JP6481443B2 - Electromagnetic flow meter - Google Patents

Description

  The present invention relates to an electromagnetic flow meter, and more particularly to a technique for detecting an abnormality based on characteristics of a fluid to be measured.

  Electromagnetic flowmeters that measure the flow rate of a conductive fluid using electromagnetic induction are widely used in industrial applications because they are robust and accurate. The electromagnetic flow meter measures the electromotive force generated by flowing a conductive fluid to be measured in a measurement tube to which a magnetic field is applied in an orthogonal direction. Since this electromotive force is proportional to the flow velocity of the fluid to be measured, the volume flow rate of the fluid to be measured can be obtained based on the measured electromotive force.

  The generated electromotive force can be measured by, for example, a pair of electrodes (electrode A503a and electrode B503b) attached to the measurement tube 501 as shown in FIG. In addition, a magnetic field in the orthogonal direction can be generated by flowing an excitation current from the excitation circuit 505 to the excitation coil 502 disposed in the vicinity of the measurement tube 501. In general, an alternating current in which a positive excitation period and a negative excitation period are alternately switched is used as the excitation current Iex.

  Conventionally, in an electromagnetic flow meter, by measuring the resistance (conductivity) of a fluid to be measured, it has been possible to detect abnormalities such as the inside of a measuring tube being emptied or an insulating foreign substance adhering to an electrode. It is. Patent Document 1 describes that an alternating current for resistance measurement flows between electrodes in order to measure resistance in parallel with measurement of the flow rate of the fluid to be measured. At this time, the AC current for resistance measurement is synchronized with the exciting current at a frequency that is an integral multiple of the frequency of the exciting current so that the resistance measurement does not affect the flow rate measurement.

JP 2003-97986 A

  Abnormalities that occur in the electromagnetic flow meter can occur in cases other than when the measuring tube is emptied or an insulating foreign material adheres to the electrode. For example, an abnormality based on the characteristics of the fluid to be measured (process fluid) itself.

  Examples of the abnormality based on the characteristics of the fluid to be measured include bubbles generated in the fluid to be measured, the fluid to be measured having a low conductivity, and a slurry (slurry) fluid. In addition, an electrode made of a material corresponding to the fluid to be measured has not been selected, and electrode corrosion due to an acid / alkali fluid to be measured is also caused by an abnormality based on the characteristics of the fluid to be measured. Furthermore, the adhesion of insulating foreign matter to the electrode may be included in the abnormality based on the characteristics of the fluid to be measured.

  Conventionally, in an electromagnetic flowmeter that measures the resistance of a fluid to be measured in addition to the flow rate of the fluid to be measured, detection of an abnormality based on the characteristics of the fluid to be measured has not been sufficiently considered. For this reason, it is convenient if an abnormality based on the characteristics of the fluid to be measured can be easily detected without adding a new hardware configuration.

  Therefore, the present invention can easily detect an abnormality based on the characteristics of the fluid to be measured without adding a new hardware configuration in an electromagnetic flowmeter that measures the resistance of the fluid to be measured in addition to the flow rate of the fluid to be measured. The purpose is to do.

In order to solve the above problems, an electromagnetic flowmeter of the present invention provides a magnetic field generated by an excitation current to a fluid to be measured flowing in a measurement tube, and the measurement target is based on a detection signal generated in an electrode provided in the measurement tube. An electromagnetic flow meter for measuring a flow rate of a fluid, comprising: an excitation circuit that generates an excitation current having a positive excitation period and a negative excitation period; and a rectangular wave resistance measurement current for measuring the resistance of the fluid to be measured. A resistance measurement output circuit that outputs to the electrode, and a period corresponding to the positive excitation period, the level difference of the detection signal in the period corresponding to the first half of the period of the resistance measurement current and the period corresponding to the second half of the period A first level difference is a level difference between detection signals in a period corresponding to the negative excitation period, a period corresponding to the first half of the period of the resistance measurement current, and a period corresponding to the second half of the period. A diagnostic unit that calculates a level difference and detects an abnormality based on a characteristic of the fluid to be measured based on a noise level obtained from the difference between the first level difference and the second level difference. It is characterized by.
Here, the diagnostic unit determines that an abnormality based on the characteristics of the fluid to be measured has occurred when a diagnostic noise level obtained by averaging the absolute values of successive noise levels is equal to or higher than a predetermined reference value. be able to.
In addition, when the abnormality is detected based on the characteristics of the fluid to be measured, the diagnosis unit may suggest the cause of the abnormality according to a predetermined criterion.
The resistance measurement current can be synchronized with the excitation current at a frequency that is an integral multiple of the frequency of the excitation current.
In any case, the abnormality based on the characteristics of the fluid to be measured detected by the diagnostic unit is any of bubble generation, low conductivity, slurry fluid, electrode corrosion by the fluid to be measured, and adhesion of insulating foreign matter to the electrode. Can be included.

