JP3909660B2 - Vortex flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vortex flow meter, and more particularly to a vortex flow meter in which no error occurs even if there is noise such as vibration.
[0002]
[Prior art]
FIG. 5A shows the configuration of the vortex detector of the Karman vortex flowmeter. In this figure, the vortex generator 7 is arranged perpendicular to the duct 6. When the fluid to be measured flowing in the pipe line 6 collides with the vortex generator 7, Karman vortex is generated, and thus the vortex generator 7 is subjected to an alternating lift and is deformed minutely.
[0003]
A pair of piezoelectric elements 81 and 82 are vertically embedded in the upper portion of the vortex generator, and minute deformation of the vortex generator 7 is detected by the piezoelectric elements 81 and 82. Since the number of Karman vortices generated per unit time is proportional to the flow velocity, it is possible to measure the flow rate of the fluid to be measured.
[0004]
The piezoelectric elements 81 and 82 detect not only a signal due to the Karman vortex but also noise generated by vibration of the pipe 6. FIG. 5B shows the stress distribution of noise due to the Karman vortex signal and vibration. In the figure, S indicates the stress distribution due to Karman vortex, and N indicates the stress distribution of noise due to vibration. As shown in the figure, these stress distributions are quite different.
[0005]
In the figure, S1 and N1 are vortex signals and noise stresses detected by the piezoelectric element 81, and S2 and N2 are vortex signals and noise stresses detected by the piezoelectric element 82. The piezoelectric elements 81 and 82 output charges corresponding to these stresses, and these charges are converted into voltages by a charge amplifier.
[0006]
When the outputs of the piezoelectric elements 81 and 82 are Q1 and Q2, respectively, these values can be expressed by the following equations (1) and (2). In addition, the output of the piezoelectric elements 81 and 82 by the stress S1, S2, N1, and N2 is represented by the same symbol.
Q1 = S1 + N1 (1)
Q2 = -S2-N2 (2)
A symbol “-” is attached to the right side of the equation (2), which indicates that the phase is reversed.
[0007]
Multiplying the equation (2) by N1 / N2 and adding the equation (1),
Q1 + (N1 / N2) × Q2 = S1 + N1- (S2 + N2) × N1 / N2
= S1- (N1 / N2) × S2 (3)
Is obtained. If S1 / S2 ≠ N1 / N2 and N1 / N2 is known, the noise components N1 and N2 can be removed as is apparent from the equation (3). Note that (N1 / N2) is called a “noise ratio”.
[0008]
[Problems to be solved by the invention]
However, such vortex flowmeters have the following problems.
[0009]
The noise ratio (N1 / N2) is determined by adjusting a standard vibration at the time of shipment. Although it is assumed that this noise ratio does not change, it may actually vary depending on the situation where the vortex flowmeter is installed. Therefore, noise cannot be completely removed, and there is a problem that an error occurs in the flow rate measurement value.
[0010]
In addition, when the operating state changes, there is a problem that the optimum noise ratio changes slightly and the error of the flow rate measurement value fluctuates.
[0011]
Furthermore, if the difference between the noise ratio set at the time of shipment and the actual noise ratio becomes large, it will be necessary to readjust the noise ratio manually, such as when a service person goes to the site, which will be costly and time consuming. There were also challenges.
[0012]
[Means for Solving the Problems]
In order to solve such a problem, the invention according to claim 1 of the present invention includes two detectors 81 and 82 for detecting a vortex signal generated by a vortex generator, and outputs each of a plurality of frequencies to a plurality of frequencies. A first spectrum analysis unit 2 that divides the signal into bands and outputs the signal intensities of the bands, a noise ratio calculation unit 3 that receives the output and determines a noise ratio, and a noise calculated by the noise ratio calculation unit 3 A ratio input, and an addition unit 41 that adds signals related to the outputs of the two detection units 81 and 82 at a ratio of the noise ratio, and obtains a flow rate value based on the output of the addition unit 41; The noise ratio calculation unit 3 determines the noise band from the ratio of the signal intensity of each band of the two detection units 81 and 82, and the signal intensity ratio of the band having the maximum signal intensity among the bands determined as noise is determined as noise. As a ratio It is obtained so as to output the calculation unit 41. An optimal noise ratio can always be set.
