JP2619133B2 - Electromagnetic flow meter - Google Patents

Description

The present invention relates to an electromagnetic flowmeter using a low-frequency alternating magnetic field, and particularly to a function of removing electrochemical noise generated on an electrode surface. The present invention relates to an electromagnetic flowmeter provided with the above.

(Prior art) The early electromagnetic flowmeters used exclusively for commercial frequencies (50/60 Hz AC)
Is widely used. However, in the case of an electromagnetic flowmeter using this AC excitation method, generation of noise as described below is unavoidable due to its measurement principle.

That is, as is well known, the electromagnetic flow meter has the following relationship: Φ = K ₁ SB (1) E = − (dΦ / dt) (2) In this equation, Φ is a magnetic flux, B is a magnetic flux density, S is an effective area of an irradiation field of the magnetic flux, and E is an electromotive force related to magnetism obtained from a pair of electrodes. here,
By substituting equation (1) into equation (2) and performing partial differentiation, E = − {K ₁ B (dS / dt) + K ₁ S (dB / dt)} = − {K ₁ B (dS / dt) + K ₂ (dB / dt)｝ = − (E _S + E _N ) (3) Here, K ₁ and K ₂ are proportional constants. The (3) of the formula, E _S is the original signal proportional to the flow velocity or flow rate flux is obtained by interlinkage that the fluid,
Meanwhile, E _N is interlinked to one turn coil composed of the signal deriving leads for deriving from each electrode (imaginary line a fluid conductor) imaginary line magnetic flux density B is connecting the electrodes trans This is the noise generated by the typical action. in this case,
When the waveform of B = Asinωt is used, (dB / dt) = Aωcos
ωt.

The magnetic flux density B links the one-turn coil not only to generate 90 ° noise having a phase of dB / dt, but also to generate a magnetic flux having a phase of B in a metal such as a metal measuring tube or core. , An eddy current flows in the metal and the dB / dt
When the secondary magnetic flux is linked to the one-turn coil, the secondary magnetic flux has the same phase noise as the opposite phase to the signal phase (the same phase noise causes zero point fluctuation) d ² B / dt ²
= −Aω ² sinωt occurs. Therefore, these B, dB / dt,
The phase relationship of d ² B / dt ² is as shown in FIG. Further, the circuit is configured as shown in FIG. 2, and further expressed by a vector, as shown in FIG. In these figures, I ₀ is a magnetizing current, V ₀ is a voltage corresponding to the magnetizing current,
I is an exciting current, V is an exciting voltage, R is a winding resistance, and I _C is a current corresponding to iron loss.

Meanwhile, the noise component E _N as described above is the noise involved in AC phenomena arise various problems by the noise. That is, for example, a zero-point drift due to the effect of deposits (adhesive substances contained in the fluid) on the electrode surface,
Indication fluctuation due to non-uniformity of electric conduction in the fluid or measurement is impossible in the case of significant fluctuation, indication fluctuation due to bubbles in the fluid Measurement is impossible in the case of significant fluctuation,
These include the influence of the jump noise on the signal line, instability of the drift instruction such as zero point and span, and the zero point drift due to the fluctuation of the ground potential due to unsafe grounding.

Therefore, an AC-excited electromagnetic flowmeter sorts unmeasurable fluids and difficult-to-measure fluids at the time of specification selection based on past experience, and does not measure such fluids, or a guideline even when such fluids are measured. It is positioned as a typical measurement.

By the way, in recent years, in order to improve the above-mentioned problems, a SW (square wave) excitation method using a low frequency has been used instead of the AC excitation method. In the case of this SW excitation method, since B = k can be expressed in the sampling section as shown in FIG. 10, dB / dt = dk / dt = 0, d ² B / dt ²
= 0, so that various problems caused by various AC phenomena can be solved. This is called the DC property of the excitation.

