JP2007263845A - Flow rate measuring device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a span error caused by insulation deterioration between a magnetic field generation means and a measuring tube, relative to a flow rate signal. <P>SOLUTION: An ammeter 100 includes a pair of measuring electrodes 4, 5 disposed in the facing state into fluid flowing in a pipe 1, an earth electrode 6 disposed in the facing state into the fluid, a coil 3 for generating a magnetic field to the fluid, an excitation circuit 30 for outputting an excitation current into the coil, a flow rate signal detection means for detecting the flow rate signal of the fluid based on a signal output from the measuring electrodes 4, 5, a leakage current detection means for detecting a leakage current from the coil 3 into the pipe 1, and a CPU 26 for calculating the span error, based on the excitation current output from the excitation circuit 30 and the detected leakage current and correcting the detected flow rate signal, based on the span error. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flow rate measuring device and a flow rate measuring method.

  Conventionally, an electromagnetic flow meter that measures the flow rate of a fluid flowing in a pipe has been implemented (see, for example, Patent Documents 1 and 2).

  FIG. 2 shows a configuration of a conventional electromagnetic flow meter 100A. As shown in FIG. 2, the electromagnetic flow meter 100A includes a detection unit 10A that detects the flow rate signals esa and esb, and a signal conversion unit 20A that generates the flow rate signal es from the detected flow rate signals esa and esb. Yes.

  The detection unit 10A includes a metallic pipe 1 through which a fluid can flow, a lining 2 that insulates the inner surface of the pipe 1, a pair of coils 3 that are disposed outside the pipe 1 and generate a magnetic field, A pair of measurement electrodes 4 and 5 that can be arranged with the free end facing in the pipe 1 and can detect a flow signal, and are equivalent to each of the pair of measurement electrodes 4 and 5 in the pipe 1 The ground electrode 6 is disposed at a position and serves as a reference potential for measuring the flow rate signal. The pipe 1 and the ground electrode 6 are electrically connected.

  The pair of measurement electrodes 4 and 5 has a configuration in which the free end portion thereof is in contact with the fluid flowing in the pipe 1 to detect the first and second flow rate signals esa and esb, and the base end portion side thereof. Is sealed so that fluid does not leak, and is insulated from the metallic pipe 1.

  The signal conversion unit 20A includes first and second input amplifiers 21 and 22 that input and amplify the first and second flow rate signals esa and esb detected by the pair of measurement electrodes 4 and 5; A differential amplifier 23 that receives the output signals of the second input amplifiers 21 and 22 and detects a difference between them, a high-pass filter 24 that removes a DC component from the signal obtained by the differential amplifier 23, and a high-pass filter 24 are provided. An A / D (Analog to Digital) conversion unit 25 that converts a transmitted signal component that has been transmitted into a digital signal, a CPU (Central Processing Unit) 26A that receives the digital signal and performs arithmetic processing to generate a flow signal, and an execution program ROM (Read Only Memory) 27A for storing data, RAM (Random Access Memory) 28 for storing temporary data necessary for calculation by CPU 26A, and set values such as span and aperture An EEPROM (Electrically Erasable Programmable ROM) 29, a current output unit 36 that outputs a normalized current indicating the flow rate signal es, and a pulse output unit 37 that outputs a normalized signal indicating the flow rate signal es, The excitation circuit 30 is configured to control and supply an excitation current applied to the pair of coils 3 in response to a control signal from the CPU 26.

In the electromagnetic flow meter 100A having such a configuration, assuming that the inner diameter D of the pipe 1 whose inner surface is insulated, the average velocity v of the fluid flowing in the pipe 1, and the magnetic flux density B of the magnetic field applied in the direction orthogonal thereto, the flow rate The signal es is calculated by the following equation (1).
es = kBvD (1)
However, k is a constant. The flow signal es is generated in a direction orthogonal to both the flow direction and the magnetic field direction.

