CN119779423B - Empty pipe detection method and system of electromagnetic flowmeter and electromagnetic flowmeter - Google Patents
Empty pipe detection method and system of electromagnetic flowmeter and electromagnetic flowmeterInfo
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- CN119779423B CN119779423B CN202411978993.XA CN202411978993A CN119779423B CN 119779423 B CN119779423 B CN 119779423B CN 202411978993 A CN202411978993 A CN 202411978993A CN 119779423 B CN119779423 B CN 119779423B
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Abstract
The invention relates to the technical field of detection of measuring instruments, and discloses a blank pipe detection method and a system of an electromagnetic flowmeter, and the electromagnetic flowmeter, wherein the method comprises the steps of applying an excitation signal to a signal electrode in a preset time period; the method comprises the steps of obtaining a signal to be sampled in a preset time period, calculating empty pipe detection voltage between a signal electrode and a grounding electrode according to the signal to be sampled, calculating conductivity of a medium in a pipe according to a first preset value, a second preset value and the empty pipe detection voltage, and detecting whether an electromagnetic flowmeter is in an empty pipe state according to the conductivity. The embodiment of the invention can reduce the influence of the common mode signal on empty pipe detection, and further improve the empty pipe detection accuracy of the electromagnetic flowmeter.
Description
Technical Field
The invention relates to the technical field of detection of measuring instruments, in particular to a blank pipe detection method and system of an electromagnetic flowmeter and the electromagnetic flowmeter.
Background
The electromagnetic flowmeter is a flow measuring instrument based on Faraday's law of electromagnetic induction, and is mainly composed of a pipeline cavity, a pair of signal electrodes, an exciting coil, an exciting driving unit and a signal processing unit, wherein the exciting driving unit drives the exciting coil to generate a magnetic field perpendicular to the flowing direction of fluid, when the fluid passes through the pipeline cavity at an average flow velocity, the signal electrodes output induced potential signals, at this time, the signal processing unit calculates the average flow velocity of the fluid according to the received induced potential signals, and then calculates the flow flowing through the pipeline cavity according to the cross-sectional area of the pipeline.
When the electromagnetic flowmeter is in an empty pipe state, namely fluid in a pipeline is not full, the electromagnetic flowmeter is easy to be subjected to strong electromagnetic interference, so that a measurement signal received by the signal processing unit is distorted, and the accuracy of subsequent flow calculation is affected. One of the preconditions for ensuring reliable measurement is therefore the need for the pipe to be in a full condition.
In the related art, an alarm prompt is needed when the fluid is not full of the pipeline. Most empty pipe alarm modes judge empty pipe states by measuring solution resistance, however, empty pipe signals always exist in a common mode, and when the grounding is poor or the grounding electrode is adopted for grounding, common mode interference is introduced at the same time, so that whether the current pipeline is in the empty pipe state or not cannot be correctly identified, and false alarm or missing alarm is caused.
Disclosure of Invention
In view of the above, the invention provides a method and a system for detecting an empty pipe of an electromagnetic flowmeter and the electromagnetic flowmeter, so as to solve the technical problem that the empty pipe alarm is misreported or missed due to common mode interference introduced when the grounding electrode is grounded or the grounding electrode is adopted in the related technology.
In a first aspect, the present invention provides a method for detecting an empty pipe of an electromagnetic flowmeter, including:
Applying an excitation signal to the signal electrode in a preset time period, wherein the preset time period is the front section of each half excitation period of the excitation signal;
Acquiring a signal to be sampled in a preset time period, and calculating an empty pipe detection voltage between a signal electrode and a grounding electrode according to the signal to be sampled;
Calculating the conductivity of the medium in the tube according to the first preset value, the second preset value and the empty tube detection voltage;
and detecting whether the electromagnetic flowmeter is in a hollow tube state according to the conductivity.
In an alternative embodiment, the calculating the empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled includes:
Sampling a signal to be sampled in a preset time of a positive half period of an excitation period, and calculating to obtain a first average voltage;
Sampling a signal to be sampled in a preset time of a negative half period in an excitation period, and calculating to obtain a second average voltage;
and taking the difference between the first average voltage and the second average voltage to obtain the empty pipe detection voltage between the signal electrode and the grounding electrode.