On the other hand, the removal of the noise E _N superimposed on the flow signal E _S taken out from the signal derivation lead wire has a voltage relationship as shown in FIG. 11, and the positive electrode side voltage A = E _N + E _S , Assuming that the negative electrode side voltage b = E _N −E _S , then E−ro = (E _N + E _S ) − (E _N −E _S ) = 2E _S , so that only the noise component is removed and only the signal component is extracted. Can be. This is called the alternating nature of the excitation.

Thus, the SW excitation method can solve the problems of the AC excitation method based on the DC characteristics of the excitation and the alternating characteristics of the excitation. In particular, in the case of the SW excitation method, a magnetic flux having a waveform such that the dB / dt becomes infinitely zero is often used. Therefore, the excitation frequency is often lowered to a low excitation frequency, for example, about 3 Hz or 6 Hz.

Therefore, although the SW excitation method apparent from the above description is very excellent, the following problem is newly pointed out. That is, the generated electromotive force of the SW excitation method can be reduced to about 1/5 to 1/10 as compared with the AC excitation method. However, when the generated electromotive force is small, not only does the gain of the signal converter increase by the reciprocal thereof, but also electrochemical noise occurs inside and outside the frequency band of SW excitation. The general noise is turned off when the excitation power supply or the electric induction source is turned off, but in the case of electrochemical noise, it is still present even when the excitation power supply or the like is turned off.

This electrochemical noise causes the electrode surface in an electrochemically stable state to be disturbed by a sudden change in the fluid or solids, fibers, bubbles, etc. contained in the fluid, causing a rapid electrochemical reaction and causing an electrochemical reaction. This is noise caused by a change in potential.

This change in electrode potential has not been elucidated accurately at present, but is generally explained by the following theory. That is, when the zinc plate Zn is immersed in dilute sulfuric acid, hydrogen bubbles are generated from the surface of the zinc plate, and when this is expressed by a chemical reaction formula, it becomes Zn + 2H ⁺ → Zn ²⁺ + H ₂ . In other words, zinc plate Zn, which becomes stable due to corrosion, reacts with hydrogen ions in the solution to form zinc ions and hydrogen molecules, and this hydrogen molecule covers the surface of the unreacted zinc plate as a single molecule and inhibits the reaction . Such a state is called polarization. The polarized hydrogen film is broken and the reaction occurs again.

Therefore, the electrode surface and the electrochemical phenomenon will be considered. Generally, in the electromagnetic flow meter, the electrodes 1, 1 'and the earth rings 2, 2' are connected as shown in FIG. Here, the materials of these electrodes and the earth ring are M ₁ , M ₂ , M ₃ , M ₄
Then, even if they are the same kind of metal, the metal must be treated as a dissimilar metal depending on the surface state (rust, attached matter) of the metal, the state of ions surrounding each metal, and the like.

Therefore, in the case of such an electrode, an extreme battery is formed as shown in FIG. That is, when the electrode 3 is composed of, for example, three kinds of metals M ₅ , M ₆ , and M ₇ , the three kinds of metals in the electrode 3 are combined. In the electrode contact part 4, each metal
M ₅ , M ₆ , and M ₇ are in contact with the liquid, respectively. Where metal
Focusing on M ₅ and M ₆ , as shown in FIG. 14, two metals M ₅ and M ₆
M ₆ is connected with a coupling resistance r ₁ in the electrode and liquid resistance in the fluid
_They are connected by r ₂ , which is equivalently represented as shown in FIG.

