JPH0222513A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To obtain a flow rate output having no error by detecting a high frequency noise which is superposed on a vortex signal through a high-pass filter. CONSTITUTION:A vortex charge (q) is converted by a charge converter 15 into an AC vortex signal SV, which is inputted to a low-pass filter 16; and the filter 16 filters the signal SV at a set low corner frequency and sends its filtering output Sf1 to an amplifier 11. The amplifier 11 amplifies the output Sf1 and then a Schmitt trigger circuit 12 converts the signal into a frequency signal Fv0, which is outputted to a terminal T2. The output Sf1 is inputted to the high-pass filter 17, which filters this signal at a high frequency and outputs the signal to a rectifying circuit 18. Then the circuit 18 rectifies the output of the filter 17 and outputs a control signal Sc1 for varying the corner frequency of the filter 16 to the filter 16. Consequently, the flow rate output having no error can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a vortex flowmeter that converts a measured flow rate into an electrical signal and outputs a vortex signal corresponding to the measured flow rate, and particularly relates to a vortex flowmeter that converts a measured flow rate into an electrical signal and outputs a vortex signal corresponding to the measured flow rate. This invention relates to a vortex flowmeter that effectively removes high-frequency noise and produces stable output.

<Conventional technology> Industrial vortex flowmeters convert the number of vortices generated in response to the measured flow rate into an electrical signal and output it. In addition to the eddy frequency component, low frequency noise caused by the state of the fluid, high frequency noise caused by the state of the piping, etc. are superimposed. In particular, the stress detection method that detects the stress generated in the vortex generator by the vortex - the force/strain detection method using a cantilever, or the capacitance detection method that detects the capacitance change due to the displacement of the diaphragm, etc. The noise superimposed by resonance etc. is large.

Therefore, in these systems, various low-frequency r-wave filters (filters) are used to reduce noise.

As a typical method of these low-frequency r-wave generators, (a)
There is a fixed low-pass filter method that fixes the corner frequency.

This is a method in which a signal frequency range determined by the measurement flow velocity range and aperture is determined, and signals at frequencies other than this are attenuated.

(b) Second, there is a tracking filter method in which the corner frequency is changed by the signal frequency. This is a method of attenuating frequency components other than the signal frequency by changing the value of a resistor or capacitor that constitutes a low-pass filter using a signal proportional to the signal frequency (vortex frequency).

Since method (a) is a basic method for noise reduction and is a well-known technique, method (b) will be briefly explained here using figures.

FIG. 8 is a block diagram illustrating a conventional tracking filter system.

A vortex signal Sv converted by a signal conversion means to a voltage corresponding to the measurement flow #Q is applied to the terminal T. This vortex signal Sv is applied to a variable low-pass filter 10 composed of a field effect transistor FET and a capacitor C1.

The output of this variable low-pass P wave generator 10 is amplified by an amplifier 11 and applied to a Schmitt trigger circuit 12, and output as a vortex frequency signal FV to a terminal T2. is applied to the gate of the FET constituting the variable low-pass filter 10.

Next, the operation of the tracking r-wave device configured as above will be explained with reference to FIG.

The vortex signal Sv (FIG. 9(A)) is input to the amplifier 11 via the variable low-frequency P-wave generator 10, and its output is converted into the frequency signal Fv (FIG. 9(A)) by the Schmitt trigger circuit 12 functioning as a frequency conversion means. B)).

This analog vortex signal Sv is transmitted to the Schmitt trigger circuit 12
is converted into a frequency signal Fv using the hysteresis width ΔH (FIG. 9(A)) as a threshold value. The converted frequency signal Fv has a frequency corresponding to the measured flow rate Q, and is converted into an analog signal by the frequency/'W&pressure converter 13 to change the gate voltage of the field effect transistor FET. The resistance R7 between the drain and source of the field effect transistor FET is changed by this gate voltage, and together with the capacitor C1 constitutes a variable low-pass filter.

