JPH09287984A - Karman vortex flow meter - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a Karman vortex flowmeter capable of detecting that an adhered substance adheres to a vortex generator and the measurement accuracy is deteriorated. SOLUTION: The frequency and amplitude voltage of the signal output from the eddy detection means are calculated, and when the frequency becomes equal to or lower than a predetermined voltage value with respect to the amplitude voltage when there is originally no deposit, measurement is performed by the deposit. It is output to the stable measurement output means as the accuracy is lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Karman vortex flowmeter for measuring the flow rate or flow velocity of fluid. More specifically, the present invention relates to a technique for detecting and outputting a decrease in measurement accuracy due to an adhered matter that adheres to a vortex generator used in a Karman vortex flowmeter.

The term "fluid" as used herein refers to gas or liquid. In addition, "flow rate" refers to the total amount of fluid that has passed through the Karman vortex flow meter at a given time, and "flow velocity" refers to the amount of fluid that passes through the Karman vortex flow meter per unit time.

[0003]

2. Description of the Related Art Conventionally, a Karman vortex flowmeter has been used to measure the flow velocity or flow rate of a fluid flowing through a pipe or the like. As shown in FIGS. 1A and 1B, the Karman vortex flowmeter 1 is mounted between the tubes 2. When the fluid to be measured flows in the direction A, a Karman vortex is generated when the fluid passes through the vortex generator 3. What is Karman vortex?
When a fluid passes through the vortex generator 3, it means a vortex in which the number of vortices is proportional to the flow rate or flow velocity. This vortex is detected by the piezoelectric element 5 which is the vortex detection means mounted on the support 4 arranged behind the vortex generator 3, and is output as an electric signal. This output signal is processed by the controller 6, which is a processing means, and the flow rate value is output to a display or an output terminal.

The frequency f of the output signal detected by the piezoelectric element 5 is proportional to the flow rate Q as shown in FIG.
(A)) and its amplitude voltage V is proportional to the square of the flow rate Q (FIG. 2 (b)). The flow rate Q is measured by using this characteristic to detect the frequency f of the output signal.

FIG. 3 is a block diagram showing the structure of a conventional Karman vortex flowmeter. The turbulence of the fluid flow caused by the vortex generator 3 is detected by the vortex detection means 11 (corresponding to the piezoelectric element 5 in FIG. 2) and amplified by the amplification means 12. The amplified signal has a threshold value Vt set in advance in the comparator 13.
Compared to 0. The output signal of the comparator 13 becomes a pulse signal, and the counter 14 counts the number of pulses. The frequency of the output signal of the vortex detection means 11 is calculated by the number of pulses, and the conversion means 1 such as a frequency-voltage converter is calculated.
5, the frequency is converted into the flow rate signal. Liquid crystal and LE
A signal corresponding to the flow rate signal is output to the display means 16 such as D and the output means 17.

Further, from the output means 17, the flow rate signal is compared with a preset flow rate value to turn on / off.
An off signal can also be output.

As the vortex detecting means of such a Karman vortex flowmeter, a strain gauge may be used instead of the piezoelectric element 5 of FIG. 1, or a pressure sensor may be used. Further, when the pressure sensor is used, as shown in FIG. 1C, the pressure sensor 7 is attached to the vortex generator 3 itself and the support is omitted.
A Karman vortex flowmeter can also be constructed.

[0008]

However, the conventional Karman vortex flowmeter has the following problems because the flow rate is calculated only by the frequency of the output signal from the vortex detection means.

In the Karman vortex flowmeter, since the vortex generator 3 is mounted in the pipe in a state of impeding the flow of fluid, impurities flowing with the fluid adhere (hereinafter referred to as "adhesion"). This deposit increases with time and the Karman vortex is disturbed. FIG. 4 shows an output signal waveform of the piezoelectric element 5, and FIG. 4 (a) shows an output signal waveform V when there is no unattached object.
s, FIG. 4 (b) is an output signal waveform Vn when an adhering substance adheres using the Karman vortex flowmeter for a long period of time.

