JPH10170317A - Electromagnetic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic flowmeter which is improved in such a way that the flowmeter can detect that a conduit becomes empty of a fluid to be measured and can detect the electric conductivity of the fluid to be mea sured flowing through the conduit. SOLUTION: In a rectangular wave exciting electromagnetic flowmeter which detects flow rate signals generated from measuring electrodes 11a and 11b installed to a conduit 10 by sampling the signals with a prescribed sampling signal, a current supplying means which supplies current signals to the electrodes 11a and 11b and a timing switching means 27 which transmits the current signals during an empty detecting period which is different from the sampling period for sampling the flow rate signals with the sampling signal so that the flowmeter can detect that the conduit 10 is empty of a fluid to be measured by using the current supplying means, timing switching means 27, and detect signals detected during the preceding empty detecting period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flowmeter of rectangular wave excitation for sampling a flow signal generated at a measuring electrode provided in a conduit by a predetermined sampling signal and detecting the signal, and more particularly to a flowmeter in a conduit. The present invention relates to an electromagnetic flowmeter improved so as to detect that the measurement fluid is empty or to know the conductivity of the measurement fluid filled in the conduit.

[0002]

2. Description of the Related Art As a conventional electromagnetic flowmeter having an empty detection function, a method in which an AC signal synchronized with an excitation frequency is applied to a measurement electrode or a signal obtained by applying a DC current to a measurement electrode is used. Sky detection. Among them, FIG. 3 is a configuration diagram showing a configuration of a conventional electromagnetic flow meter of a system that performs empty detection by applying a direct current to a measurement electrode.

[0003] Reference numeral 10 denotes a conduit having an insulated inner surface through which a measurement fluid Q can flow, and a pair of measurement electrodes 11a and 11b in contact with the measurement fluid Q are fixed to the conduit 10 while being insulated from the conduit 10. , Ground electrode 1 for grounding measurement fluid Q
1c is connected to the common potential point COM.

An exciting coil 12 for applying a magnetic field to the measuring fluid Q is disposed close to the conduit 10, and a rectangular wave-like exciting current _If flows from the exciting circuit 13 to the exciting coil 12. ing.

[0005] These conduits 10 and exciting coils 1
2, etc., constitute the detector 14. A preamplifier 15 is connected to the measuring electrodes 11a and 11b.
a, 11b connected to buffer amplifiers 15a, 15b
And a differential amplifier 15 whose output terminal is connected to the input terminal.
c.

Further, these measuring electrodes 11a, 11b
Are connected to the cathodes of diodes D ₁ and D ₂ . The anodes of these diodes D ₁ and D ₂ are connected to a negative power supply −
V, and diodes D ₁ and D ₂ and a negative power supply
V forms a constant current circuit 16 (16a, 16b).

A series circuit formed by connecting zener diodes D _Z1 and D _Z2 in series with opposite polarities is connected between the output terminal of the buffer amplifier 15b and the common potential point COM.

[0008] The output terminal of the differential amplifier 15c is connected to the input terminal of the signal processing circuit 17, the signal processing circuit 17 is output by calculating the flow rate signal V _Q using the measured voltage V _M1 appearing at the output terminal 18 is output.

The empty detection circuit 19 detects the DC voltage E _a of the measurement voltage V _M1 that appears on the measurement electrodes 11a and 11b,
A difference voltage E _d1 corresponding to the difference between E _{b and} a first threshold voltage V _R1 from the reference voltage source 20 are compared, and an empty detection signal V _e1 is output to an output terminal 21 thereof.

In the above configuration, the timing circuit 22
Is measured in the excitation circuit 13 at a timing signal T ₁ for switching the excitation current as a rectangular wave, and in the signal processing circuit 17 during a stable period after switching to the rectangular wave, that is, at a timing in a predetermined period immediately before the next switching. It sends a timing signal T ₂ for sampling the voltage.

Next, the operation of the electromagnetic flow meter configured as described above will be described. From the excitation circuit 13, a rectangular wave exciting current _If flows through the exciting coil 12, whereby a rectangular wave magnetic field is applied to the measurement fluid Q.