[0013]
The invention described in claim 2 has a bandpass filter 43 to which the output of the adder 41 is input in the invention described in claim 1, and the band which the noise ratio calculation unit 3 has determined as a signal by the bandpass filter 43. The flow rate value is obtained from the output of the band pass filter so that only the filter is allowed to pass through. Noise can be reduced.
[0014]
The invention according to claim 3 is the invention according to claim 1, further comprising a second spectrum analysis unit 42 to which the output of the addition unit 41 is input, and a bandpass filter 43 to which the output of the addition unit 41 is input. Then, the second spectrum analysis unit 42 divides the input into a plurality of frequency bands to determine the signal strength of each band, determines a band having a signal strength greater than a predetermined sensitivity curve as a signal band, The band-pass filter 43 is controlled so as to pass only the signal of this band, and the flow rate value is obtained from the output of the band-pass filter 43. Noise can be further reduced.
[0015]
According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the noise ratio calculation unit 3 is clogged when the signal intensity ratio of the band determined to be a signal is equal to or less than a predetermined clogging determination ratio. An alarm is output. A clogged pipeline can be detected.
[0016]
According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the noise ratio calculation unit 3 is configured to detect abnormal vibration in which the signal strength of the output of the addition unit 41 in a band determined as noise is predetermined. An abnormal vibration alarm is output when it is smaller than one threshold or larger than a second threshold for abnormal vibration determination. Abnormal vibration can be detected.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a vortex flowmeter according to the present invention. The same elements as those in FIG. 5 are denoted by the same reference numerals and description thereof is omitted.
[0018]
In FIG. 1, reference numeral 1 denotes a charge-digital conversion unit, which includes charge converters 11 and 12 and A / D converters 13 and 14. The charge output of the piezoelectric element 81 is input to the charge converter 11 and converted into a voltage signal. The voltage signal is converted into a digital signal by the A / D converter 13. Similarly, the charge output of the piezoelectric element 82 is converted into a voltage signal by the charge converter 12 and further converted into a digital signal by the A / D converter 14.
[0019]
Reference numeral 2 denotes a spectrum analysis unit, which includes spectrum analyzers 21 and 22. The output of the A / D converter 13 is input to the spectrum analyzer 21 for spectrum analysis. That is, the spectrum analyzer 21 decomposes the input signal into a plurality of frequency bands and outputs the signal intensity of each band. Similarly, the spectrum analyzer 22 decomposes the output of the A / D converter 14 into a plurality of frequency bands and outputs the signal intensity of each band.
[0020]
Reference numeral 3 denotes a CPU which receives the output of the spectrum analyzer 2 and determines and outputs a noise ratio from these inputs. Reference numeral 5 denotes an output circuit to which the output of the CPU 3 is input.
[0021]
Reference numeral 4 denotes a signal processing unit. An adder 41 to which the output of the charge-digital conversion unit 1 is input, a spectrum analyzer 42 and a bandpass filter 43 to which an output of the adder 41 is input, and the bandpass filter 43 A Schmitt trigger 44 to which an output is input and a counter 45 to which an output of the Schmitt trigger 44 is input are configured.
[0022]
The adder 41 performs the following equation (4) using the outputs of the A / D converters 13 and 14 and the noise ratio output by the CPU 3. That is, if the output values of the A / D converters 31 and 32 are A and B, the noise ratio is λN, and the output of the adder 41 is C,
C = A + λN × B (4)
The calculation result C is output to the spectrum analyzer 42 and the band pass filter 43.
[0023]
The spectrum analyzer 42 analyzes the spectrum of the output C of the adder 41, and sets the pass frequency band of the bandpass filter 43 via the bandpass filter controller 43C. The output C of the adder 41 is filtered by the band pass filter 43 to remove out-of-band frequency components.
[0024]
The output of the bandpass filter 43 is converted into a pulse signal by the Schmitt trigger 44, and this pulse signal is counted by the counter 45. FIG. 1A shows the output of the band-pass filter 43, and the waveform thereof is almost a sine wave. (B) shows the output of the Schmitt trigger 44, which is a pulse wave.