4 (a) and 4 (b) have the same flow rate, the vortex is affected by the adhering matter at Vn compared to Vs, so that a noise signal with a high frequency is generated. Overlapping, the amplitude voltage is further reduced.

When the frequency of this output signal is calculated, the frequency as the calculation result of the comparator 13 in FIG. 3 differs. That is, the frequency when impurities are attached is higher than the frequency when there is no deposit due to the superimposed noise. Therefore, a measurement error occurs and the measurement accuracy decreases.

In order to remove the deposits adhering to the Karman vortex flowmeter, the Karman vortex flowmeter is removed and cleaned by switching the fluid flow as a pipe as shown in FIG. Specifically, the valves 20 and 21 are both closed, and the valve 22 is opened to change the fluid flow to remove the Karman vortex flowmeter and remove the deposits on the vortex generator and the support. Therefore, if the decrease in measurement accuracy due to the adhered matter cannot be detected, periodical removal work is required, which is a heavy burden on the user.

The present invention reduces the burden on the user by detecting the presence or absence of non-adherent matter in the Karman vortex flowmeter and outputting an alarm signal only when adhering is detected to prompt removal of the adhering matter. With the goal. At the same time, it is intended to inform the user whether or not the flow rate is accurately measured.

[0014]

In the first aspect of the invention, the vortex detecting means detects the Karman vortex generated by the fluid passing through the vortex generator, thereby measuring the flow rate or the flow velocity of the fluid. In Karman vortex flowmeter,
Amplifying means for amplifying the output signal of the vortex detecting means, frequency calculating means for calculating the frequency of the output signal of the amplifying means, amplitude calculating means for calculating the amplitude of the output signal of the amplifying means, and the frequency calculating means. By a threshold voltage calculation means for calculating a threshold voltage based on the output signal of, and a comparison means for comparing the output signal of the amplitude calculation means and the magnitude of the threshold voltage, a Karman vortex flowmeter, The deposit is detected by using not only the frequency signal of the Karman vortex but also the amplitude signal.

In the second and third inventions, in the Karman vortex flowmeter for measuring the flow rate or the flow velocity of the fluid by the vortex detecting means detecting the Karman vortex generated by the fluid passing through the vortex generator, Amplification means for amplifying the output signal of the vortex detection means, and a first frequency calculation for outputting a signal based on the first frequency of the output signal of the amplification means by comparing the output signal of the amplification means with a predetermined voltage. Means for calculating a first threshold voltage higher than the predetermined voltage based on the signal based on the first frequency, and second means for calculating a threshold voltage based on the signal based on the first frequency. Second threshold voltage calculating means for calculating a threshold voltage, and a second frequency for outputting a signal based on a second frequency obtained by comparing the output signal of the amplifying means with the first threshold voltage. A comparator for comparing the second threshold voltage and the output signal of the second frequency calculator, or a signal based on the first frequency and the second frequency. By using a Karman vortex flowmeter equipped with a comparison means for outputting a signal based on the difference between the output signals, the frequency of the Karman vortex is calculated using two types of threshold voltages, and the signal based on the frequency difference is added. Detect a kimono.