FIG. 16 is a view electrochemically showing a polarization state of a voltaic cell type. Now, the electrode material M _P, and M _N, and a fluid outside of the electrode material M _P, the connection resistance between the M _N and r, if tentatively M _P <M _N ionization tendency, M _P is a positive electrode, M _N becomes the negative electrode. Then, the negative electrode (M _{N ^{surface), M N → M N +}} n + ne - performs consists electrochemical reaction, the M _N surface e ^- lot accumulate. However, since M _P and M _N are connected by r, e ⁻ moves from M _N to M _P via r and causes the next reaction. That is, in the positive electrode (the surface of the ^{_{M P), 2e - + 2H}} + → H 2 , and the part ^{2e - + 2H + → 2 (} H) 4 (H) + the dissolved O ₂ → 2H ₂ O in the solution. Also, when a large amount of O ₂ enters the fluid, it becomes O ₂ + 2H ₂ O + 4e ⁻ → 4 (OH) ⁻ , and _MN is more and more dissolved by the transfer and consumption of electrons.
Also, if CO ₂ , NH _3, etc., which ionizes when dissolved in a fluid, dissolves, a change in e ⁻ occurs.

However, when the temperature of the fluid, the dissolved gas, the electrolyte concentration, and the like are constant, that is, when the fluid is stable, the sum of the potential differences between the negative electrode and the positive electrode becomes zero, and the electrode 3 is in an electrochemically stable state. When a change occurs in the temperature, dissolved gas, electrolyte concentration, or the like, an electrochemical reaction occurs to change the electrode potential.

In addition, colloid particles having charges opposite to the poles are attracted to the positive electrode and the negative electrode on the electrode surface, and an electric double layer is formed around the particles as shown in FIG. 16 so that the electrode surface is electrochemically stable. Similarly, if the electric double layer is disturbed, the generation of hydrogen changes the electrode potential, and similarly generates electrochemical noise.

(Problems to be Solved by the Invention) In general, among the noise generation mechanisms on the electrode surface, “noise due to electric double layer structure” and “noise due to passive body forming current” are problematic. "
In the case of fluids such as cement mortar (containing sand), there is no problem because it is a transient phenomenon. In other words, a large noise is generated at the moment when the electric double layer on the electrode surface, the passive body, etc. are brushed and peeled off by the collision of the solid material such as fibrous material and sand, but the same state cannot be immediately obtained after the peeling. It is hard to generate continuous noise.

However, the above-mentioned battery-shaped polarization state of the volta and the electric double layer of the colloid solution correspond to the electrochemically stable state of the electrode surface, and the electrode surface is washed violently by rapid changes in the fluid and bubbles contained in the fluid. When this occurs, the electric double layer and the like are disturbed, hydrogen is generated from the electrode surface, and accordingly, the electrode potential changes and electrochemical noise is generated. Therefore, the noise generated on the electrode surface has a problem of fluctuation of electrochemical DC noise. In other words, the above-mentioned electrochemical phenomena of the electrodes (battery-like phenomena) cause an ionic reaction due to the battery action that occurred on the surface of the electrodes, and the DC electric potential accumulated as a result of the ionic reactions causes the slurry in the fluid to flow. Fluctuates due to changes in the concentration of air, bubbles, oxygen, etc.
Causes AC-like noise changes and affects measured values. Here, if it is a DC noise, if it is cut by the coupling capacitor in the signal conversion means, only the flow signal can be received, and the measurement is not affected at all. However, there is a problem that when fluctuation occurs in the DC noise, the DC noise jumps over the coupling capacitor and greatly affects the measurement.

The present invention has been made in view of the above circumstances, and neutralizes a noise component generated on an electrode surface to zero or nearly zero, thereby reducing charges (ions) accumulated on the electrode surface and extracting only a flow signal. It is an object to provide an electromagnetic flowmeter.

[Means for Solving the Problems] First, in order to solve the above problems, an electromagnetic flowmeter according to claim 1 links a low-frequency alternating magnetic field to a conductive fluid flowing through a pipe. By doing so, the electromotive force induced in the conductive fluid is taken out by a pair of electrodes, and guided to the signal conversion means through the direct current impedance element and the direct current cutoff element, and the signal conversion means is proportional to the flow rate or flow rate of the conductive fluid. In the electromagnetic flow meter for obtaining a signal, a first switch branched to the output side of the DC impedance element, and the first switch turned on when not energized to take in a detection signal from the electrode, The electric potential generated at the electrode on the input side of the DC impedance element via the second switch is zero or near zero so that A configuration in which a neutralizing controller for negative Kikan electrical potential to neutralize.