[0025]
The count value accumulated by the counter 45 is input to the CPU 3. The CPU 3 calculates the frequency of the vortex signal based on this count value, obtains a flow rate measurement value from this frequency, and outputs it to the output circuit 5.
[0026]
Next, of the operation of this embodiment, determination of clogging and abnormal vibration and setting of the noise ratio will be described based on the flowchart of FIG. First, the outputs of the spectrum analyzers 21 and 22 are acquired, and the ratio of the output of the spectrum analyzer 21 and the output of the spectrum analyzer 22 in the band where the signal intensity of the spectrum analyzer 21 is the maximum, that is, the signal intensity of that band. Find the ratio.
[0027]
When the signal strength ratio is obtained, it is determined whether the signal is a vortex signal or noise. If it is determined that the band is a vortex signal, it is determined whether there is a clogging, and if there is a clogging, the clogging alarm is turned on. Then, it is checked whether the band is a noise band in descending order of the signal intensity, and the signal intensity ratio of the noise band is set in the adder 41 as a noise ratio.
[0028]
If it is determined that there is noise, it is determined whether there is abnormal vibration, and if there is abnormal vibration, the abnormal vibration alarm is turned on. Then, regardless of the presence or absence of abnormal vibration, the signal intensity ratio of the band is set in the adder 41 as a noise ratio. Note that these processes are performed by software by the CPU 3.
[0029]
Next, signal and noise determination and clogging determination will be described with reference to FIG. The vertical axis of the graph in FIG. 3 represents the ratio of the outputs of the spectrum analyzer 21 and the horizontal axis, and the horizontal axis represents the degree of clogging. SP1 and NP1 in the figure are the outputs of the spectrum analyzer 21 and represent signals and noise, respectively. Similarly, SP2 and NP2 are outputs of the spectrum analyzer 22 and represent signals and noise, respectively.
[0030]
These SP1, NP1, SP2, and NP2 correspond to the stresses S1, S2, N1, and N2 in FIG. 5B, respectively. As can be seen from the figure, in the case of the signal (S1, S2), the stress S1 detected by the piezoelectric element 81 is larger than the stress S2 detected by the piezoelectric element 82, and in the case of noise (N1, N2) The noise N2 detected by the piezoelectric element 82 is larger.
[0031]
The output of the piezoelectric element 81 corresponds to the output of the spectrum analyzer 21, and the output of the piezoelectric element 82 corresponds to the output of the spectrum analyzer 22. Therefore, in the case of a signal, the output of the spectrum analyzer 21 is larger than the output of the same 22, and in the case of noise, the output is the same. Therefore, if the output of the spectrum analyzer 21 / the output of the spectrum analyzer 22 on the vertical axis in FIG.
[0032]
Actually, if this ratio is larger than a predetermined minimum signal ratio, it is determined as a signal, and if it is smaller, it is determined as noise. This minimum signal ratio varies depending on the aperture. For example, when the aperture is 50 A, a value of 1.1 is used.
[0033]
As shown in FIG. 3, the signal ratio SP1 / SP2 tends to decrease as clogging increases. Therefore, a clogging judgment ratio is set, and when SP1 / SP2 becomes smaller than this value, it is judged that clogging has occurred.
[0034]
The determination of abnormal vibration is made based on the output of the adder 41. If the signal intensity of the band determined by the CPU 3 as a noise band is larger than the sensitivity curve and smaller than the first threshold value T1 or the signal intensity is larger than the second threshold value T2, it is determined as abnormal vibration. The second threshold value T2 is larger than the first threshold value T1, and these values are predetermined.
[0035]
Next, the operations of the spectrum analyzer 42 and the band pass filter 43 will be described with reference to FIG. 4, (A) shows the waveform of the vortex signal on which noise is superimposed, and (B) shows the result of spectrum analysis of the signal (A) by the spectrum analyzer 42. FIG. The horizontal axis of (B) is a frequency plotted on a logarithmic scale, and is divided into six bands SB1 to SB6 here. In addition, the vertical axis in the figure represents the signal intensity in each band.
