JPH0674799A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To obtain a vortex flowmeter which can detects a flow rate accurately without deteriorating S/N even upon increase of frequency of a vortex signal. CONSTITUTION:A negative feedback AGC circuit 6 is provided for an amplifier circuit 4 and a filter circuit 3 for removing noise from an electric signal representative of a flow rate generated from a signal converting circuit 1. The AGC circuit 6 is controlled through an average value circuit based on an average value of output signals from the amplifier circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flow meter capable of obtaining flow rate information by detecting a vortex frequency proportional to a flow velocity.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a basic signal processing system of a conventional vortex flowmeter. In the figure, reference numeral 1 is a signal conversion circuit for converting an eddy signal into an electric signal, which is connected to a reference voltage 2 to output an electric signal centering on the reference voltage 2. Reference numeral 3 is a filter circuit connected to the output side of the signal conversion circuit 1 for removing electrical noise, and 4 is an output circuit connected to the output side of the filter circuit 3 for amplifying the electric signal passing through the filter circuit 3. Reference numeral 5 denotes a waveform shaping circuit which is connected to the output side of the amplifier circuit 4 and which shapes the output of the amplifier circuit 4 into a rectangular wave and transmits it to a control unit (not shown).

Next, the operation of the prior art will be described with reference to FIG. In FIG. 6, V ₁ is the output of the signal conversion circuit 1, and V _1
2 is the output of the filter circuit 3, V ₃ is the output of the amplifier circuit 4,
V ₄ represents the output of the waveform shaping circuit 5. Output V ₁ of the signal converter circuit 1 has a small spectrum of the signal component as shown in FIG. 6, it is superimposed high frequency noise and low frequency noise, too to do waveform shaping and amplifying as S / N The ratio is bad. By inputting the output V ₁ of the from the signal conversion circuit 1 to the filter circuit 3, a high frequency noise as shown in V ₂ of FIG. 6, to remove low frequency noise, by taking out only the electrical signal of the signal components, It becomes possible to reliably perform signal processing in the subsequent stage. The filter circuit 3 is preset to have a certain frequency characteristics as shown in FIG. 7, f ₁
Is called the lower limit cutoff frequency, and f ₂ is called the upper limit cutoff frequency. The area between f ₁ and f ₂ is called the pass band,
The filter circuit 3 operates so as to pass the frequency components in the meantime without attenuating and to attenuate the frequency components below f ₁ and above f ₂ along the characteristic curve of FIG. 7. The output V ₂ of the filter circuit 3 which has passed through the filter circuit 3 and in which the noise component has been removed to become only the signal component is amplified by the amplification circuit 4 at a preset amplification factor, and as shown by V ₃ in FIG. Waveform shaping circuit 5
Output to. The waveform shaping circuit 5 has an upper limit threshold value and a lower limit threshold value, and a hysteresis voltage is provided to a comparison voltage which is a reference for waveform shaping to secure a noise margin. Waveform shaping is performed at a voltage between the upper and lower thresholds, and the waveform shaping circuit 5 causes the rectangular wave as shown by V ₄ in FIG. 6 each time the upper and lower thresholds are crossed. Is output. The flow rate information is transmitted by transmitting the frequency of this rectangular wave to the control unit.

[0004]

Since the conventional vortex flowmeter is constructed as described above, the signal component is attenuated and becomes smaller along the attenuation characteristic curve of the filter circuit as the frequency of the vortex signal increases. However, the S / N ratio with the low-frequency noise in the pass band is significantly deteriorated, and reliable waveform shaping becomes impossible. As a result, accurate flow rate information cannot be transmitted.