  According to the present invention, in an electromagnetic flow meter that measures the resistance of a fluid to be measured in addition to the flow rate of the fluid to be measured, an abnormality based on the characteristics of the fluid to be measured can be easily detected without adding a new hardware configuration. can do.

It is a block diagram which shows the basic composition of the electromagnetic flowmeter which concerns on this embodiment. It is a figure which shows the specific example of an excitation circuit. It is a figure explaining the waveform of an exciting current. It is a flowchart explaining operation | movement of the electromagnetic flowmeter which concerns on this embodiment. It is a figure which shows a flow signal sampling period and a resistance signal sampling period. It is a flowchart explaining the abnormality diagnosis process based on the characteristic of the fluid to be measured. It is a figure explaining the flow measurement by an electromagnetic flowmeter.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of an electromagnetic flow meter 100 according to the present embodiment. As shown in the figure, an electromagnetic flow meter 100 includes a measurement tube 101, an excitation coil 102, an electrode A 103a, an electrode B 103b, a ground electrode 104, a buffer 105, a differential amplifier circuit 106, a flow signal sampling unit 107, and an excitation signal sampling unit. 108, a resistance signal sampling unit 109, a control unit 110, an excitation circuit 120, a resistance measurement output circuit 130, a display unit 141, an operation reception unit 142, a current output unit 143, a pulse output unit 144, a status output unit 145, and a communication unit 146. I have.

  The control unit 110 can be configured by a CPU, a memory, and the like, and includes a circuit control unit 111, a calculation unit 112, and a diagnosis unit 113.

  The circuit control unit 111 includes a flow rate signal sampling unit 107, an excitation signal sampling unit 108, a resistance signal sampling unit 109, an excitation circuit 120, a resistance measurement output circuit 130, a display unit 141, a current output unit 143, a pulse output unit 144, and a status output. The control unit 145 and the communication unit 146 are controlled, and various instructions from the user are received via the operation receiving unit 142.

  The calculation unit 112 calculates the flow velocity and volume flow rate of the fluid to be measured flowing through the measurement tube 101 based on the output data of the flow rate signal sampling unit 107, and the resistance of the fluid to be measured (based on the output data of the resistance signal sampling unit 109. Conductivity) is calculated.

  The diagnosis unit 113 diagnoses an abnormality based on the characteristics of the fluid to be measured based on the output data of the resistance signal sampling unit 109. That is, the electromagnetic flow meter 100 of this embodiment diagnoses an abnormality based on the characteristics of the fluid to be measured using the resistance measurement signal. For this reason, a new hardware configuration is not required for diagnosis of an abnormality based on the characteristics of the fluid to be measured.

  Here, both the flow rate signal sampling unit 107 and the resistance signal sampling unit 109 sample the output signal of the differential amplifier circuit 106 to obtain output data, but both have different sampling periods. Details of the sampling period of the flow rate signal sampling unit 107 and the sampling period of the resistance signal sampling unit 109 will be described later.

  In the electromagnetic flow meter 100, when the excitation circuit 120 supplies the excitation current Iex to the excitation coil 102 under the control of the control unit 110, an electromotive force proportional to the flow velocity of the fluid to be measured is detected by the electrodes A103a and B103b. This detection signal is input to the differential amplifier circuit 106 via the buffer 105, and the external noise generated in the common mode is removed and amplified to a desired amplitude level. However, the detection signal includes a signal based on a resistance measurement current described later.

  The detection signal output from the differential amplifier circuit 106 is converted into digital data by the flow rate signal sampling unit 107 and input to the control unit 110. A value corresponding to the excitation current Iex output from the excitation circuit 120 is converted into digital data by the excitation signal sampling unit 108 and input to the control unit 110.

  The resistance measurement output circuit 130 causes a predetermined resistance measurement current to flow through the fluid to be measured via the electrodes A103a and B103b. A detection signal including a signal based on the current for resistance measurement is converted into digital data by the resistance signal sampling unit 109 and input to the control unit 110.

