JPH0814971A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To accurately measure the flow rate of a fluid regardless of the temperature change of the fluid by finding a measurement error at a predetermined flow rate from storage tables respectively indicating the relations between previously measured inter-coil voltages and the temperature of the fluid and between the temperature of the fluid and measurement errors. CONSTITUTION:A first storage table indicating the relation between the inter-coil voltage of an exciting coil 2 and the temperature of a fluid to be measured and second storage table indicating the relation between the temperature of the fluid when the flow rate of the fluid is 100% and measurement errors of signal electromotive forces are prepared from measured results and stored in an EEPROM 12. An electromotive force detecting circuit 6 detects the signal electromotive force between electrodes 4a and 4b and a CPU 9 finds measured values based on the electromotive force. At the time of finding the electromotive force, the CPU 9 fetches the inter-coil voltage of the coil 2 and reads out the fluid temperature corresponding to the voltage from the first storage table in the ROM 12 and the measurement error when the flow rate is 100% at the fluid temperature from the second storage table. Then the CPU 9 finds the measured flow rate value of the fluid which is not affected by the temperature change of the fluid by calculating and eliminating the measurement error contained in the signal electromotive force based on the read-out measurement error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flow meter for measuring the flow rate of electrically conductive fluid in various process systems.

[0002]

2. Description of the Related Art Conventionally, in this type of electromagnetic flowmeter, an exciting current is supplied at a predetermined frequency to an exciting coil arranged such that a magnetic field is generated in a direction perpendicular to a flow direction of a fluid flowing in a measuring tube. , The signal electromotive force (a signal proportional to the flow rate) obtained between the electrodes arranged in the measuring tube at right angles to the magnetic field generated by the exciting coil is detected, and based on the detected signal electromotive force, the CPU performs arithmetic processing. Seeking the measured value. That is, an exciting current is periodically supplied to the exciting coil to generate an alternating magnetic field in the measuring tube. This allows
A signal electromotive force is generated between the electrodes arranged in the measuring tube due to the interaction between the flow velocity and the magnetic field. This signal electromotive force is detected by the signal electromotive force detection circuit. Then, the detected signal electromotive force is held (sampled) immediately before the supply of the exciting current is interrupted periodically, and the signal electromotive force is converted to C via the A / D converter.
Give to PU. The CPU obtains a measured value as a 0-100% value of the measurement range based on the supplied signal electromotive force, and outputs an output current of 4-20 mA according to the obtained measured value.
Adjust within the current range of.

[0003]

However, in such an electromagnetic flowmeter, when the fluid temperature changes, the resistance value of the exciting coil changes and the exciting waveform changes. For example, the excitation waveform when the fluid temperature is 20 ° C. is shown in FIG.
If the waveform is as shown by the solid line in (a), the excitation waveform will be as shown by the broken line as the fluid temperature changes to 160 ° C. Therefore, the obtained signal electromotive force also changes from the waveform shown by the solid line in FIG. 4B to the waveform shown by the broken line, and the sampling values e ₂₀ and e of the signal electromotive force are changed.
The difference Δe is _160, and this difference Δe becomes an error component included in the measured value. That is, in the past, changes in fluid temperature hindered accurate flow rate measurement.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electromagnetic flow meter capable of accurately measuring a flow rate regardless of changes in fluid temperature. To provide.

[0005]

In order to achieve such an object, a first invention thereof (an invention according to claim 1) is to detect the inter-coil voltage of an exciting coil in the electromagnetic flowmeter described above. Then, based on the detected inter-coil voltage, an error component caused by a change in fluid temperature is removed from the measured value. A second invention (an invention according to claim 2) of the electromagnetic flowmeter described above is to detect a voltage between coils of an exciting coil,
From the detected inter-coil voltage, the temperature of the fluid is obtained with reference to the first storage table (the storage table indicating the relationship between the inter-coil voltage and the fluid temperature), and the second storage table is obtained from the obtained fluid temperature. An error caused by a change in the fluid temperature based on the calculated measurement error at the predetermined flow rate at that fluid temperature with reference to (a memory table indicating the relationship between the fluid temperature and the measurement error at the predetermined flow rate) The component is removed from the measured value. The third invention (the invention of claim 3)
In the electromagnetic flowmeter described above, the constants obtained by actually measuring the signal electromotive force and the inter-coil voltage at the first and second fluid temperatures at a predetermined flow rate are stored,
Further, the voltage between the coils of the exciting coil is detected, and the signal electromotive force from which the error component caused by the change in the fluid temperature is removed is calculated from the detected value of the voltage between the coils and the signal electromotive force and the stored constant. It was done like this.