That is, it is generally well known that the amplitude of the vortex signal is extremely small at a low frequency, and the amplitude of the vortex signal also increases as the frequency increases. Even when a signal is converted into an electric signal, its output has the same relationship as above.
It is necessary to determine the frequency characteristic of the filter circuit 3 in FIG. 5 as shown in FIG. 7 in consideration of the frequency region in which the vortex signal is generated and the amplitude of the vortex signal converted into the electric signal. In FIG. 7, f ₁ is determined by the lowest frequency of the vortex signal, and f ₂ is determined by the S / N ratio of the output of the signal conversion circuit 1 near the lowest frequency. In other words, it is necessary to remove only the noise of the vortex signal having a very small amplitude in the vicinity of the lowest frequency of the vortex signal so that only the signal component can be extracted and transmitted to the amplifier circuit 4 of the next stage. Therefore, as in many cases, when the S / N ratio of the output of the signal conversion circuit 1 is extremely low, f ₂ must be set to a considerably low frequency side. Shows an example in which moving the f ₂ in the low frequency range side in FIG. 8, reference numeral f ₃ is a cut-off frequency when you move the f ₂ to the low frequency band side, passband ensure maximum gain The vortex frequency is compressed to the low frequency side around the lowest frequency. In the case where the frequency characteristic of the filter circuit 3 is set in this way, although it often occurs, the frequency of the vortex signal increases to the region of f ₄ as shown in FIG. 9, and the low frequency noise component is generated. When it occurs in the region of f ₅ , it has a waveform in which the low frequency noise component is superimposed on the signal component as indicated by V ₁ in FIG. Originally, the region of f ₅ in FIG. 9 is the lowest frequency region of the vortex frequency, and since the amplitude of the vortex signal in this region is extremely small, it is passed without being attenuated so that the S / N ratio can be as high as possible. Therefore, when the vortex frequency is in the region of f ₄ , the signal component is attenuated along the attenuation characteristic curve, and on the other hand, in the region of f ₅ , that is, f
_Since the low frequency noise in the frequency region between ₁ and f ₃ is passed through without being attenuated, the S / N ratio at the point of V ₂ is significantly deteriorated. Since the signal on which the low frequency noise is superimposed is amplified by the amplifier circuit 4 in the subsequent stage, V _{3 in} FIG.
Such a phenomenon occurs. As a result, accurate waveform shaping by the waveform shaping circuit 5 in the subsequent stage becomes impossible, and a serious problem that the correct flow rate information cannot be transmitted to the control unit becomes apparent.

The present invention has been made to solve the above-mentioned problems, and an accurate flow rate (flow velocity) can be detected without deteriorating the S / N ratio even if the frequency of the vortex signal increases. The purpose is to obtain a vortex flowmeter.

[0007]

A vortex flowmeter according to the present invention detects a vortex generating column provided in a fluid flow path and a vortex generated by the vortex generating column in proportion to a flow velocity to detect an electric signal. A conversion circuit for converting into a conversion circuit, a filter circuit connected to the output side of the conversion circuit, and an AGC circuit connected between the input side and the output side of the filter circuit for negatively feeding back the output of the filter circuit as an input. And an average value circuit connected to the AGC circuit and controlling the AGC circuit with an average value of the output signal of the filter circuit based on the output signal of the filter circuit.

[0008]

The vortex flowmeter according to the present invention controls the AGC circuit that provides negative feedback to the input side of the filter circuit by the average value based on the output signal of the filter circuit obtained by the average circuit. Output can always be kept constant, and by varying the feedback ratio of this feedback loop, reliable signal processing can be performed without deteriorating the S / N ratio of the vortex signal.