In this case, the corner frequency of the variable low-pass filter 10 determined by the degree time constants of R and C is determined by the vortex frequency.

<Problems to be Solved by the Invention> However, the conventional vortex flowmeter using such a tracking r-wave device has the following problems.

What is ultimately discriminated as the vortex frequency is the hysteresis width ΔH of the Schmitt trigger circuit, so if the amplitude fluctuates due to high-frequency noise contained in the vortex signal, an error occurs. This point will be explained using the waveform diagram shown in FIG.

As shown in FIG. 10(A), the amplitude of the vortex signal SV is ρ
(density) and V2 (flow velocity)2, but generally the noise NZ superimposed on the vortex signal SV also tends to increase in proportion to ρ2. As shown in the figure, the frequency signal F■ of the output of the Schmitt trigger circuit.

is increased by the frequency FN due to noise from the frequency signal FV corresponding to the vortex signal Sv, resulting in an error.

To prevent this, it is necessary to widen the hysteresis width ΔtoI of the Schmitt trigger circuit, but this creates a new problem: the signal level becomes smaller at low flow velocities, and the low flow velocity region where measurement becomes impossible expands. arise.

Means for Solving the Problems> As a first means for solving the above problems, the present invention provides a signal conversion means for converting a measured flow rate into a vortex signal, and a signal conversion means for converting the output of the signal conversion means by a control signal. A low i! that generates a low P wave at the determined corner frequency! ! l1iP wave means, a frequency converting means for converting the output of the low range r technique means into a frequency signal corresponding to the measured flow rate, and a high frequency P wave means for detecting high frequency noise superimposed on the vortex signal from the output of the low range r technique means. a wave filter, and a rectifying means for rectifying the output of the high-pass filter and outputting a control signal, and as a second means, a signal conversion for converting the measurement 'a foot into a vortex signal. a low-pass P technique means for generating a low 1jllP wave at a corner frequency that is switched from the output of the signal conversion means by a switch; and a frequency conversion means for converting the output of the low-pass filter means into a frequency signal corresponding to the measured flow rate. a high-frequency filter that detects high-frequency noise superimposed on the vortex signal from the output of the low-pass filter; a rectifier that rectifies the output of the high-pass filter; a comparison means for comparing with a comparison voltage and outputting a switching signal for switching the switch in accordance with the comparison voltage, and as a third means, a signal conversion means for converting the measured flow rate into a vortex signal. , variable amplification means for amplifying the output of the signal conversion means with an amplification degree determined by the amplification degree control signal, and low-pass filtering means for low-pass filtering the output of the variable amplification means at a predetermined corner frequency. , a frequency conversion means for converting the output of the low-pass P technique means into a frequency signal corresponding to the measured flow rate;
The present invention is equipped with a high-frequency filter for detecting high-frequency noise superimposed on the vortex signal from the output of the technical means, and a rectifying means for rectifying the output of the high-frequency r-wave filter and outputting an amplification control signal. It is something.

According to the first means, the high-frequency noise appearing in the output of the low-frequency P-wave generator is detected by the high-frequency wave generator, and the corner frequency of the low-frequency P-wave generator is continuously adjusted according to the magnitude of the noise. According to the second means, the high-frequency noise appearing in the output of the low-pass P-wave filter is detected by the high-pass filter. According to the third means, the corner frequency of the low-pass filter is changed stepwise according to the size of the noise so that high-frequency noise does not occur in the output of the low-pass filter. High-frequency noise appearing in the output of the filter is detected by a high-pass filter, and the amplification degree of the variable amplification means is changed according to the magnitude of the noise to prevent high-frequency noise from appearing in the output of the low-pass P-wave filter. act.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. Note that the same reference numerals are given to the constituent parts having the same R capability as in the prior art, and the explanation thereof will be omitted as appropriate.