[0006]

Therefore, according to the first aspect of the present invention, the error component caused by the change in the fluid temperature is generated based on the inter-coil voltage of the exciting coil, that is, the inter-coil voltage that reflects the change in the fluid temperature. Removed from measurement. In the second aspect of the invention, the temperature of the fluid is obtained from the inter-coil voltage of the exciting coil with reference to the first storage table, and the predetermined fluid temperature is obtained with reference to the second storage table from the obtained fluid temperature. The measurement error at the time of the flow rate is obtained, and the error component caused by the change of the fluid temperature is removed from the measurement value based on the obtained measurement error. In the third aspect of the invention, the signal electromotive force from which the error component caused by the change in fluid temperature is removed is calculated from the detected values of the inter-coil voltage and the signal electromotive force and the stored constants, and as a result, the fluid electromotive force is calculated. The error component caused by the temperature change is removed from the measured value.

[0007]

【Example】

Example 1 The present invention will be described in detail below based on examples. FIG. 1 is a block circuit configuration diagram showing a main part of an electromagnetic flowmeter showing an embodiment of the present invention. In the figure, 1
Is a measuring tube, 2 is an exciting coil arranged such that the direction of its magnetic field is perpendicular to the flow direction of the fluid flowing in the measuring tube 3, and 3 is a rectangular wave exciting current I _EX to the exciting coil 2 periodically. The exciting circuits 4a and 4b to be supplied are detection electrodes arranged in the measuring tube 1 at right angles to the magnetic field generated by the exciting coil 2.
Reference numeral 5 is a ground electrode, 6 is a signal electromotive force detection circuit that detects a signal electromotive force obtained between the electrodes 4a and 4b, 7 is a sample hold circuit that samples and holds the signal electromotive force detected by the signal electromotive force detection circuit 6, 8 is an A / D converter, 9 is C
PU, 10 is a D / A converter, 11 is an A / D converter for detecting the voltage between the coils of the exciting coil 2 and converting the detected voltage to a digital value and giving it to the CPU 9, 12 is an EEPROM
Is.

This electromagnetic flowmeter 100 has cables L1 and L.
It is connected to the DC power supply (DC 24V) 200 via the line 2. The excitation circuit 3 includes an excitation voltage circuit 3-1 and a constant current circuit 3
-2 and. The constant current circuit 3-2 includes an exciting current switching circuit whose switching operation is controlled by a command from the CPU 9. EEPROM 1
2 shows a first storage table (FIG. 2A) showing the relationship between the inter-coil voltage of the exciting coil 2 and the temperature of the fluid to be measured.
2) and a second storage table (see FIG. 2B) showing the relationship between the fluid temperature and the measurement error of the signal electromotive force at a flow rate of 100%. These storage tables are obtained in advance based on actual measurement results.

In this electromagnetic flowmeter 100, the exciting circuit 3 periodically supplies an exciting current I _EX (4 mA) to the exciting coil 2 to generate an alternating magnetic field in the measuring tube 1. As a result, a signal electromotive force is generated between the electrodes 4a and 4b due to the interaction between the flow velocity and the magnetic field, and this is detected by the signal electromotive force detection circuit 6. The detected signal electromotive force is held in the sample hold circuit 7 immediately before the supply of the exciting current is interrupted periodically, and the held signal electromotive force is A / D.
It is given to the converter 8 and converted into a digital value, and the CPU
Taken in 9. The CPU 9 measures the measured value based on the signal electromotive force from the A / D converter 8 in the measurement range of 0 to 10
Obtained as 0% value, and the obtained measured value is D / A converter 1
0, and the current I _out flowing through the cables L1 and L2 is
Adjust in the current range of 4 to 20 mA according to the measured value obtained above.

Here, when the CPU 9 obtains the measured value based on the signal electromotive force, the temperature is corrected as follows. That is, the CPU 9 causes the inter-coil voltage E _x of the exciting coil 2 immediately before the supply of the exciting current I _EX is periodically interrupted.
Are taken in via the A / D converter 11. Then, the fluid temperature T _x corresponding to the captured inter-coil voltage E _x is
The data is read from the first storage table stored in the EEPROM 12. Then, the measurement error N _{x (100)} at the time of 100% flow rate at the read fluid temperature T _x is calculated as EEP
It is read from the second storage table stored in the ROM 12. On the basis of the read measurement error N _{x (100),} calculates the signal electromotive force detection value e _{x (y)} in the included measurement error N _{x (y),} the measurement error N _{x (y)} Detected value e _{x (y)}
To remove from. Then, from the signal electromotive force ex _(y) 'from which this measurement error _{Nx (y)} has been removed, a measurement value Qx _(y) ' is obtained as a value from which an error component caused by a change in fluid temperature has been removed. Thereby, the flow rate can be accurately measured regardless of the change in the fluid temperature.