  The display unit 141 can be composed of a liquid crystal display device or the like, and displays measured values, diagnosis results, and the like. The operation receiving unit 142 can be composed of a plurality of keys and the like, and receives an operation from the user. The current output unit 143 scales and outputs the measured value, diagnosis result, etc. to a current value in a predetermined range such as 4-20 mA. The pulse output unit 144 scales and outputs the measured values and diagnosis results to frequency pulses in a predetermined range. The status output unit 145 outputs the internal state of the electromagnetic flow meter 100 to the outside by turning on / off the contacts. The communication unit 146 communicates various information with an external device using various communication protocols. However, each output unit is an example, and is not limited to this example.

  FIG. 2 is a configuration example of the excitation circuit 120 that causes the excitation current Iex to flow through the excitation coil 102. The excitation circuit 120 includes a DC power source E1, a constant current source CCS, and switching elements Q1, Q2, Q3, and Q4. The switching elements Q1, Q2, Q3, and Q4 are controlled to be turned on and off by signals T1, T2, T3, and T4 from the circuit control unit 111. The voltage Viex generated in the resistor Ri connected in series to the excitation coil 102 indicates a value corresponding to the excitation current Iex, and is sampled by the excitation signal sampling unit 108 and input to the control unit 110.

  As shown in FIG. 3, the circuit control unit 111 divides one cycle of excitation into two periods. Then, signals T1 and T3 are output so that Q1 and Q3 are turned on only in the previous period, and signals T2 and T4 are output so that Q2 and Q4 are turned on only in the subsequent period. As a result, the excitation current Iex repeats a cycle composed of a positive excitation period of current + I and a negative excitation period of current -I.

  In addition, the resistance measurement output circuit 130 outputs the resistance measurement current Ir in a rectangular wave shape and outputs the current Ir in synchronization with the excitation current Iex at a frequency that is an integral multiple of the frequency of the excitation current Iex. Thereby, it is possible to prevent the resistance measurement from affecting the flow measurement by appropriately setting each sampling period. In the waveform example shown in FIG. 3, the frequency of the resistance measurement current Ir is four times the frequency of the excitation current Iex. Here, the first half of the period of the current Ir is Ir1, and the second half is Ir2.

  FIG. 4 is a flowchart showing the operation of the electromagnetic flow meter 100 of the present embodiment. The electromagnetic flow meter 100 can simultaneously measure the flow rate of the fluid to be measured, measure the resistance (conductivity) of the fluid to be measured, and detect an abnormality based on the characteristics of the fluid to be measured.

  First, the electromagnetic flow meter 100 accepts setting of measurement conditions from the user prior to the start of measurement (S101). In setting the measurement conditions, for example, parameter settings such as a flow rate span and unit are accepted.

  When the measurement is started (S102), the excitation circuit 120 generates the excitation current Iex and outputs it to the excitation coil 102, and the resistance measurement output circuit 130 generates the resistance measurement current Ir and passes through both electrodes 103. And output to the fluid to be measured (S103). As described above, the resistance measurement current Ir is synchronized with the excitation current Iex at a frequency that is an integer multiple of the frequency of the excitation current Iex.

  Since the voltage is detected between the electrodes 103 by the excitation current Iex and the resistance measurement current Ir, the output signal Eex of the differential amplifier circuit 106 is the excitation current Iex and the resistance measurement current Ir as shown in FIG. And a waveform that is superimposed. However, when the excitation current Iex is switched between + I and -I, differential noise is generated in the output signal Eex.

  In the output signal Eex, the difference between the average value of the voltage obtained during the period corresponding to the positive excitation period of the excitation current Iex and the average value of the voltage obtained during the period corresponding to the negative excitation period is proportional to the flow velocity of the fluid to be measured. Amount. Further, an amount in which the difference between the average value of the voltage obtained in the period corresponding to the first half of the period of the resistance measuring current Ir and the average value of the voltage obtained in the period corresponding to the second half of the period is proportional to the resistance of the fluid to be measured. It becomes. However, in any case, the differential noise portion is excluded.

  For the output signal Eex of the differential amplifier circuit 106, the flow rate signal sampling unit 107 samples the flow rate signal in the flow rate signal sampling period ESn. Further, the resistance signal sampling unit 109 samples the resistance signal in the resistance signal sampling period ENn (S104).

  Here, as shown in FIG. 5, the flow rate signal sample period ESn is a period that is an integral multiple of the period of the resistance measurement current Ir in each of the periods corresponding to the positive excitation period and the negative excitation period of the excitation current Iex. . By doing so, the change in the output signal Eex due to the resistance measurement current Ir is canceled out, so that the influence of the resistance measurement current Ir on the flow signal can be eliminated.