In the fourth and fifth inventions, in the Karman vortex flowmeter for measuring the flow rate or the flow velocity of the fluid by the vortex detecting means detecting the Karman vortex generated by the fluid passing through the vortex generator, Amplifying means for amplifying the output signal of the vortex detecting means; frequency calculating means for calculating a first frequency of the output signal of the amplifying means by comparing the output signal of the amplifying means with a predetermined voltage; A first threshold voltage calculating means for calculating a first threshold voltage higher than the predetermined voltage based on the frequency, and a second threshold voltage calculating means for calculating a second threshold voltage based on the first frequency. And a signal based on a second frequency is output from the frequency calculating means by comparing the output signal of the amplifying means with the first threshold voltage, and the first and second
The signal based on the frequency is calculated by switching the first and second threshold voltages of the frequency calculating means in a time-division manner, and the output of the second threshold voltage and the output of the second frequency calculating means. Comparison means for comparing signals,
Alternatively, the Karman vortex flowmeter is provided with a comparison unit that outputs a signal based on the difference between the signal based on the first frequency and the output signal based on the second frequency, so that the frequency of the Karman vortex can be set to two types. The threshold voltage is used to perform time-division switching for calculation, and the adhered matter is detected by a signal corresponding to the frequency difference.

A sixth aspect of the present invention is the Karman vortex flowmeter according to any one of the first to fifth aspects, further comprising display means for displaying the output signal of the comparison means to inform the user of the adherence of the adhered matter. There is.

A seventh aspect of the present invention is the Karman vortex flowmeter according to any one of the first to fifth aspects, which further comprises an output means for outputting the output signal of the comparing means to output the attachment of the deposit to the outside. .

[0019]

FIG. 6 is a block diagram showing the configuration of a Karman vortex flowmeter according to one embodiment of the present invention. In this Karman vortex flowmeter, the output signal from the vortex detection means 31 is amplified by the amplification means 32. The amplified signal Va is compared with the threshold voltage Vt0 by the comparator 33. The output signal of the comparator 33 becomes the pulse signal Vb and the signal V corresponding to the frequency of Va (assumed to be f1) is outputted by the counter 34 which is the counting means.
c is output. Here, the comparator 33 and the counter 34 constitute the frequency calculation means 35. The flow rate is calculated by the conversion means 36 based on this output signal and output to the display means 37A and the output means 37B, and the threshold voltage Vt1 is determined by the threshold voltage calculation means 39. This threshold voltage Vt1 is determined based on the frequency f1 of Va, and is set to a value lower than the amplitude voltage in the case where the signal output from the amplifying means 32 at the time corresponding to the frequency f1 does not include an improper object. There is.

Further, the amplitude signal Vd of the output signal Va of the amplifying means 32 is outputted by the amplitude voltage calculating means 38,
The threshold voltage Vt1 described above is compared with the comparator 40. The output of the comparator 40 is output to the stable measurement output means 41. The stable measurement output unit 41 may be an output unit that outputs a signal to an external device, an indicator lamp such as an LED, or a buzzer.

The signal processing of FIG. 6 will be briefly described with reference to FIG. As described with reference to FIG. 2, the detection signal frequency f is proportional to the flow rate Q, and the amplitude voltage V is output in proportion to the square of the flow rate Q.

First, the flow rate Q1 is calculated from the frequency f1 calculated from the characteristic diagram of FIG. 7 (a). Next, the flow rate is Q
When it is 1, the amplitude voltage must be V0 from the output amplitude voltage curve C0 when no impurities are attached. However, if impurities are attached to the vortex generator,
The amplitude voltage becomes smaller than V0 (for example, V1 in FIG. 7B). In FIG. 7B, the threshold voltage Vt1 is set to a curve C1 so that the value is always smaller than the output amplitude voltage curve C0.
When the amplitude voltage when the flow rate is Q1 is smaller than the threshold voltage curve C1 (for example, when it is V1), impurities adhere to the vortex generator to deteriorate the measurement accuracy. As the stable measurement output means 41 of FIG.
The output signal is output from.

In FIG. 7B, the threshold voltage Vt1 is represented by the curve C1.
However, it may be a broken line (FIG. 6C). Further, in consideration of the fact that the Karman vortex flowmeter has the characteristic that the measurement accuracy becomes extremely poor when the flow rate is small, an erroneous output signal is not output, so as shown in FIG. Is less than a predetermined value, the threshold voltage Vt1 is set to 0 and the stable measurement output means 4
The output from 1 may be omitted.

