JPH0791994A - Method for eliminating noise in electromagnetic flowmeter and converter - Google Patents

Abstract

PURPOSE:To obtain a method for effectively eliminating electrochemical noise and fluid noise by selectively amplifying only the flow rate signal of a square wave and to obtain a converter. CONSTITUTION:The electrode signal of a detector is amplified by a preamplifier and then is inputted to a noise elimination circuit 4 as an input signal V1. The input signal is amplified by an integration amplifier 7 by R2/R1 and integrated with a time constant, R2.C2. An output V3 which is amplified and integrated is fed to a first integration circuit 5 via a switch S1 which opens for a specific period after the switching of excitation, is integrated by a time constant, R0.C0, and then is fed back to a non-inverted input of an amplifier A1. The time constants, R0.C0 and R2.C2, are selected and only the flow rate signal of a rectangular wave is selectively amplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removing method and a converter suitable for a battery-powered low power consumption type electromagnetic flowmeter.

[0002]

2. Description of the Related Art An electromagnetic flow meter is one which applies an alternating magnetic field to a fluid flowing in a pipe and measures the fluid flow rate from a flow rate signal induced between two electrodes arranged in a direction perpendicular to the magnetic field. Noise other than the flow rate signal is generated between the electrodes.

Among them is the electrochemical noise generated by the ionic components of the fluid. The frequency characteristic of this noise shows a so-called 1 / f characteristic, and the level becomes larger as the frequency becomes lower, so that the DC offset voltage is several hundred meters.
It may reach a large value of V.

As a compensating circuit for removing such electrochemical noise, the one disclosed in JP-A-2-12018 is well known. A circuit diagram of this prior art is shown in FIG. 7, and its timing is shown in FIG.

In this circuit diagram, an exciting coil of the detector, an exciting circuit for supplying an exciting current to the exciting coil, and a control circuit for sending a timing signal to the exciting circuit are omitted.

In the figure, this is the first half cycle of excitation (T ₁
+ T ₂ ), a positive magnetic field is held, and a constant negative magnetic field is held during the next second half cycle (T ₃ + T ₄ ). When this is repeated one after another, a magnetic field is generated between the electrodes 2a and 2b. A flow rate signal proportional to the flow velocity is induced at the same timing as, and is amplified by the preamplifier 3 to become the flow rate signal E ₁ .

Now, description will be made assuming that the magnetic field at time t ₁ and the accompanying flow signal E ₁ ideally start.
First, the operation during the period T ₁ will be described.

When the flow rate signal E ₁ is input to the offset compensation circuit 20 as a positive value at time t ₁ , the output E ₃ of the integration circuit 21 is zero, which is the initial value, so that the amplifier A ₁₀
Output E ₂ is E ₂ = − (R ₁₂ / R ₁₁ ) · E ₁ . Since the switch S ₁₀ is off, the period T
_{During 1} , the output E ₂ of amplifier A ₁₀ is held at this negative constant value.

Next, the operation during the period T ₂ will be described. When the switch S ₁₀ is turned on at time t ₂ , the integrator circuit 21 integrates the negative value of E ₂ with a time constant of R ₁₀ · C ₁₀ to generate a positive feedback voltage E ₃ .

This feedback voltage E ₃ is applied to the amplifier A ₁₀
However, since the voltage E ₃ has the same polarity as the flow rate signal E ₁ applied to the inverting input of the amplifier A ₁₀ through the resistor R ₁₁ , the output of the amplifier A ₁₀ with respect to this flow rate signal E ₁ is canceled. Then, the value of the output E ₂ decreases as the feedback voltage E ₃ increases.

The value E ₂ (t ₃ ) of the output E ₂ at the time t ₃ which is the end of the period T ₂ is the value E _{2 at} the time t ₂ .
₂ (t ₂ ) 30 to 60% of time constant R ₁₀ · C
₁₀ is decided.

Next, the operation during the period T ₃ will be described. At time t ₃ , switch S ₁₀ is turned off, and flow rate signal E ₁
Is changed from a plus value to a minus value, the integration circuit 21
Acts as a hold circuit and holds the value E ₃ (t ₃ ) of the feedback voltage E ₃ immediately before the switch S ₁₀ is turned off for the period T ₃ .

On the other hand, the amplifier A_TenOutput E₂At time t₃
Flow signal E at₁Change amount of 2E ₁Is R₁₂/ R₁₁Doubled
Value 2E₁(R₁₂/ R₁₁) Only increases in the positive direction,
Period T₃Constant value between₂(T_Four) Hold.

Next, the operation during the period T ₄ will be described. When the switch S ₁₀ is turned on at time t ₄ , the integrating circuit 21 outputs R ₁₀
Since the positive E ₂ value E ₂ (t ₄ ) is integrated with the time constant of C ₁₀ , the feedback voltage E ₃ decreases toward zero, and further exceeds zero to become a negative value.

