JP5530331B2 - Electromagnetic flow meter - Google Patents

Description

  The present invention relates to an electromagnetic flowmeter that measures the flow rate of a fluid having conductivity.

  Conventionally, in this type of electromagnetic flow meter, a current having a predetermined frequency whose polarity is alternately changed is applied to an excitation coil arranged with the direction of generation of the magnetic field perpendicular to the flow direction of the fluid flowing in the measurement tube. The excitation current is supplied. This frequency fex of the excitation current is called an excitation frequency.

  Then, by supplying an excitation current having an excitation frequency fex to the excitation coil, an electromotive force (signal electromotive force) is generated between a pair of electrodes arranged in the measurement tube perpendicular to the magnetic field generated by the excitation coil. The signal electromotive force is detected as an analog flow rate signal, and the detected analog flow rate signal is converted into a digital signal and processed to obtain a measured flow rate.

  In this electromagnetic flow meter, when a foreign substance adheres to the electrode, a noise component due to the adhesion of the foreign substance affects the signal electromotive force, and the fluid flow rate cannot be measured accurately (see, for example, Patent Document 1). . That is, the signal electromotive force generated between the electrodes includes a flow rate signal component and a noise component, and the ratio of the noise component included in the signal electromotive force increases, making it impossible to accurately measure the fluid flow rate.

  Therefore, if a function that automatically detects that foreign matter has adhered to the electrode (electrode adhesion detection function) is added to the electromagnetic flowmeter, foreign matter can be removed and cleaned in a timely manner, improving convenience. it can. Examples of electromagnetic flowmeters having such an electrode adhesion detection function are shown in Patent Documents 2 and 3.

  In the electromagnetic flow meter shown in Patent Document 2, the resistance of the electrode is measured, and when the measured resistance of the electrode becomes a predetermined value or more (when an increase in electrode resistance is detected), It is determined that foreign matter has adhered to the electrode.

Patent Document 3 discloses two types of electromagnetic flow meters. In the first type of electromagnetic flow meter disclosed in Patent Document 3, excitation with positive excitation current is positive excitation, excitation with zero excitation current is non-excitation, and excitation with negative excitation current is negative excitation. a ternary excitation mode to the period _{K 1 ~K 5 (K 1,} K 3, K 5: non-excited, K _2: positive excitation, K _4: negative excitation) signal EMF (V ₁₁ obtained in ~V ₁₅ : Signal electromotive force in a state where no foreign matter is attached, V _{21 to} V ₂₅ : Signal electromotive force in a state where the foreign matter is attached), and calculation results R _{1 to} R ₄ (R ₁ = −V ₂₁ + V ₂₂ + V ₂₃ −V ₂₄ , R ₂ = (− V ₂₁ + 2V ₂₂ −2V ₂₄ + V ₂₅ ) / 2, R ₃ = −V ₁₁ + V ₁₂ + V ₁₃ −V ₁₄ , R ₄ = (− V ₁₁ + 2V ₁₂ -2V ₁₄ + V ₁₅ ) / 2) is calculated, and foreign matter adhesion-influencing components are determined from the calculated calculation results R _{1 to} R ₄ .

In the second type of electromagnetic flow meter disclosed in Patent Document 3, a binary excitation method having two excitation frequencies (use excitation frequency f _H , low excitation frequency f _L ) is used, and no foreign matter is attached. The differential noise component is obtained by subtracting the average value of the signal electromotive force at the low excitation frequency f _L from the average value of the signal electromotive force during the period of the used excitation frequency f _H , and the obtained differential noise component is stored in the RAM. Stored in memory as variable A. Then, with the foreign matter attached, the signal electromotive force averaging process value at the low excitation frequency f _L is subtracted from the signal electromotive force averaging process value during the period of the used excitation frequency f _H , and this subtraction value is used. By subtracting the RAM variable A (differential noise component) stored in the memory, a foreign substance adhesion influencing component is obtained.

Special table 2010-521659 gazette JP 2003-28684 A JP 2002-168666 A Japanese translation of PCT publication No. 2004-528527

  However, the electromagnetic flow meter disclosed in Patent Document 2 employs a method of detecting an increase in electrode resistance, which may lead to erroneous diagnosis. That is, the increase in electrode resistance occurs not only when foreign matter adheres to the electrode but also when the resistance value in the measurement fluid changes. For this reason, an increase in electrode resistance cannot be uniquely regarded as adhesion of foreign matter to the electrode, which may lead to erroneous diagnosis. Further, the electromagnetic flow meter disclosed in Patent Document 2 requires a special configuration such as an electrode lead wire in order to measure the resistance of the electrode.

  In addition, in the electromagnetic flow meter disclosed in Patent Document 3, a three-value excitation method or a two-value excitation method having two excitation frequencies should be used instead of a normal binary excitation method with one excitation frequency. In addition, the circuit configuration and processing for realizing this special excitation method are complicated.