[0036]
The straight line that rises to the right is a sensitivity curve and represents the detection sensitivity of the signal. As the frequency increases, the detection sensitivity tends to increase. This sensitivity curve can be obtained in advance from the characteristics of the vortex generator 7 and the piezoelectric elements 81 and 82.
[0037]
A band whose signal intensity is higher than the sensitivity curve is defined as a band of the vortex signal, and the characteristics of the bandpass filter 43 are set so as to pass only that band. In FIG. 4, since the signal intensity of the SB2 band is maximum but below the sensitivity curve, it is determined that the band of SB5 whose signal intensity exceeds the sensitivity curve is a vortex signal.
[0038]
FIG. 4C shows the characteristics of the bandpass filter 43 set in this way. The characteristic of passing only the band of SB5 is shown. FIG. 4D shows the output of the band pass filter 43. You can see that the noise has been removed.
[0039]
When there are a plurality of bands whose signal intensity is higher than the sensitivity curve, the band pass filter 43 is set so that only the band having the maximum signal intensity is used as a band of the vortex signal. When a large abnormal vibration occurs, the noise band may be erroneously determined as a signal band. In this case, the abnormal vibration alarm described with reference to FIGS. 2 and 3 is output.
[0040]
The output of the band pass filter 43 is input to the Schmitt trigger 44 and converted into a rectangular wave, and is counted by the counter 45. The count value of the counter 45 is input to the CPU 3 to calculate a flow rate signal, and this flow rate signal is output from the output circuit 5 to the outside.
[0041]
Since the bandpass filter 43 has to switch frequency characteristics at high speed, the bandpass filter 43 is installed by installing a bandpass filter controller 43C.
[0042]
Further, the spectrum analyzer 42 and the band pass filter 43 may be omitted, and the output of the adder 41 may be input to the Schmitt trigger 44 to obtain the flow rate value. The noise removal effect is slightly worsened, but the configuration is simplified.
[0043]
Further, the band pass filter 43C may be omitted and the band pass filter 43 may be controlled by software from the CPU 3. That is, the band pass filter 43 may be controlled so as to pass only the band determined by the CPU 3 as a signal.
【The invention's effect】
As is clear from the above description, the following effects can be expected according to the present invention. According to the first aspect of the present invention, the two detectors 81 and 82 for detecting the vortex signal generated by the vortex generator and the output of each of the detectors 81 and 82 are divided into a plurality of frequency bands, and the signal intensity of these bands is obtained. The first spectrum analysis unit 2 to be output, the noise ratio calculation unit 3 that receives the output and determines the noise ratio, and the noise ratio calculated by the noise ratio calculation unit 3 are input to the two detection units 81 and 82. And an adder 41 for adding a signal related to the output at the ratio of the noise ratio. The flow rate value is obtained based on the output of the adder 41, and the noise ratio calculator 3 includes two detectors 81, The noise band is determined from the signal intensity ratio of each of the 82 bands, and the signal intensity ratio of the band having the maximum signal intensity among the bands determined to be noise is output to the adding unit 41 as the noise ratio. .
[0044]
Since the noise is determined by always analyzing the frequency of the output of the detection unit to determine the noise ratio, the noise ratio can be set according to the situation. Therefore, there is an effect that an accurate flow rate value can be obtained even in a noisy environment such as vibration.
[0045]
Even if the operating conditions change, the noise ratio according to the operating conditions can be set, so there is no need to manually reset the noise ratio, and there is an effect that the maintenance is simplified.
[0046]
The invention described in claim 2 has a bandpass filter 43 to which the output of the adder 41 is input in the invention described in claim 1, and the band which the noise ratio calculation unit 3 has determined as a signal by the bandpass filter 43. Only the flow rate is allowed to pass through, and the flow rate value is obtained from the output of the band pass filter 43.
[0047]
Since noise removal by the bandpass filter 43 is added, the noise resistance is further increased, and there is an effect that the flow rate value can be accurately measured even in an environment where noise such as vibration is large.