With the change of the feedback voltage E ₃ , the output E ₂ of the amplifier A ₁₀ is E ₂ = − (R ₁₂ / R ₁₁ ) · E ₁ + [(R ₁₂ / R ₁₁ ) +
1] ・ It will decrease due to E ₃ . Thus, the output E _{2 at} time t ₅
The value E ₂ (t ₅ ) of the value E ₂ (t ₅ ) is 30 to 30 of the value E ₂ (t ₄ ) at time t ₄ , as in the case of the first half cycle (T ₁ + T ₂ ).
It becomes 60%.

As described above, one cycle (T ₁ + T ₂ + T ₃ + T ₄ ) in the measurement of the electromagnetic flow meter is completed, and the next cycle (T ₁ ′).
+ T ₂ ′ + T ₃ ′ + T ₄ ′). In the next period T ₁ ′, since the switch S ₁₀ is OFF as in the period T ₁ , the final value E ₃ (t ₅ ) of the feedback voltage E ₃ is obtained.
Is retained.

By repeating such a few cycles, the circuit becomes in a steady state. The above description is for the case of only the ideal flow rate signal, but when the direct current component is superimposed on the flow rate signal E ₁ , the integrating circuit 21 outputs the output E _{2 of the} amplifier A _10.
Has a function of removing the DC component superimposed on the output E ₂ by integrating the DC component superimposed on the DC voltage and adding the feedback voltage E ₃ for the DC component to the non-inverting input of the amplifier A ₁₀ .

Also, when low-frequency electrochemical noise is added, it has a removing ability as in the case of the direct current component.

[0019]

The so-called two-wire type is mainly used as the low power consumption type electromagnetic flowmeter, but in recent years, the demand for the battery driven low power consumption type electromagnetic flowmeter has increased.

As a result, the electric power that can be used to generate the magnetic field becomes inevitably small, and the electromotive force induced between the electrodes has a flow velocity of 1 m.
It became as small as 2 to 5 μV / S. On the other hand, in addition to electrochemical noise, fluid noise, which is called high-speed fluid noise or flow noise, proportionally increases with the flow velocity is generated at the electrode. This fluid noise has a relatively large noise of a high frequency component as compared with the electrochemical noise exhibiting the 1 / f characteristic, and the noise level becomes 1 when the flow velocity approaches 10 m / S.
When it reaches 00 μV and the conductivity of the fluid decreases, it tends to increase further.

In the prior art shown in FIG. 7, the offset compensating circuit 21 as a noise removing circuit has a high noise removing capability for low frequency noise, but tends to have a low noise removing capability for high frequency noise.

In addition to the lack of the ability to remove low frequency noise due to the decrease in the signal level and the decrease in S / N, the adverse effect of fluid noise having a large high frequency component becomes remarkable.

Therefore, the variation in the output of the sample and hold circuit 10 in FIG. 7 is increased.
In the A / D conversion circuit 11 in the figure, when the input exceeds the allowable value, the output is saturated and the information contained in the signal is lost, which causes a large error.

Since fluid noise is particularly large at the full-scale flow rate, saturation of the A / D conversion circuit 11 is likely to occur. For this reason, it was necessary to reduce the signal level input to the A / D conversion circuit 11 at the time of full scale to about 1/2 of the effective dynamic range of the A / D conversion circuit to prevent saturation. , One of the capabilities of the A / D conversion circuit
There was a big disadvantage that only / 2 could be effectively used.

Even if the signal level input to the A / D conversion circuit is reduced to prevent saturation of the conversion circuit, a large variation occurs in the output. This variation has the property that the error is zero at the average value for a long time, but it has an error that fluctuates positively and negatively at the moment-to-moment value.

In addition, 5 is obtained by induction from a commercial AC power source.
As a countermeasure when 0 Hz or 60 Hz noise is superimposed on the flow rate signal, a method is generally used in which the excitation frequency is set to an even number of the AC power supply frequency and synchronization is performed to remove induced noise. It is difficult to use this method in total.

As another method of removing noise, A /
There is a method of comparing the D-converted value with the previous value in the CPU, removing the abnormal value, and retaining the previous value. This method requires a high-speed CPU and consumes a large amount of power, so it is not suitable for a battery-driven electromagnetic flowmeter and cannot be used.

Therefore, it is an object of the present invention to provide a noise removing method and a converter suitable for a low power consumption type electromagnetic flow meter driven by a battery.

[0029]

In order to achieve the above object, a method for removing noise in an electromagnetic flowmeter according to claim 1 is
In an electromagnetic flow meter that measures the flow rate of a fluid by a square-wave exciting magnetic field whose polarity changes periodically, an output (V ₃ ) obtained by amplifying and integrating a square-wave flow signal (V ₁ ) is synchronized with the excitation ( T ₂ ) Integration, and the integrated output (V ₄ ) is differentially fed back to the flow signal of the square wave as the input of the amplification / integration, thereby selecting the flow signal of the square wave synchronized with the excitation. It is characterized in that it is designed to be amplified.