  In Patent Document 4, an analog signal including a flow rate signal component and a noise component from an electrode is converted into a digital signal, and the digital signal is processed to generate a spectral component. An electromagnetic flowmeter is illustrated that separates and extracts a known noise component and generates a noise diagnostic output based on the extracted known noise component.

  However, in the electromagnetic flow meter disclosed in Patent Document 4, noise targeted for noise diagnosis output is noise that matches the commercial power supply frequency or known noise that is lower than the excitation frequency called 1 / F noise. In the electromagnetic flow meter shown in Patent Document 4, noise of a frequency component caused by adhesion of foreign matter to the electrode is not extracted, as can be seen from the description of the embodiment of the present invention described later. It is impossible to detect the presence or absence of foreign matter.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an electromagnetic flowmeter that can accurately detect the presence or absence of foreign matter adhering to an electrode with a simple configuration. Is to provide.

  In order to achieve such an object, an electromagnetic flow meter according to the present invention includes a measurement tube for flowing a fluid, and an excitation coil arranged with the direction of generation of the magnetic field perpendicular to the flow direction of the fluid flowing in the measurement tube. And an excitation current supply means for supplying an excitation current having an excitation frequency fex whose polarity alternately changes to the excitation coil, and a flow direction of the fluid flowing in the measurement tube and a direction of the magnetic field generated by the excitation coil in the measurement tube A pair of electrodes arranged, a flow signal detection means for detecting an electromotive force generated between the electrodes as an analog flow signal, and a first A for converting the analog flow signal detected by the flow signal detection means into a digital signal / D conversion means, sampling means for sampling the flow rate signal converted into the digital signal by the first A / D conversion means at a predetermined cycle, and sampling means A first integrating means for calculating a value obtained by integrating the absolute values of all frequency components of the sample data sampled for a predetermined period as a first integrated value, and the frequency of the sample data for the predetermined period sampled by the sampling means Among the components, a high-frequency component extracting means for extracting a frequency component equal to or higher than a predetermined frequency higher than the excitation frequency fex, and a value obtained by integrating the absolute values of the frequency components extracted by the high-frequency component extracting means as a second integrated value. The second integrating means for calculating, and the ratio of the second integrated value calculated by the second integrating means to the first integrated value calculated by the first integrating means affects the electromotive force on the electrode. Adhesion noise evaluation value calculating means for calculating an adhesion noise evaluation value for evaluating the influence level of noise components due to adhesion, An electrode adhesion diagnostic means for comparing the adhesion noise evaluation value calculated by the means with a predetermined diagnostic threshold value and determining the presence or absence of foreign matter adhesion to the electrode based on the comparison result. Features.

  According to the present invention, an electromotive force generated between the electrodes is detected as an analog flow signal, the detected analog flow signal is converted into a digital signal, and a flow signal including a noise component converted into the digital signal is generated. It is sampled at a predetermined period. Then, a value obtained by integrating the absolute values of all the frequency components of the sampled sample data for a predetermined period is calculated as the first integrated value, and is higher than the excitation frequency fex among the frequency components of the sampled sample data for the predetermined period. A value obtained by integrating absolute values of frequency components higher than a predetermined frequency is calculated as a second integrated value, and a ratio of the second integrated value to the calculated first integrated value is calculated as an adhesion noise evaluation value. The Then, the calculated adhesion noise evaluation value and the diagnostic threshold are compared, and the presence / absence of adhesion of foreign matter to the electrode is determined based on the comparison result.

  According to the present invention, an electromotive force generated between the electrodes is detected as an analog flow signal, the detected analog flow signal is converted into a digital signal, and the flow signal converted into the digital signal is converted at a predetermined cycle. A value obtained by sampling and summing absolute values of all frequency components of the sampled sample data for a predetermined period is calculated as a first integrated value, and an excitation frequency among the frequency components of the sampled sample data for the predetermined period is calculated. A value obtained by integrating absolute values of frequency components equal to or higher than a predetermined frequency higher than fex is calculated as a second integrated value, and a ratio of the second integrated value to the calculated first integrated value is used as an adhesion noise evaluation value. The calculated adhesion noise evaluation value and the diagnostic threshold value are compared, and the presence or absence of foreign matter adhering to the electrode is determined based on the comparison result. Since the, with a simple configuration, it is possible to accurately detect the presence or absence of adhesion of foreign matter into the electrodes.