In an alternative embodiment, the duration of the excitation period is T, the duration of the preset time period is T, and the duration T of the preset time period and the duration T of the excitation period satisfy the following relationship that T is more than or equal to 0 and less than or equal to T/6.
In a second aspect, the invention provides an empty pipe detection system of an electromagnetic flowmeter, which comprises a signal electrode, a grounding electrode, an excitation module, an empty pipe sampling module and a microprocessor;
The signal electrode is fixedly connected to a pipeline of the electromagnetic flowmeter and is in contact with a medium in the pipeline of the electromagnetic flowmeter;
The grounding electrode is connected with the signal grounding end;
the excitation module is connected with the signal electrode and used for applying an excitation signal to the signal electrode;
the empty pipe sampling module is connected with the signal electrode and used for acquiring an output signal of the signal electrode and generating a signal to be sampled according to the output signal of the signal electrode;
The microprocessor is respectively connected with the excitation module and the empty pipe sampling module and is used for controlling the excitation module to apply excitation signals to the signal electrodes in a preset time period; the electromagnetic flowmeter comprises a signal electrode, a grounding electrode, a preset time period, a first preset value, a second preset value, a first empty tube detection voltage, a second empty tube detection voltage, and an electromagnetic flowmeter.
In an alternative embodiment, the microprocessor includes:
The first average voltage calculation unit is used for sampling a signal to be sampled in a preset time of a positive half cycle of an excitation period and calculating to obtain a first average voltage;
The second average voltage calculation unit is used for sampling the signal to be sampled in the preset time of the negative half period in the excitation period and calculating to obtain a second average voltage;
and the empty pipe detection voltage calculation unit is used for carrying out difference on the first average voltage and the second average voltage to obtain the empty pipe detection voltage between the signal electrode and the grounding electrode.
In an alternative embodiment, the signal electrodes comprise a first signal electrode and a second signal electrode, and the excitation module comprises a square wave generating chip, a first capacitor, a second capacitor, a third capacitor, a first resistor, a second resistor and a third resistor;
The input pins of the square wave generating chip are connected with the microprocessor, the ground pins of the square wave generating chip are directly grounded, the power supply pins of the square wave generating chip are connected with a power supply, the output pins of the square wave generating chip are connected with one end of a first capacitor, the other end of the first capacitor is connected with one end of a first resistor, the other end of the first resistor is respectively connected with one end of a second resistor and one end of a third resistor, the other end of the third resistor is directly grounded, the other end of the second resistor is respectively connected with one end of a second capacitor and one end of a third capacitor, and the other end of the second capacitor and the other end of the third capacitor are respectively connected with a signal electrode.
In an alternative embodiment, the empty pipe sampling module comprises a band-pass filtering unit, a rectifying unit and a low-pass filtering unit which are connected in sequence;
The band-pass filtering unit is used for obtaining the output signal of the sampling electrode and carrying out band-pass filtering on the output signal of the sampling electrode to obtain an empty pipe detection alternating current signal;
the rectification unit is used for rectifying the empty pipe detection alternating current signal to obtain an empty pipe detection ripple signal;
The low-pass filtering unit is used for carrying out low-pass filtering on the empty pipe detection ripple signal to obtain a signal to be sampled.
In an alternative implementation mode, the band-pass filtering unit comprises a fourth capacitor, a fifth capacitor, a fourth resistor and a fifth resistor, wherein one end of the fourth capacitor is electrically connected with the output end of the signal electrode, the other end of the fourth capacitor is respectively connected with one end of the fourth resistor and one end of the fifth resistor, the other end of the fourth resistor is directly grounded, the other end of the fifth resistor is respectively connected with one end of the fifth capacitor and the input end of the rectifying unit, and the other end of the fifth capacitor is directly grounded;
The low-pass filter unit comprises a sixth resistor, a seventh resistor, a sixth capacitor and a seventh capacitor, wherein one end of the sixth resistor is connected with the output end of the rectifying unit, the other end of the sixth resistor is respectively connected with one end of the sixth capacitor and one end of the seventh resistor, the other end of the sixth capacitor and one end of the seventh capacitor are directly grounded, and the other end of the seventh capacitor and the other end of the seventh resistor are connected with the input end of the microcontroller.
