JPH07248240A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To achieve a lower power consumption of an electromagnetic flowmeter without adversely affecting measuring accuracy by stopping excitation during a fixed period immediately after turning ON or OFF of a shortcircuiting switch in ON or OFF periods of the shortcircuiting switch for measuring conductivity. CONSTITUTION:An electromagnetic flowmeter has a shortcircuiting switch S1 for measuring conductivity adapted to earth electrodes 2 and 3 for inducing a flow rate signal intermittently through a shortcircuiting resistance Rin and an offset compensation circuit 10 to remove a DC component contained in the flow rate signal. An output E3 of the offset compensation circuit 10 immediately after the turning ON or OFF of the shortcircuiting switch S1 is not sampled as flow rate signal. On the other hand, excitation is stopped during a fixed period immediately after the turning ON or OFF of the short-circuiting switch S1 among ON or OFF periods of the short circuiting switch S1. Thus, exciting power will not be consumed during the stoppage of the excitation. In addition, during the stoppage of the excitation, no flow rate signal corresponding to a flow velocity is induced thereby achieving a lowering of power consumption.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to electromagnetic flow meters.

[0002]

2. Description of the Related Art The applicant previously proposed an electromagnetic flowmeter for measuring the electrical conductivity of a fluid in Japanese Patent Application No. 3-222939.

Thereafter, the shortcomings of the first prior art were noticed, and an electromagnetic flowmeter which eliminates this shortcoming was proposed in Japanese Patent Application No. 4-1202.
No. 05 (Japanese Patent Laid-Open No. 5-313610).
This is hereinafter referred to as the second conventional technique.

These conventional techniques were as follows.

[0005]

[First Prior Art] FIG. 7 shows a part of an equivalent circuit in a flow tube of an electromagnetic flow meter detector and an electric circuit of a converter in the first prior art.

In FIG. 7, reference numeral 1 is a cylindrical flow tube, and 2, 3
Is an electrode which is arranged to face the inner peripheral wall of the flow tube 1, 4 and 5 are exciting coils which are arranged above and below the flow tube 1, 6 is a ground electrode, and a well-known electromagnetic flow rate is used in the flow tubes 1 to 6 It constitutes a total detector.

Reference numeral 7 is a short circuit for measuring conductivity, which is a series circuit of a short-circuit resistance R _in connected between the electrode 2 and the ground electrode 6 and a short-circuit switch S ₁ for measuring conductivity, the electrode 3 and the ground electrode. And a series circuit of a short-circuit resistance R _in and a short-circuit switch S ₁ for measuring conductivity.

A high-pass filter 8 is connected with two capacitors C and two resistors R as shown in the figure. 9
Is a differential amplifier that amplifies the voltage of the electrodes 2 and 3 that has passed through the high-pass filter 8, and its amplification degree is G.

Reference numeral 10 designates an offset compensation circuit, which comprises resistors R ₁ ,
R _2, R _3, operational amplifier A _1, A _2, which are connected as shown to the capacitor C ₁ and the switch S _2. As is well known, the switch S ₂ is turned on / off in synchronization with the square wave of the exciting current of the exciting coils 4 and 5.

Е ₁ and е ₂ are flow rate signal voltages with respect to the ground electrode 6, and even if the shape of the detector is left-right pair, it does not have the same value unless the flow velocity distribution is left-right pair. The frequencies of the flow signal voltages е ₁ and е ₂ are f _ex, which is the same as the excitation frequency.

V ₁ and V ₂ are the electrochemical potential differences between the electrodes 2 and 3 and the ground electrode 6, respectively, and their fluctuation frequencies f _c
Is very small, and henceforth referred to as DC offset voltage for convenience. The left and right DC offset voltages V ₁ and V ₂ are usually different values.

R _w is the electric resistance of the fluid between the electrodes 2 and 3 and the earth electrode 6, and if the geometrical shape of the detector is left and right and the conductivity of the fluid is uniform, the same value is obtained on the left and right. Becomes Therefore, normally, R _w has the same value on the left and right.

The time constant CR determined by the capacitance C of the capacitor C of the high-pass filter 8 and the resistance value R of the resistor R is selected so that 1 / f _ex << CR << 1 / f _c .

By thus defining the time constant CR, the flow rate signal voltages е ₁ and е ₂ pass through the high-pass filter 8 with almost no attenuation, and the DC offset voltages V ₁ and V ₂ are greatly attenuated by the high-pass filter 8. Hardly passes.

[0015] If a short switch S ₁ is representative of the output E ₁ of the differential amplifier 9 when the off [E _1] and _{OFF, [E 1] OFF =} G [(1-δ) (е 1 -е 2) + Ε (V ₁ −V ₂ )] ... (1). However, δ << 1, ε << 1.

The output when the short-circuit switch S ₁ is on [E
₁ ] _ON , [E ₁ ] _ON = [R _in / (R _w + R _in )] G [(1-δ) (е ₁ −е ₂ ) + ε (V ₁ −V ₂ )] ... (2 ).

When the ratio of the above equations (1) and (2) is taken, the following equation (3) is obtained. Since the short circuit resistance R _in is known, the electrical resistance R _{w of the} fluid is known. Moreover, the electrical resistance of the fluid R _w
Since is in inverse proportion to the conductivity, the conductivity of the fluid can be specified from the equation (3).

[E ₁ ] _OFF / [E ₁ ] _ON = 1 + R _w / R _in (3) That is, using the output E ₁ of the differential amplifier 9, in principle, the conductivity W _c of the fluid is Can be used as is for flow rate correction.