It is a figure which shows the principal part of one Embodiment (Embodiment 1) of the electromagnetic flowmeter which concerns on this invention. It is a flowchart of the calculation operation | movement of the adhesion noise evaluation value including calculation of the 1st integrated value and the 2nd integrated value in the control part of this electromagnetic flowmeter. It is a flowchart of the electrode adhesion diagnostic routine based on the adhesion noise evaluation value in the control part of this electromagnetic flowmeter. It is a figure which illustrates the observation waveform of the analog flow signal (flow signal component + noise component) from the AC amplification circuit in this electromagnetic flow meter. It is a figure which shows the frequency component of this observation waveform. It is a figure which shows the observation waveform of the analog flow signal (flow-rate signal component + noise component) in the electromagnetic flowmeter (meter of sample No. 1) from which the adhesion state of the foreign material to an electrode differs. It is a figure which shows the observation waveform of the analog flow signal (flow-rate signal component + noise component) in the electromagnetic flowmeter (meter of sample No. 2) from which the adhesion state of the foreign material to an electrode differs. It is a figure which shows the observation waveform of the analog flow signal (flow-rate signal component + noise component) in the electromagnetic flowmeter (meter of sample No. 3) from which the adhesion state of the foreign material to an electrode differs. It is a figure which shows the observation waveform of the analog flow signal (flow-rate signal component + noise component) in the electromagnetic flowmeter (meter of sample No. 4) from which the adhesion state of the foreign material to an electrode differs. It is a figure which shows the observation waveform of the analog flow signal (flow-rate signal component + noise component) in the electromagnetic flowmeter (meter of sample No. 5) from which the adhesion state of the foreign material to an electrode differs. It is a figure which shows the observation waveform of the analog flow signal (flow-rate signal component + noise component) in the electromagnetic flowmeter (meter of sample No. 6) from which the adhesion state of the foreign material to an electrode differs. Sample No. 0-NO. It is a figure which shows the relationship between the high frequency ratio HR [%] calculated in 6 meters, and the flow measurement error Error [%]. It is a figure which shows the graph which plotted the relationship between the high frequency ratio HR and the flow measurement error Error, with the high frequency ratio HR as the vertical axis and the flow measurement error Error as the horizontal axis. It is a figure which shows the specific example of the excitation frequency fex in the case of synchronizing excitation frequency fex with commercial power supply frequency AC50Hz, the excitation period, the sampling number, and the cutoff frequency fc. It is a figure which shows the specific example of the excitation frequency fex in the case of synchronizing excitation frequency fex with commercial power supply frequency AC60Hz, the excitation period, the sampling number, and the cut-off frequency fc. It is a figure which shows the specific example of the excitation frequency fex in the case of AC asynchronous, the excitation period, the number of samplings, and the cut-off frequency fc. It is a flowchart of the electrode adhesion diagnostic routine of Embodiment 2 (Modification 1 of Embodiment 1). It is a flowchart of the electrode adhesion diagnostic routine of Embodiment 3 (Modification 2 of Embodiment 1). It is a figure which shows the principal part of the electromagnetic flowmeter of Embodiment 4 (Modification 3 of Embodiment 1).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Embodiment 1]
FIG. 1 is a diagram showing a main part of an embodiment of an electromagnetic flow meter according to the present invention. In the figure, reference numeral 1 denotes a detector that receives an excitation current Iex having a frequency fex whose polarity alternately changes, applies a magnetic field to a fluid flowing in the measuring tube 11, and outputs an electromotive force generated in the fluid; 2 supplies an excitation current Iex to the detector 1, detects an electromotive force from the detector 1 as an analog flow signal, converts the analog flow signal into a digital signal, and processes it by processing it. 11 is a converter that calculates the flow rate of the fluid flowing in the interior of The detector 1 and the converter 2 constitute an electromagnetic flow meter 100.

  In the detector 1, reference numeral 12 denotes an exciting coil 12 arranged with the direction of generation of the magnetic field perpendicular to the flow direction of the fluid flowing in the measurement tube 11, and reference numerals 13 </ b> A and 13 </ b> B denote the flow of fluid flowing in the measurement tube 11. These are a pair of electrodes arranged in the measuring tube 11 perpendicular to the direction and the direction of the magnetic field generated by the exciting coil 12.

  The exciting current Iex from the converter 2 is supplied to the exciting coil 12. As a result, a magnetic field generated from the exciting coil 12 is applied to the fluid flowing in the measurement tube 11, and an electromotive force having an amplitude corresponding to the flow velocity of the fluid is generated between the electrodes 13A and 13B. The electromotive force generated between the electrodes 13A and 13B is sent to the converter 2.

  The converter 2 includes a first stage circuit 21, an AC amplification circuit 22, an excitation unit 23, a DC amplification circuit 24, a noise removal circuit 25, a first A / D conversion unit 26, and a second A / D. A conversion unit 27, a control unit 28, a flow rate output unit 29, and an adhesion diagnosis output unit 30 are provided.

  In this embodiment, the control unit 28 is realized by hardware including a processor (CPU) and a storage device, and a program that realizes various functions in cooperation with these hardware, and has a normal flow rate calculation function. In addition, an electrode adhesion diagnosis function is provided as a function unique to the present embodiment.

  In this embodiment, as the first A / D converter 26, an A / D converter with a built-in CPU in the controller 28 is used. Further, as the second A / D converter 27, an A / D converter having a higher conversion accuracy of the analog signal to the digital signal than the first A / D converter 26 is used.

  In the converter 2, the electromotive force from the detector 1 is given to the first stage circuit 21. The electromotive force applied to the first stage circuit 21 is amplified by the AC amplifier circuit 22 and sent to the first A / D converter 26 and the DC amplifier circuit 24 as an analog flow signal. This analog flow signal includes a flow signal component and a noise component.