In an alternative embodiment, the band pass filter has a bandwidth of 150Hz-50kHz.
The invention provides an electromagnetic flowmeter, which comprises a pipeline, a signal electrode, a grounding electrode and an excitation module, wherein the grounding electrode is connected with a signal grounding end, and the excitation module is used for applying a magnetic field to a medium in the pipeline;
the excitation module is connected with the signal electrode and used for applying an excitation signal to the signal electrode;
the empty pipe sampling module is connected with the signal electrode and used for acquiring an output signal of the signal electrode and generating a signal to be sampled according to the output signal of the signal electrode;
The microprocessor is respectively connected with the excitation module and the empty pipe sampling module and is used for controlling the excitation module to apply excitation signals to the signal electrodes in a preset time period; the electromagnetic flowmeter comprises a signal electrode, a grounding electrode, a preset time period, a first preset value, a second preset value, a first empty tube detection voltage, a second empty tube detection voltage, and an electromagnetic flowmeter.
According to the embodiment of the invention, the excitation signal is applied to the signal electrode at the front section of each half excitation period of the excitation signal, and the empty pipe detection voltage for eliminating common mode interference between the signal electrode and the grounding electrode corresponding to the period of applying the excitation signal is acquired, so that the conductivity is calculated, the influence of the common mode signal on the empty pipe detection is reduced, and the empty pipe detection accuracy of the electromagnetic flowmeter is further improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flow chart of a method for detecting empty pipe of an electromagnetic flowmeter according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a conventional electromagnetic flowmeter according to an embodiment of the present invention;
Fig. 3 is a waveform diagram of an excitation signal and an excitation signal according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of an empty pipe detection system of an electromagnetic flowmeter according to an embodiment of the present invention;
FIG. 5 is a schematic circuit diagram of an excitation module according to an embodiment of the invention;
fig. 6 is a schematic circuit diagram of an empty pipe sampling module according to an embodiment of the present invention.
Reference numerals:
1. The excitation module, the 2-blank pipe sampling module, the 201, the band-pass filtering unit, the 202, the rectifying unit, the 203, the low-pass filtering unit, the A, the first signal electrode, the B, the second signal electrode, the U1, the square wave generating chip, the AMP1, the first operational amplifier, the AMP2, the second operational amplifier, the AMP3, the third operational amplifier, the D1, the first diode, the D2, the second diode, the C13, the first capacitor, the C11, the second capacitor, the C12, the third capacitor, the C211, the fourth capacitor, the C212, the fifth capacitor, the C241, the sixth capacitor, the C242, the seventh capacitor, the C21, the eighth capacitor, the C22, the ninth capacitor, the R11, the first resistor, the R12, the second resistor, the R13, the third resistor, the R212, the fourth resistor, the R211, the fifth resistor, the R241, the sixth resistor, the R242, the seventh resistor, the R222, the eighth resistor, the R221, the ninth resistor, the R231, the tenth resistor, the R232, the eleventh resistor, the R233, the twelfth resistor, the R234, the thirteenth resistor and the thirteenth resistor.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be noted that the positional or positional relationship indicated by the terms such as "upper", "lower", "left", "right", "inner", "outer", etc. are based on the positional or positional relationship shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected, mechanically connected, electrically connected, directly connected, indirectly connected via an intermediate medium, and in communication with each other between two elements, and wirelessly connected, or wired. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
In addition, the technical features of the different embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
According to an embodiment of the present invention, there is provided a method for empty pipe detection of an electromagnetic flowmeter, it being noted that the steps shown in the flowchart of the drawings may be performed in a computer system such as a set of computer executable instructions, and that although a logical order is shown in the flowchart, in some cases the steps shown or described may be performed in an order different from that herein.
Fig. 1 is a schematic flow chart of a method for detecting empty pipe of an electromagnetic flowmeter according to an embodiment of the invention, as shown in fig. 1, the flow chart includes the following steps:
and step S101, applying an excitation signal to the signal electrode in a preset time period, wherein the preset time period is the front section of each half excitation period of the excitation signal.