  In order to avoid the influence of differential noise, the flow rate signal sample period ESn is set to a period in which the differential noise is settled and the waveform is stable in the periods corresponding to the positive excitation period and the negative excitation period.

  In the example of this figure, the resistance measurement current Ir in one period ES1 of the resistance measurement current Ir in the period corresponding to the positive excitation period of the excitation current Iex and the period corresponding to the negative excitation period in the excitation current Iex. A period ES2 for one cycle is a flow rate signal sample period ESn.

  The resistance signal sampling period ENn is a first half period and a second half period of a period corresponding to a certain period of the resistance measurement current Ir for each of the periods corresponding to the positive excitation period and the negative excitation period of the excitation current Iex. Since the detection signal based on the flow velocity of the fluid to be measured does not change in the same period of the resistance measurement current Ir, the voltage difference between the first half period and the second half period and the current between the first half period and the second half period of the resistance measurement current Ir. Based on the difference (Ir1-Ir2), the resistance of the fluid to be measured can be measured. The resistance signal sampling period ENn is also set to a period that is not affected by the differential noise.

  In the example of this figure, in the period corresponding to the positive excitation period of the excitation current Iex, the first half period EN1 and the second half period EN2 of the period corresponding to the second period of the resistance measurement current Ir, and the negative of the excitation current Iex. The first half period EN3 and the second half period EN4 of the period corresponding to the second period of the resistance measurement current Ir in the period corresponding to the excitation period are set as the resistance signal sampling period ENn.

  During each sampling period, the acquisition of sample data is repeated at a predetermined sampling rate. The average value of the repeatedly acquired sample data is used as a detection signal for that period.

  The computing unit 112 calculates the flow rate of the fluid to be measured based on the detection signal Eex (ESn) acquired during the flow rate signal sample period ESn (S105). The calculation of the flow rate of the fluid to be measured is the same as the conventional one.

  Further, the resistance (conductivity) of the fluid to be measured is calculated based on the detection signal Eex (ENn) acquired in the resistance signal sampling period ENn (S106). The resistance calculation of the fluid to be measured is the same as in the past, and the voltage difference of at least one of Eex (EN1) −Eex (EN2), Eex (EN3) −Eex (EN4), and the current difference (Ir1−Ir2) It can be calculated from

  Further, the diagnosis unit 113 performs an abnormality diagnosis based on the characteristics of the fluid to be measured based on the detection signal Eex (ENn) acquired during the resistance signal sampling period ENn (S107). The detection signal Eex (ENn) obtained during the resistance signal sampling period ENn includes noise generated by fluctuations in the electrode potential. The causes of this noise include bubble generation, low conductivity, slurry fluid, Examples include electrode corrosion, fluid conductivity change, and adhesion of insulating foreign matters to the electrode. That is, by acquiring the noise level generated in the resistance signal sampling period ENn, it is possible to detect an abnormality based on the characteristics of the fluid to be measured.

  Note that the spectrum of noise caused by an abnormality based on the characteristics of the fluid to be measured generally has a characteristic of decreasing by 1 / f with a corner frequency of about 10 Hz to several tens of Hz. A detailed procedure of the abnormality diagnosis process based on the characteristics of the fluid to be measured will be described later.

  The computing unit 112 outputs the calculated flow rate as a measurement result from the current output unit 143 or the like (S108). At this time, the resistance (conductivity) may also be output. The electromagnetic flow meter 100 repeats the above processing (S103 to S108) until the measurement is completed (S109: Yes).

  Next, details of the abnormality diagnosis process (S107) based on the characteristics of the fluid to be measured will be described with reference to the flowchart of FIG. In this process, the noise level for abnormality diagnosis is calculated from the detection signal Eex (ENn) acquired in the resistance signal sampling period ENn (S201).

To calculate the noise level for abnormality diagnosis, first, as with resistance calculation,
Level difference E1 = Eex (EN1) −Eex (EN2)
Level difference E2 = Eex (EN3) −Eex (EN4)
Is calculated. You may use the value calculated at the time of resistance calculation.

The level difference E1 and the level difference E2 have the same value with respect to the resistance component, but include noise generated due to fluctuations in the electrode potential in reverse polarity. Therefore, the noise component can be extracted by calculating the level difference E1-level difference E2. For this reason, in this embodiment,
Level difference E1−Level difference E2 = {Eex (EN1) −Eex (EN2)} − {Eex (EN3) −Eex (EN4)}
Is calculated as a noise level.

  Then, an abnormality diagnosis noise level is obtained by calculating an average value of absolute values of a plurality of continuous noise levels (dumping calculation).