Reference numeral 14 denotes a vortex sensor. The vortex sensor 14 detects a stress change in the vortex frequency corresponding to the measured flow rate Q as a change in charge using, for example, a piezoelectric element, and outputs it as a vortex charge q.

This vortex charge q is converted into an alternating current vortex signal Sv by a charge converter 15 serving as a signal conversion means, and is input to a low-pass P wave generator 16.

The low-pass filter 16 low-pass filters the vortex signal SV at a set corner frequency fc and outputs a P-wave output Sf+ to the amplifier 11. The amplifier 11 amplifies this filtered output Sft, and then converts it into a frequency signal FVo in the Schmitt trigger circuit 12 and outputs it to the terminal T2.

On the other hand, this P-wave output Sft is input to the high-frequency filter 17, and the high-frequency filter 17 high-frequency filters this to the rectifier circuit 18.
Output to. The rectifier circuit 18 rectifies the output of the high-frequency wave filter 17 and outputs a control signal SCI for changing the corner frequency fc of the low-pass filter 16 to the low-frequency wave filter 16.

FIG. 2 is a circuit diagram showing details of essential parts of the embodiment shown in FIG. 1.

Operational amplifier Q+, resistors R1 to Ra, capacitors C1, C
2. A low-pass filter 16 is composed of a FET transistor Q4 and the like.

Further, a high-frequency P-wave unit 17 is constituted by an operational amplifier Q2, resistors R5, R15, capacitors C, , C, and the like.

Furthermore, operational amplifier Q3, resistors R7 to R3, and diode D
7, D2, a capacitor 05, and the like constitute a rectifier circuit 18.

The internal resistance between the drain and source of the FET transistor Q4 connected in parallel with the resistor R4 is changed by the control signal Sc+ from the rectifier circuit 18, and the corner frequency fc of the low-pass filter 16 configured in combination with the capacitor C2 is changed. change.

When the high frequency noise is small, the high frequency r wave generator 17 outputs a voltage close to zero. Therefore, the value of the control signal Sc+ is also small, and the resistance between the drain and source of the FET transistor is several ohms, which is negligible compared to the resistance R2.

Therefore, the corner frequency fc of the low-pass filter 16 constituted by the operational amplifier Q1 has a high value, and there is no attenuation of the vortex signal SV+.

On the other hand, when the high frequency noise becomes large,
The high-frequency P-wave device 17 outputs only noise. This noise voltage is rectified by the rectifier circuit 18 and output as a large control signal S01, increasing the resistance between the drain and source of the F'ET transistor Q4.

Therefore, the corner frequency fc of the low-pass filter 16 constituted by the operational amplifier Q is lowered, and this P-wave output Sf+ has a value with reduced high-frequency noise. In this case, generally when the high frequency noise is large, the value of the vortex signal Sv is also large, so the filtered output Sf does not affect the frequency conversion in the subsequent Schmitt trigger circuit 12.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the present invention.

The vortex signal Sv appearing at the output end of the charge converter 15 is input to one amplifier, which outputs the vortex signal Sv- at its output end. This vortex signal SV- is low-pass filtered by a low-pass filter 20, outputting a P wave output Sf2 at its output terminal, converted into a frequency by a Schmitt trigger circuit 12 via an amplifier 11, and a flow rate Q is sent to a terminal T2. A frequency signal FV+ corresponding to the frequency signal FV+ is output.

On the other hand, the P-wave output Sf2 is output to the rectifier circuit 18 via the high-pass filter 17, and its output is output to the comparator 21. The comparator 21 waits for set voltages having a plurality of different values, and the output of the rectifier circuit 18 is compared with these set voltages, and the low-pass P wave generator 1 is supplied with a control signal SC2 corresponding to these set voltages.
6 corner frequency fC is changed.

FIG. 4 is a block diagram illustrating in detail the main parts of the embodiment shown in FIG.