As shown in FIG. 2, the conventional electromagnetic flowmeter comprises a pipeline, an excitation coil (coil 1 and coil 2), signal electrodes (a first signal electrode A and a first signal electrode B), a grounding electrode, an excitation module and a flow sampling module, wherein the signal electrodes and the grounding electrode are arranged on the pipeline, fluid in the pipeline is connected with a signal grounding end through the grounding electrode, and the flow sampling module is connected with the grounding electrode. The exciting module is used for outputting exciting signals to the exciting coil to enable the exciting coil to generate a magnetic field perpendicular to the flowing direction of the pipeline fluid, when the fluid passes through the pipeline cavity at the average flow velocity, the magnetic induction wire is cut, so that induced electromotive force is generated, the induced electromotive force is collected by the signal electrode, the signal electrode transmits induced potential signals to the flow sampling module, at the moment, the flow sampling module calculates the average flow velocity of the fluid according to the received induced potential signals, and then calculates the flow flowing through the pipeline cavity according to the cross section area of the pipeline body.
In step S101, the excitation signal is an alternating signal applied to the excitation coil by the excitation module of the electromagnetic flowmeter, and the alternating signal is periodically changed, so that the excitation coil generates an alternating magnetic field, and the alternating magnetic field causes the fluid to cut the induction line when flowing through the pipeline, thereby generating induced electromotive force. For one excitation period, the voltage corresponding to the first half of the excitation period is positive, and the voltage corresponding to the second half of the excitation period is negative.
The excitation signal is preferably a square wave signal with a duty cycle of 50%.
In one example, the excitation signal may be a 6.25Hz low frequency square wave excitation signal.
Under the action of the excitation signal, the alternating magnetic field generated by the excitation coil changes once in each half excitation period, the magnetic field is unstable in the initial period of the change, and the accuracy of the subsequent flow calculation is reduced due to the influence of poor grounding or common mode interference caused by grounding of a third electrode. Therefore, the embodiment of the invention carries out the empty pipe detection on the electromagnetic flowmeter at the initial stage of the magnetic field direction change, can better eliminate common mode interference and further improves the empty pipe detection precision.
In one example, for the flow sampling module, induced electromotive force sampling and flow calculation are not performed at the initial stage of magnetic field direction change, and the influence of the excitation signal on flow calculation is reduced during empty pipe detection.
The preset time period may be set according to actual requirements, and is not specifically limited herein.
In one example, the excitation signal and the excitation signal are synchronized, and the time at which the excitation module outputs the excitation signal may be controlled by a program such that the excitation signal is synchronously applied to the signal electrode in the front of each half of the excitation period of the excitation signal.
In an alternative embodiment, the duration of the excitation period is T, the duration of the preset time period is T, and the duration T of the preset time period and the duration T of the excitation period satisfy the following relationship that T is more than or equal to 0 and less than or equal to T/6.
In one example, as shown in fig. 3, assuming that the excitation period of the excitation signal is 160ms, the excitation signal may be synchronously applied to the signal electrodes during the 0ms to 20ms, and 80ms to 100ms of the excitation period for each excitation period.
Of course, after the preceding half of the excitation period, the excitation signal may be applied to the signal electrodes simultaneously, and the excitation signal may be at a low level.
Step S102, obtaining a signal to be sampled in a preset time period, and calculating the empty pipe detection voltage between the signal electrode and the grounding electrode according to the signal to be sampled.
In step S102, the signal to be sampled may be directly acquired, and the empty pipe detection voltage after the common mode signal is eliminated may be directly calculated according to the acquired signal to be sampled. Wherein the empty pipe detection voltage is one of the parameters for calculating the conductivity of the medium in the pipe.
Step S103, calculating the conductivity of the medium in the tube according to the first preset value, the second preset value and the empty tube detection voltage.
In step S103, the first preset value and the second preset value may be calibrated in advance, and specific values may be set according to actual requirements, which are not limited herein.
Step S104, detecting whether the electromagnetic flowmeter to be detected is in an empty pipe state according to the conductivity.