  If the calculated diagnostic noise level is equal to or higher than a predetermined reference value (S202: Yes), a warning is displayed on the display unit 141, or warning information or the like is output from the pulse output unit 144, the status output unit 145, or the like. (S203). Thereby, the user can know that an abnormality based on the characteristics of the fluid to be measured has occurred, and can take measures such as maintenance. However, the calculated diagnostic noise level value may be output regardless of the diagnostic noise level value.

  In the present embodiment, when outputting a warning, the cause of the abnormality may be suggested to the user. When the cause of the abnormality is suggested (S204), the cause is estimated according to a predetermined criterion (S205), and a message based on the estimation result is displayed from the display unit 141, the pulse output unit 144, the status output unit 145, and the like. Output (S206).

  For example, if the conductivity of the fluid to be measured exceeds a predetermined first reference value as a result of the resistance calculation (S106) of the fluid to be measured in the computing unit 112, the cause of the abnormality in which the noise level is increased As mentioned above, bubbles such as electrode corrosion, solid slurry or cavitation are considered. In this case, for example, “if the electrode is appropriately selected for the fluid to be measured, the fluid to be measured is a solid slurry, otherwise bubbles such as cavitation may be generated”. A message to that effect is output.

  Furthermore, a message stating that “in the case of slurry fluid, the lining material may have been damaged or worn” may be output. This is because when the lining material around the electrode is damaged or worn by the slurry fluid, the wetted area of the electrode is increased and the noise level is increased.

  Further, if the conductivity of the fluid to be measured is lower than a predetermined second reference value as a result of the resistance calculation (S106) of the fluid to be measured in the computing unit 112, for example, “If the fluid viscosity is low, The message “Measurement conductivity may be low” is output.

  Further, when the conductivity of the fluid to be measured is within a predetermined range, for example, a message saying “If the fluid to be measured is acid / alkali, there is a possibility of electrode corrosion” is output.

DESCRIPTION OF SYMBOLS 100 ... Electromagnetic flowmeter, 101 ... Measuring tube, 102 ... Excitation coil, 103 ... Electrode, 104 ... Ground electrode, 105 ... Buffer, 106 ... Differential amplifier circuit, 107 ... Flow rate signal sampling part, 108 ... Excitation signal sampling part, DESCRIPTION OF SYMBOLS 109 ... Resistance signal sampling part 110 ... Control part 111 ... Circuit control part 112 ... Operation part 113 ... Diagnosis part 120 ... Excitation circuit 130 ... Resistance measurement output circuit 141 ... Display part 142 ... Operation reception part , 143 ... current output unit, 144 ... pulse output unit, 145 ... status output unit, 146 ... communication unit

Claims (5)

An electromagnetic flowmeter that applies a magnetic field generated by an excitation current to a fluid to be measured flowing in a measurement tube and measures a flow rate of the fluid to be measured based on a detection signal generated in an electrode provided in the measurement tube,
An excitation circuit for generating an excitation current having a positive excitation period and a negative excitation period;
A resistance measurement output circuit for outputting a resistance measurement current having a rectangular wave shape for measuring the resistance of the fluid to be measured to the electrode;
A first level difference which is a period corresponding to the positive excitation period and which is a level difference of a detection signal in a period corresponding to the first half of the period of the resistance measurement current and a period corresponding to the second half of the period; and the negative excitation period A second level difference that is a level difference of a detection signal in a period corresponding to the first half of the period of the resistance measurement current and a period corresponding to the second half of the period, and the first level difference And a diagnostic unit for detecting an abnormality that changes the electrode potential based on a noise level obtained from a difference between the second level difference and the second level difference;
An electromagnetic flow meter comprising: The diagnostic unit determines that an abnormality that changes the electrode potential has occurred when a diagnostic noise level obtained by averaging the absolute values of successive noise levels is equal to or greater than a predetermined reference value. The electromagnetic flow meter according to claim 1. 3. The electromagnetic flow meter according to claim 1, wherein the diagnosis unit suggests a cause of an abnormality according to a predetermined criterion when an abnormality that changes the electrode potential is detected.   The electromagnetic flowmeter according to claim 1, wherein the resistance measurement current is synchronized with the excitation current at a frequency that is an integral multiple of the frequency of the excitation current. The abnormality that fluctuates the electrode potential detected by the diagnostic unit includes any of bubble generation, low conductivity, slurry fluid, electrode corrosion due to the fluid to be measured, and adhesion of insulating foreign matter to the electrode. The electromagnetic flowmeter of any one of Claims 1-4.