[Embodiment 2] In the embodiment described above,
Although the signal electromotive force ex _(y) 'is obtained by referring to the storage table stored in the EEPROM 12, a calculation formula as shown in the following formula (1) may be used. That is, if this calculation formula is used, the signal electromotive force e from which the error component caused by the change of the fluid temperature has been removed is simply substituted by the inter-coil voltage E _x and the detected value e _{x (y)} of the signal electromotive force.
You can get _{x (y)} '. As a result, the storage table used in the first embodiment becomes unnecessary, and the memory capacity can be saved.

Ex _(y) '= A · ex _(y) / (A + _Ex · B) (1) In this equation (1), A and B are A = (E
_{160 -E 25) · e 25 (} 1 00), B = e 160 (100) -e 25 (100)
Is a constant represented by. Here, E ₂₅ has a fluid temperature of 25
Actual measured value of coil voltage at ℃, E ₁₆₀ is fluid temperature 1
The measured value of the voltage between the coils at 60 ° C., e _{25 (100)} is the measured value of the signal electromotive force at a fluid temperature of 25 ° C. and a 100% flow rate,
e _{160 (100)} is a measured value of the signal electromotive force at a fluid temperature of 160 ° C. and a flow rate of 100%. That is, the constants A and B are constants obtained by actually measuring E ₂₅ , E ₁₆₀ , e _{25 (100)} and e _{160 (100)} , and these constants are the EEPROM 1
Remember in 2.

The above equation (1) is derived as follows. Now, assume that the fluid temperature is x ° C. and the signal electromotive force is obtained as e _{x (y)} (see FIG. 3). This signal electromotive force ex _(y) contains an error component caused by a change in fluid temperature. The signal electromotive force from which this error component is removed is defined as e _{x (y)} '. Here, if the signal electromotive force at a 100% flow rate at a fluid temperature of x ° C. is ex ₍₁₀₀₎ , this signal electromotive force ex ₍₁₀₀₎ is expressed by the following equation (2). _{e x (100) = e 25} (100) + (e 160 (100) -e 25 (100)) · E x / (E 160 -E 25) ··· (2)

The signal electromotive force e _{x (y)} 'to be obtained is
It is expressed by the following equation (3). ex _(y) '= ex _(y) -(ex ₍₁₀₀₎ -e25 ₍₁₀₀₎ ). ex _(y) / ex ₍₁₀₀₎ ... (3) When transformed, ext _(y) -ex _(y) '= (ex ₍₁₀₀₎ -e25 ₍₁₀₀₎ ). Ex _(y) / ex ₍₁₀₀₎ = (ex _{(100 )} .e _{x (y)} −e _{25 (100)} · ex _{x (y)} ) / ex _{x (100)} = ex _{x (y)} −e _{25 (100)} · ex _{x (y)} / ex _{x (100)} , and e _{x (y)} '= e25 ₍₁₀₀₎ * ex _(y) / ex ₍₁₀₀₎ ... (4).

Substituting the equation (2) into the equation (4), e _{x (100)} , e _{x (y)} '= (E ₁₆₀ -E ₂₅ ) · e _{25 (100)} · e _{x (y)} / _{{(E 160 -E 25) ·} e 2 5 (100) + E x · (e 160 (100) -e 25 (100))} ··· (5) _{next, A = (E 160 -E 25} ) · e _{25 (100)} , B = e
_{If 160 (100)} −e _{25 (100)} , the above formula (1) can be obtained. The equation (1) is derived by obtaining the measurement error included in the signal electromotive force e _{x (100)} at 100% flow rate when the fluid temperature is x ° C., and calculating the signal electromotive force e _{x (} at 100% flow rate e _{x ( 100)} and the detected value e _{x (y)} of the signal electromotive force, the measurement error included in the detected value e _{x (y)} is obtained, and the obtained measurement error is removed from the detected value e _{x (y).} It is based on the idea of deafening.

In the first and second embodiments described above, the error component generated due to the change in the fluid temperature is removed from the signal electromotive force e _{x (y),} so that the result is included in the measured value Q _{x (y).} Although the error component caused by the change in the fluid temperature is eliminated, the error component may be directly removed from the measured value Q _{x (y)} . That is, in the first embodiment, the measurement error stored in the second storage table is used as the measurement error of the measurement value, and in the second embodiment, the signal electromotive force e _x is replaced with the measurement value Q _x for consideration. It is possible to directly remove the error component from the value Q _{x (y)} .