The converter of the electromagnetic flowmeter according to claim 2 is used for implementing the noise removing method according to claim 1. That is,
In electromagnetic flowmeter for measuring the flow rate of a fluid by the excitation magnetic field periodically square wave polarity is changed, an amplifier for amplifying the square wave flow rate signal _{(V 1) (A 1)} , an amplifier (A ₁₎
Second integrator circuit (6) for integrating the output (V ₂ ) of the switch, the switch (S ₁ ) that is turned on in synchronization with the excitation, and the second integrator circuit for the period in which the switch (S ₁ ) is on. (6)
First integrating circuit for integrating the output of the (V ₃₎ (5) and said amplifier output (V ₄₎ of the integrating circuit (5) (A ₁₎
And a feedback loop for inputting to.

A converter for an electromagnetic flowmeter according to a third aspect is characterized in that the amplifier (A ₁ ) according to the second aspect and the second integrating circuit (6) are configured as one integral type amplifier (7). To do.
A converter for an electromagnetic flowmeter according to a fourth aspect is characterized in that, in the invention of the first or second aspect, the ON period of the switch (S ₁ ) is the latter half of the half cycle of the excitation.

The converter of the electromagnetic flowmeter according to claim 5 is the switch (S ₁ ) according to the invention of claim 1 or 2.
Is turned on (T _2, T ₄ , T ₂ ′ _, T ₄ ′, ...) Matches the signal sampling period.

[0033]

[Action] amplifier (A ₁₎ one input to the input terminal a square wave flow rate signal (V ₁₎ is amplified by an amplifier (A _1), is integrated in the further second integrator (6) . The output (V ₃ ) is integrated by the first integrator circuit (5) during the ON period of the switch (S ₁ ), and is supplied to the other input terminal of the amplifier (A ₁ ) by the square wave flow signal. Feedback is performed with a polarity that cancels the output (V ₂ ).

The time constants of the two integrating circuits (5) and (6) are set to be smaller than the time constant of the conventional integrating circuit, and the switch (S ₁ ) is turned on only in the latter half of each half cycle of excitation. Therefore, a phase delay occurs in the feedback system.

As a result, only the square wave flow signal synchronized with the excitation is resonantly amplified. Noise that is not synchronized in phase with excitation or that has a frequency component different from that of excitation is attenuated.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a first embodiment of an electromagnetic flow meter according to the present invention.
The first embodiment will be described below based on FIG. 2 of the timing chart.

1 is a tube for flowing a fluid, 2a and 2b are electrodes,
These constitute a known detector together with an exciting coil (not shown). Reference numeral 3 is a preamplifier for amplifying the induced voltage between the electrodes 2a and 2b, and 4 is a noise removing circuit, which includes resistors R ₁ and R ₂ and an amplifier A ₁ , a first integrating circuit 5, and a second integrating circuit 5.
Of the integrating circuit 6 and the switch S ₁ .

The first integrating circuit 5 has a resistor R₀, Capacitors
C₀And amplifier A₂Are connected and configured as shown.
It The second integrating circuit 6 has a resistor R₃, Capacitor C₁as well as
Buffer amplifier A with gain of 1 ₃Connect as shown
I have made it.

The switch S ₁ is turned on / off by a timing signal from a control circuit (not shown), and as shown in FIG. 2, every time the direction of the exciting magnetic field is switched, a predetermined period T ₁ , T ₃ , T is reached. ₁ ′, ... OFF, and other period T ₂ ,
T ₄ , T ₂ ′, ... Turn on.

The output of the preamplifier 3 is output from the noise removing circuit 4.
Input V₁And this input V₁Is amplifier A₁Inverted input of
Join in. Amplifier A₁Output V₂Is the second integration circuit 6
And R ₃・ C₁Is integrated with the time constant of
Output V of removal circuit 4₃Becomes

This output V ₃ is turned on / off in synchronization with the exciting magnetic field.
It is input to the first integrator circuit 5 through the switch S _{1 that is} turned off, integrated into the feedback voltage V ₄ by the time constant of R ₀ · C ₀ , and applied to the non-inverting input of the amplifier A ₁ .

Reference numeral 10 is a sample and hold circuit, which is a switch S ₃ , S that is turned on / off in synchronization with the exciting magnetic field.
₄ and a capacitor and amplifiers A ₄ , A ₅ , and A ₆ connected between these switches and ground, respectively. This sample and hold circuit is a noise removal circuit 4
The output V ₃ is input to hold only the flow rate signal excluding the inductive noise generated when switching the excitation.

Reference numeral 11 is an A / D conversion circuit, 12 is a CPU, 1
3 is an indicator. Now, assume that the input signal V ₁ is _first applied and the operation starts at time t ₁ in FIG. Further, T _M = (T ₁ + T ₂ + T ₃ + T ₄ ) is set as one measurement cycle of the electromagnetic flow meter.

First, the operation in the period T ₁ will be described. When the positive input V ₁ is applied at time t ₁ , the feedback voltage V ₄ which is the output of the first integrator circuit 5 has an initial value of zero, and the switch S ₁ is OFF, so that the period T ₁
During that time the feedback voltage V ₄ is held at zero.