The first and second flow rate signals esa and esb detected by the pair of measurement electrodes 4 and 5 are respectively input to the first and second input amplifiers 21 and 22 having sufficient input impedance. The outputs of the first and second input amplifiers 21 and 22 are input to the differential amplifier 23 to remove common mode noise, and further input to the high-pass filter 24 to remove DC components. After various noises are removed from the flow rate signal in this way, they are input to the A / D conversion unit 25 and converted into digital values, and the flow rate signal es is generated by the CPU 26 and is standardized from the current output unit 36 and the pulse output unit 37. Is output as a current signal.
JP 2003-97986 A JP 2002-195861 A

  In the conventional electromagnetic flow meter 100A, when the insulation between the coil 3 and the pipe 1 deteriorates, the leakage current of the exciting current flows from the coil 3 to the pipe 1, and the magnetic flux density B of the magnetic field generated by the coil 3 decreases. . For this reason, the generated flow rate signal is also reduced, and a span error is generated in the detected flow rate signal.

  However, the conventional electromagnetic flow meter such as the configuration described in Patent Document 2 cannot correct the span error due to the insulation deterioration between the coil 3 and the pipe 1 with respect to the flow signal.

  The subject of this invention is correct | amending the span error by the insulation degradation between a magnetic field generation means and a measurement pipe | tube with respect to a flow signal. Further, when the insulation deterioration progresses beyond a certain level, an alarm for insulation deterioration is generated.

In order to solve the above-described problem, the flow rate measuring device according to the invention described in claim 1 is:
At least a pair of measurement electrodes disposed facing the fluid flowing in the measurement tube;
A grounding means disposed facing the fluid;
Magnetic field generating means for generating a magnetic field with respect to the fluid;
Exciting means for outputting an exciting current to the magnetic field generating means;
A flow rate signal detecting means for detecting a flow rate signal of the fluid based on a signal output from the measurement electrode;
Leakage current detection means for detecting leakage current from the magnetic field generation means to the measurement tube;
Control means for calculating a span error based on the excitation current output from the excitation means and the detected leakage current, and correcting the detected flow rate signal based on the span error. To do.

The invention according to claim 2 is the flow rate measuring device according to claim 1,
Provided with an informing means for informing the alarm information;
The control means determines whether or not the detected leakage current is equal to or greater than a predetermined threshold value, and if it is equal to or greater than the threshold value, insulation deterioration has occurred between the magnetic field generating means and the measurement tube. The alarm means is notified of the fact to the effect.

The invention according to claim 3 is the flow rate measuring device according to claim 2,
The notification means notifies at least one of display of the alarm information, contact output of the alarm information, and transmission of the alarm information to an external device.

The invention according to claim 4 is the flow measurement device according to claim 2 or 3,
Storage means for storing the threshold value;
The control unit reads the threshold value from the storage unit, and determines whether or not the detected leakage current is equal to or greater than the read threshold value.

The flow rate measuring method of the invention according to claim 5 is:
Detecting a flow signal of the fluid based on signals output from at least a pair of measurement electrodes disposed facing the fluid flowing in the measurement tube;
Detecting leakage current from the magnetic field generating means for generating a magnetic field to the fluid to the measuring tube;
Calculating a span error based on the excitation current input to the magnetic field generating means and the detected leakage current, and correcting the detected flow rate signal based on the span error. To do.

The invention according to claim 6 is the flow rate measuring method according to claim 5,
It is determined whether or not the detected leakage current is equal to or greater than a predetermined threshold value. When the detected leakage current is equal to or greater than the threshold value, alarm information indicating that insulation deterioration has occurred between the magnetic field generating means and the measurement tube is displayed. An informing step of informing.

The invention according to claim 7 is the flow rate measurement method according to claim 6,
The notifying step is a step of notifying at least one of display of the alarm information, contact output of the alarm information, and transmission of the alarm information to an external device.

The invention according to claim 8 is the flow rate measuring method according to claim 6 or 7,
In the control step, the threshold value is read from a storage unit that stores the threshold value, and it is determined whether or not the detected leakage current is equal to or greater than the read threshold value.