[0009]

【Example】

Example 1. The first embodiment of the present invention will be described below with reference to the block diagram shown in FIG. In the figure, 1 to 5 are shown in FIG.
The description is omitted because it is the same as or equivalent to that shown in FIG. Reference numeral 6 denotes an AGC circuit connected between the output side of the amplifier circuit 4 and the input side of the filter circuit 3, which is between the input and output of the filter circuit 3. The AGC circuit 6 is amplified by a signal from the outside. The rate can be varied, and is composed of a variable transconductance, a field effect transistor, or the like. Reference numeral 7 is an average value circuit whose input side is connected to the output side of the amplifier circuit 4 and whose output side is connected to the control terminal of the AGC circuit 6. This average value circuit 7 is an average of the outputs of the amplifier circuit 4. A value is obtained and the AGC circuit 6 is controlled by this average value. V ₁ is the output of the signal conversion circuit 1, V ₂ is the output of the filter circuit 3, V ₃ is the output of the amplifier circuit 4, V ₄ is the output of the waveform shaping circuit 5, V ₅ is the output of the average value circuit 7, V ₆ represents the output of the AGC circuit 6.

Next, the operation of the first embodiment will be described with reference to FIG. The major difference between the first embodiment and the prior art shown in FIG. 8 is that the output V ₃ of the amplifier circuit 4 is negatively fed back to the input side of the filter circuit 3. If the transfer function of the filter circuit 3 is G ₁ , the transfer circuit of the amplifier circuit 4 is G ₂ , and the transfer function of the AGC circuit 6 is β, then the overall transfer function G ₀ in the prior art is:

G ₀ = G ₁ · G ₂ (1)

[0012] On the other hand, the overall transfer function of Example 1 is

G _N = G ₁ · G ₂ / (1 + G ₁ · G ₂ · β) (2)

The difference is that the characteristic equation is generated in the transfer function (2) of the first embodiment. The transfer function β of the AGC circuit 6 included in the equation (2) is specially called a feedback ratio, and the feature of the first embodiment is that the feedback ratio β is changed to change the overall transfer function G _N. There is a point to let.

In order to solve the problems of the prior art, for example, both the frequency of the signal component and the frequency of the low frequency noise component are attenuated or passed at the same rate, or vice versa. do it. In the latter case, the amplification factor increases as the frequency of the signal component increases, making it more susceptible to various noises, and when the amplified output saturates the power supply voltage, the frequency component changes extremely and is expected. There is a risk of causing problems such as being unable to perform street operations.

Therefore, in the first embodiment, the former method is adopted, and the characteristic that the S / N ratio of the vortex amplitude is improved with the increase of the vortex frequency is obtained by attenuating it at the same rate and passing it at the same rate. It is possible to obtain advantages such as sufficient utilization.

The frequency characteristics of the closed loop gain of the filter circuit 3, the amplifying circuit 4, and the AGC circuit 6 which form the feedback loop when this method is used, the input is V ₁ , the output is V ₃ , and the feedback ratio β is changed. FIG. 2 shows the characteristic diagram represented by the above. FIG. 2 shows the result of G _N obtained by sequentially changing the value of β in the equation (2). As β increases, the upper limit cutoff frequency changes to f ₃₁ , f ₃₂ , and f ₃₃ in the higher direction, and the lower limit cutoff frequency changes to f ₁₁ , f ₁₂ , and f ₁₃ in the lower direction. Then, the gain of the pass band is set to a certain magnitude by β, and the pass band width is widened. Even if the vortex frequency increases, if β is controlled so that the vortex frequency is always located in the pass band of the frequency characteristic as shown in FIG. 2, the S / N ratio of V ₃ becomes equal to that of the signal conversion circuit 1 at this time. Output V
It is possible to secure the same level as the S / N ratio of ₁ . Further, since the S / N ratio of V ₁ is improved as the vortex frequency increases, the vortex signal component and low frequency noise component of the output V ₁ of the signal conversion circuit 1 are controlled by controlling as described above. Since the signals are passed (or amplified) at the same rate, the improved S / N ratio can be used as it is.
The phenomenon like 0 will not occur.

