JPH0324609B2 - - Google Patents

Description

Detailed Description of the Invention The present invention transmits ultrasonic pulses, receives reflected waves from an object to be measured, detects the amount of phase change received by the reflected waves due to the Doppler effect, and calculates the flow velocity of the object to be measured. This article relates to an ultrasonic current meter for measurement.

In the conventional pulse method ultrasonic anemometer, the detectable flow velocity limit v _nax is the ultrasonic transmission center frequency.
fc, ultrasonic transmission repetition frequency f _r , and fluid sound velocity C, it is uniquely determined as v _nax = f _r ·C/4fc. To increase v _nax , increase f _r and decrease f _c , but the reflected wave must return before sending out the next pulse, so f _r
There is a limit to how big it can be. Further, due to signal processing, the transmission repetition frequency f _r of ultrasonic pulses must always be regular, and there is a problem in that irregular operations such as stopping transmission of ultrasonic pulses once in the middle are not possible.

The present invention focuses on the fact that the speed of an object under test does not change rapidly due to inertia, and uses data interpolation to predict the next amount of phase change from the amount of phase change between Doppler signals obtained discretely. By doing this, the maximum measurable flow velocity can be increased (if interpolated, f _r has effectively been increased), and it is also possible to transmit irregular ultrasonic pulses. That is, the ultrasonic anemometer of the present invention measures the velocity of a fluid by measuring the amount of phase change of an intermittently received ultrasonic signal. The method is characterized in that the upper and lower limits of the velocity of the next fluid are predicted, and the velocity of the next fluid is measured within the predicted velocity range. In addition, when calculating the predicted phase change amount, more accurate prediction can be achieved by not only using the corrected phase change amount but also weighting with the amplitude of the reflected wave. Further, by adding a circuit that interpolates and generates data so that the amount of phase change between each data is within ±π, the same type of analysis circuit as the conventional one can be used. This will be explained in detail below with reference to the illustrated embodiments.

FIG. 1 is a schematic block diagram showing one embodiment of the present invention. In the ultrasonic current meter of this example, the ultrasonic pulses repeatedly sent out by the transmitter 1 and the transducer 2 are reflected by the object to be measured (not shown),
The reflected wave is received by the same transducer 2 (this may be a different transducer) and amplified by the receiver 3. The amplified signal R is detected by an orthogonal detection type detector 4, and becomes Doppler signals X and Y in an orthogonal coordinate system. FIG. 2 shows an example of the circuit of this detector 4, in which 41a and 41b are multipliers, 42a and 42b
is a low-pass filter with a cutoff frequency of approximately f _c , 43
a, 43b are sampling and holding circuits operated by a sampling signal S indicating a measurement point;
44a and 44b are high-pass filters that remove reflected waves (fixed waves) from stationary objects (such as blood vessels in the case of blood flow velocity measurement). This filter 44a, 4
4b can be omitted if there is no stationary object. The outputs X and Y of the detector 4 are led to an extended data creation circuit 5, where they are converted into extended data (described later) for the analyzer 6. Note that 7 is a controller that controls each part.

FIG. 3 shows a specific example of the extended data creation circuit 5.
1 is the output X, Y of the detector 4 with amplitude r and phase θ
(From the relationship r _e ^j 〓=X+jY, r, θ
) is a coordinate conversion circuit. The phase θ of each Doppler signal obtained discretely is sequentially led to the phase change detection circuit 52, where it is temporarily stored and compared to the previous θ _i-1
The phase difference Δθ _i between this time and θ _i is found. In other words, Δθ _i
= θ _i −θ _i-1 , which will hereinafter be referred to as the measured phase change amount. The phase difference shift circuit 53 adds nπ to Δθ _i to obtain the corrected phase change amount Δθ′ _i , and the n value is the predicted phase change amount w _i from the phase change prediction circuit 54.
Select so that the following equation is satisfied.

w _i +π＞Δθ _i +nπ＞w _i −π …(1) n=0, ±1, ±2…… Δθ′ _i =Δθ _i +nπ …(2) n is a value that satisfies equation (1) The predicted phase change amount w _i is the sum of the previous predicted phase change amount w _i-1 and the previous corrected phase change amount Δθ' _i-1 in an appropriate ratio, as shown in the following equation.

w _i =a・w _i-1 +b (Δθ′ _i-1 −w _i-1 )……(3) a≧0, b>0 (constant) Corrected phase change amount Δθ′ _i latched in latch 532
is supplied to the phase change prediction circuit 54. The phase change prediction circuit 54 predicts which phase change amount will be the next amount of change from the corrected amount of phase change Δθ′ _i , and outputs the predicted amount of phase change w _i expressed by the following equation.

w _i =a・w _i-1 +b(Δθ′ _i-1 −w _i-1 )……(4) However, a, b are constants of a≧0, b>0, i is an integer, and w _i-1 is the predicted phase change amount obtained at the timing immediately before the timing when the predicted phase change amount w _i was obtained,
Δθ′ _i−1 is the corrected phase change amount obtained at the timing immediately before the corrected phase change amount Δθ′ _i .