  According to the first and fifth aspects of the present invention, the leakage current from the magnetic field generation means to the measurement tube can be detected, and based on the excitation current and the leakage current, the magnetic field generation means and the measurement tube It is possible to correct span errors due to insulation degradation between the two. In addition, the flow rate signal can be corrected simultaneously with the measurement of the flow rate signal.

  According to the second and sixth aspects of the invention, it is possible to determine the occurrence of insulation deterioration between the magnetic field generating means and the measuring tube, and to notify alarm information about the occurrence of insulation deterioration. Moreover, the alarm information can be notified simultaneously with the measurement of the flow signal.

  According to the third and seventh aspects of the invention, an administrator or the like can know alarm information about the occurrence of insulation deterioration between the magnetic field generating means and the measurement tube visually or by a response from an external device.

  According to the fourth and eighth aspects of the present invention, the threshold value can be easily read out from the storage means, and can be used to determine the occurrence of insulation deterioration between the magnetic field generating means and the measuring tube.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the illustrated examples.

  With reference to FIG. 1, the electromagnetic flowmeter 100 as a flow measuring device of this Embodiment is demonstrated. The same parts as those of the electromagnetic flow meter 100A described with reference to FIG.

  The electromagnetic flow meter 100 according to the present embodiment includes a detection unit 10 and a signal conversion unit 20.

  The detection unit 10 detects a flow signal of a conductive fluid flowing in the pipe 1. The signal conversion unit 20 inputs the excitation current Iex to the coil 3 of the detection unit 10, performs signal processing on the flow rate signals esa and esb detected and input by the detection unit 10, acquires and outputs the flow rate signal es. This is notified when the leakage current ΔIex of the excitation current Iex is greater than or equal to a predetermined threshold.

  The detection unit 10 includes a pipe 1 as a measurement tube, a lining 2, a coil 3 as a magnetic field generation unit, measurement electrodes 4 and 5, and a ground electrode 6 as a ground unit.

  The pipe 1 is a metallic pipe through which a fluid can flow. The lining 2 is an insulating layer such as a fluororesin or rubber disposed on the inner surface of the pipe 1. The coils 3 are a pair of coils that are disposed outside the pipe 1 and generate a magnetic field.

  The measurement electrodes 4 and 5 are a pair of measurement electrodes that are arranged in a state where the free end faces the pipe 1 and detect a flow signal. More specifically, the pair of measurement electrodes 4 and 5 has a configuration in which the free end side is in contact with the fluid, and detects and outputs the first flow rate signal esa and the second flow rate signal esa, respectively. The base end side is sealed so that the fluid does not enter the detector main body, and is insulated from the metallic pipe 1.

  The ground electrode 6 is disposed at an equal distance from each of the pair of measurement electrodes 4 and 5 and serves as a reference potential for detecting a flow signal. The grounding means has the same configuration even if a grounding ring (not shown) is used instead of the grounding electrode 6.

  In the present embodiment, it is assumed that in the electromagnetic flow meter 100, insulation deterioration has occurred between the coil 3 and the pipe 1. This insulation deterioration is expressed as an equivalent resistance 7 between the coil 3 and the pipe 1.

  The signal converter 20 includes first and second input amplifiers 21 and 22, a differential amplifier 23, a high-pass filter 24 and an A / D converter 25 as flow rate signal detection means, a CPU 26, a ROM 27, a RAM 28, EEPROM 29 as storage means, excitation circuit 30 as excitation means, earth 31, sensing resistor 32, earth 33, amplifier 34 and A / D converter 35 as leakage current detection means, current output part 36, A pulse output unit 37, a display unit 38 serving as a notification unit, an alarm output unit 39, and a communication unit 40 are provided.

  The first and second input amplifiers 21 and 22 amplify and output the first and second flow rate signals esa and esb input from the measurement electrodes 4 and 5, respectively. The signal source impedance of the electromagnetic flow meter 100 is about 1 MΩ at maximum.