Further, it can be realized by preliminarily storing as data in a table in the threshold voltage calculation means 39, a storage means such as a memory, and outputting the threshold voltage Vt1 corresponding to the value of f1. In this case, the threshold voltage curve C1 can be set freely.

Further, the threshold voltage curve C1 shown in FIG. 7B is formed by combining the operational amplifiers to form the square operation circuit.
Can also be generated. That is, the square transformation circuit can be constructed by logarithmically transforming the input signal, subsequently doubling it, and further inversely logarithmically transforming it.

FIG. 8 is a block diagram showing the configuration of the Karman vortex flowmeter according to the second embodiment of the present invention. In this Karman vortex flowmeter, the output signal from the vortex detection means 31 is amplified by the amplification means 32. The amplified signal Va is sent to the comparator 3
3 is compared with the threshold voltage Vt0. The output signal of the comparator 33 becomes the pulse signal Vb and the counter 34 serving as counting means.
Then, the signal Vc for the frequency f1 of the output signal of the vortex detector 31 is calculated. Based on this output, the conversion means 36 calculates the actual flow rate, and the display means 37A and the output means 3 are used.
7B and the threshold voltage Vt2 is calculated by the threshold voltage calculation means 42. This threshold voltage Vt2
Is determined based on the calculated frequency f1, and is set to a value lower than the amplitude voltage signal in the case where the signal output from the amplifier 32 does not have an unattached object and higher than Vt0. Therefore, the frequency f2 at the threshold voltage Vt2 becomes lower than the frequency f1 at the threshold voltage Vt0. Here, the comparator 33 and the counter 34 constitute the frequency conversion means 35. The signal output from the amplifier 32 is input to the comparator 43 in which Vt2 is set as the threshold voltage, the output signal of the comparator 43 is counted by the counter 44, and the signal Vd for the counted frequency f2 is output. If Vd is smaller than the threshold voltage Vt3 determined with respect to Vc, the comparing means 46 determines that the adhering matter is attached to the vortex generator or the support, and outputs it to the stable measurement output means 41.

The signal processing of FIG. 8 will be briefly described with reference to FIG. As described with reference to FIG. 2, the detection signal frequency f is proportional to the flow rate Q, and the amplitude voltage V is output in proportion to the square of the flow rate Q.

First, the flow rate Q1 is calculated from the frequency f1 calculated from the characteristic diagram of FIG. 9 (a). Next, the flow rate is Q
When it is 1, the amplitude voltage must be V0 from the output amplitude voltage curve C0 when the non-adherent matter is not attached. As shown in FIG. 9B, a curve C1 having a threshold voltage Vt2 that is lower than the output amplitude voltage curve C0 and higher than the threshold voltage Vt0 of the comparator 33 is set. At 43, the frequency f2 is calculated by comparing with Va. If the frequency f2 is lower than the frequency f1 by a predetermined value or more, it is determined that the adhered matter is adhered, and an output signal is output from the stable measurement output means.

Therefore, the Karman vortex flowmeter in the second embodiment has a threshold voltage calculating means 42 (threshold voltage curve C1 in FIG. 9B) for determining the threshold voltage Vt2 for the flow rate Q.
And for the signal Vc for the frequency f1, the frequency f2
The attachment of the deposit is detected by the provision of the threshold voltage calculation means 45 for determining the threshold voltage Vt3 to be compared with the signal Vd.

Although the threshold voltage Vt2 is continuously changed as the curve C1 in FIG. 9, it may be a broken line (FIG. 6C). The threshold voltage calculation means 42 and the threshold voltage calculation means 45 are previously stored in a storage means such as a memory as data in a table, and configured to output the threshold voltages Vt2 and Vt3 corresponding to the value of f1. be able to. In this case, the threshold voltages Vt2 and Vt3 can be set freely.