[0019]

[Disadvantage 1 of First Prior Art] Short-circuit switch S₁On
-When the off interval is long. In the first conventional technique described above, the dark
In silence, he made important assumptions. It is a flow signal
Voltage₁， Е₂, DC offset voltage V₁, V₂,as well as
Electrical resistance of fluid R _wBut the output [E₁]_OFFAnd [E₁]_ON
The assumption is that it is constant during the measurement of.

However, in reality, these amounts change every moment to some extent, which causes an error in conductivity measurement. The error caused by this is that the short-circuit switch S ₁
The longer the on / off interval of, the greater the chance of these quantities changing during that time, thus increasing the risk of increase.

[0021]

[Disadvantage 2 of the first prior art] When the ON / OFF interval of the short-circuit switch S ₁ is short. From the viewpoint of the defect 1, it is better to shorten the ON / OFF interval of the short-circuit switch S ₁ .

However, the short-circuit switch S₁Is on and off each
State, flow signal е₁， Е₂Need to measure properly
Therefore, at least during one cycle of excitation, the short-circuit switch
Chi S ₁Must be either on or off.
It

Considering in this way, as shown in FIG.
It is considered optimal to turn on / off the short-circuit switch S ₁ every one cycle of excitation. However, in this case, the following new problems, which hardly cause a problem when the ON / OFF interval is long, occur.

It is a problem of fluctuations of the DC offset voltages V ₁ and V ₂ . The DC offset voltage is an amount generated by electrochemical equilibrium between the electrode and the ground electrode and the fluid, and it takes a certain time to reach the equilibrium state.

When the short-circuit switch S ₁ is turned on / off, the electrodes 2 and 3 and the earth electrode 6 are connected between two equilibrium states, that is, a state in which they are connected via a short-circuit resistance R _in and a state in which they are disconnected. Try to come and go (see Figure 9).

For example, the DC offset voltage V₁about
Considering, short circuit switch S₁Short circuit switch while is off.
Chi S₁Saturation voltage [V_{1 SAT}]
_OFFAsymptotically approaching, as indicated by the symbol a in FIG.
Rise to. Short circuit switch S₁While the switch is on, the short-circuit switch
Touch S₁Saturation voltage [V_{1 SAT}]
_ONAsymptotically approaching, as indicated by the symbol b in FIG.
To descend.

Although the DC offset voltage V ₂ changes in the same manner as V ₁ , the values of the saturation voltage [V _{1 SAT} ] _OFF and [V _{2 SAT} ] _OFF generally have some differences, and likewise the saturation voltage [ The values of V _{1 SAT} ] _ON and [V _{2 SAT} ] _ON do not match.

Since such changes in the DC offset voltages V ₁ and V ₂ occur at a frequency half the excitation frequency, they easily pass through the high pass filter 8 of FIG. 7 with little attenuation. Therefore, the output E ₁ of the differential amplifier of FIG.
It will change like.

In FIG. 10, the output E ₁ of the differential amplifier is such that the electrode voltage is the electrical resistance R of the fluid while the short-circuit switch S ₁ is on.
_{Since the} voltage is divided by _w and the short-circuit resistance R _in , the short-circuit switch S ₁
When the switch is turned on, the step δ _1
A step δ ₂ occurs when ₁ is switched off.

Thus, the DC offset voltages V ₁ , V
₂ is switched by the short circuit 7, passes through the high pass filter 8, is amplified by the differential amplifier 9, and its output E
_{When 1} has steps δ ₁ and δ ₂ as shown in FIG. 10, this change amount is processed by the offset compensation circuit 10 and becomes an error in flow rate measurement.

The mechanism will be described in detail below. Generally, in the converter circuit of the electromagnetic flowmeter, an offset compensating circuit 10 for removing the offset voltage is provided after amplifying the voltage of the electrodes 2 and 3 of FIG. Is normal.

The offset compensation circuit 10 includes a differential amplifier 9
To prevent the DC component than the remaining flow rate signal to the output E ₁ is becomes saturated further being successively amplified by the subsequent amplifier amplifier, one that is provided so as to remove the offset voltage, the operational amplifier A _An inverting amplifier composed of ₁ and resistors R ₁ and R ₂ , an integrator circuit composed of an operational amplifier A ₂ , a resistor R ₃ and a capacitor C ₁ and a switch S ₂ for offset compensation control are shown in the drawing. Connected / configured.

The switch S ₂ is turned on / off in synchronization with the switching of the exciting current. Further, the amplification degree of the inverting amplifier including the operational amplifier A ₁ is assumed to be 1 in order to simplify the explanation.

When the switch S ₂ is turned on, the integrating circuit integrates the output E ₃ of the operational amplifier A ₁ , and the switch S ₂
When is turned off, the value of the output E ₂ at that time is held.
In the offset compensation circuit 10, the output E _{2 of the} integration circuit is fed back to the input of the operational amplifier A ₁ , so that when the switch S ₂ is turned on, the output of the operational amplifier A ₁ (that is, the output of the offset compensation circuit 10) E. _The entire offset compensation circuit is activated so that ₃ is zero volts.

This operation will be described with reference to the timing chart of FIG. It is assumed that a DC component V _D is superposed on the output E ₁ of the differential amplifier 9 in addition to the flow rate signal е. Flow signal е
Is the G (1-δ) (е ₁ −е ₂ ), and the DC component V _D
Corresponds to Gε (V ₁ −V ₂ ).