The low-frequency r wave generator 20 includes an operational amplifier Q1, resistors R7, R2, capacitors C2, C6, ~C, switches SW, ~S
It consists of W3 etc. Series circuit of switch SW and capacitor CL3, switch SW2 and capacitor C
Series circuit with 7, and switch SW3 and capacitor C
The series circuits with 8 are connected in parallel between the connection point between the resistors R1 and R2 and the common potential point COM.

Further, the comparator 21 includes comparators Qs, .about.Qy, Zener diodes D3 . It is composed of resistors R1o, ~R, 3, etc. The power supply voltage Eb is set to the set voltage ESj by the Zener diode D3 via the resistor R7°, and this is set to the set voltage ESj by the resistor RI I~R.
13 to obtain the set voltages E, . . . Es2. The noise voltage ■π which is the output of the rectifier circuit 18 applied to each non-inverting input @(+) of the comparators Q5 to Q7 is the set voltage Es1 applied to each inverting input terminal (-) of the comparators Q5 to Q7. , Es2, and ES3, and output control signals 5C21, 5C22, and 5C23 to their output terminals, respectively.

Switches sw, , sw7, and sw3 are opened and closed by these control signals SC2+, SC22, and SC2, respectively.

When the level of high-frequency noise included in the output of the low-pass P-wave filter 20 increases, the high-pass filter 17 detects this and outputs a noise voltage Vπ to the output terminal of the rectifier circuit 18. This noise voltage ■π is compared with the set voltages ESI to ES of the comparator 21 composed of Q5 to Q7, and this noise voltage ■
1 is larger than either of these set voltages Es1, .about.ES3, the output of the corresponding comparator turns on the switches SW, .about.SW3.

In other words, when the noise voltage V1 increases, the switch corresponding to this magnitude is turned on, lowering the corner frequency fc of the low-frequency P-wave generator 20, and as a result, the attenuation of high-frequency noise increases and the low-frequency P-wave generator The level of high frequency noise included in the r-wave output Sf2 of No. 20 is reduced. Therefore, errors in the Schmitt trigger circuit 12 of the f& stage can be eliminated.

In the above description, an example is shown in which three comparators 21 are used, but by increasing this number, output fluctuations caused by corner frequency switching can be reduced.

Furthermore, although the circuit shown in FIG. 4 uses a system in which the capacitor is switched, it is also possible to switch the resistor R7 or the like.

FIG. 5 is a block diagram showing the configuration of a third embodiment of the present invention.

The vortex signal Sv appearing at the output end of the charge converter 15 is input to the variable amplifier 22, which outputs the vortex signal SV-1 at its output end. This vortex signal SV -- is low-pass filtered by a low-pass filter 23, outputting a P-wave output Sfz at its output terminal, converted into a frequency by a Schmitt trigger circuit 12 via an amplifier 11, and sent to a terminal T2. Frequency signal corresponding to extended Q2
Output.

On the other hand, the P-wave output Sf3 is output to the rectifier circuit 18 via the high-frequency wave transducer 17, and its control output SC3 is output to the variable amplifier 2.
2, and its amplification degree is changed in accordance with the control output Sc.

FIG. 6 is a block diagram illustrating in detail the main parts of the embodiment shown in FIG.

The variable amplifier 22 includes an operational amplifier Qs whose non-inverting input terminal (+) is connected to a common potential point COM and whose inverting input terminal (-) is connected to an output terminal via a resistor R16, and a resistor R1a.
, R+ 5 , and an FE'f' transistor Q9.

The control signal Sc3 from the rectifier circuit 18 changes the drain-source resistance of the FE transistor Q, for example, from several Ω to several MΩ, as shown in FIG. For example, when the amplification degree is changed,
R+a=IKΩ, R+5=100Ω, R+g=100
If Ω is selected, the amplification degree is 1.00/(100+1)
It can be changed between ~100/'1. In this way, high frequency noise appearing in the output of the low-pass P wave generator 23 can be reduced.