As described above, in the embodiment of FIG. 8, the threshold voltage Vt2 is determined by the signal Vc with respect to the frequency f1 of the output signal Va of the amplifying means, but as shown in FIG. 10, the threshold voltages Vt0 and Vt2 are time-divided. 8 by switching
The same processing as can be performed. The time division switching means 51 of FIG. 10 switches the threshold voltage between Vt0 and Vt2 of the output voltage of the threshold value computing means 50.
The threshold voltage Vt2 is calculated by the signal Vc corresponding to the frequency of the output signal Va of the amplifying means 32 calculated by the threshold voltage Vt0.
Is set, and the signal Vd for the frequency of the output signal Va of the amplifying means 32 calculated by the threshold voltage Vt2 is calculated.

The time division switching means 51 outputs the threshold voltage Vt3 from the signal Vc input to the threshold voltage calculating means 52. Vt3 and Vd are input to the comparator 46 and compared with each other.

When Vd is smaller than Vt3, the stable measurement output means 41 outputs an output signal as if the adhered matter is adhered.

In FIGS. 8 and 10, the output signal V
The threshold voltage Vt3 was calculated based on c
Alternatively, the difference between 1 and f2 may be directly calculated, and the signal may be output to the stable measurement signal output means 41 based on the frequency difference. At this time, in FIG. 9, the threshold frequency f3 is set when the frequency is f1, and it is assumed that the measurement can be stably performed if the frequency is higher than this frequency. Therefore, it suffices to set a threshold frequency for each frequency.

[Brief description of drawings]

FIG. 1 is a view showing a state in which a Karman vortex flowmeter is attached to a pipe.

FIG. 2 is a diagram showing characteristics of frequency f and amplitude V with respect to flow rate Q of a Karman vortex flowmeter.

FIG. 3 is a block diagram showing a configuration of a conventional Karman vortex flowmeter.

FIG. 4 is an output signal waveform from the vortex detection means of the Karman vortex flowmeter.

FIG. 5 is a diagram showing a configuration of piping for cleaning the Karman vortex flowmeter.

FIG. 6 is a block diagram showing a configuration of a Karman vortex flowmeter according to an embodiment of the present invention.

FIG. 7 is a characteristic diagram illustrating signal processing of the Karman vortex flowmeter of FIG.

FIG. 8 is a block diagram showing a configuration of a Karman vortex flowmeter according to a second embodiment of the present invention.

9 is a characteristic diagram illustrating signal processing of the Karman vortex flowmeter of FIG.

FIG. 10 is a block diagram showing a configuration of a Karman vortex flowmeter according to a third embodiment of the present invention.

[Explanation of symbols]

 1 Karman Vortex Flowmeter 2 Tube 3 Vortex Generator 4 Support 5 Piezoelectric Element 6 Controller 7 Pressure Sensor 20, 21, 22 Valve 11, 31 Vortex Detection Means 12, 32 Amplification Means 13, 33, 40, 43, 46, 48 comparator 14, 34, 44, 49 counter 15, 36 conversion means 16, 37A display means 17, 37B output means 18, 35, 47, 52 frequency calculation means 39, 42, 45, 50, 52 threshold voltage calculation means 41 Stable measurement output means 38 Amplitude voltage calculation means

Claims (7)