[0048]
The invention according to claim 3 is the invention according to claim 1, further comprising a second spectrum analysis unit 42 to which the output of the addition unit 41 is input, and a bandpass filter 43 to which the output of the addition unit 41 is input. Then, the second spectrum analysis unit 42 divides the input into a plurality of frequency bands to determine the signal strength of each band, determines a band having a signal strength greater than a predetermined sensitivity curve as a signal band, The band-pass filter 43 is controlled so as to pass only the signal of this band, and the flow rate value is obtained from the output of the band-pass filter 43.
[0049]
Since the signal whose noise has been reduced by the adder 41 is further subjected to frequency analysis and only the band of the signal is passed through the band pass filter 43, the noise resistance is further improved and the noise caused by vibration and other factors is large. But there is an effect that the flow rate can be measured accurately.
[0050]
According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the noise ratio calculation unit 3 is clogged when the signal intensity ratio of the band determined to be a signal is equal to or less than a predetermined clogging determination ratio. An alarm is output. The blockage of the pipe line can be detected in advance, and an accident can be prevented.
[0051]
According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, when the signal strength of the output of the adder 41 in a band determined as noise is smaller than a predetermined abnormal vibration determination first threshold value or An abnormal vibration alarm is output when it is larger than the abnormal vibration determination second threshold.
[0052]
Abnormal vibration can be detected, and an increase in error due to this can be prevented, so that there is an effect that it can be used safely even in an environment with large vibration. In addition, there is an effect that an accident due to abnormal vibration can be prevented in advance.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of the present invention.
FIG. 2 is a flowchart for explaining the operation of the embodiment of the present invention.
FIG. 3 is a diagram for explaining a vortex signal and noise determination procedure;
FIG. 4 is a diagram for explaining a vortex signal band determination procedure;
FIG. 5 is a cross-sectional view of a vortex detector of the vortex flowmeter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Charge-digital conversion part 11,12 Charge amplifier 13,14 A / D converter 2 Spectrum analysis part 21,22,42 Spectrum analyzer 3 CPU
4 Signal Processing Unit 41 Adder 43 Band Pass Filter 43C Band Pass Filter Controller 44 Schmitt Trigger 45 Counter

Claims (5)

A vortex generator, two detectors for detecting vortex signals generated by the vortex generator, and outputs of the two detectors are divided into a plurality of frequency bands, and the signal intensities of those bands are output. A first spectrum analysis unit; a noise ratio calculation unit that receives an output of the first spectrum analysis unit to determine a noise ratio; and a noise ratio calculated by the noise ratio calculation unit is input to the two detection units. An adder for adding a signal related to the output at a ratio of the noise ratio, and obtaining a flow rate value based on the output of the adder, and the noise ratio calculator is the two detectors of each band The noise band is determined from the signal intensity ratio of the signal, and the signal intensity ratio of the band having the maximum signal intensity among the bands determined to be noise is output to the adding unit as a noise ratio. Vortex flow meter that. A band-pass filter to which the output of the adder is input is provided, and the band-pass filter is used to pass only the band determined by the noise ratio calculator as a signal, and the flow rate value is obtained from the output of the band-pass filter. The vortex flowmeter according to claim 1, which is configured as described above. A second spectrum analysis unit to which the output of the addition unit is input; and a bandpass filter to which the output of the addition unit is input. The second spectrum analysis unit converts the input into a plurality of frequency bands. Dividing and obtaining the signal intensity of each band, determining that the band whose signal intensity is larger than a predetermined sensitivity curve is a signal band, and controlling the bandpass filter so as to pass only the signal of this band The vortex flowmeter according to claim 1, wherein a flow value is obtained from an output of the bandpass filter. 4. The noise ratio calculation unit outputs a clogging alarm when a ratio of signal intensities of a band determined to be a signal is equal to or less than a predetermined clogging determination ratio. The vortex flowmeter described. The noise ratio calculation unit detects an abnormal vibration alarm when the signal intensity of the output of the addition unit in a band determined to be noise is smaller than a predetermined abnormal vibration determination first threshold value or larger than an abnormal vibration determination second threshold value. The vortex flowmeter according to any one of claims 1 to 4, wherein the vortex flowmeter is output.

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