In step S104, the empty pipe detection voltage after the common mode signal is eliminated is used as one of the parameters of the conductivity, so that the influence of the common mode signal on the empty pipe detection can be reduced, and the accuracy of the empty pipe detection can be improved. When the fluid conductivity of the pipeline is lower than a set threshold value, the generated induced electromotive force is very weak and even cannot be detected, so that the flowmeter cannot work normally, and an empty pipe alarm is triggered.
According to the embodiment of the invention, the excitation signal is applied to the signal electrode at the front section of each half excitation period of the excitation signal, and the empty pipe detection voltage for eliminating common mode interference between the signal electrode and the grounding electrode corresponding to the period of applying the excitation signal is acquired, so that the conductivity is calculated, the influence of the common mode signal on the empty pipe detection is reduced, and the empty pipe detection accuracy of the electromagnetic flowmeter is further improved.
In an alternative embodiment, the step S102 further includes:
Step S1021, sampling a signal to be sampled in a preset time of a positive half period of an excitation period, and calculating to obtain a first average voltage;
step S1022, sampling the signal to be sampled in the preset time of the negative half period in the excitation period, and calculating to obtain a second average voltage;
Step S1023, the first average voltage and the second average voltage are subjected to difference to obtain the empty pipe detection voltage between the signal electrode and the grounding electrode.
The method comprises the steps of obtaining a signal to be sampled in a preset time period, obtaining the waveform of the signal to be sampled in the preset time period according to the excitation signal and the excitation signal through a series of processing, obtaining the average voltage of the signal to be sampled corresponding to the preset time period when the preset time period is in the positive half excitation period of the excitation signal, obtaining the average voltage of the signal to be sampled corresponding to the preset time period when the preset time period is in the negative half excitation period of the excitation signal, and finally subtracting the average voltage and the average voltage to eliminate common mode signal interference, thereby obtaining the empty pipe detection voltage between the signal electrode and the grounding electrode.
According to the embodiment of the invention, the common-mode interference can be eliminated by means of averaging and subtracting the signals to be sampled, and finally, the conductivity calculation is carried out according to the empty pipe detection voltage after the common-mode interference is eliminated, so that the accurate empty pipe detection of the electromagnetic flowmeter can be realized under the condition of poor grounding or direct grounding through the grounding electrode.
The embodiment also provides an empty pipe detection system of an electromagnetic flowmeter, which is used for realizing the above embodiment and the preferred implementation manner, and the description is omitted. As used below, the term "module" may be a combination of software and/or hardware that implements a predetermined function. While the means described in the following embodiments are preferably implemented in software, implementation in hardware, or a combination of software and hardware, is also possible and contemplated.
The present embodiment provides an empty pipe detection system of an electromagnetic flowmeter, as shown in fig. 4 (omitting a microprocessor), which includes a signal electrode, a ground electrode, an excitation module 1, an empty pipe sampling module 2 and a microprocessor (not shown in fig. 4).
The signal electrode is fixedly connected to a pipeline of the electromagnetic flowmeter and is in contact with a medium in the pipeline of the electromagnetic flowmeter;
Of course, the number of the signal electrodes includes but is not limited to 2, but can also be 3, 4, 6, etc., the number of the electrodes may have a certain influence on the accuracy of empty pipe detection, the greater the number of the electrodes, the higher the measurement accuracy, and the stability and accuracy of the measurement signals can be improved by a plurality of signal electrodes. The number of signal electrodes may be set according to the specific case, and is not particularly limited herein.
The electromagnetic flowmeter comprises an excitation module 1, an empty pipe sampling module 2, a microprocessor, a signal electrode, an excitation module 1, an empty pipe sampling module 2, a first preset value, a second preset value and an empty pipe detection voltage, wherein the excitation module 1 is connected with the signal electrode, the excitation module 1 is used for applying an excitation signal to the signal electrode, the empty pipe sampling module 2 is connected with the signal electrode, the empty pipe sampling module 2 is used for obtaining an output signal of the signal electrode and generating a signal to be sampled according to the output signal of the signal electrode, the microprocessor is respectively connected with the excitation module 1 and the empty pipe sampling module 2, the microprocessor is used for controlling the excitation module to apply the excitation signal to the signal electrode in a preset time period, the preset time period is the front part of each half excitation period of the excitation signal, the signal to be sampled in the preset time period is also used for obtaining the signal to be sampled, the empty pipe detection voltage between the signal electrode and the ground electrode is calculated according to the signal to be sampled, the electrical conductivity of a medium in the pipe is calculated according to the first preset value, the second preset value and the empty pipe detection voltage.