Along with this, the measuring electrodes 11a and 11b
The generated measurement voltage is impedance-controlled by the preamplifier 15.
It is converted and the measured voltage V_M1Output as
You. The next-stage signal processing circuit 17
Output timing signal T _TwoBased on the measured voltage V
_M1Is sampled.

[0013] The sampling is carried out during a period following immediately before switching of the excitation current of the square wave excitation is stable, the output to the output terminal 18 by executing the flow rate operation using the sampling signal as a flow rate signal V _Q I do.

On the other hand, since a constant current circuit 16 is formed on the measurement electrodes 11a and 11b by the diodes D ₁ and D ₂ whose anodes are connected to the negative power supply -V,
There empty, wetted resistance R _A between the measuring electrodes 11a and 11b, R _b is increased when the diode D _1, a DC voltage measuring electrodes 11a and 11b by reverse leakage of D ₂ E _a, E _b increases.

The differential amplifier 15c receives these DC voltages E
The difference between _a and _Eb is calculated, and a difference voltage E _d1 is output to the output terminal. The sky detection circuit 19 determines that the difference voltage _Ed1 is equal to the threshold voltage _VR1.
Is exceeded, it is determined that the measurement fluid Q in the conduit 10 is empty, and an empty detection signal is output to the output end 21 thereof, for example, which swings negatively.

[0016]

However, the conventional electromagnetic flow meter having an empty detecting function shown in FIG. 3 has an empty detecting electrode on the measuring electrodes 11a and 11b regardless of whether or not the measuring voltage _VM1 is sampled. Since a DC current is supplied for the measurement, there is a factor that makes detection of the measurement voltage _VM1 unstable.

Also, in the electromagnetic flowmeter of the type in which an AC signal synchronized with the above-described excitation frequency is applied to the measurement electrode, an AC current for empty detection is applied to the measurement electrode even when the flow rate is detected. As with the electromagnetic flow meter shown in FIG. 3, there is a problem that the flow rate measurement includes an error factor and the detection becomes unstable.

[0018]

According to the present invention, as a main structure for solving the above problems, a flow rate signal generated at a measuring electrode provided on a conduit is sampled by a predetermined sampling signal to detect a signal. In a rectangular wave excitation electromagnetic flowmeter, current supply means for supplying a current signal to the previous measurement electrode, timing switching means for transmitting the previous current signal in an empty detection period different from the sampling period by the previous sampling signal, In this case, it is detected that the inside of the previous conduit is empty using the detection signal detected in the empty detection period. Further, in the present invention, the conductivity of the fluid to be measured can be calculated using the detection signal.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. Parts having the same functions as those of the conventional electromagnetic flow meter shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

The excitation circuit 13, the exciting coil 12a as an excitation current I _f which is formed in a rectangular wave shape across the positive and negative at a timing determined by the timing signals T _1, flowing in 12b, to the measuring fluid Q present in the conduit 10 A rectangular wave magnetic field is applied.

The voltages generated at the measuring electrodes 11a and 11b are output to the non-inverting input terminals (+) of the buffer amplifiers 15a and 15b. These output terminals are subjected to a differential operation by the differential amplifier 15d and output to the analog / digital converter 23.

The analog / digital converter 23 outputs a measured voltage V _M2 appearing at the output terminal of the differential amplifier 15 based on the timing signal T ₃ output from the microprocessor 24.
Is sampled, converted into a digital signal, and transmitted to the microprocessor 24.

The microprocessor 24 includes the excitation circuit 13
And it outputs a flow rate signal to an output terminal 25 by executing the flow calculation based on the data of the analog / digital converter 23 which is sampled with a timing signal T ₁ to.