During the period t ₁ , when the switch S ₂ for offset compensation control is turned on, the operational amplifier A ₁
Output E ₃ charges the capacitor C ₁ of the integrator circuit, the output E _{2 of the} integrator circuit gradually decreases, and the outputs E ₁ and E
The difference between ₂ will be reduced. Then, the value of the output E ₃ also decreases and the charging speed of the capacitor C ₁ decreases.

Thus, the circuit is stable with the output E ₃ at zero volts, at which time E ₁ = E ₂ .
Therefore, the time constant C ₁ × R ₃ of the integrating circuit is set to the periods t ₁ , t _3, ...
If determined Unto small compared to, it may be the E ₁₁ ≒ E ₂₁ at the end of period t _1.

During the period t ₂ , the offset compensation control switch S ₂ is turned off. Therefore, E ₂ = E ₂₁ =
It becomes constant, and as the output E ₃ , this E ₂ = E ₂₁ ≈E ₁₁
The changed amount with respect to appears.

In the period t ₃ , the switch S ₂ is turned on again,
The output E ₂ changes towards E ₂₂ so that the output E ₃ is at zero volts, and at the end of this period E ₂ = E ₂₂ ≈E ₁₂ .

In the period t ₄ , the switch S ₂ is turned off and the output E ₂ becomes E ₂ = E ₂₂ = constant. Then, in the output E ₃ , a change amount with respect to E ₂ = E ₂₂ ≈E ₁₂ appears. After that, the above period t ₁ to period t ₄ is repeated after the period t ₅ .

After all, the offset compensating circuit 10 has compensation periods t ₁ , t ₃ , t ₅ ,
to t ₇ ... each end of, the voltage E _{1 1} including a flow rate signal е DC component _{V D, E 12, E 13} , E 14, and hold ..., in the following period, the output only variation with respect to the voltage To remove the DC component V _D.

For the sake of simplicity, what error will occur when the DC component V _D changes as shown in FIG. 12 assuming that the flow rate signal е is zero volt. in this case,
The DC component V _D is the output E ₁ itself. Also, since the flow rate signal е is zero volt, the output E of the offset compensation circuit is
₃ should originally be at zero volts.

However, as described with reference to FIG. 11, the offset compensation circuit 10 always compensates for the compensation periods t ₁ and t.
_3, t _5, ... last output voltage E _11, E _12, and for issuing as output E ₃ the variation with respect ..., DC offset voltages V _1, V ₂ is switched by a short circuit 7, the output E
_If there is a jump as shown in FIG.
_{As if 11} , δ ₁₂ , δ ₁₃ , ... are signals.
It appears at the output E ₃ , which is an error.

Up to this point, the time constant C ₁ × R ₃ of the integrator circuit in FIG. 1 is much smaller than the periods t ₁ , t ₂ , ..., Therefore, the output E ₂ at the end of the period t ₁
It has been considered that the value E ₂₁ of E is almost equal to the output E ₁₁ , but even if the time constant C ₁ × R ₃ becomes large, the output E during the period t ₁
The output E of the weighted average value of ₁ in the period t ₁ at the end
There is no change in that an error occurs only when the value is ₂ .

As shown in FIG. 8, how the error appears when the conductivity measuring short-circuit switch S ₁ is turned on and off at short intervals is shown in FIG. 13 including the flow rate signal. Output E
₁ is the amplitude е above the DC offset voltage indicated by the dotted line.
The flow signal of is on.

In this case, if there is no DC offset voltage indicated by the dotted line, a signal as shown by the one-dot chain line C in FIG. 11 should be output as the output E ₃ (E in FIG. 11). _Like the waveform in ₃ ).

However, since the output E ₁ has the DC offset voltage component shown by the dotted line, the actual output E ₃ becomes as shown by the solid line D, and a large error occurs immediately after the jump occurs in the DC offset voltage component. Occurs. The portion where such a large error occurs in the output E ₃ is shown by an arrow C.

The jump in the DC offset voltage of the output E ₁ is caused by the short circuit switch S ₁ for conductivity measurement.
When it is turned on or off. Then, the signal indicated by the arrow D immediately following the signal indicated by the arrow C immediately after the short-circuit switch S ₁ is turned on / off does not have an error due to the jump generated in the DC offset voltage.

[0049]

[Second Prior Art] In the first prior art, the short circuit switch is used.
Touch S₁If the on / off interval of the
₁， Е₂, DC offset voltage V₁, V₂, And fluid
Electric resistance R _wBut the output [E₁]_OFFAnd [E₁]_ONMeasure
Since the chances of changing during
There is a risk that the measurement error will increase (defect 1).

Therefore, the short-circuit switch S₁On / off
If the interval is shortened, the short-circuit switch S ₁Turn on / off
Output E each time₁The DC offset voltage of
Immediately after the jump occurs in the DC offset voltage of
Output E of the compensation circuit 10₃A large error occurs (missing
Point 2).

In the second prior art, the electromagnetic flowmeter described above as this defect 2 is such that the error of the output E ₃ of the offset compensation circuit 10 immediately after the short-circuit switch S ₁ is turned on / off does not adversely affect the conductivity measurement. Is proposed.

Therefore, a conductivity measuring short-circuit switch for intermittently grounding the electrode for inducing the flow rate signal via a short-circuit resistor and an offset compensating circuit for removing the DC component contained in the flow rate signal are provided. Moreover, the output of the offset compensation circuit immediately after the short-circuit switch is turned on / off is not sampled.