Therefore, the output V ₂ of the amplifier A ₁ becomes a negative constant value V ₂ =-(R ₂ / R ₁ ) · V ₁ .

This output V ₂ is integrated by the RC series circuit having the time constant R ₃ · C ₁ of the second integrating circuit 6 to obtain the capacitor C ₁
Will be charged. And a gain 1 buffer amplifier A ₃
Then, the impedance is converted into the output of the integrating circuit 6, that is, the output V ₃ of the noise removing circuit 4.

Since the output V ₂ of the amplifier A ₁ holds the negative constant value for the period T ₁ , the output of the second integrating circuit 6, that is, the output V ₃ of the noise removing circuit 4 is shown in FIG.
As shown in, it decreases exponentially from zero in the negative direction.

Next, the operation in the period T ₂ will be described. When the switch S ₁ is turned on at time t ₂ , the negative output V ₃ is integrated by the first integrator circuit 5 with the time constant of R ₀ · C ₀ , and the feedback rises in the positive direction as shown in FIG. The voltage becomes V ₄ .

This feedback voltage is applied to the amplifier A₁Non of
Amplifier A applied to the inverting input and ₁The inverting input of
Input V at that time₁Is resistance R₁Is applied through
Therefore, amplifier A at this time₁Output V₂Is V₂=-(R₂/ R₁) ・ V₁+ [(R₂/ R₁) +
1] ・ V_Four Therefore, the feedback voltage V_FourChanges with
It

Since the time constant R ₀ · C ₀ is selected to be a small value as compared with the circuit of the prior art shown in FIG. 7, the feedback voltage V ₄ rapidly increases in the positive direction, and accordingly, the negative value becomes negative. The output V ₂ has a waveform that rises rapidly toward zero as shown in FIG.

The output V ₃ of the output V ₂ is a value obtained by integrating a time constant of R ₃ · C ₁ is also a waveform toward zero direction,
Due to the phase delay due to the integration effect of the RC series circuit with the time constant R ₃ · C ₁ , the output V ₂ of the amplifier A ₁ becomes zero,
After that, even if it becomes a positive value, the output V ₃ of the second integrating circuit 6 keeps a negative value for a while.

By properly selecting the time constants R ₃ .C ₁ and R ₀ .C ₀ , the output which is the output of the second integrating circuit 6 and the output of the noise removing circuit 4 at the final point of the period T _2. It is possible, and is possible, to make the value of V ₃ almost zero.

Next, the operation in the period T ₃ will be described. When the switch S ₁ is turned off at the time t ₃ , the feedback voltage V ₄ which is the output of the first integrating circuit 4 holds the value V ₄ (t ₃ ) at the final point of the period T ₂ for the period T ₃ .

At the time t ₃ , the input V ₁ is switched from the positive value to the negative value, so the output V of the amplifier A _{1 is} changed.
_{2 V 2 = - (R 2 /} R 1) · V 1 + [(R ₂ / R ₁₎ +
1] · V ₄ , which is held for the period T ₂ .

As shown in FIG. 2, the value of the output V ₂ is the final value V ₂ (t ₃ ) of the period T ₂ and the input V at the time t ₃ .
₁ of the variation _{2V 1 (R 2 / R 1} ) is a sum of a value obtained by multiplying these two values V ₂ (t ₃₎ and 2V ₁ · (R ₂ /
Since both R ₁ ) are positive values, the output V ₂ of the amplifier A ₁ is significantly increased as compared with the value − (R ₂ / R ₁ ) · V ₁ in the period T ₁ .

[0056] The output V ₃ of the noise elimination circuit 4 which is the output of the second integrator 6, the output V ₂ during this period T ₂
Is the value obtained by integrating with the time constant of R ₃ · C ₁ , and at time t
_Since the increase in the output V ₂ at ₃ is large, it changes rapidly in the positive direction.

As a result, the value of the output V ₃ of the first embodiment is larger than the output E ₂ of the circuit of FIG. 7 of the prior art. Next, the operation in the period T ₄ will be described.

At time t ₄ , the switch S ₁ is turned on, and the positive output V ₃ is integrated by the first integrating circuit 5 with the time constant of R ₀ · C ₀ . As described above, the time constant R ₀ · C ₀ is as shown in FIG.
Since the value is smaller than the time constants R ₁₀ and C ₁₀ of the circuit of (1), the feedback voltage V ₄ rapidly goes to zero, and the output V _{2 of the} amplifier A ₁ rapidly goes to zero accordingly.
The output of the second integration circuit 6, that is, the output V ₃ of the noise removal circuit 4 continues to increase while V ₂ > V ₃ and decreases toward zero after V ₂ <V ₃ is reached. Become.