On the other hand, the constant current circuit 26 is provided for empty detection, and supplies constant currents I _C1 and I _C2 to the common potential point COM via the measurement electrodes 11a and 11b. Further, the constant current circuit 26 is connected to a timing switching circuit 27,
This timing switching circuit 27 is a microprocessor 24
The driving voltages + V _E and −V _E are supplied to the constant current circuit 26 by being switched by the timing signal T ₄ output from the control circuit 26.

Further, the analog / digital converter 28
Is determined by the constant currents I _C1 and I _C2 .
The superimposed signals V _S1 and V _{S2 in} which the DC voltage V _CM generated in 1b and the measured voltage V _M2 are superimposed are converted into buffer amplifiers 15a and 15b.
To detect through.

For this purpose, the analog / digital converter 2
8, at the timing based on the timing signal T ₅ supplied from the microprocessor 24, sends to the microprocessor 24 converts the superimposed signal V _S1, V _S2 corresponding to the constant current I _C1, I _C2 to sampled digital signals I do.

The microprocessor 24 calculates the difference between the superimposed signals V _S1 and V _S2 and calculates the conductivity σ of the fluid to be measured, determines empty detection, determines an alarm by using a predetermined arithmetic expression described later, and issues an alarm. Or to emit.

Here, the timing switching circuit 27 and the constant current circuit 26 will be specifically described. The timing switching circuit 27 switches the switch S ₁ according to the timing signal T ₄ output from the microprocessor 24 to the driving voltage +
V _E, the common potential point COM, by switching each of the driving voltage -V _E, and outputs the constant current circuit 26 as a switching voltage V _E0.

The constant current circuit 26 includes a first constant current circuit 26a.
And a second constant current circuit 26b. 1st fixed
The current circuit 26a includes a buffer amplifier Q₁₁, Q_{twenty one}, Operational amplification
Container Q ₃₁, Resistance R₁₁, R_{twenty one}, R₃₁, R₄₁, R₅₁Composed of
The second constant current circuit 26b includes a buffer amplifier Q₁₂,
Q_{twenty two}, Operational amplifier Q₃₂, Resistance R₁₂, R_{twenty two}, R₃₂, R₄₂,
R₅₂It is composed of

The first constant current circuit 26a includes an operational amplifier Q ₃₁
The non-inverting input terminal of the (+), via a resistor R ₁₁ from the output of Baffua amplifier Q _11, are connected via a further measuring electrode 11b Baffua amplifier Q ₂₁ and resistors R ₂₁ from.

Further, the inverting input of the operational amplifier Q ₃₁ (-)
Includes a common potential point COM through the resistor R _31, are respectively output via a resistor R ₄₁ connected, the output end is connected to the measuring electrode 11b via a resistor R _51.

The second constant current circuit 26b sets the number of the second suffix from 1 to 2 among the suffixes of the signs of the buffer amplifier, the operational amplifier, and the resistor, which are the components of the first constant current circuit 26a. Since the same configuration can be obtained by changing and reading the description, the description thereof is omitted.

The constant current I _C1 from the first constant current circuit 26a is supplied to the common potential point COM via the measuring electrode 11b, and the constant current I _C2 is supplied from the second constant current circuit 26b via the measuring electrode 11a to the common potential point COM. COM, respectively.

For the sake of simplicity, each resistor R ₁₁ ,
Assuming that the resistance values of R ₂₁ , R ₃₁ , R ₄₁ , and R ₅₁ have a constant resistance value R ₀ and the output voltage of the first constant current circuit 26 a is E ₀₁ , the non-inversion of the operational amplifier Q ₃₁ Input end (+)
Voltage, the voltage V _E0 of the output end of Baffua amplifier Q ₁₁ and E
₀₁ is obtained as a _divided voltage (V _E0 + E ₀₁ ) / 2 obtained by dividing the sum voltage (V _E0 + E ₀₁ ) by the resistors R ₁₁ and R ₄₁ .