The main part of the second prior art circuit is shown in FIG. The circuit of FIG. 14 shows a short circuit switch S for conductivity measurement.
Unlike the circuit of the prior art shown in FIG. 7, the point that ₁ is turned on and off every 1.5 cycles of the exciting current does not change the apparent circuit configuration, so the description of the circuit configuration will be omitted.

As described above with reference to FIG. 13, a large error occurs in the output of the offset compensating circuit immediately after the jump occurs in the DC offset voltage of the output E ₃ of the differential amplifier. If the signal indicated by arrow C is not used, the error will be small.

When the variation of the DC offset voltage can be regarded as linear, this method can reduce the error to zero. The circuit of FIG. 14 will be described below with reference to the timing chart of FIG.

(A) The short circuit switch S ₁ for conductivity measurement is turned on at the timing shown in FIG. 15 in response to changes in the exciting current.
Turn off. In this case, the short-circuit switch S ₁ is turned on / off in synchronization with the switching of the exciting current for 1.5 cycles of the exciting current.

(B) At the input of the offset compensating circuit 10, as shown by E ₁ in FIG. 15, a flow rate signal having an amplitude е is carried by a DC offset voltage which changes linearly as indicated by a broken line. (C) The output E ₃ of the offset compensation circuit 10 is as shown by the solid line in FIG. On the other hand, as the signal output, the output E ₃
Therefore, the difference between the solid line and the alternate long and short dash line, that is, the difference between the solid line and the alternate long and short dash line in the portion where the dots are scattered in the figure of the output E ₃ is an error.

(D) Since the error is large in the signal E ₃ immediately after the conductivity measuring short-circuit switch S ₁ is switched also in FIG. 15, even if the signal at this time is not used for the flow rate measurement, The error is small.

(E) Further, intuitively, a'and b ',
Since the areas of c ′ and d ′ are equal, if a + b and c + d of the hatched portion are used as signals when the short-circuit switch S ₁ for conductivity measurement is turned off or on, respectively, The error is canceled out by using the signal. This point will be described below.

(F) Only the periods t ₁ and t ₂ will be described. Since the areas a and b are targeted now, the signal during the period t ₁ is inverted. The signal of the period t ₂ and the originally desired signal are shown in FIG.

In FIG. 16, the signal in the period t ₁ is A−D−H, the signal in the period t ₂ is A−B−F, and the originally desired signal is A−C−G.

Twice the area CGE in FIG. 16 is equal to the area BFG.
It is equal to the sum of E and the area DHGE. This will be described below. As the input E ₁ of the offset compensation circuit 10,
When a signal E ₁ = αt + β which is defined by constants α and β and changes linearly with respect to time t is input, the output E _{2 of the} integrating circuit is

[0063]

[Equation 1]

Since E ₃ = − (E ₂ −E ₁ ), E ₃ = C ₁ R ₃ α + kе ^{−t / C1R3} . The formula of this output E ₃ is the curves BF and C in FIG.
This is an expression representing G and DH, and α corresponds to tan θ in FIG. Also, е in this equation is the base of the natural logarithm.

With reference to FIG. 16, AO = е, this е is the flow signal е, CB = DC = δ, and points B, C, D,
If the time point of E is t = 0, then at t = 0, BE = е + δ, CE = е, DE = е-δ. Therefore, if this is the initial condition, the curve BF is E ₃ = C ₁ R ₃ tan θ + (Е + δ-C ₁ R ₃ αtan
θ) е ^{-t / C1R3} curve CG is E ₃ = е ・ е ^{-t / C1R3} Note that the two е on the right side of the above formula are the flow signal е in Fig. 15 in the front and the natural logarithm in the latter е. Means the bottom of. The same applies to similar formulas described below.

The curve DH is E ₃ = -C ₁ R ₃ tan θ +
(Е−δ + C ₁ R ₃ αtan θ) е ^{-t / C1R3} . If the length of the period EH is T, the area CGE is

[0067]

[Equation 2]

The sum of the area BFGE and the area DHGE is

[0069]

[Equation 3]

Therefore, area CGE × 2 = area BFGE +
The area becomes DHGE, and the error component is canceled by using a + d and c + d as signals.

(G) As is clear from the above description, when the DC offset voltage component changes linearly, do not use only the signal immediately after the conductivity measuring short-circuit switch S ₁ is turned on / off. The error can be eliminated with.

Actually, as described with reference to FIG. 9, the DC offset voltage component often changes exponentially.
The feature of exponential change is that the nonlinearity of the change is strong at first, but the nonlinearity becomes gradually smaller with the passage of time.

Therefore, the short-circuit switch S ₁ for measuring conductivity is used.
After switching, the sampling may be practically performed until the change in the DC offset voltage is in a region where it can be considered to be linear. This is also described in the second conventional technique.

For example, when the DC offset voltage component is fluctuated as shown by the symbol E in FIG. 17, the nonlinearity is strong at the times t ₁ and t ₂ , but it can be regarded as a straight line at the periods t ₃ and t _4. Is changing. So in this case,
The data in the periods t ₁ and t ₂ are discarded, and the data in the periods t ₃ and t ₄ are sampled and used.