Next, the electromagnetic flow meter according to the second aspect integrates a detection signal from the electrode regardless of the presence or absence of excitation on the output side of the DC impedance element to extract a noise component, and the noise component is minimized. In this manner, a high-impedance neutralization controller is provided on the input side of the DC impedance element for negatively feeding back an electric potential for neutralizing an electric potential generated from the electrode surface to zero or near zero.

(Operation) Therefore, the invention corresponding to claim 1 takes the above-described means, so that the controller for neutralization takes in the detection signal from the electrode through the first switch at the time of non-excitation, and By turning off the first switch and turning on the second switch to negatively feed back the electric potential that minimizes the detection signal, the electric potential generated from the electrode surface is neutralized to zero or near zero. Is what you do.

Next, a second aspect of the present invention provides a high impedance neutralization controller which integrates a detection signal from the electrode regardless of the presence or absence of excitation to extract a noise component so that the noise component is minimized. The electric potential is negatively fed back to neutralize the electric potential generated from the electrode surface to zero or near zero.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG. That is, the electromagnetic flow meter converts the electromotive force detected by the measuring unit 10 into a predetermined signal proportional to the flow rate or flow rate of the conductive fluid from the measuring unit 10 that detects the electromotive force induced in the conductive fluid. And signal conversion means 20.

The measurement unit 10 includes a tube 11 serving as a conductive fluid passage,
Exciting coils 12a and 12b that generate a magnetic flux by receiving an exciting current by the SW excitation method and form a magnetic field in the tube 11, and a tube 11
And a pair of electrodes 13 and 13 ′ that take out electromotive forces e ₁ and e ₂ that are brought into contact with the internal fluid and induced in the conductive fluid by linkage of the magnetic field. In the figure, e ₁ and e ₂ are the electromotive force between the ground G and each of the electrodes 13 and 13 ′, and r ₁ and r ₂ are the impedance between the ground G and each of the electrodes 13 and 13 ′. It was done. 14, 14 'are signal lead wires.

On the other hand, the signal conversion means 20 includes
4 'impedance for DC such as resistance and choke 21, 21'
A main circuit 23 for converting the signal into a required signal is connected via filter capacitors 22 and 22 '. This main circuit
Reference numeral 23 denotes an amplifying means for amplifying a signal at a predetermined amplification degree, a signal converting means for converting the signal into a required signal, and a signal evaluating means for evaluating the fluctuation of the signal as required. 24 is a timing signal generating source for generating a predetermined timing signal, 25 is a timing signal generated from the timing signal generating source 24, and receives an exciting current having a square wave exciting waveform as shown in FIG. This is an excitation power supply that supplies the excitation coils 12a and 12b with an excitation current having a square wave ternary excitation waveform as shown in (b) or an excitation current having a square wave one-sided excitation waveform as shown in FIG.

Switches 26 and 26 'are provided at the output terminals of the DC impedances 21 and 21', respectively.
The other end of 26 'and the ground G side are connected to the respective input terminals of low impedance (of course, high impedance) neutralization controllers 27 and 27'. These neutralization controllers 27 and 27 'switch 2
6, 26 'is turned on to take in the detection signal from the electrode, find an electric potential that minimizes the detection signal, and provide a negative feedback to the input side of the DC impedance 21, 21'.

Further, a switch 28, is provided between the output side of the neutralization controller 27, 27 'and the input side of the DC impedance 21, 21'.
28 'is provided. 29 and 29 'are negative feedback points of the electric potential.

When the neutralization controllers 27 and 27 'are high impedance, at least the switches 26 and 2 on the signal input side are used.
Except for 6 ', it may be directly connected to the output side of the DC impedance 21, 21'.