On the other hand, the operational amplifier Q₃₁The voltage at the output terminal of
_XThen, this E_XIs the resistance R₄₁And R ₃₁Voltage divided by
That is, E_X/ 2 becomes the voltage of the inverting input terminal (-),
Input terminal (-) voltage E_X/ 2 is the voltage at the non-inverting input terminal (+).
Operational amplifier Q₃₁Works, so E_X/ 2 = (V_E0+ E₀₁) / 2. Arranging this, E_X= (V_E0+ E₀₁(1) Obtain the relationship (1).

Furthermore, since there is a relationship of _{E X -E 01 = I C1 ·} R 51 (2), these (1) and (2) the _{relationship, V E0 = I C1 · R} 51 (3 ) Get a relationship.

This I_C1Is the resistance on the load side (measurement electrode 11
b) _E0I.e. the switch
S₁Drive voltage + V applied by switching_E, 0, -V_E
To the measuring electrode 11b in proportion to
And this I_C1Means a constant current. Second
The constant current circuit 26b operates in the same manner, and the measurement electrode 11a
Constant current I_C2Flow.

Next, the operation of the entire circuit configured as described above and shown in FIG. 1 will be described with reference to the waveform diagram shown in FIG. First, a normal operation in which the sky detection function is not activated will be described.

In this case, the switch S ₁ is switched to the common potential point COM side by the timing signal T ₄ output from the microprocessor 24, and the values of the constant currents I _C1 and I _C2 are zero and the output of the constant current circuit 26 is Keep the impedance high.

Upon receiving the timing signal T ₁ , the exciting circuit 13 switches the constant current contained in the exciting circuit 13 to generate a rectangular wave-like exciting current _If (FIG. 2 (A)) which changes between positive and negative. By flowing the coils through the coils 12a and 12b, a rectangular magnetic field is applied to the measurement fluid Q.

The analog / digital converter 23 converts the measurement voltages generated at the measurement electrodes 11a and 11b corresponding to the flow rate of the measurement fluid Q into the preamplifiers 15a and 15b and the differential amplifier 1
It is received as the measured voltage V _M2 (FIG. 2B) via 5d.

The analog / digital converter 23, the timing signal T ₃ shown in FIG. 2 (C) which is outputted from the microprocessor 24 outputs the measured voltage V _M2 to sampled microprocessor 24 into a digital signal .

The running period timing for sampling the measured voltage V _M2 (see FIG. 2 (B)) by the timing signal T ₃ is the exciting current I _f (FIG. 2 (A)) is switched to a stable measured voltage V _M2 Is done.

The digital signal converted by the analog / digital converter 23 is calculated by a microprocessor 24 in accordance with a predetermined flow rate calculation program, and is output to an output terminal 25.

Next, the case of detecting the sky will be described. Driving power by the timing signal T ₄ output from the microprocessor 24 is switched to + V _E and -V _E at the timing switch circuit 27.

The constant current circuit 26 converts this into a constant current to generate a constant current I _C1 from the measurement electrode 11b to the common potential point COM.
And as a constant current I _C2 from the measurement electrode 11a to the common potential point COM.

The constant current value in this case is expressed as I _C1 = I _C2 = V _E0 / R ₅₁ = ± V _E / R ₅₁ (4) as shown in FIG.

The timing at which the constant currents I _C1 and I _C2 flow is different from the timing at which the voltage VM ₂ is sampled (FIGS. 2B and 2C), as shown in FIG. 2D. _It is set near the rise period of _f , and is set not to flow during other periods.

FIG. 2E shows a common potential point COM when the DC voltage V _CM generated by the constant currents I _C1 and I _C2 is superimposed on the measurement electrodes 11a and 11b on the measurement voltage V _M2 / 2 indicating the flow signal. Are shown as waveforms of superimposed signals V _S1 and V _S2 generated on the measurement electrodes 11a and 11b.

V ₊ is a constant current I corresponding to + V _E / R ₅₁
Superimposed signals V _S1 , V _S detected when _C1 (I _C2 ) flows
_S2 is a value, V _- the constant current I _C1 corresponding to -V _E / R ₅₁
(I _C2 ) and superimposed signals V _S1 and V _S2 detected when flowing
Is the value of However, for simplicity, the measurement electrodes 11a and 1
The liquid contact resistance of 1b is the same.