Therefore, the electrodes 2 for inducing the flow rate signal 2
3 has an electrical conductivity measuring short-circuit switch S ₁ for intermittently grounding 3 via a short-circuit resistance R _in, and an offset compensating circuit 10 for removing a direct current component contained in the flow rate signal. The output E ₃ of the offset compensation circuit 10 is not sampled as a flow rate signal in a period immediately after the ON / OFF of ₁ is judged to have a strong nonlinearity in the change of the DC offset voltage.

Then, the offset compensating circuit 1 is applied until the change in the DC offset voltage enters the region where it can be regarded as linear.
In FIG. 17, the waiting period without sampling the output E ₃ of 0 as the flow rate signal is one cycle of the excitation at t ₁ + t ₂ . This waiting time is generally fixed to an integral multiple of the excitation period.

Next, the electromagnetic flowmeter of FIG. 18 including the circuit of FIG. 14 will be described based on the timing chart of FIG. Reference numeral 1 is a cylindrical flow tube provided with electrodes 2 and 3, and reference numeral 7 is a short circuit for measuring conductivity, which is composed of two short-circuit switches R _in and S ₁ .

Reference numeral 9 is a differential amplifier (preamplifier) for amplifying the flow rate signals of the electrodes 2 and 3, 10 is an offset compensation circuit, and 1
Reference numeral 1 is an inverting / non-inverting amplifier circuit, 12 is an integrating circuit, 13 is an A / D converting circuit for converting the output of the integrating circuit 12 into a digital signal, and 14 is a digital output value of the A / D converting circuit for calculating a fluid A signal processing circuit that calculates conductivity and flow rate,
By using the measured conductivity of the fluid, an error due to the conductivity of the flow rate measurement may be corrected, or the conductivity may be output to the outside.

The inverting / non-inverting amplifier circuit 11 switches between inverting and non-inverting operations by the inverting / non-inverting control signal from the timing generating circuit 15, and rectifies the output E ₃ of the offset compensating circuit 10 (FIG. 19). See E ₄ ).

This rectified output E ₄ is integrated by the integration circuit 12 only during the compensation period t _4, t ₆ or t _10, t ₁₂ of the offset compensation circuit 10 (a + b of E ₄ in FIG. 19 is obtained). This is converted into a digital value each time by the A / D conversion circuit 13.

The synchronization relationship between the excitation switching and the conductivity measuring short-circuit switch S ₁ is the same as in the case of FIG. In this way, for every three excitations, the data at the time of two excitations is integrated by the integration circuit 12, converted by the A / D conversion circuit 13 into a digital value each time, and the signal processing circuit 14 conducts the electric conductivity and the flow rate. To calculate.

The timing generation circuit 15 also generates a conductivity measurement short-circuit switch control signal, an offset compensation control signal, an integration control signal, an A / D control signal, etc., and the operation of each target circuit is as shown in the timing chart of FIG. It will be easily understood from the description of FIGS. 14 and 15.

[0083]

In the electromagnetic flowmeter, reducing the current consumption has been an ongoing problem.
In particular, there is a strong demand for an integrating electromagnetic flowmeter that uses a primary battery (dry battery) such as a lithium battery as a power source.

[0084] However, in the second prior art, without sampling the output E ₃ of the offset compensation circuit 10 immediately after turning on and off the short-circuit switch S ₁ as a flow rate signal, among the subsequent output E _3, a, The conductivity and flow rate of the fluid are measured by sampling b, c, d and the like.

In the second prior art, the output E ₃ of the offset compensating circuit 10 during the period immediately after the short-circuit switch S ₁ is turned on / off is judged to have a strong nonlinearity in the change of the DC offset voltage. Instead of sampling as a flow rate signal, a, b, c, d, etc. of the subsequent output E ₃ are sampled to measure the conductivity and flow rate of the fluid.

In view of this, the present invention focuses on the feature that the output E ₃ of the offset compensation circuit 10 is not sampled during the period including immediately after the short-circuit switch S ₁ is turned on / off in the second conventional technique. , With this feature,
A first object of the present invention is to reduce the power consumption of the electromagnetic flowmeter with almost no adverse effect on the measurement accuracy.

In the second prior art, the output E ₃ of the offset compensation circuit 10 is sampled immediately after the short-circuit switch S ₁ is turned on and off until the change in the DC offset voltage enters a region where it can be regarded as linear. Since the waiting time without waiting is fixed to an integral multiple of the excitation period, there is a problem that wasteful time occurs and the response of measurement is not good.

Therefore, a second object of the present invention is to provide an electromagnetic flow meter which can improve the poor response due to the dead time due to the waiting time being fixed to an integral multiple of the excitation period. .

[0089]

In order to achieve the first object, the invention according to claim 1 intermittently connects electrodes (2, 3) for inducing a flow rate signal through a short-circuit resistance (R _in ). It has a short-circuit switch (S ₁ ) for measuring conductivity, which is grounded to, and an offset compensation circuit (10) for removing the DC component contained in the flow rate signal, and also turns on / off the short-circuit switch (S ₁ ). Immediately after the output of the offset compensation circuit (10) (E ₃ ) is not sampled as a flow rate signal, the short circuit switch (S ₁ ) is turned on during each ON / OFF period of the short circuit switch (S ₁ ). It is characterized in that the excitation is stopped for a certain period (t ₀ ) immediately after turning off.