In this case, the neutralization controllers 27 and 27 'at least integrate a detection signal from the electrode regardless of the presence or absence of excitation to extract a noise component, and further perform an operation described later to minimize the noise component. It has a function of negatively feeding back to the input side of the DC impedance element which has obtained such an electric potential to neutralize the electric potential generated on the electrode surface to zero or near zero.

Next, the operation of the electromagnetic flowmeter configured as described above will be described separately for the case of non-excitation and the case of excitation.

That is, at the time of non-excitation, a clock signal is transmitted from the timing signal generation source 24 to turn on the switches 26 and 26 ′, so that the detection signals from the pair of electrodes 13 and 13 ′ are transmitted through the switches 26 and 26 ′. Introduced to neutralization controllers 27 and 27 '. Thereafter, a clock is sent from the timing signal generation source 24 to turn off the switches 26 and 26 'and set the switches 28 and 28' on. At this time, the neutralization controllers 27 and 27 'determine the electric potentials at which the detection signals from the electrodes 13 and 13' are minimized to determine the switches 28 and 2 '.
Negative feedback to the input side of DC impedance 21, 21 'via 8' to discharge or neutralize the electric potential (charge) appearing on the electrode surface, thereby making the electric potential on the electrode surface zero or zero. It decreases near.
These neutralization treatments are repeated a plurality of times as necessary.
When measuring the flow rate by excitation, each switch 26, 26 ',
Switches 28 and 28 'are set to the off state.

Next, the timing relationship between the components during the excitation operation will be described. FIG. 3 (a) from the timing signal source 24
When the timing signal shown in
In response to the timing signal, an exciting current having a square wave exciting waveform as shown in FIG. 3B is generated and supplied to the exciting coils 12a and 12b. As a result, a magnetic field is formed in the tube 11 by the magnetic flux generated from the exciting coils 12a and 12b,
The fluid is linked to this magnetic field, and a pair of electrodes 13, 1
An electromotive force signal as shown in FIG. 3 (c) can be extracted from 3 '. At this time, the timing signal source 24
3 (d) to turn on the switches 26, 26 'and 28, 28' simultaneously or at different times, the detection signals from the electrodes 13, 13 '
It is introduced into the neutralization controllers 27 and 27 'through 26'. Here, the neutralization controllers 27 and 27 'will be described in detail later.The detection signals from the electrodes 13 and 13' are integrated to extract a noise component, and for example, the noise component is minimized except for a measurement sampling period. If an electrical potential is obtained and negative feedback is provided to the input side of the DC impedance 21, 21 'through the switches 28, 28', the electrochemical noise component generated on the electrode surface is discharged to zero or zero. It can be reduced to the vicinity. Further, when the timing signal source 24 sends a sampling clock signal as shown in FIG. 3 (e), the main circuit 23 receives the clock signal and samples detection signals from the electrodes 13, 13 'in a sampling interval. I do. The thick line in FIG. 3 (c) indicates a sampling interval.

When the built-in amplifiers of the neutralization controllers 27 and 27 'are high impedance, the neutralization controllers 27 and 27'
Irrespective of the presence or absence of excitation and the presence or absence of the measurement sampling period, the detection signal from the electrodes 13 and 13 'is directly taken in without passing through the switches 26 and 26' to extract a noise component. The negative potential is obtained and negative feedback is made to the input side of the DC impedances 21 and 21 '.

Next, the neutralization controllers 27 and 27 '
That is, an example of extracting the neutralizing electric potential will be described. First, FIG. 4 is a diagram showing a detection signal including noise from the electrode during the flow rate measurement. Now, FIG. 3 (b)
Excitation coils 12a and 12b
After excited, when observed in front of the 'capacitor 22 and 22 for the detection waveform from' the pair of electrodes 13 and 13, as shown in FIG. 4, E '= E _S (flow rate signal) + E _N' (noise component ). E _N '= a E _N + e _n.
E _S is the transformer noise generated when performing the excitation, e _n
Is the electrochemical noise generated even when not excited.