  The first A / D conversion unit 26 converts the analog flow rate signal from the AC amplification circuit 22 into a digital signal and sends the digital signal to the control unit 28. The DC amplification circuit 24 converts and amplifies the analog flow rate signal from the AC amplification circuit 22 into a DC flow rate signal, and sends it to the noise removal circuit 25. The noise removal circuit 25 removes a noise component included in the DC flow rate signal from the DC amplification circuit 24 and sends only the flow rate signal component to the second A / D conversion unit 27. The second A / D conversion unit 27 converts the DC flow rate signal from which the noise component from the noise removal circuit 25 is removed into a digital signal and sends the digital signal to the control unit 28. The excitation unit 23 receives an instruction from the control unit 28 and outputs an excitation current Iex having an excitation frequency fex whose polarity changes alternately.

  The control unit 28 includes a flow rate calculation unit 28A as a functional block for realizing a flow rate calculation function, and a sampling unit 28B, a digital high-pass filter 28C, and a first integration unit 28D as functional blocks for realizing an electrode adhesion diagnosis function. , A second integration unit 28E, an adhesion noise evaluation value calculation unit 28F, a diagnostic threshold storage unit 28G, and an electrode adhesion diagnosis unit 28H. Reference numeral 28I denotes an excitation control unit that instructs the excitation unit 23 to generate an excitation current Iex. The diagnostic threshold storage unit 28G stores a predetermined diagnostic threshold SPHR.

(Flow rate calculation function)
In the control unit 28, the flow rate calculation unit 28A calculates the flow rate of the current fluid flowing in the measurement tube 11 from the DC flow rate signal converted into a digital signal by the second A / D conversion unit 27, and the calculation. The flow rate is output via the flow rate output unit 29.

[Electrode adhesion diagnostic function]
In the control unit 28, the electrode adhesion diagnosis function includes a first integrated value calculation function, a second integrated value calculation function, and an adhesion noise evaluation value from the first integrated value and the second integrated value. It comprises a calculation function and an electrode adhesion presence / absence determination function based on the calculated adhesion noise evaluation value.

[Calculation of first integrated value]
During operation with the electromagnetic flow meter 100 installed at the site, the control unit 28 sets one cycle of the excitation frequency fex as a predetermined period, and calculates the value of the digital signal from the first A / D conversion unit 26 during this predetermined period. A sample data is read at a sampling timing generated at a predetermined cycle, and a value obtained by integrating the absolute values of all frequency components of the read sample data for a predetermined period is calculated as a first integrated value. In this case, sampling of the digital signal is performed by the sampling unit 28B, and calculation of the first integrated value is performed by the first integrating unit 28D.

  In this example, the predetermined period is one period of the excitation frequency fex, but the predetermined period is not limited to one period of the excitation frequency fex, and may be two periods, three periods, four periods, and the like. A long cycle may be used. Further, the predetermined period including the idle period may be arbitrarily determined regardless of the excitation frequency fex.

[Calculation of second integrated value]
During operation with the electromagnetic flow meter 100 installed at the site, the control unit 28 sets one cycle of the excitation frequency fex as a predetermined period, and calculates the value of the digital signal from the first A / D conversion unit 26 during this predetermined period. A sample data is read at a sampling timing generated at a predetermined cycle, and a predetermined frequency higher than the excitation frequency fex (in this example, eight times the excitation frequency fex) among the frequency components of the read sample data for a predetermined period. The cut-off frequency fc is calculated, and a value obtained by integrating the absolute values of frequency components equal to or higher than the cut-off frequency fc is calculated as the second integrated value.

  In this case, the sampling of the digital signal is performed by the sampling 28B, and the extraction of the frequency component higher than the cutoff frequency fc is performed by the digital high-pass filter 28C, and the absolute values of the extracted frequency components higher than the cutoff frequency fc are integrated. The second integrated value is calculated by the second integrating unit 28E. The calculation of the second integrated value is performed for the same predetermined period as the first integrated value, and the calculation of the first integrated value and the second integrated value is repeated every predetermined period.

[Calculation of adhesion noise evaluation value (high frequency ratio HR)]
The control unit 28 determines the adhesion noise evaluation value (high frequency ratio) as a ratio of the second integrated value to the first integrated value from the calculated first integrated value and second integrated value for each predetermined period. HR) is calculated. The calculation of the adhesion noise evaluation value is performed by the adhesion noise evaluation value calculation unit 28F.

  FIG. 2 shows a flowchart of the operation for calculating the adhesion noise evaluation value including the calculation of the first integrated value and the second integrated value.

