of the measurement frequency measured continuously while made different measurement frequencies thereafter ultrasonic flowmeter according to any one of claims 1 to 7, characterized in that to perform. Apply a drive pulse for measuring the forward or backward propagation time at one measurement frequency, and before the corresponding received pulse propagates, the forward propagation time at the next measurement frequency or The ultrasonic flowmeter according to claim 8, wherein a driving pulse for measuring the backward propagation time is applied.

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