Thus, from among the detected waveforms E 'from the electrodes 13, 13', E
'When retrieving only integrates the signal waveform of FIG. 4, i.e. _{{(E S + E N'} N) + (- E S + E N ')} + {(E S + E N') + (- E S + E _N ′)｝ …… →→ E _N ′ (moving average) In addition, it is also possible to extract only E _N ′ by performing integration of a section excluding the sampling section, integration of only the sampling section, integration of an arbitrary section, and the like.

The E _N 'obtained as described above is amplified by an amplifier in the neutralization controllers 27 and 27', and then the switch 2
By performing negative feedback to the negative feedback points 29, 29 'via the 8, 28', control is performed so that the detection signal from the electrode is minimized.

Next, FIG. 5 is a diagram showing a measured waveform from the electrode after neutralization of the electric potential during the flow rate measurement. This waveform has an electrochemical noise e _n due to neutralization of the electric potential.
Show that has become smaller △ e _n. In this state, when solids, bubbles, etc. in the slurry fluid rub the surface of the electrodes 13, 13 ', the contact resistance between the electrodes 13, 13' and the fluid decreases, and the charges rapidly move in the direction in which the charges become stable. Also, since the electrochemical reaction on the electrode surface becomes active, fluctuations occur in the electrochemical DC noise, which changes to AC noise, and saturates the amplifier in the main circuit 23 through the filter capacitors 22 and 22 '. Let it. If the electric charge on the electrode surface is always close to zero, even if the electrode surface is rubbed, if the electric potential is close to zero, the electrochemical noise generated by the fluctuation of the electrochemical DC noise is weak even if it occurs,
There is no particular problem.

Incidentally, the noise component E _N 'is can be taken out by integration of the waveform indicated by FIG. 5, further continuously noise component E _N' in the case of taking out, the size of the "integration, moving average and noise E _N ' Adjustment etc. "may be performed. That is,
By performing the integration and the moving _{average, {(E S + E N} ') + (- E S + E N')} + {(E S + E N ') + (- E S + E N')} + ...... = 2E _N ′ + 2E _N ′ +... Can be obtained, and by adjusting the magnitude of this noise, E _N ′
Can be continuously taken out. In this case, E _N ′
= It is a _{E N + △ e n, △} e n can be neglected so small. That is, E _N ′ = E _N.

Then, when extracting only E _S in the main circuit 23 may be subtracted in the lower waveform from the waveform on the time axis of FIG. 5. _{That, {(E S + E N} ) - (- E S + E N)} + {(E S + E N) - (- E S + E N)} + ...... = 2E S + 2E S + ...... is obtained, by adjusting the magnitude of the 2E _S + 2E _S + ......,
E _S can be taken out.

Further, FIG. 6 shows an observation waveform in the main circuit 23 when excited by using a square wave ternary excitation waveform as shown in FIG. 2 (b). Even with such a waveform, ｛E _S + (E _N + △ E _n ) + ｛E _n △ + ｛-E _S + △ E _n + △ E _n △ + ｛E _S + (E _N + △ _{e n) + △ e n}} + {- E S + △ e n + △ e n} + ...... = E n + 4 △ e n becomes integral and moving average makes it possible to take out the noise component.

Therefore, according to the configuration of the embodiment described above, if negative feedback is performed so that the electric potential generated on the electrode surface becomes zero or near zero, the ionic reaction on the electrode surface becomes slow, and the switches 28 and 28 ' When the switch is turned off, the electrochemical reaction on the electrode surface does not occur rapidly, and the electrochemical noise does not increase so much. Because the filter capacitors 22,2
Switch 2 'has a function to cut direct current.
Even if 8, 28 'is turned off, the current remains as the filter capacitor 22, 22'.
If the negative feedback of the electric potential is applied to the electrode with a negative polarity, a bubble film of hydrogen is formed, and the component or the component of the electrode surface is independent of the feedback. This is because an electrochemical reaction occurs between the components in the fluid, and polarization due to hydrogen bubbles (monomolecular film-like) occurs. Therefore, if the feedback is performed while the stable state continues, even if the electrode surface is rubbed by the slurry, by performing the rate limit control and the like,
The movement of charges can be suppressed relatively stably.