[0017]

As is apparent from the above description, according to the present invention, in the first invention, it is based on the inter-coil voltage of the exciting coil, that is, based on the inter-coil voltage reflecting the change in fluid temperature. , The error component caused by the change of the fluid temperature is removed from the measured value, and in the second invention, the temperature of the fluid is obtained by referring to the first memory table from the inter-coil voltage of the exciting coil. A measurement error at a predetermined flow rate at the fluid temperature is obtained from the obtained fluid temperature with reference to the second storage table, and an error component caused by a change in the fluid temperature is removed from the measurement value based on the obtained measurement error. In the third aspect of the invention, the error caused by the change in fluid temperature is detected from the detected values of the voltage between the coils and the signal electromotive force and the stored constants. The signal electromotive force with the component removed is calculated, and as a result, the error component caused by the change in fluid temperature is removed from the measured value, and accurate flow rate measurement can be performed regardless of the change in fluid temperature. It will be possible.

[Brief description of drawings]

FIG. 1 is a block circuit configuration diagram showing a main part of an electromagnetic flow meter showing an embodiment of the present invention.

FIG. 2 is a diagram exemplifying first and second storage tables stored in an EEPROM of this electromagnetic flow meter.

FIG. 3 is a diagram exemplifying a waveform of a signal electromotive force used for explaining a derivation process of equation (1).

FIG. 4 is a diagram illustrating changes in an excitation waveform and a signal electromotive force waveform caused by a change in fluid temperature.

[Explanation of symbols]

1 ... Measuring tube, 2 ... Excitation coil, 3 ... Excitation circuit, 4a, 4
b ... Detection electrode, 5 ... Ground electrode, 6 ... Signal electromotive force detection circuit, 7 ... Sample hold circuit, 8 ... A / D converter, 9
... CPU, 10 ... D / A converter, 11 ... A / D converter,
12 ... EEPROM.

Claims (3)

[Claims] 1. Exciting current supplying means for supplying an exciting current at a predetermined frequency to an exciting coil arranged such that a magnetic field is generated in a direction perpendicular to a flow direction of a fluid flowing in a measuring tube, and a magnetic field generated by the exciting coil. A signal electromotive force detecting means for detecting a signal electromotive force obtained between electrodes arranged in the measuring tube orthogonally to the measurement tube, and a measured value for obtaining a measured value based on the signal electromotive force detected by the signal electromotive force detecting means. In an electromagnetic flowmeter provided with a calculating means, an inter-coil voltage detecting means for detecting the inter-coil voltage of the exciting coil, and the measured value calculating means based on the inter-coil voltage detected by the inter-coil voltage detecting means An electromagnetic flowmeter, comprising: a temperature correction unit that removes an error component caused by a change in fluid temperature from the measured value. 2. An exciting current supplying means for supplying an exciting current at a predetermined frequency to an exciting coil arranged such that a magnetic field is generated in a direction perpendicular to a flow direction of a fluid flowing in the measuring tube, and a magnetic field generated by the exciting coil. A signal electromotive force detecting means for detecting a signal electromotive force obtained between electrodes arranged in the measuring tube orthogonally to the measurement tube, and a measured value for obtaining a measured value based on the signal electromotive force detected by the signal electromotive force detecting means. In an electromagnetic flowmeter provided with a calculating means, an inter-coil voltage detecting means for detecting an inter-coil voltage of the exciting coil, and an inter-coil voltage and a fluid temperature are detected from the inter-coil voltage detected by the inter-coil voltage detecting means. With reference to the first storage table showing the relationship, a fluid temperature derivation means for obtaining the temperature of the fluid and a flow at a predetermined flow rate based on the fluid temperature obtained by the fluid temperature derivation means. Based on the measurement error deriving means for obtaining the measurement error at the predetermined flow rate at the fluid temperature and the measurement error obtained by the measurement error deriving means with reference to the second storage table showing the relationship between the body temperature and the measurement error. An electromagnetic flowmeter, comprising: a temperature correction unit that removes an error component caused by a change in fluid temperature from the measurement value obtained by the measurement value calculation unit. 3. Exciting current supply means for supplying an exciting current at a predetermined frequency to an exciting coil arranged such that the direction of the magnetic field is perpendicular to the flow direction of the fluid flowing in the measuring tube, and the magnetic field generated by the exciting coil. A signal electromotive force detecting means for detecting a signal electromotive force obtained between electrodes arranged in the measuring tube orthogonally to the measurement tube, and a measured value for obtaining a measured value based on the signal electromotive force detected by the signal electromotive force detecting means. In an electromagnetic flowmeter provided with a calculating means, an inter-coil voltage detecting means for detecting an inter-coil voltage of the exciting coil, a signal electromotive force and a inter-coil voltage at a first and a second fluid temperature at a predetermined flow rate, Storage means for storing constants obtained by actual measurement, constants stored in the storage means, inter-coil voltage detected by the inter-coil voltage detection means, and detection by the signal electromotive force detection means An electromagnetic flowmeter, comprising: a temperature correction unit that calculates a signal electromotive force from which an error component caused by a change in fluid temperature is removed from the signal electromotive force.