As described above, in order to make the feedback rate β variable, in the first embodiment, the gain of the AGC circuit 6, that is, the feedback rate β is controlled so that the amplitude of the V ₃ signal is always a certain magnitude. There is. The output of the average value circuit 7 for obtaining the average value of the amplitude of V ₃ is used for this control signal, and the amplitude of V ₃ is automatically adjusted so as to always have a constant magnitude regardless of the frequency. . The state is shown in FIG. 3 and will be described in association with FIG. The filter circuit 3 and the amplifier circuit 4 have the above-mentioned V
_In order to amplify the difference between ₁ and the output V ₆ of the AGC circuit 6, V
_When the amplitude of the signal voltage of ₁ increases, the gain of the AGC circuit 6, that is, the feedback ratio β increases and the amplitude of V ₆ also increases so that the amplitude of V ₃ is always kept constant. As a result, (V ₁ -V
Value of ₆₎ also operates as to maintain a constant, low-frequency noise component and the high frequency noise component gain superimposed on the V ₁ descends s ordinal for V ₁ of the V ₃ is the frequency as shown in FIG. 2 It will be removed according to the characteristics. The waveform shaping circuit 5 shapes the signal waveform from which this noise is removed into a rectangular wave, and transmits it to the control unit.

By operating as described above, the vortex flowmeter can take out only the signal component without being affected by the low frequency noise and the high frequency noise, and can transmit the accurate flow rate information to the control unit.

Example 2. Incidentally, in the above-mentioned first embodiment, A
Although the output of the average value circuit 7 for obtaining the average value of V ₃ is used for the control signal of the GC circuit 6, as shown in FIG. 4, the frequency-voltage conversion for converting the frequency of V ₄ of the rectangular wave output into the DC voltage is performed. The circuit may be connected to the output of the waveform shaping circuit 5 as the average value circuit 8 and the output of the average value circuit 8 may be used as the control signal of the AGC circuit 6. Further, the AGC circuit 6 does not need to be configured by an analog circuit that can be continuously changed, and can be amplified by an external control signal even if it is configured by a method of switching in several stages or a digital circuit such as a D / A conversion circuit. Any structure may be used as long as the rate can be controlled, and the same effect as that of the first embodiment can be obtained.

[0021]

As described above, according to the present invention, the vortex generating column provided in the fluid flow path and the vortex generated by the vortex generating column in proportion to the flow velocity are detected and converted into an electric signal. A conversion circuit; a filter circuit connected to the output side of the conversion circuit; an AGC circuit connected between the input side and the output side of the filter circuit for negatively feeding back the output of the filter circuit as an input; An average value circuit that is connected to the AGC circuit and controls the AGC circuit with the average value of the output signal of the filter circuit based on the output signal of the filter circuit is provided, so that the signal component is not affected by noise. It is possible to obtain only the vortex flowmeter that is reliable, has high performance, is highly accurate, and is inexpensive, because it is possible to take out only the information and to transmit reliable flow rate information to the control unit. That.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram showing the operation of the first embodiment of the present invention.

FIG. 3 is a diagram showing an operation of the first embodiment of the present invention.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a block diagram showing an example of a conventional technique.

FIG. 6 is a diagram showing an ideal operation of a conventional technique.

FIG. 7 is a frequency characteristic of a general amplifier circuit of the related art.

FIG. 8 is a frequency characteristic of a general amplifier circuit of the related art.

FIG. 9 is a frequency characteristic showing a relationship between a signal component and a noise component that often occur in the conventional technique.

FIG. 10 is a diagram showing an actual operation of a conventional technique.

[Explanation of symbols]

 1 signal conversion circuit 3 filter circuit 6 AGC circuit 7 and 8 average value circuit

Claims (1)

[Claims] 1. A vortex generating column provided in a fluid flow path, a conversion circuit for detecting a vortex generated by the vortex generating column in proportion to a flow velocity and converting it into an electric signal, and an output side of the conversion circuit. Connected between the input side and the output side of this filter circuit,
An AG that negatively feeds back the output of the filter circuit as an input
A C circuit, and an average value circuit connected to the AGC circuit and controlling the AGC circuit with an average value of the output signal of the filter circuit based on the output signal of the filter circuit. Vortex flow meter.