  The differential amplifier 23 detects and outputs the difference between the amplified signals of the first and second flow rate signals esa and esb input from the first and second input amplifiers 21 and 22. The high-pass filter 24 removes the DC component of the difference signal between the amplified signals of the first and second flow rate signals esa and esb input from the differential amplifier 23 and outputs the result. The A / D converter 25 converts the transmission signal component of the difference signal transmitted through the high-pass filter 24 into a digital signal and outputs it as a flow signal es.

  The CPU 26 performs control of the input / output circuit and the excitation circuit, flow rate calculation, and correction calculation according to various programs stored in the ROM 27.

  The CPU 26 controls the excitation circuit 30 to generate a magnetic field from the coil 3 and acquires the flow signal es output from the A / D converter 25. In addition, in cooperation with the control program, the CPU 26 acquires the flow rate signal es and corresponds to the excitation current value Iex input from the excitation circuit 30 and the leakage current value ΔIex input from the A / D conversion unit 35. Based on the voltage, the span error ε is calculated, the flow rate signal es is corrected for the span error, and the current output unit 36 and the pulse output unit 37 output the flow rate signal es as a current pulse. Further, in cooperation with the control program, the CPU 26 acquires the flow rate signal es and, when the leakage current value ΔIex is equal to or greater than a predetermined threshold value, the coil 3 via the display unit 38, the alarm output unit 39, and the communication unit 40. Alarm information indicating that the insulation deterioration between the pipe 1 and the pipe 1 has occurred.

  The ROM 27 stores various programs including control programs and data. The RAM 28 stores temporary data necessary for calculation by the CPU 26. The EEPROM 29 is a nonvolatile memory in which data can be electrically read and written. The EEPROM 29 stores setting values such as a span and a diameter, and a threshold value of a leakage current ΔIex for determining whether or not a span error correction of the flow rate signal es is possible. Is stored.

  The excitation circuit 30 outputs an excitation current Iex for exciting the coil 3 to the coil 3 and a signal indicating a current value of the excitation current Iex to the CPU 26 under the control of the CPU 26.

  The sensing resistor 32 is a resistor for detecting a leakage current flowing from the coil 3 to the pipe 1 as a voltage. The voltage of the sensing resistor 32 is a voltage corresponding to the leakage current ΔIex. The amplifier 34 amplifies and outputs a weak voltage applied to the sensing resistor 32. The amplifier 34 amplifies and outputs a weak voltage applied to the sensing resistor 32. The A / D converter 35 converts the voltage amplified by the amplifier 34 into a digital signal and outputs it as a voltage corresponding to the leakage current value ΔIex.

  The current output unit 36 outputs a normalized current signal of the flow rate signal esc after span error correction under the control of the CPU 26. The pulse output unit 37 standardizes and outputs the flow rate signal esc after span error correction under the control of the CPU 26.

  The display unit 38 includes a display unit such as an LCD (Liquid Crystal Display), and displays alarm information indicating that the span error correction of the flow rate signal es is impossible under the control of the CPU 26. The alarm output unit 39 transmits alarm information indicating that the span error correction of the flow rate signal es is impossible under the control of the CPU 26 by turning on / off the switch, and sounds an alarm in a remote instrument room to turn on the lamp. Light up. The communication unit 40 communicates with an external device via a communication line (not shown). For example, the communication unit 40 transmits alarm information indicating that the span error correction of the flow rate signal es is impossible to the external device (instrument room) under the control of the CPU 26.

  Next, the operation of the electromagnetic flow meter 100 will be described. First, when the flow rate is measured by the electromagnetic flow meter 100, the flow rate signal es (= esa−) digitized based on the first and second flow rate signals esa and esb from the pair of measurement electrodes 4 and 5 of the detection unit 10. esb) is output from the A / D converter 25. In the CPU 26, the flow rate is calculated, but since the flow rate signal es has individual differences, a constant (correction constant value) for correcting this is obtained by actual flow calibration. The correction constant value is stored in the EEPROM 29 by the CPU 26.

  The correction constant values stored in these EEPROMs 29 are used when performing calculations for obtaining a correct flow rate signal output.