In the waveform of the measurement voltage _VM2 shown in FIG. 2B, the waveform indicated by the dotted line shows the waveform when the liquid contact resistance of the measurement electrodes 11a and 11b is unbalanced. This is based on the difference in liquid contact resistance and the constant current I _C1
This is because the voltage drop generated by (I _C2 ) is superimposed.

The analog / digital converter 28 corresponds to FIG.
Timing defined by the timing signal T ₅ shown by (F), i.e. a superimposed signal in a period in which a constant current I _C1 (I _C2) is flowed V _+, V _- and is converted into sampling and digital signal microprocessor 24.

If σ is the conductivity of the measurement fluid and r is the radius of the measurement electrode, the liquid contact resistance R of the measurement electrodes 11a and 11b
_{Since M} is represented by R _M = 1 / σ · r, the superimposed signal V ₊ (or V ₋ ) is represented by V ₊ = I _C1 / σ · r.

Therefore, when the measuring fluid in the conduit 10 becomes empty, it becomes equivalent to the conductivity σ becoming extremely small, so that the superimposed voltage V ₊ becomes the maximum value, that is, the power supply voltage equivalent (V _{+ S} ) Is reached by the microprocessor 24, it can be determined that the measurement fluid is empty.

[0055] The microprocessor 24 is superimposed signal V ₊ and V _- by using, (V ₊ -V _-) by calculating / 2, while removing the component of the measured voltage V _M, the measurement electrodes 11a And the voltage drop due to the liquid contact resistance of 11b.

This can be expressed by the following equation: I _C1 / σ · r = (V ₊ −V ₋ ) / 2. By transforming this equation, σ = 2I _C1 / [r (V ₊ −V ₋ )] (5) is obtained.

Therefore, the microprocessor 24
An operation program for executing the operation of this formula is stored in a ROM, for example.
(Read only memory) can be used to calculate the conductivity σ of the measurement fluid.

Further, the conductivity at the lower limit of the measurement range is defined as σ _min
With the setting, (5) V ₊ -V from the relationship _- a _{= 2I C1 / rσ min (6} ). Difference voltage (V ₊ -V _-) is exceeds the value of the right side, it is possible to determine the range of normal measurement to alarm the abnormal condition.

[0059]

As described above, according to the first or second aspect of the present invention, the current signal applied to the measurement electrode for detecting the empty state is a signal. Because it was configured to flow during the period when sampling is not performed,
There is an advantage that a stable flow signal can be secured.

According to the third aspect of the present invention, the conductivity of the measurement fluid can be calculated using two types of detection signals obtained by applying a current signal to the measurement electrode,
Since it is possible to know from the calculation result whether or not the conductivity is within the measurement range, a reliable flow signal can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a block diagram showing a configuration of a conventional electromagnetic flow meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Conduit 11a, 11b Measurement electrode 12 Excitation coil 13 Excitation circuit 14 Detector 15 Preamplifier 16a, 16b Constant current circuit 17 Signal processing circuit 19 Empty detection circuit 20 Reference voltage source 22 Timing circuit 23, 28 Analog / digital converter 24 Microprocessor 26 Constant current circuit 27 Timing switching circuit

Claims (3)

[Claims] 1. A current supply means for supplying a current signal to a measuring electrode in a rectangular wave excitation electromagnetic flow meter for sampling a flow signal generated at a measuring electrode provided in a conduit by a predetermined sampling signal and detecting the signal. Timing switching means for transmitting the current signal in an empty detection period different from the sampling period by the sampling signal, and detecting that the inside of the conduit is empty by using a detection signal detected in the empty detection period. An electromagnetic flowmeter characterized by the following. 2. The electromagnetic flow meter according to claim 1, wherein the empty detection period is set only in a rising period of the rectangular wave excitation. 3. The electromagnetic flowmeter according to claim 1, further comprising a calculating means for calculating the electric conductivity of the measurement fluid in the conduit using the detection signal.