[Claims] 1. A Karman vortex flowmeter for measuring a flow rate or a flow velocity of a fluid by detecting a Karman vortex generated by a fluid passing through a vortex generator, the Karman vortex type flowmeter measuring the output signal of the vortex detecting means. Amplifying means for amplifying, frequency calculating means for calculating the frequency of the output signal of the amplifying means, amplitude calculating means for calculating the amplitude of the output signal of the amplifying means, and a threshold voltage based on the output signal of the frequency calculating means. A Karman vortex flowmeter, comprising: a threshold voltage calculating means for calculating the above; and a comparing means for comparing the output signal of the amplitude calculating means with the magnitude of the threshold voltage. 2. A Karman vortex flowmeter for measuring the flow rate or flow velocity of the fluid by detecting the Karman vortex caused by the fluid passing through the vortex generator, and outputting the output signal of the vortex detection means. Amplifying means for amplifying; first frequency calculating means for outputting a signal based on a first frequency of the output signal of the amplifying means by comparing the output signal of the amplifying means with a predetermined voltage; and the first frequency A first threshold voltage calculating means for calculating a first threshold voltage higher than the predetermined voltage based on a signal based on the above, and a second threshold voltage obtained by comparing the output signal of the amplifying means with the first threshold voltage. Second frequency calculation means for outputting a signal based on the frequency of, and comparison means for outputting a signal based on a difference between the signal based on the first frequency and the output signal based on the second frequency,
Karman vortex flowmeter characterized by having. 3. A Karman vortex flowmeter for measuring the flow rate or flow velocity of the fluid by detecting the Karman vortex generated by the fluid passing through the vortex generator, and outputting the output signal of the vortex detecting means. Amplifying means for amplifying; first frequency calculating means for outputting a signal based on a first frequency of the output signal of the amplifying means by comparing the output signal of the amplifying means with a predetermined voltage; and the first frequency A first threshold voltage calculating means for calculating a first threshold voltage higher than the predetermined voltage based on a signal based on the second voltage, and a second threshold voltage calculating means for calculating a second threshold voltage based on the signal based on the first frequency. Threshold voltage calculating means; second frequency calculating means for outputting a signal based on a second frequency obtained by comparing the output signal of the amplifying means with the first threshold voltage; and the second threshold. Karman vortex flow meter, characterized in that it comprises comparing means for comparing the output signal voltage and the second frequency computing unit. 4. A Karman vortex flowmeter for measuring a flow rate or a flow velocity of the fluid by detecting the Karman vortex generated by the fluid passing through the vortex generator, the Karman vortex flowmeter measuring the output signal of the vortex detection means. Amplifying means for amplifying; frequency calculating means for calculating a first frequency of the output signal of the amplifying means by comparing the output signal of the amplifying means with a predetermined voltage; and the predetermined voltage based on the first frequency. Higher first
Threshold voltage calculating means for calculating a threshold voltage of the second threshold voltage, second threshold voltage calculating means for calculating a second threshold voltage based on the first frequency, an output signal of the amplifying means and the first A signal based on a second frequency is output from the frequency calculating means by comparing with a threshold voltage of, and a signal based on a difference between the signal based on the first frequency and the output signal based on the second frequency is output. Kalman, wherein the comparison means and the signals based on the first and second frequencies are calculated by time-divisionally switching the predetermined voltage and the first threshold voltage of the frequency calculation means, respectively. Vortex flow meter. 5. A Karman vortex flowmeter for measuring a flow rate or a flow velocity of the fluid by detecting the Karman vortex generated by the fluid passing through the vortex generator, the Karman vortex flowmeter measuring the output signal of the vortex detection means. Amplifying means for amplifying; frequency calculating means for calculating a first frequency of the output signal of the amplifying means by comparing the output signal of the amplifying means with a predetermined voltage; and the predetermined voltage based on the first frequency. Higher first
Threshold voltage calculating means for calculating a threshold voltage of the second threshold voltage, second threshold voltage calculating means for calculating a second threshold voltage based on the first frequency, an output signal of the amplifying means and the first A signal based on a second frequency is output from the frequency calculation means by comparing the second threshold voltage with a signal based on the second frequency; The Karman vortex flowmeter, wherein the signal based on the second frequency is calculated by time-divisionally switching the predetermined voltage and the first threshold voltage of the frequency calculating means. 6. A Karman vortex flowmeter according to claim 1, further comprising display means for displaying an output signal of said comparison means. 7. The Karman vortex flowmeter according to claim 1, further comprising output means for outputting the output signal of the comparison means.