  The CPU 26 controls the excitation circuit 30 to excite the coil 3, and the excitation current Iex is acquired from the excitation circuit 30. In this case, the flow rate signal es obtained from the difference between the first and second flow rate signals esa and esb from the first and second measurement electrodes 5 and 6 and DC component removed and digitized is the A / D converter. 25 to the CPU 26. At the same time, the voltage of the leakage current ΔIex from the coil 3 to the pipe 1 is amplified and digitized and output from the A / D converter 35 to the CPU 26.

The CPU 26 reads the individual constant correction constant value from the EEPROM 29, corrects the flow rate signal es based on the correction constant value, and calculates the span error ε by the following equation (3).
ε = Iex / ΔIex (3)

Then, the CPU 26 calculates the flow rate signal esc after the span error correction using the flow rate signal es by the following equation (4).
esc = es / (1-ε) (4)

  In addition, when the leakage current (the magnitude) ΔIex exceeds a certain level, the span error correction becomes inaccurate. For this reason, the CPU 26 reads the threshold value of the leakage current ΔIex that is preset and stored from the EEPROM 29, and determines whether or not the leakage current ΔIex is equal to or larger than the read threshold value. When the CPU 26 determines that the leakage current ΔIex is larger than the threshold value, the alarm information indicating the occurrence of the insulation deterioration is displayed on the display unit 38 on the assumption that the insulation deterioration has occurred between the coil 3 and the pipe 1. Notification is given by at least one of alarm output by the alarm output unit 39 and transmission to an external device (for example, a host device) by the communication unit 40. The determination of the insulation deterioration is not performed once, but the data of a plurality of times can be averaged to determine the phenomenon of reliable insulation deterioration between the coil 3 and the pipe 1.

  As described above, according to the present embodiment, the flow rate signal es of the fluid flowing in the pipe 1 is detected based on the flow rate signals esa and esb output from the measurement electrodes 4 and 5, and leakage from the coil 3 to the pipe 1 is detected. A current ΔIex is detected, a span error ε is calculated based on the excitation current Iex output from the excitation circuit 30 and the detected leakage current ΔIex, and the detected flow rate signal es is corrected based on the span error ε. And output from the current output unit 36 and the pulse output unit 37 as a flow rate signal esc. Therefore, the leakage current ΔIex from the coil 3 to the pipe 1 can be detected, and the span error ε due to the insulation deterioration between the coil 3 and the pipe 1 with respect to the flow rate signal es based on the exciting current Iex and the leakage current ΔIex. Can be corrected. In addition, the flow rate signal es can be corrected for span error simultaneously with the measurement of the flow rate signal es.

  Further, it is determined whether or not the leakage current ΔIex is equal to or greater than a predetermined threshold value. If the leakage current ΔIex is equal to or greater than the predetermined threshold value, the span error correction of the flow rate signal es is impossible, and the gap between the coil 3 and the pipe 1 is not possible. Alarm information indicating that insulation deterioration has occurred is notified. For this reason, the occurrence of insulation deterioration between the coil 3 and the pipe 1 can be determined, and alarm information on the occurrence of the insulation deterioration can be notified. Moreover, alarm information can be notified simultaneously with the measurement of the flow rate signal es.

  Further, alarm information about the occurrence of insulation deterioration between the coil 3 and the pipe 1 is notified via the display unit 38, the alarm output unit 39, and the communication unit 40. For this reason, the administrator or the like can know the alarm information visually or by a response from an external device.

  Further, the threshold value of the leakage current ΔIex is stored in the EEPROM 29. For this reason, the threshold value can be easily read from the EEPROM 29 and can be used to determine the occurrence of insulation deterioration between the coil 3 and the pipe 1.

  The description in the above embodiment is an example of the flow rate measuring device and the flow rate measuring method according to the present invention, and the present invention is not limited to this.

  For example, in the above embodiment, the sensing resistor 32 is provided for detecting the voltage of the leakage current ΔIex. However, the present invention is not limited to this. For example, another means such as a current transformer as an element for measuring a current value may be used.