Further, in the phase change prediction circuit 54, 541 is a constant generator, which generates constants b ₁ to b _o corresponding to the constant b.
543 is a switch that generates each of
One that outputs one of the constants b ₁ to _{b o} as the constant b, 547 is a constant generator that generates the constant a, and 549 is a tap that only serves as a unit timing. It delays input.

To explain the operation, the predicted phase change amount w _i-1 delayed by the unit timing by the tap 549,
The corrected phase change amount Δθ′ _i is supplied to a subtracter 544. The subtracter 544 calculates and outputs the value "Δθ' _i -w _i-1 " from these phase change amounts. Multiplier 5
This calculation output “Δθ _i −w _i-1 ” and constant b are supplied to 45, and the calculation output “b(Δθ′ _i-1 − w _i-1 )” to adder 5
48.

On the other hand, the constant a generated by the constant generator 547
and the predicted phase change amount w _i-1 are multiplied by a multiplier 546, and an output corresponding to the first term on the right side of the above equation (1) is outputted to an adder 548. As a result, adder 5
48 generates and outputs the predicted phase change amount w _i .

Figure 5 shows an example of calculating w _i when Δθ′ _i-1 changes stepwise from 20 to 100 (although such a change is not planned in the present invention) with a=0.8 and b=0.3. be. The followability of w _i is determined by the values of a and b, and a,
The closer both b are to 1, the better the followability becomes. However, the better the followability, the more likely it will malfunction due to noise. To prevent malfunctions, it is best to devise a method for b. That is, the larger the amplitude r is, the more reliable the information on θ is, so it is preferable to change the value of b with the amplitude information r, as shown in FIG. 6, instead of making b a constant. The reason why the amplitude information r is guided to the phase change prediction circuit 54 in FIG. 3 is to take this point into consideration, and if b is set as a constant, this path is unnecessary.

Figure 4 shows the change in the corrected phase change amount θ′ _i , with the upper limit of the prephase phase change range being w _i +π, and w _i
This is a hatched area with a width of 2π with −π as the lower limit. These upper limit values and lower limit values are determined by the comparator 53.
6,537, it is compared with the output value Δθ _i +nπ of the adder 531. The comparator 536 outputs the output value Δθ _i +
nπ is compared with the upper limit value w _i +π, and when the output value Δθ _i +nπ is smaller than the upper limit value _{w i} +π, the comparator 537 outputs a level “1 _” signal. When the output value Δθ _i +nπ is larger than the lower limit value w _i −π, the level “1” signal is
If each condition cannot be met, a signal of level "0" is generated.

The gate circuit 538 has both comparators 536,5
When a level "1" signal is obtained from only one of the counters 37, a pulse is output for incrementing the counter 539 by one. Furthermore, when a level "1" signal is obtained from both comparators 536 and 537, gate circuit 538 outputs a pulse for causing latch circuit 532 to latch the output value of adder 531.

When the counter 539 is reset by a control unit (not shown), it becomes a constant value -m (for example, -2),
(The reset timing is set immediately after the value is latched in the latch 532.) Gate circuit 5
Count the pulse signals from 38. The count value of this counter and the constant π from the constant generator 533 are multiplied by the multiplier 530, and the multiplied value is used as the correction amount for the measured phase change amount Δθ _i by the adder 5.
31.

Therefore, the corrected phase change amount latched by the latch circuit 532 satisfies the following equation.

w _i +π>Δθ _i +nπ>w _i −π n=, ±1, ±2... In interval I, _{w i =}
It is fixed at +π. Also, in the section, the measured phase change amount Δθ _i is outside the shaded area (indicated by the dotted line), so
+2π is added to this to obtain the corrected phase change amount Δθ′ _i .

The above is a case where the transmission repetition period of ultrasonic waves is constant, but when the repetition is not constant, equations (1) and (2) are changed to equations (5) and (6), respectively.

T _i w _i +π＞Δθ _i +nπ＞T _i w _i −π …(5) w _i =aw _i +b(Δθ′ _i-1 /T _i-1 −w _i-1 ) …(6) T _i is a value shown in the following formula.

T _i =t _i −t _i-1 /Δt _S where t _i indicates the time at which the i-th ultrasonic pulse was transmitted. Further, since Δt _S uses either the average repeat interval, the maximum time, or the minimum time for ease of calculation, Δt _S =1 may be used.