The control unit 28 starts sampling by interruption of the fixed cycle timer (step S101), and reads the value (A / D conversion value) of the digital signal from the first A / D conversion unit 26 at the sampling timing n as Xn. (Step S102). Further, a calculated value Yn is calculated from the digital signal by the digital high-pass filter 28C (step S103). The calculated value Yn is specifically calculated from Yn = AYn− ₁ + BYn− ₂ + C (Xn−2Xn− ₁ + Xn− ₂ ) (where A, B, and C are constants). Then, the read absolute value of Xn is integrated, and the integrated value is set to X = Σ | Xn | (step S104). Further, the calculated absolute value of Yn is integrated, and the integrated value is set to Y = Σ | Yn | (step S105).

  The control unit 28 repeats the processing operations of steps S102 to S105 for one cycle of the excitation frequency fex determined as a predetermined period, and if the accumulated number of Xn and Yn becomes a predetermined value k indicating the end of the predetermined period ( YES in step S106), X = Σ | Xn | at that time is set as the first integrated value, and Y = Σ | Yn | is set as the second integrated value. Then, the ratio of the second integrated value Y to the first integrated value X is obtained as a high frequency ratio HR (HR = Y / X) (step S107), and this high frequency ratio HR is a noise due to adhesion of foreign matter to the electrodes 13A and 13B. The adhesion noise evaluation value indicates the magnitude of the influence of the component on the flow rate measurement. If the high frequency ratio HR is obtained, X and Y are cleared to zero in preparation for the next calculation of the high frequency ratio HR (step S108). Then, the process proceeds to an electrode adhesion diagnosis routine based on the calculated adhesion noise evaluation value (high frequency ratio HR) (step S109).

[Electrode adhesion diagnosis based on adhesion noise evaluation value]
FIG. 3 shows a flowchart of an electrode adhesion diagnosis routine based on the adhesion noise evaluation value (high frequency ratio HR). When the calculation of the high frequency ratio HR ends, the control unit 28 reads the diagnostic threshold value SP _HR stored in the diagnostic threshold value storage unit 28G (step S201). Then, the calculated high frequency ratio HR is compared with the read diagnostic threshold value SP _HR (step S202).

Here, if the high frequency ratio HR exceeds the diagnostic threshold value SP _HR (YES in step S203), the control unit 28 determines that foreign matter is attached to both or one of the electrodes 13A and 13B (step S204). ), The presence of electrode adhesion is reported as a diagnosis result (step S205). If the high frequency ratio HR is less than or equal to the diagnostic threshold value SP _HR (NO in step S203), the control unit 28 determines that no foreign matter has adhered to the electrodes 13A and 13B (step S206), and the electrode adhesion as a diagnostic result. The absence is notified (step S207).

  The electrode adhesion diagnosis based on the adhesion noise evaluation value is performed by the electrode adhesion diagnosis unit 28H, and the diagnosis result of the presence / absence of electrode adhesion from the electrode adhesion diagnosis unit 28H is output from the adhesion diagnosis output unit 30.

[Cutoff frequency fc]
FIG. 4 illustrates an observation waveform of an analog flow signal (flow signal component + noise component) from the AC amplification circuit 22 in the electromagnetic flow meter 100 in a state where foreign matter is attached to the electrodes 13A and 13B. In FIG. 4, W1 is an observed waveform, and a waveform W0 in a normal state in which no foreign matter adheres to the electrodes 13A and 13B is compared with the observed waveform W1.

  FIG. 5 shows frequency components of the observed waveform W1. In FIG. 5, WF1 is a waveform (observation frequency component waveform) indicating the frequency component of the observed waveform W1, and a normal frequency component waveform (normal frequency component waveform) WF0 of the waveform W0 at the normal time with respect to this observed frequency component waveform WF1. In contrast. In this example, the commercial power supply frequency is AC 50 Hz and the excitation frequency fex is 12.5 Hz.

  In FIG. 5, when the observed frequency component waveform WF1 and the normal frequency component waveform WF0 are compared, the observed frequency component waveform WF1 has a frequency component of the normal frequency component waveform WF0 from around 100 Hz (eight times the excitation frequency fex = 12.5 Hz). It can be seen that the difference from the normal frequency component waveform WF0 is widened in a frequency range of 100 Hz or more. That is, it can be seen that the frequency component of 100 Hz or more is increased in the observed frequency component waveform WF1 due to the adhesion of foreign matter to the electrodes 13A and 13B. Accordingly, it can be seen that the diagnosis of the adhesion of foreign matter to the electrodes 13A and 13B is possible based on the ratio of the frequency component of 100 Hz or more to the entire frequency component. Therefore, in this example, 100 Hz is determined as the cut-off frequency fc.

[Diagnosis threshold SP _HR ]
6 to 11, a plurality of electromagnetic flow meters 100 having different adhesion states of foreign matters to the electrodes 13A and 13B are used as sample meters, and an analog flow signal (flow rate) from the AC amplification circuit 22 observed in the sample meters. The waveform of signal component + noise component) is shown.

  FIG. 1 shows the waveform observed by the meter of FIG. 2 shows the waveform observed by the meter of FIG. 3 shows the waveform observed by the meter of FIG. 4 shows the waveform observed by the meter of FIG. 5 shows the waveform observed by the meter of FIG. The observation waveform with the meter of 6 is shown.