In order to achieve the first and second objects, the invention of claim 2 intermittently connects the electrodes (2, 3) for inducing a flow rate signal through a short-circuit resistance (R _in ). A short-circuit switch (S ₁ ) for grounding the conductivity and an offset compensation circuit (10) for removing the DC component contained in the flow rate signal are provided, and the short-circuit switch (S ₁ ) is turned on / off. Immediately after that, in the electromagnetic flowmeter that does not sample the output (E ₃ ) of the offset compensation circuit (10) as a flow rate signal during the period when it is determined that the change in the DC offset voltage is strongly nonlinear, the short-circuit switch (S ₁ ) is turned on.・ OFF During each period, the short-circuit switch (S ₁ ) is turned on.
It is characterized in that the excitation is stopped for a certain period (t _x , t _x + t ₀ ) immediately after turning off.

[0091]

[Function] The excitation power is not consumed while the excitation is stopped. Further, a flow rate signal corresponding to the flow velocity is not induced in the electrodes while the excitation is stopped.

In the invention of claim 2, the period (t _x or t _x + t ₀ ) for stopping the excitation can be optimized without being fixed to an integral multiple of the excitation period, and the entire measurement period can be achieved. Can be as short as possible.

[0093]

1 is a block diagram of a first embodiment of the present invention, and FIG. 2 shows a part of an equivalent circuit in a flow tube of an electromagnetic flow meter detector and an electric circuit of a converter in the embodiment of FIG. It is a thing. This first embodiment corresponds to the invention of claim 1.

In both figures, 1 is a cylindrical flow tube, 2 and 3
Is an electrode which is arranged to face the inner peripheral wall of the flow tube 1, 4 and 5 are exciting coils which are arranged above and below the flow tube 1, 6 is a ground electrode, and a well-known electromagnetic flow rate is used in the flow tubes 1 to 6 It constitutes a total detector.

Reference numeral 7 is a short circuit for measuring conductivity, which is a series circuit of a short resistance R _in connected between the electrode 2 and the ground electrode 6 and a short circuit switch S ₁ for measuring conductivity, and the electrode 3 and the ground electrode. And a series circuit of a short-circuit resistance R _in and a short-circuit switch S ₁ for measuring conductivity.

Reference numeral 8 is a high-pass filter to which two capacitors C and two resistors R are connected as shown. Although the high-pass filter 8 is not shown in FIG. 1, the high-pass filter 8 is omitted in order to avoid the drawing from becoming complicated, so that the high-pass filter 8 is actually provided as in FIG.

Reference numeral 9 denotes an electrode 2 which has passed through the high pass filter 8.
3 is a differential amplifier (preamplifier) that amplifies the voltage of 3.
Reference numeral 10 is an offset compensation circuit, which is the output E of the differential amplifier 9.₁
The DC component other than the flow signal remaining in the amplifier is further amplified in the subsequent stage.
To prevent the amplifier from saturating one after another and becoming saturated
In order to eliminate the offset voltage,
Therefore, operational amplifier A₁And resistance R₁, R₂Consisting of
Inverting amplifier and operational amplifier A₂And resistance R ₃And capacitor
C₁And an offset compensation controller
Switch S₂And are connected and configured as shown.
ing.

Reference numeral 11 is an inverting / non-inverting amplifier circuit, which switches between inverting and non-inverting operations by an inverting / non-inverting control signal from the timing generating circuit 15 and rectifies the output E ₃ of the offset compensating circuit 10.

Reference numeral 12 is an integrating circuit, which is an inverting / non-inverting circuit 11
The rectified output E _{4 of} is sampled and integrated only during a specific period. Reference numeral 13 is an A / D conversion circuit that converts the output E ₅ of the integration circuit 12 into a digital signal, and 14 is a signal processing circuit that calculates the digital output value of the A / D conversion circuit to calculate the conductivity and flow rate value of the fluid. Then, using the measured conductivity of the fluid, the error of the flow rate measurement value may be corrected by the conductivity, or the value of the conductivity may be output to the outside.

Reference numeral 16 is an exciting power supply circuit for supplying a predetermined exciting current to the exciting coils 4 and 5. Timing generation circuit 1
5 is a short circuit switch control signal for conductivity measurement, an offset compensation control signal (switch S ₂ is turned on,
A signal to turn off), an integration control signal, an A / D control signal, an excitation control signal, etc. are also generated to control each target circuit.

Since the hardware configuration of the first embodiment shown in FIGS. 1 and 2 is generally similar to that of the second conventional technique described with reference to FIGS. 14 and 18, the description of the same parts will be described in detail. do not do.

In FIG. 2, е ₁ and е ₂ are flow rate signal voltages to the ground electrode 6, which are induced when the exciting coils 4 and 5 are excited and a magnetic field is applied to the flow path. V ₁ and V ₂ are electrochemical potential differences between the electrodes 2 and 3 and the ground electrode 6, respectively, which are called DC offset voltages in the above-mentioned prior art.

R _w is the electrical resistance of the fluid between the electrodes 2 and 3 and the ground electrode 6. The timing charts of the first embodiment of FIGS. 1 and 2 are shown in FIGS. 3 and 4, and the first embodiment is
As is clear from FIGS. 3 and 4, the excitation is stopped during the period t ₀ preceding the period t ₁ of the timing chart of FIG. 15 for explaining the operation of the second conventional technique. Although the reference sign of the period t ₀ is not shown in FIG. 15 but only in FIGS. 3 and 4, the period t ₀ is the same time as the other periods t ₁ and t ₂ , so The power required for the excitation of the embodiment is 2/3 that of the second conventional technique described with reference to FIG.

The respective times of turning on / off the short-circuit switch S ₁ are the same as those of the second prior art described in the first embodiment and FIG. Then, it is turned on / off in synchronization with the stop of the exciting current.