Thus, the output of the second integrating circuit 6, that is,
Output V of noise removal circuit 4₃Change of amplifier A₁Output
V₂The operation is delayed with respect to
V₂Output V₃Is still positive
Therefore, the feedback voltage that is the output of the first integration circuit 5 is
Pressure V_FourIs zero. And after passing zero, it becomes a minor
Its absolute value continues to increase as a negative value,
Value feedback voltage V_FourIs amplifier A₁Non-inverting input of
Is fed back to the amplifier A ₁Output
V₂Also becomes a negative value, and the
The logarithmic value increases.

The absolute value of the output V ₂ of the amplifier A ₁ at the end of the period T ₄ is considerably larger than the absolute value of the output V ₂ of the amplifier A ₁ at the end of the period T ₂ . Along with this, the values of the output V ₃ and the feedback voltage V ₄ also increase during the half cycle.

This is the end of the description of the operation during the first period T _M. In the second cycle, the switch S ₁ is turned off and the input V ₁ becomes a positive value at time t ₅ or t ₁ ′, and the operations from the beginning are repeated.

However, during the period T ₁ ′ in this second cycle, the value of the feedback voltage V ₄ which is the output of the second integrating circuit 5 is not the initial value zero but a large negative value at the final value of the period T ₄ . The value is V ₄ (t ₅ ).

Further, the output V ₂ of the amplifier A ₁ is the time t ₁ ′.
Change amount 2 when input V ₁ changed from negative to positive
V ₁ is reduced by the amount of (R ₂ / R ₁ ) times, and the absolute value of the output V ₂ is increased accordingly.

[0064] The absolute value of the period T ₁ of the first period T _M of the output V ₃ of the output that is the noise eliminating circuit 4 of the second integrator 6 that the output V ₂ integrated over the time constant of R ₃ · C _1, It becomes larger than the absolute value of the output V _{3 at} T ₂ .

By repeating the first, second, third, ... Cycles as described above, the outputs V ₂ , V ₃ and the feedback voltage V ₄ gradually increase each time the cycle is repeated. That is, the noise removal circuit 4 operates as a kind of resonance circuit by operating as a feedback system as described above.

However, by selecting an appropriate circuit constant, it is possible to construct a stable amplifier for a square wave signal that reaches a constant amplification degree in several cycles without increasing the amplification degree indefinitely and is synchronized with the excitation. , Like that.

The amplification degree of the amplifier constituted by this noise elimination circuit becomes larger than (R ₂ / R ₁ ), and the larger the amplification degree, the more advantageous in terms of noise elimination. If it is set too much, the feedback system tends to become unstable, so the original amplification degree (R
_It is considered to be advantageous to make the ratio 1.5 / 3 times ₂ / R ₁ ).

It should be noted that the fact that the noise removing circuit can remove the DC offset voltage does not need to be explained again.
The output V ₃ of the noise removing circuit 4 is held by the sample and hold circuit 10 only for the flow rate signal excluding the induced noise generated when the excitation is switched. A sample like this
The operation of the hold circuit 10 is the same as that of the prior art disclosed in Japanese Patent Laid-Open No. 2-1
Since it is well known in Japanese Patent Publication No. 2018, its detailed description is omitted here.

The value of the flow rate signal held by the sample and hold circuit 10 is converted into a digital amount by the A / D conversion circuit 11, processed by the CPU 12, and the integrated value or the instantaneous value is displayed on the display 13. .

It is also possible to output the integrated value and the instantaneous value as a code signal to the outside.

[0071]

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIGS. FIG. 3 shows only a portion corresponding to the noise removing circuit 4 in FIG. 1 of the first embodiment.
Other parts not shown in are the same as those in the first embodiment of FIG.

In the second embodiment, the resistors R ₁ and R ₂ , the amplifier A ₁ and the second integrating circuit 6 in the first embodiment shown in FIG. 1 are used.
A circuit that operates in the same manner as in is replaced with an integrating amplifier 7. That is, the second in the first embodiment of FIG.
Abolished the integrating circuit 6, a feedback capacitor C ₂ to the amplifier A _1, and connected in parallel with the resistor R _2, which was to have a function of the integrator and amplifier of the amplifier A _1, as it were integral The type amplifier 7 is constructed.

The time constant of this new integrating amplifier 7 is R ₂
C ₂ and the time constants R ₃ · C ₁ of the second integrator 6 and R ₂ · C ₂ = R ₃ · C _{1 in} the _first embodiment of FIG. The second embodiment operates almost the same as the embodiment of FIG. 1 as a whole.

In the second embodiment of FIG. 3, the amplifier A ₁
Of the noise eliminating circuit 4 is applied to the first integrating circuit 5 through the switch S ₁ . In the operation of the circuit of FIG. 3, since the integrating amplifier 7 also has the function of the second integrating circuit 6 of FIG. 1, there is no waveform corresponding to the output V ₂ in the timing chart of FIG. 1 is the same as the output of the second integrator 6 in FIG. 1, that is, the output of the noise elimination circuit 4, and therefore the same symbol V ₃ is used.