Incidentally, in the case of the ¥ right shown in FIG. 5, the input resistance was changed, but the same result can be obtained by changing the feedback resistance. Further, in the embodiment shown in FIG. 6, high frequency noise is detected from the output of the wave generator 23 in the low frequency range, but it may be detected from the output of the variable amplifier 22.

<Effects of the Invention> As specifically explained above with the embodiments, according to the inventions according to the first to third claims, the high frequency noise superimposed on the vortex signal is filtered out through the high frequency filter. Since the influence of this high frequency noise is removed by detecting it through a wave generator and feeding it negative feedback to the previous stage, it is possible to obtain an error-free flow rate output. Further, when the high frequency noise is large, the eddy signal is also large, so no error occurs due to the formation and decay of the eddy signal due to fL feedback.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a circuit diagram explaining in detail the main part of the embodiment shown in FIG. 1, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of an example; FIG. 4 is a circuit diagram explaining in detail the main parts of the embodiment shown in FIG. 3; FIG. Fig. 6 is a circuit diagram explaining in detail the main part of the embodiment shown in Fig. 5, Fig. 7 is a characteristic diagram showing the characteristics of the FET transistor shown in Fig. 6, and Fig. 8 is a diagram showing the characteristics of the conventional tracking filter. FIG. 9 is a block diagram without showing the configuration; FIG. 9 is a waveform diagram explaining the operation of the tracking r-wave device shown in FIG. 8;
FIG. 0 is a waveform diagram illustrating the problems of the conventional tracking filter shown in FIG. 10... variable low-pass filter, 11... amplifier, 12...
... Schmitt trigger circuit, 13... Frequency/pressure converter, 14... Vortex sensor, 15... Charge converter, 16... Low-pass filter, 17... High-pass filter ,
18... Rectifier circuit, 19... Amplifier, 20... Low-pass P wave device, 21... Comparator, 22... Variable amplifier,
23...Low pass filter, q...Eddy electric front, Sv...Eddy signal, Sft~Sfs...Filtering output, Sc1~Sc3
···Control signal. No. 17 Comparison 17 Kando Kaitoku ÷ In the figure, 1st section Jippl recognition, 5c3

Claims (3)

[Claims] (1) A signal converting means for converting the measured flow rate into a vortex signal, a low-pass filtering means for low-pass filtering the output of this signal converting means at a corner frequency determined by a control signal, and this low-pass filtering means a frequency conversion means for converting the output of the filter into a frequency signal corresponding to the measured flow rate; a high-pass filter for detecting high-frequency noise superimposed on the vortex signal from the output of the low-pass filter; 1. A vortex flow meter comprising: rectifying means for rectifying the output of the wave generator and outputting the control signal. (2) Signal conversion means for converting the measured flow rate into a vortex signal, low-pass filtering means for low-pass filtering the output of this signal conversion means at a corner frequency that can be switched by a switch, and the output of this low-pass filtering means. a frequency conversion means for converting the signal into a frequency signal corresponding to the measured flow rate; a high-pass filter for detecting high-frequency noise superimposed on the vortex signal from the output of the low-pass filtering means; and this high-pass filter. and a comparison means for comparing the output of the rectification means with a plurality of comparison voltages and outputting a switching signal for switching the switch in response to these comparison voltages. Vortex flow meter. (3) signal conversion means for converting the measured flow rate into a vortex signal; variable amplification means for amplifying the output of the signal conversion means with an amplification degree determined by the amplification degree control signal; low-pass filtering means for low-pass filtering at a corner frequency; frequency conversion means for converting the output of the low-pass filtering means into a frequency signal corresponding to the measured flow rate; A vortex flow rate characterized by comprising a high-pass filter for detecting high-frequency noise superimposed on a vortex signal, and a rectifying means for rectifying the output of the high-pass filter and outputting the amplification control signal. Total.