The switch S of the offset compensation circuit 10
₂ is turned on / off by an offset compensation control signal from the timing generation circuit 15 in synchronization with the stop and switching of the excitation.

Therefore, the output E ₂ of the integration circuit of the offset compensation circuit 10 and the output E ₃ of the offset compensation circuit 10 change as shown in FIG. In the first embodiment, the output E ₁ of the differential amplifier 9 is the same as in the second prior art shown in FIG.
The flow rate signal of amplitude е is carried on the DC offset voltage of the linearly changing broken line shown in (1). However, the first aspect of the present invention
In the embodiment, since the excitation is stopped during the period t ₀ ,
During this time, the flow signal is zero.

In this way, the output E ₁ of the differential amplifier 9 is
The first embodiment of the present invention (FIG. 3) and the second prior art (FIG. 1)
5), the output E ₃ of the offset compensation circuit 10 is also different between the first embodiment (FIG. 3) of the present invention and the second prior art (FIG. 15).
The operating principle itself of (2) is not different between the embodiment of the present invention and the second prior art (FIG. 15).

[0108] So, although not detailed description of the process of the output E ₃ obtained in FIG. 3, during the period t ₀ of the first offset compensation have stopped the excitation, because during this time the flow signal is zero , The magnitude of the output E ₃ of the offset compensation circuit in the period t ₁ becomes е / 2, which is smaller than е in the case of the second conventional technique of FIG. Output E of period t ₂
The magnitude of ₃ is the same value in both the first embodiment of the present invention and the second prior art of FIG.

Therefore, the output E ₅ of the integrating circuit 12 for obtaining a + b or c + d has a value of 3/4 in the first embodiment of the present invention as compared with the second prior art. This output E ₅
In order to obtain the above, the embodiment of the present invention requires only 2/3 of the exciting power as compared with the second prior art of FIG. 15 as described above. To obtain the same output E ₅ as in the second prior art shown in FIG. 19), (2/3) / (3 /
4) = 8/9 excitation power is enough, and the excitation power can be saved by about 11%.

The values a + b and c + d obtained as the output E ₅ of the integrating circuit 12 are the values when the short-circuit switch S ₁ is turned off and when they are turned on, respectively, and are described in the first prior art (3). ) Corresponding to (proportional to) [E ₁ ] _OFF and [E ₁ ] _ON , these outputs E ₅ are converted into digital values by the A / D conversion circuit 13, and the electrical resistance of the fluid is converted by the signal processing circuit 14. It is obtained by calculating R _w .

At this time, it can be calculated using the relationship of (a + b) / (c + d) = 1 + R _w / R _in as in the equation (3). The electrical conductivity of the fluid can be known from the electrical resistance R _{w of} the fluid thus obtained. Further, it is possible to correct the flow rate measurement error using the obtained conductivity.

In the first embodiment, the short circuit switch S₁Oh
The signal sampling period (that is, the
Switch S₂Is on or the integration control in Fig. 4
Offset compensation with roll signal in it)
The first operation cycle t of the circuit 10 ₁Precedes the time that begins
Period t₀Then, the excitation was stopped, but Fig. 5 shows
Similar to the first embodiment, the short circuit switch S₁On / off
Of each period, the signal sampling period is included in it
The first operation cycle t of the offset compensation circuit₁Time when
Period t preceding_x+ T₀That stops excitation during
Then, the timing of the second embodiment corresponding to the invention of claim 2
It is a figure.

The hardware structure of the circuit and block diagram of the second embodiment is similar to that of the first embodiment shown in FIGS. 1 and 2. In the second embodiment, the output E ₁ of the differential amplifier 9 includes a DC offset voltage component that is non-linear initially and then linearly during the ON or OFF period of the short-circuit switch S _1. ing.

Then, the excitation is stopped during the period t _x + t ₀ during which the DC offset voltage changes non-linearly. The switch S ₂ of the offset compensation circuit 10 is turned on / off as shown. Therefore, period t _x +
The operation is performed once during each of t ₀ , t ₁ , and t ₂ . Then, a obtained during the period t ₀ and b obtained during the period t _2.
The electric conductivity of the fluid is determined from the sum a + b of the above as a signal corresponding to the above [E ₁ ] _OFF , and c + d obtained in the same manner as a signal corresponding to the above [E ₁ ] _ON .

In the timing chart of FIG. 5 of the second embodiment, the horizontal axis (time axis) is shown in FIGS. 3 and 4 due to the size of the figure.
It is drawn with a scale of 1/2 compared to. for that reason,
Period t _0, t _1, t ₂ of FIG. 5, t ₀ in FIG. 3, t _1, t
It is visible at half the time compared to ₂ , but it is actually the same time as in FIG.

Therefore, a + b and c + d are the first in FIG.
This is the same as in the embodiment. In addition, in the second embodiment, as compared with the first embodiment, in addition to the period t ₀ , the period t _x
Since the excitation is also stopped during this period, the excitation power can be further reduced accordingly.

In the second embodiment, the period t _x +
There is no reason to limit the time of t _{0 to} an integral multiple of the half cycle of excitation as in the case of the second conventional technique, and the DC offset voltage of the DC offset voltage is not changed after the short-circuit switch S ₁ is turned on or off. The optimum value can be set according to the waiting time until the change becomes linear.