  Moreover, in the said embodiment, although it was set as the structure which detects leakage current (DELTA) Iex and converts it into a digital value by the A / D conversion part 35 after amplification, it is not limited to this. For example, the A / D converter 25 for the flow rate signal es may be time-shared to share the leakage current ΔIex.

  Moreover, in the said embodiment, although it was set as the structure which converts the leakage current (DELTA) Iex into a digital value with the A / D conversion part 35, it is not limited to this. For example, the leakage current ΔIex may be used as an analog signal to perform a calculation such as calculation of the span error ε.

  Furthermore, in the said embodiment, the structure in which a measurement electrode is formed in multiple pairs may be sufficient.

  In addition, the detailed configuration and detailed operation of the electromagnetic flow meter 100 in the above embodiment can be changed as appropriate without departing from the spirit of the present invention.

It is a figure which shows the structure of the electromagnetic flowmeter 100 of embodiment which concerns on this invention. It is a figure which shows the structure of the conventional electromagnetic flowmeter 100A.

Explanation of symbols

100, 100A Electromagnetic flow meter 10, 10A Detector 1 Pipe 2 Lining 3 Coils 4, 5 Measuring electrode 6 Ground electrode 7 Equivalent resistance 20, 20A Signal converter 21 First input amplifier 22 Second input amplifier 23 Differential amplifier 24 high-pass filter 25 A / D converter 26, 26A CPU
27,27A ROM
28 RAM
29 EEPROM
30 Excitation Circuit 31 Ground 32 Sensing Resistance 33 Ground 34 Amplifier 35 A / D Converter 36 Current Output Unit 37 Pulse Output Unit 38 Display Unit 39 Alarm Output Unit 40 Communication Unit

Claims (8)

At least a pair of measurement electrodes disposed facing the fluid flowing in the measurement tube;
A grounding means disposed facing the fluid;
Magnetic field generating means for generating a magnetic field with respect to the fluid;
Exciting means for outputting an exciting current to the magnetic field generating means;
A flow rate signal detecting means for detecting a flow rate signal of the fluid based on a signal output from the measurement electrode;
Leakage current detection means for detecting leakage current from the magnetic field generation means to the measurement tube;
Control means for calculating a span error based on the excitation current output from the excitation means and the detected leakage current, and correcting the detected flow rate signal based on the span error. Flow rate measuring device. Provided with an informing means for informing the alarm information;
The control means determines whether or not the detected leakage current is equal to or greater than a predetermined threshold value, and if it is equal to or greater than the threshold value, insulation deterioration has occurred between the magnetic field generating means and the measurement tube. The flow rate measuring apparatus according to claim 1, wherein the notification means is notified of the alarm information.   3. The flow rate according to claim 2, wherein the notification unit notifies at least one of display of the alarm information, contact output of the alarm information, and transmission of the alarm information to an external device. Measuring device. Storage means for storing the threshold value;
4. The flow rate measurement according to claim 2, wherein the control unit reads the threshold value from the storage unit and determines whether or not the detected leakage current is equal to or greater than the read threshold value. 5. apparatus. Detecting a flow signal of the fluid based on signals output from at least a pair of measurement electrodes disposed facing the fluid flowing in the measurement tube;
Detecting leakage current from the magnetic field generating means for generating a magnetic field to the fluid to the measuring tube;
Calculating a span error based on the excitation current input to the magnetic field generating means and the detected leakage current, and correcting the detected flow rate signal based on the span error. How to measure the flow rate.   It is determined whether or not the detected leakage current is equal to or greater than a predetermined threshold value. When the detected leakage current is equal to or greater than the threshold value, alarm information indicating that insulation deterioration has occurred between the magnetic field generating means and the measurement tube is displayed. The flow rate measuring method according to claim 5, further comprising: a notifying step for notifying.   The notifying step is a step of notifying at least one of display of the alarm information, contact output of the alarm information, and transmission of the alarm information to an external device. The flow rate measuring method described.   8. The control process according to claim 6, wherein in the control step, the threshold value is read from a storage unit that stores the threshold value, and it is determined whether or not the detected leakage current is equal to or greater than the read threshold value. Flow measurement method.

Images