When the input V ₁ is input, the switch S ₁ is off during the period T ₁ , so that the integrating amplifier 7 multiplies the input V ₁ by (R ₂ / R ₁ ), and R ₂ · C ₂ It is integrated with the time constant to obtain the output V ₃ .

The switch S ₁ is turned on after the period T ₂ is reached.
Then, the phase-delayed output V ₃ is converted to R by the first integrating circuit 5.
_By integrating with a time constant of ₀ · C ₀ and feeding back to the non-inverting input of the amplifier A ₁ that constitutes the integrating amplifier 7,
As a whole, the same operation as that of the noise removing circuit 4 of FIG. 1 is performed.

As a result, also in the second embodiment, as in the first embodiment, a resonant amplifier in which the amplification degree is increased only for the square wave signal synchronized with the excitation is selected, and only the flow rate signal is selected. Can be amplified.

The configuration is such that one capacitor C ₂ is added to the conventional circuit of FIG. 7, and the time constant R ₀ · C ₀ of the first integrating circuit 6 is set to the integrating circuit 21 of FIG. An appropriate value smaller than the time constant R ₁₀ · C ₁₀ of became possible only by selecting.

[0079]

Third embodiment of the third embodiment] Fig. 5 is formed by connecting another switch S ₂ in series with the resistance R ₁ of the circuit of the second embodiment of FIG. 2, the separate switch S ₂ is 6 To S timing diagram
Turn on / off at the timing shown in ₂ .

Immediately after the switching of the excitation, spike-like induced noise is generated between the electrodes 2a and 2b in FIG. 1 and superposed on the flow rate signal. This is amplified by the preamplifier 3 in the figure, and is the input V ₁ ′ of the noise elimination circuit 4 in FIG.

When the induced noise is large, the second noise of FIG.
In the embodiment, by integrating with the time constant R ₂ · C ₂ of the integrating amplifier 7, so-called tailing occurs and causes the zero point fluctuation of the electromagnetic flowmeter.

Therefore, as shown in the timing chart of FIG.
In the third embodiment of FIG. 5, the switch S ₂ is turned off during the period in which the induced noise is generated, that is, the period T _{1a in} FIG. 6 so that the noise removal circuit 4 is not adversely affected by the induced noise. .

The basic operation of the third embodiment is the second operation of FIG.
Because it is exactly the same as in Example, the symbols of each portion of the waveform 3, was the same as FIG. 4, the period T ₁ in FIG. 4, the switch S ₂ in FIG. 6 is OFF period T _1a and the other of It was divided into periods T _1b .

The waveforms of the output V ₃ of each part and the feedback voltage V ₄ with respect to the input signal V ₁ ′ on which spike-like induced noise is superimposed are similar to those of FIG. 4, but the switch S ₂ is OFF during the period T _1a. there so, the output V ₃ is rising after becoming period T _1b, the switch S ₂ even period T _3a is OFF, the output V ₃ in the period T _3a is slowly increased rapidly in the subsequent period T _3b It has a rising waveform. Except for this point, the operation is exactly the same as that of the second embodiment of FIG.

As an example of removing the influence of inductive noise, a third embodiment in which another switch S ₂ is added to the _second embodiment of FIG. 3 is shown in FIG. 5, but it is different from the first embodiment of FIG. The same operation and effect can be obtained even if another switch S ₂ is connected in series with the resistor R ₁ . In the above three embodiments, the noise removal method for removing the noise by selectively amplifying the square wave signal synchronized with the excitation by applying the resonance characteristic, and the converter used therefor have been described.

It is the first reason that such resonance characteristics are obtained.
In the embodiment, the time constant R ₀ · C ₀ of the first integrating circuit 5 is set.
And the time constant R ₃ · C ₁ of the second integrating circuit has a relation of approximately R ₀ · C ₀ = R ₃ · C ₁ , and when the excitation frequency is f _L ,
It is the case where there is a relationship of f _L / 2 = 1 / (2πR ₀ · C ₀ ).

Further, in the second embodiment, the resonance characteristic is obtained between the time constants of the first integrating circuit 5 and the integrating amplifier 7 by approximately R ₀ · C ₀ = R ₂ · C ₂ . When there is a relationship, the excitation frequency f _L is also shown in FIG.
Similar to the case of the first embodiment of No. 3, there is a relationship of approximately f _L / 2 = 1 / (2πR ₀ · C ₀ ).

In the case of the above relationship, the noise removing circuit 4 has a resonance characteristic, but the above-mentioned time depends on the period during which the switch S ₁ is ON / OFF, that is, the ratio of the periods T ₁ and T _2. The relational expression of constants is slightly affected.

In the explanation of the timing of FIG. 2, the periods T ₂ and T ₄ in which the switch S ₁ is turned on are made to coincide with the period in which the signal is sampled by the sample and hold circuit 10. However, the sampling period is not limited to this. It can be decided independently of the period.

However, the switch S ₁ is turned on only during this sampling period in which noise is sampled as a part of the signal.
Then, integrating the noise in the first integrating circuit 5 and feeding it back is advantageous in terms of noise removal.