As described above, when the change in the DC offset voltage is strongly nonlinear, the period t _x + t during which the excitation is stopped is stopped.
_By optimizing _{0 according} to the above waiting time, the entire measurement cycle can be shortened as much as possible, and the responsiveness can be accelerated compared with the conventional technique.

FIG. 6 is a timing chart of the third embodiment of the present invention, and the hardware configuration is the same as that of the first embodiment of FIGS. 1 and 2. In the third embodiment, the excitation is performed during the periods t ₀ , t ₁ and t ₂ , but the excitation is stopped during the period t _x , and this is repeated. The third embodiment corresponds to the invention of claim 2.

Similar to FIG. 5, this FIG. 6 is also drawn with the horizontal axis (time axis) reduced to ½ as compared with FIG.

This third embodiment is also similar to the second embodiment.
When the change in the DC offset voltage has a strong non-linearity, the period t _x + t ₀ can be optimized in accordance with the waiting time, so that the responsiveness can be accelerated.

In the third embodiment, since the excitation is also performed during the period t ₀ of the straight line of the period t ₁ , the output E ₃ of a
Is twice as large as that in the second embodiment. However, for that reason, the excitation power is consumed during the period t ₀ , but since the excitation is stopped during the period t _x , the excitation power can be reduced as compared with the prior art.

In FIG. 3 of the first embodiment, the period t ₀
Has the same length (time) as t ₁ and t ₂ ,
The time during which the offset compensation is not performed in the period t ₀ , that is, the length of time that the switch S ₂ is off can be arbitrarily shortened.

In the first place, in the periods t ₁ and t ₂ , the offset compensation period in which the switch S ₂ is on, that is, the flow rate signal sampling period, is the offset compensation circuit 10.
Is set to be shifted in the latter half of one cycle of the operation so that spike-like noise (not shown in FIGS. 3, 5, and 6) that often occurs immediately after the polarity reversal of excitation is not sampled. This is to wait for the spike noise to subside.

However, in the first embodiment of FIG. 3, the period t ₀
Since the excitation is not performed at, the length of time that the switch S ₂ is off during the period t ₀ can be arbitrarily shortened and may be zero. This can also speed up the responsiveness.

[0126]

Since the electromagnetic flowmeter of the present invention is constructed as described above, the power consumption can be reduced without adversely affecting the measurement accuracy for measuring the conductivity and flow rate of the fluid.

According to the invention of claim 2, which is suitable for use in the case where the DC offset voltage changes non-linearly for the first time, in addition to reducing power consumption, responsiveness can be accelerated.

[Brief description of drawings]

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

FIG. 2 is an electric circuit diagram of the first embodiment of the present invention.

FIG. 3 is a timing diagram of the first embodiment of the present invention.

FIG. 4 is a timing chart of the same.

FIG. 5 is a timing diagram of the second embodiment of the present invention.

FIG. 6 is a timing diagram of the third embodiment of the present invention.

FIG. 7 is a conventional electric circuit diagram.

FIG. 8 is a diagram for explaining operation timings of an exciting current and a conductivity measuring short-circuit switch.

FIG. 9 is a diagram illustrating a change in DC offset voltage.

FIG. 10 is a diagram showing a change in a DC offset voltage component caused by turning on / off a short-circuit switch.

FIG. 11 is a timing diagram of the related art of FIG. 7.

FIG. 12 is a timing chart of the same.

FIG. 13 is a timing chart of the same.

FIG. 14 is a conventional electric circuit diagram.

FIG. 15 is a prior art timing diagram of FIG.

16 is a diagram illustrating signal processing in the conventional technique of FIG.

FIG. 17 is a diagram illustrating a cause of an error in the related art.

FIG. 18 is a block diagram of a conventional technique.

FIG. 19 is a prior art timing diagram of FIG. 18.

[Explanation of symbols]

1 Flow tube 2,3 Electrode 4,5 Excitation coil 6 Earth electrode 7 Short circuit 10 Offset compensation circuit R _in Short resistance S ₁ Short circuit switch t ₀ , t ₁ , t ₂ , t _x period E ₁ , E ₃ output

Claims (2)

[Claims] 1. A conductivity measuring short-circuit switch (S ₁ ) for intermittently grounding electrodes (2, 3) for inducing a flow rate signal via a short-circuit resistance (R _in ) and a flow rate signal. An electromagnetic wave that has an offset compensation circuit (10) for removing a direct current component, and does not sample the output (E ₃ ) of the offset compensation circuit (10) immediately after the short-circuit switch (S ₁ ) is turned on / off as a flow rate signal. in flowmeter, of the on-off each period of the short-circuit switch (S _1), a fixed period immediately after the short-circuit switch (S ₁₎ was turned on and off (t
An electromagnetic flowmeter characterized by stopping excitation during ₀ ). 2. A conductivity measuring short circuit switch (S ₁ ) for intermittently grounding the flow rate signal inducing electrodes (2, 3) via a short circuit resistance (R _in ) and a flow rate signal included in the flow rate signal. An offset compensation circuit (10) for removing a direct current component, and an offset compensation for a period immediately after the short-circuit switch (S ₁ ) is turned on / off and when it is determined that the change in the direct current offset voltage is highly nonlinear. in the electromagnetic flow meter output without sampling (E ₃₎ as a flow rate signal of the circuit (10), of the on-off each period of the short-circuit switch (S _1), a fixed immediately after the short-circuit switch (S ₁₎ was turned on and off Period (t
_x , t _x + t ₀ ), an electromagnetic flowmeter characterized by stopping excitation.