  6 to 11, S1 to S6 shown in the upper diagram (a) are observation waveforms of the analog flow signal, and SF1 to SF6 shown in the lower diagram (b) are equal to or higher than the cutoff frequency fc. It is a waveform of the frequency component. The observed waveforms S1 to S6 in FIGS. 6A to 11A are compared with the normal waveform S0 in which no foreign matter is attached to the electrodes 13A and 13B. Further, the waveforms SF1 to SF6 having a frequency component higher than the cutoff frequency fc in FIGS. 6B to 11B are compared with the waveform SF0 in a normal state in which no foreign matter adheres to the electrodes 13A and 13B. It shows. Here, a normal electromagnetic flow meter 100 in which no foreign matter adheres to the electrodes 13A and 13B is used as a sample NO. 0 meter.

  In FIG. 0-NO. 6 shows the relationship between the high frequency ratio HR [%] calculated by the meter No. 6 and the flow rate measurement error Error [%]. FIG. 13 is a graph in which the relationship between the high frequency ratio HR and the flow rate measurement error Error is plotted with the high frequency ratio HR as the vertical axis and the flow rate measurement error Error as the vertical axis.

  FIG. 12 shows that there is a good correlation between the high frequency ratio HR and the flow rate measurement error Error. That is, the cut-off excitation in the error rate between the actual flow rate of the measured fluid actually flowing through the electromagnetic flow meter and the measured flow rate measured by the electromagnetic flow meter, and the signal voltage (flow signal component + noise component) obtained from the electrode It can be seen that there is a good correlation between the ratio between the integrated value of power of frequency components equal to or higher than the frequency fc and the integrated value of power of all frequency components of the signal voltage.

In this embodiment, by using this relationship, the high frequency ratio HR is obtained and compared with the diagnostic threshold value SP _HR to determine whether or not foreign matter has adhered to the electrode. In FIG. 13, if the diagnostic threshold value SP _{HR is set} to 10%, for example, NO. 1-NO. It is determined that the meter No. 6 is a meter to which foreign matter is attached. In this manner, in this embodiment, it is possible to accurately detect the presence or absence of foreign matter on the electrode that affects the flow rate measurement accuracy by appropriately determining the diagnostic threshold value SP _HR .

  Further, in this embodiment, normal data in a state where no foreign matter is attached to the electrode is not required, so that it is not affected by a flow rate difference or a fluid state at the time of normal data acquisition. That is, if there is a difference between the flow rate at the time of normal data acquisition and the flow rate at the time of diagnosis, or if the fluid state is different (the flow rate signal itself is different), there is a risk of erroneous diagnosis. Since the first integrated value X and the second integrated value Y are calculated with the same flow rate and fluid state, there is no possibility of such a false diagnosis.

  FIG. 14 shows specific examples of the excitation frequency fex, the excitation cycle, the number of samplings, and the cut-off frequency fc when the excitation frequency fex is synchronized with the commercial power supply frequency AC 50 Hz. FIG. 15 shows a specific example of the excitation frequency fex, the excitation cycle, the number of samplings, and the cutoff frequency fc when the excitation frequency fex is synchronized with the commercial power supply frequency AC 60 Hz.

  When synchronizing with the commercial power supply frequency AC50 Hz, as a standard type, the excitation frequency fex is set to 12.5 Hz which is a quarter of the commercial power supply frequency, and the cut-off frequency fc is set to 25 Hz which is eight times the excitation frequency fex. When synchronizing with the commercial power supply frequency AC 60 Hz, as a standard type, the excitation frequency fex is set to 15 Hz which is a quarter of the commercial power supply frequency, and the cut-off frequency fc is set to 120 Hz which is eight times the excitation frequency fex.

  FIG. 16 shows specific examples of the excitation frequency fex, the excitation cycle, the number of samplings, and the cutoff frequency fc in the case of AC asynchronous. In the case of AC asynchronous, as a standard type, the excitation frequency fex is set to 12.5 Hz, and the cut-off frequency fc is set to 100 Hz which is eight times the excitation frequency fex.

  When the cut-off frequency fc is determined, the electrode adhesion diagnosis can be performed without being affected by low frequency noise such as 1 / F noise. However, if the cutoff frequency fc is lower than the commercial power supply frequency, the same noise as the commercial power supply frequency may be included. On the other hand, if the cutoff frequency fc is set higher than the commercial power supply frequency, the possibility that the same noise as the commercial power supply frequency is included can be eliminated, and the reliability of the electrode adhesion diagnosis is further improved.

  If the digital high-pass filter 31C has a function of cutting the same frequency component as the commercial power supply frequency, the same frequency component as the commercial power supply frequency can be removed without setting the cut-off frequency fc higher than the commercial power supply frequency. This can improve the reliability of electrode adhesion diagnosis. In the first embodiment, the cut-off frequency fc is eight times the excitation frequency fex, but it goes without saying that the cut-off frequency fc is not limited to eight times the excitation frequency fex.