The present invention is not limited to the above embodiment. For example, when the electrode surface is rubbed from the beginning of the flow of the fluid by the slurry fluid, an evaluation means for detecting that the signal in the main circuit 23 or the output thereof is most stable is provided inside the main circuit 23, and the evaluation means stably outputs the signal. When an instruction to the effect is received, the stabilizing amount may be negatively fed back from the neutralization controllers 27 and 27 'via the switches 28 and 28'.

In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] As described above, according to the present invention, the charge (ion) accumulated on the electrode surface is reduced by neutralizing the noise component generated on the electrode surface to zero or near zero, and the flow signal It is possible to provide an electromagnetic flowmeter that can accurately measure only the flow rate.

[Brief description of the drawings]

1 to 6 show an embodiment of an electromagnetic flow meter according to the present invention. FIG. 1 is an overall configuration diagram of the electromagnetic flow meter, and FIG. 2 is a view showing various excitation waveforms. FIG. 3 is a signal timing diagram of each component of the electromagnetic flowmeter, FIGS. 4 to 6 are diagrams showing the level states of signal components and noise components, and FIGS. FIG. 7 is a diagram for explaining an electromagnetic flow meter, FIG. 7 is a diagram for explaining a phase relationship between signals by AC excitation, FIG. 8 is an electrical equivalent circuit diagram of AC excitation, and FIG. 9 is FIG. FIG. 10 is a diagram showing output waveforms when the SW excitation method is used, FIG. 11 is a diagram for explaining the properties of the SW excitation method, and FIGS. It is a figure explaining a chemical phenomenon. 10… Measurement unit, 11… Tube, 12a, 12b… Excitation coil, 1
3,13 ... Electrode, 20 ... Signal converter, 21,21 '... DC impedance, 22,22' ... Filter capacitor, 23
... Main circuit, 24 ... Timing signal source, 25 ... Excitation power supply, 26,26 ', 28,28' ... Switch, 27,27 '... Neutralization controller.

Claims (2)

(57) [Claims] An electromotive force induced in the conductive fluid is taken out by a pair of electrodes by interlinking a low-frequency alternating magnetic field with the conductive fluid flowing through the tube, and is passed through a DC impedance element and a DC cutoff element. An electromagnetic flowmeter which leads to a signal conversion means and obtains a signal proportional to the flow rate or flow rate of the conductive fluid by the signal conversion means, comprising: a first switch branched to an output side of the DC impedance element; The first switch is turned on to take in the detection signal from the electrode, and the electric signal generated at the electrode on the input side of the DC impedance element via the second switch so that the detection signal is minimized. A neutralization controller for negatively feeding back an electric potential for neutralizing the potential to zero or near zero. 2. An electromotive force induced in the conductive fluid is taken out by a pair of electrodes by interlinking a low-frequency alternating magnetic field with the conductive fluid flowing in the tube, and is passed through a DC impedance element and a DC cutoff element. In an electromagnetic flowmeter which leads to a signal conversion means and obtains a signal proportional to the flow rate or flow rate of the conductive fluid with the signal conversion means, the electromagnetic flowmeter is directly connected to the output side of the DC impedance element, regardless of whether or not excitation is performed. To extract a noise component, and to neutralize the electric potential generated at the electrode on the input side of the DC impedance element to zero or near zero so that the noise component is minimized. An electromagnetic flowmeter comprising: a high-impedance neutralization controller that negatively feeds back.