Further, the ON periods T ₂ and T _{4 of the} switch S ₁ are
Since the output of the second integrating circuit 6, that is, the output V ₃ of the noise removing circuit 4 has a larger phase delay with decreasing
Although the resonance characteristic is strengthened, it tends to be difficult to find a circuit condition that is stable and has a high noise removal capability. Switch S ₂
ON period T ₂ and T ₄ of 60% to 50% of the excitation half cycle
% Is easy to obtain good conditions.

The ON period of another switch S ₂ is set to time t ₃
Or ending earlier than t ₅ , that is, the periods T ₂ and T
Turning off the switch S ₂ during the final 5 to 20 mS of ₄ makes it easy to obtain a good result in terms of improving the noise removal capability.

The noise removing circuit 4 has a property of resonantly amplifying only a square wave signal synchronized with the excitation due to the phase delay of the feedback system due to the addition of the integrating function in addition to the first integrating circuit 5. I had

While the amplification degree by this is larger than (R ₂ / R ₁ ), it does not resonately amplify noise other than a square wave but having a different waveform or phase even at the same frequency as the excitation.

For waveforms having different frequencies, that is, for input waveforms of frequency components that do not resonate, the first integrating circuit 5
Serves as a high-pass filter, and the second integrating circuit 6 serves as a low-pass filter.

As described above, due to the resonance amplification for the flow rate signal and the filter effect for noise, the frequency is close to the same frequency as the excitation that causes the largest variation in the measurement in the frequency band of fluid noise or the excitation frequency. Demonstrate a strong removal ability against the noise of the upper and lower frequencies.

Thus, while fluid noise was strongly attenuated, it was possible to selectively amplify only the square wave flow rate signal synchronized with the excitation, and the variation in output could be greatly reduced.

Further, the induction noise of 50 Hz or 60 Hz of the commercial power source can be strongly removed by setting the excitation period number f _L to a low frequency that is far from the commercial frequency. In addition, in the third embodiment of FIG. 5, another switch S _{2 is connected} to the period T _1a.
By OFF during, as compared with the case where no OFF switch S _2, the amplification degree of the same circuit constant is less likely to find a good noise rejection is reduced. In particular, when the period T _1a is lengthened to approach the OFF period of the switch S ₁ , the circuit constants that give good results are limited.

However, due to the limitation, the selectivity between signal and noise becomes sharper, and there is a tendency that a good noise removing circuit is obtained. As described above, the noise removing circuit having excellent characteristics can be realized with a low power consumption and a simple circuit configuration suitable for a battery-driven electromagnetic flowmeter.

In particular, in the second embodiment of FIG. 3, only one capacitor C ₂ is added to the circuit of the prior art to select the circuit constant, and it is only two that consume power. Only operational amplifiers A ₁ and A ₂ . If this operational amplifier is also a programmable operational amplifier, the entire noise elimination circuit can operate with a current consumption of only 3 to 4 μA.

[0101]

Since the noise removing method of the present invention and the converter are configured as described above, the following effects (1) to (4) are obtained.

(1) Fluid noise can be attenuated, and output variations can be greatly reduced. (2) Since the variation is greatly reduced, the signal level can be increased without worrying about the saturation of the A / D conversion circuit (11), so that the dynamic range of the A / D conversion circuit can be effectively used and the measurement accuracy is improved. To do.

(3) 50 Hz or 6 from commercial AC power source
The 0 Hz induced noise can be strongly removed. Therefore, there is no need to synchronize the excitation timing with the AC power supply, which is suitable for battery driving.

(4) It is not necessary to use a high-speed CPU that consumes a large amount of power for removing noise, and also in this respect, a noise removing circuit suitable for battery driving can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of a first embodiment of an electromagnetic flowmeter including a converter according to the present invention.

FIG. 2 is a timing diagram of the circuit of FIG.

FIG. 3 is a circuit diagram of a main part of a second embodiment of the converter according to the present invention.

4 is a timing diagram of the circuit of FIG.

FIG. 5 is a circuit diagram of a main part of a third embodiment of the converter of the present invention.

FIG. 6 is a timing diagram of the circuit of FIG.

FIG. 7 is a circuit diagram of a conventional technique.

FIG. 8 is a prior art timing diagram of FIG. 7.