[Embodiment 2 (Modification 1 of Embodiment 1)]
In the first embodiment described above, if the high frequency ratio HR exceeds the diagnosis threshold value SP _HR even once, it is determined that foreign matter is attached to the electrode. On the other hand, in the second embodiment, it is determined that there is electrode adhesion when the high frequency ratio HR exceeds the diagnosis threshold value SP _HR continuously for a predetermined number of times without determining electrode adhesion at a time.

FIG. 17 shows a flowchart of the electrode adhesion diagnosis routine in this case. Each step in the flowchart of FIG. 17 is given the same step number as the step having the same contents in the flowchart of FIG. In this electrode adhesion diagnosis routine, as can be seen by comparing with the flowchart in the first embodiment shown in FIG. 3, step S208 is provided between step S203 and step 204, and the high frequency ratio HR sets the diagnosis threshold value SP _HR . It is confirmed whether or not N times (for example, 10 times) have been exceeded continuously.

As a result, the foreign matter continues to adhere to the electrode, and when the high frequency ratio HR continuously exceeds the diagnosis threshold value SP _HR N times (YES in step S208), it is determined that the foreign matter is attached to the electrode for the first time. (Steps S204 and S205). Therefore, even if a foreign object temporarily adheres to the electrode, if it immediately peels off from the electrode, it is not determined that the electrode is attached, and the reliability of the determination is increased.

[Embodiment 3 (Modification of Embodiment 2)]
Although it is rare that the foreign matter adhering to the electrode continuously peels for a certain period of time, it may be peeled off by a fluid or a substance mixed in the fluid. Assuming such a case, in the third embodiment, the high frequency ratio HR continuously falls below the diagnosis threshold value SP _HR for a predetermined number of times after it is determined in the second embodiment that foreign matter is attached to the electrode. If it is determined that there is no electrode adhesion.

FIG. 18 shows a flowchart of the electrode adhesion diagnosis routine in this case. In this case, the calculation of the high frequency ratio HR is continued even after the high frequency ratio HR exceeds the SP _HR continuously N times and it is determined that the electrode is attached, and the calculated high frequency ratio HR is compared with the threshold value for diagnosis SP _HR. (Steps S301 to S303)

Then, when it is confirmed that the high frequency ratio HR continuously falls below the diagnosis threshold value SP _HR N times (for example, 10 times) (YES in step S308), it is determined that the foreign matter has not adhered to the electrode (YES in step S308). Steps S304 and S305). Until it is determined that the foreign matter has not adhered to the electrode, the process proceeds to steps S306 and S307 according to NO in step S303 or NO in step S308, and it is determined that the foreign matter is continuously adhered to the electrode.

  As a result, after it is determined that foreign matter has adhered to the electrode, it is determined that the foreign matter has not been adhered to the electrode, and it is determined that no foreign matter has adhered to the electrode. This increases the reliability of the determination.

[Embodiment 4 (Modification 3 of Embodiment 1)]
In the first embodiment, the first A / D converter 26 A / D-converts a signal including noise, so the conversion accuracy may not be relatively high, but A / D conversion with a high conversion speed is possible. A vessel is desired. For this reason, an A / D converter with a built-in CPU in the control unit 28 is used. On the other hand, since the second A / D converter 27 handles a flow rate signal that is the basis of the flow rate calculation by the flow rate calculator 28A, an A / D converter with high conversion accuracy is desired even if the sampling period is relatively long. It is. For this reason, as the second A / D converter 27, an A / D converter having higher conversion accuracy of the analog signal to the digital signal than the first A / D converter 26 is used. As a result, an electromagnetic flow meter with high flow rate calculation accuracy and high reliability in electrode adhesion diagnosis can be obtained.

  On the other hand, in the fourth embodiment, as shown in FIG. 19, the second A / D converter 27 is not provided, and the analog flow signal from the AC amplifier circuit 22 and the DC flow rate from the noise removal circuit 25 are provided. The signal is supplied to the first A / D conversion unit 26, and the first A / D conversion unit 26 receives the analog signal from the AC amplification circuit 22 according to a command from the time division unit 28 J provided in the control unit 28. Conversion of the flow rate signal into a digital signal and conversion of the DC flow rate signal from the noise removal circuit 25 into a digital signal are performed in a time-sharing manner.

  By doing so, the first A / D converter 26 performs A / D conversion for electrode adhesion diagnosis and A / D conversion for calculating the flow rate in a time-sharing manner, and the second A / D conversion is performed. The cost can be reduced by eliminating the need for the D converter 27 (see FIG. 1). The electromagnetic flow meter according to the fourth embodiment is denoted by reference numeral 101. In the electromagnetic flow meter 101, the first A / D conversion unit 26 handles a flow rate signal, so that a high conversion accuracy is desired. In this case, the CPU built-in A / D converter in the control unit 28 may have high conversion accuracy, but the A / D converter with high conversion accuracy is used as the first A / D conversion unit 26 separately from the control unit 28. You may make it provide.