In this way, the corrected phase change amount Δθ′ _i obtained by the extended data creation circuit 5 may exceed ±π, so
The analyzer 6 must be able to analyze this data and calculate the flow velocity, but if the circuit shown in FIG. good. This auxiliary circuit 8 includes an amplitude interpolation circuit 81 and a phase change amount interpolation circuit 8.
2, a phase difference addition circuit 83, and a coordinate conversion circuit 84. The coordinate conversion circuit 84 converts r, θ polar coordinates into XY orthogonal coordinates. Amplitude interpolation circuit 81
The phase change amount interpolation circuit 82 performs data interpolation as shown in FIGS. 8a and 8b, respectively. D is real data and H is interpolated data. In this example, one interpolated data is added between each actual data, but if the phase change is expanded from within ±π to within ±2π, it is necessary to do as in this example in order to perform sampling at the Nyquist interval. There is. The phase difference addition circuit 83 integrates the output of the interpolation circuit 82 (also assumed to be Δθ′ _i ) using the following equation to obtain θ′ _i .

θ' _i = θ' _i-1 +A・Δθ' _i A=1/(N+1) However, i=1, 2, 3..., and N is the number of interpolated data H between the actual data D, Therefore, in Fig. 8, A=1/2. Actually, analysis is possible if the added value is within ±π, so |A|≦1/(N+1)
If so, N can be set arbitrarily. Note that if the repetition period of the ultrasonic pulse is not constant, Δθ′ _i should be
Interpolated data is obtained as T _i ·Δθ′ _i at regular intervals T ₀ , and after appropriate multiplication is performed so that the amount of phase change is within ±π, addition is performed.

FIG. 9 shows various data created by the interpolation data creation circuit, and a is an example of creating intermediate data (H between D and D) similar to that in FIG. b is an example of interpolation when 1/4 of the actual data D is missing, c is an example of creation in which irregularly generated data is converted to regular data, and D' is the actual data. Of these, the actual data D and the auxiliary data H are used as analysis data, but the irregular actual data D' is not used. Missing data may occur, for example, when a plurality of ultrasonic transceivers are used to perform measurements in each system, and the transmission timings of both systems may overlap, so one is suspended.

The functional blocks shown in FIGS. 3 and 7 described above do not necessarily have to correspond to predetermined hardware; in fact, many operations can be processed by software using a microprocessor.

As described above, according to the present invention, it is possible to increase the maximum detectable flow velocity v _nax , which is convenient for measuring the speed of objects to be measured that move at high speed.
Furthermore, since there are fewer restrictions on the transmission timing of ultrasonic waves, it can be applied to ultrasonic current meters where the transmission timing is irregular, which is highly effective.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a specific example of a quadrature detector, FIG. 3 is a block diagram showing a specific example of an extended data creation circuit, and FIG. The figure is an explanatory diagram of the corrected phase change amount, FIG. 5 is an explanatory diagram of the predicted phase change amount, FIG. 6 is an explanatory diagram of weighting of the predicted phase change amount by amplitude information, and FIG. 7 is an illustration of the interpolation data creation circuit. The block diagrams, FIGS. 8 and 9, are explanatory diagrams of various data interpolations. In the figure, 1 is an ultrasonic transmitter, 3 is a receiver, 4 is a detector, 5 is an extended data creation circuit, 6 is an analyzer, and 8
is an interpolation data generation circuit.

Claims (1)

[Claims] 1. Transmitting/receiving circuits 1, 2, and 3 that intermittently transmit and receive ultrasonic pulses; a detection circuit 4 that orthogonally detects the received signal of the transmitting/receiving circuit; and sampling the output of the detection circuit 4. Analog/digital converters 43a, 43b; a measured phase difference detector 52 for detecting the measured phase difference Δθ _i of adjacent received data discretized by the A/D converter 51; a phase difference prediction circuit 54 which predicts the phase difference with the discrete signal and outputs a phase difference prediction signal W _i ; and a modified phase from the phase difference signal Δθ _i which is the output of the measured phase difference detector and the phase difference prediction signal W _i . Amount of change Δθ′ _i
The phase difference prediction circuit 54 includes a corrected phase change amount determination circuit 53 for determining a predicted phase difference signal predicted by a discrete signal previous to the current discrete signal.
W _i-1 and the previous corrected phase change amount Δθ′ _i-1 of the current discrete signal output from the corrected phase change amount determination circuit 53
A phase difference prediction circuit 54 predicts the current phase difference W _i of the discrete _signal from
The signal Δθ _i +nπ obtained by adding a phase difference of nπ (n≧0, n is an integer) is shifted by a predetermined ±π from the phase difference predicted signal W _i of the discrete signal obtained from the phase difference prediction circuit. This is a modified phase change amount determination circuit 53 which determines n such that it falls within the phase, and obtains a signal Δθ _i +nπ obtained by adding the determined nπ as a modified phase change amount Δθ′ _i , and the modified phase change amount Δθ′ An ultrasonic current meter characterized by determining the velocity of a fluid from _i .