[Explanation of symbols]

2a, 2b electrode 3 preamplifier 4 noise elimination circuit 5 first integration circuit 6 second integration circuit 7 integration type amplifier A ₁ amplifier S ₁ switch T ₂ , T ₄ , T ₂ ′, T ₄ ′ period V ₁ Flow rate signal V ₂ output V ₃ output V ₄ output (feedback voltage)

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 16, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claim 4

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

As a result, the electric power that can be used to generate the magnetic field becomes inevitably small, and the electromotive force induced between the electrodes has a flow velocity of 1 m.
It was as small as 2 to 5 μV / s . On the other hand, in addition to electrochemical noise, fluid noise, which is called high-speed fluid noise or flow noise, proportionally increases with the flow velocity is generated at the electrode. This fluid noise has a relatively large noise of a high frequency component as compared with the electrochemical noise showing the 1 / f characteristic, and the noise level becomes 1 when the flow velocity approaches 10 m / s.
When it reaches 00 μV and the conductivity of the fluid decreases, it tends to increase further.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

The converter of the electromagnetic flowmeter according to claim 3 is a converter according to claim 1.
2 amps (A₁) And the second integrating circuit (6)
It is characterized in that it is configured as an integrating amplifier (7).
The converter of the electromagnetic flowmeter according to claim 4 is the same as the converter according to claim 2 or
In the light, the resistance (R ₁) Inserted in series
Induction noise occurs due to switching of excitation of (S ₂ ).
It is characterized in that it is turned off only during the period (T _1a ).Claim
5The electromagnetic flowmeter converter according to claim 1 is the invention according to claim 1 or 2.
Switch (S₁) ON period is after the half cycle of excitation
It is characterized by being half.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

The electromagnetic flowmeter converter according to claim 6 is the switch (S ₁ ) according to the invention of claim 1 or 2.
Is turned on (T ₂ , T ₄ , T ₂ ′, T ₄ ′, ...) Matches the signal sampling period.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0072

[Correction method] Change

[Correction content]

In the second embodiment, a circuit which operates similarly to the resistors R ₁ and R ₂ , the amplifier A ₁ and the second integrating circuit 6 in the first embodiment of FIG. It has been replaced. That is, abolished the second integrator 6 in the first embodiment of FIG. 1, the feedback capacitor C ₂ to the amplifier A _1, and connected in parallel with the resistor R _2, an amplifier and an integrator amplifier A ₁ Which has the function of, and so to speak, constitutes an integral amplifier 7.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0078

[Correction method] Change

[Correction content]

The configuration is such that one capacitor C ₂ is added to the conventional circuit of FIG. 7, and the time constant R ₀ · C ₀ of the first integrating circuit 6 is set to the integrating circuit 21 of FIG. Time constant R
It made possible by simply selecting the ₁₀ · C ₁₀ is less than the appropriate value.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0092

[Correction method] Change

[Correction content]

[0092] The another ON period of the switch S _2, time t ₃ or t ₅ to end sooner, i.e. also during the last 5 to 20 m s periods T ₂ and T ₄ to turn OFF the switch S ₂ It is easy to obtain good results in terms of improving the noise removal capability.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0098

[Correction method] Change

[Correction content]

[0098] Further, the induction noise of the commercial power supply of 50Hz or 60Hz may be strongly removed by determining the excitation Frequency f _L to a lower frequency away larger than the commercial frequency. In addition, in the third embodiment of FIG. 5, another switch S _{2 is connected} to the period T _1a.
By OFF during, as compared with the case where no OFF switch S _2, the amplification degree of the same circuit constant is less likely to find a good noise rejection is reduced. In particular, when the period T _1a is lengthened to approach the OFF period of the switch S ₁ , the circuit constants that give good results are limited.

Claims (6)

[Claims] 1. A magnetic flowmeter for measuring the flow rate of a fluid by the excitation magnetic field periodically square wave polarity changes, the output obtained by amplifying, integrating the flow signal square wave (V ₁₎ to (V _3), exciting For a period (T ₂ ) in synchronism with the square wave, and the integrated output (V ₄ ) is differentially fed back to the flow signal of the square wave as the input of the amplification / integration, thereby the square wave synchronized with the excitation. A method for removing noise in an electromagnetic flow meter, characterized in that the flow rate signal of the above is selectively amplified. 2. A magnetic flowmeter for measuring the flow rate of a fluid by the excitation magnetic field periodically square wave polarity changes, the amplifier for amplifying the square wave flow rate signal (V ₁₎ (A ₁₎
And a second integrator circuit (6) for integrating the output (V ₂ ) of the amplifier (A ₁ ) and a switch (S
₁ ), a first integrator circuit (5) for integrating the output (V ₃ ) of the second integrator circuit (6) only while the switch (S ₁ ) is ON, and the integrator circuit (5) A feedback loop for inputting an output (V ₄ ) to the amplifier (A ₁ ), and a converter for an electromagnetic flow meter used for carrying out the noise removal method according to claim 1. 3. An amplifier (A ₁ ) and a second integrating circuit (6)
3. The converter of the electromagnetic flow meter according to claim 2, characterized in that and are configured as one integral type amplifier (7). 4. The switch (2) inserted in series with the resistor (R ₁ ) is turned off only during a period (T _1a ) in which induction noise accompanying switching of excitation occurs. Item 3 converter. 5. The converter for an electromagnetic flow meter according to claim 1, wherein the ON period of the switch (S ₁ ) is the latter half of the half cycle of excitation. 6. A switch (S₁) Is ON (T
_2,T_Four, T₂′_,T _Four′,…) Sample the signal
3. The period according to claim 1, wherein the period is set to match.
The converter of the described electromagnetic flowmeter.