In the first to fourth embodiments described above, the diagnosis threshold value SP _{HR is set} to two stages, for example, the first stage is a light alarm, the second stage is a heavy alarm, and foreign substances adhere to the electrodes step by step. A diagnosis may be performed.

  The electromagnetic flow meter of the present invention can be used in various process systems as an electromagnetic flow meter for measuring the flow rate of a fluid having conductivity.

  DESCRIPTION OF SYMBOLS 1 ... Detector, 2 ... Converter, 11 ... Measuring tube, 12 ... Excitation coil, 13A, 13B ... Electrode, 21 ... First stage circuit, 22 ... AC amplification circuit, 23 ... Excitation part, 24 ... DC amplification circuit, 25 ... Noise removal circuit 26 ... first A / D conversion unit 27 ... second A / D conversion unit 28 ... control unit 28A ... flow rate calculation unit 28B ... sampling unit 28C ... digital high pass filter 28D ... First accumulation unit, 28E ... second accumulation unit, 28F ... adhesion noise evaluation value calculation unit, 28G ... diagnostic threshold storage unit, 28H ... electrode adhesion diagnosis unit, 28I ... excitation control unit, 28J ... time division unit, 29 ... Flow rate output unit, 30 ... Adhesion diagnosis output unit, 100, 101 ... Electromagnetic flow meter.

Claims (6)

A measuring tube for flowing fluid;
An exciting coil arranged with the direction of generation of the magnetic field perpendicular to the flow direction of the fluid flowing in the measuring tube;
Excitation current supply means for supplying an excitation current having an excitation frequency fex whose polarity alternately changes to the excitation coil;
A pair of electrodes disposed in the measurement tube perpendicular to the flow direction of the fluid flowing in the measurement tube and the direction of the magnetic field generated by the excitation coil;
Flow rate signal detecting means for detecting an electromotive force generated between the electrodes as an analog flow rate signal;
First A / D conversion means for converting an analog flow signal detected by the flow signal detection means into a digital signal;
Sampling means for sampling a flow rate signal converted into a digital signal by the first A / D conversion means at a predetermined period;
First integrating means for calculating, as a first integrated value, a value obtained by integrating absolute values of all frequency components of the sample data sampled for a predetermined period sampled by the sampling means;
High-frequency component extraction means for extracting a frequency component of a predetermined frequency higher than the excitation frequency fex from among the frequency components of the sample data sampled by the sampling means for a predetermined period;
Second integrating means for calculating a value obtained by integrating the absolute values of the frequency components extracted by the high frequency component extracting means as a second integrated value;
The ratio of the second integrated value calculated by the second integrating means to the first integrated value calculated by the first integrating means affects the electromotive force. An adhesion noise evaluation value calculating means for calculating an adhesion noise evaluation value for evaluating the degree of influence;
Electrode adhesion diagnostic means for comparing the adhesion noise evaluation value calculated by the adhesion noise evaluation value calculating means with a predetermined diagnostic threshold and determining the presence or absence of foreign matter adhesion to the electrode based on the comparison result An electromagnetic flow meter comprising: and. The electromagnetic flow meter according to claim 1,
The high frequency component extraction means includes
The frequency component to be extracted does not include the same frequency component as the commercial power supply frequency. The electromagnetic flow meter according to claim 1,
The electrode adhesion diagnostic means includes
The electromagnetic flow meter, wherein when the ratio calculated as the adhesion noise evaluation value exceeds the diagnostic threshold continuously for a predetermined number of times, it is determined that a foreign substance is adhered to the electrode. The electromagnetic flow meter according to claim 3,
The electrode adhesion diagnostic means includes
After it is determined that foreign matter has adhered to the electrode, no foreign matter has adhered to the electrode when the ratio calculated as the adhesion noise evaluation value falls below the diagnostic threshold continuously for a predetermined number of times. An electromagnetic flow meter characterized by The electromagnetic flow meter according to claim 1,
DC flow signal conversion means for converting the electromotive force into a DC flow signal;
Noise removing means for removing noise components contained in the DC flow rate signal;
Second A / D conversion means for converting the DC flow rate signal from which the noise component has been removed into a digital signal;
Flow rate calculation means for calculating the flow rate of the fluid from the DC flow rate signal converted into the digital signal,
The second A / D conversion means has higher accuracy in converting analog signals into digital signals than the first A / D conversion means. The electromagnetic flow meter according to claim 1,
DC flow signal conversion means for converting the electromotive force into a DC flow signal;
Noise removing means for removing noise components contained in the DC flow rate signal;
Means for causing the first A / D conversion means to perform conversion of the electromotive force including a noise component into a digital signal and conversion of the DC flow rate signal from which the noise component has been removed into a digital signal in a time-sharing manner;
An electromagnetic flowmeter comprising: a flow rate calculation means for calculating a flow rate of the fluid from a DC flow rate signal converted into the digital signal.

Images