In some alternative embodiments, the microprocessor includes a first average voltage calculation unit, a second average voltage calculation unit, and an empty pipe detection voltage calculation unit.
The method comprises the steps of carrying out sampling on a signal to be sampled in a preset time of a positive half cycle in an excitation period and calculating the signal to be sampled to obtain a first average voltage, carrying out sampling on the signal to be sampled in the preset time of a negative half cycle in the excitation period and calculating the signal to be sampled to obtain a second average voltage, and carrying out blank pipe detection voltage calculation on the first average voltage and the second average voltage to obtain a blank pipe detection voltage between a signal electrode and a ground electrode.
In an alternative embodiment, as shown in fig. 5, the signal electrode includes a first signal electrode a and a second signal electrode B, and the excitation module 1 includes a square wave generating chip U1, a first capacitor C13, a second capacitor C11, a third capacitor C12, a first resistor R11, a second resistor R12, and a third resistor R13;
The input pin (A pin and B pin) of the square wave generating chip U1 is connected with the microprocessor, the ground pin (GND pin) of the square wave generating chip is directly grounded, the power pin (VCC) of the square wave generating chip U1 is connected with a power supply, the output pin (Y pin) of the square wave generating chip U1 is connected with one end of a first capacitor C13, the other end of the first capacitor C13 is connected with one end of a first resistor R11, the other end of the first resistor R11 is respectively connected with one end of a second resistor R12 and one end of a third resistor R13, the other end of the third resistor R13 is directly grounded, the other end of the second resistor R12 is respectively connected with one end of a second capacitor C11 and one end of a third capacitor C12, and the other end of the second capacitor C11 and the other end of the third capacitor C12 are both connected with a signal electrode.
The two input pins (pin a and pin B) of the square wave generating chip U1 are connected to the microprocessor, and are used for receiving PWM signals sent by the microprocessor, so that the excitation module 1 can output square wave signals to the first signal electrode a and the second signal electrode B. The power supply pin (VCC) of the square wave generating chip U1 is connected to a power supply to determine the magnitude of the positive and negative voltages of the square wave signal output by the excitation module 1.
In one example, assuming that the power supply voltage is 2.5V, square wave signals of ±2.5V are output to the first signal electrode a and the second signal electrode B. Wherein the supply voltage may also be used as a reference voltage.
Of course, the output pins of the square wave generating chip U1 are not limited to two paths, and when a plurality of signal electrodes are provided, the output pins thereof can be correspondingly increased.
It should be noted that, in fig. 5, vx1 and Vx2 correspond to the voltage values between the first signal electrode a and the second signal electrode relative to the ground electrode, respectively, and may be directly obtained by the hollow tube sampling module, and Rx1 and Rx2 correspond to the equivalent resistances between the first signal electrode a and the second signal electrode relative to the ground electrode, that is, the fluid resistances, respectively.
In an alternative embodiment, the first preset value and the second preset value may be defined by kirchhoff's law according to Vx1 and Vx2, the resistance values of the respective resistors of the excitation circuit, and the reference voltage.
In an alternative embodiment, as shown in fig. 6, the empty pipe sampling module 2 includes a band-pass filtering unit 201, a rectifying unit 202, and a low-pass filtering unit 203 connected in sequence;
Specifically, the band-pass filtering unit 201 is configured to obtain an output signal of the sampling electrode, and perform band-pass filtering on the output signal of the sampling electrode to obtain an empty pipe detection ac signal, the rectifying unit 202 is configured to rectify the empty pipe detection ac signal to obtain an empty pipe detection ripple signal, and the low-pass filtering unit 203 is configured to perform low-pass filtering on the empty pipe detection ripple signal to obtain a signal to be sampled.
In an alternative embodiment, the band-pass filtering unit 201 includes a fourth capacitor C211, a fifth capacitor C212, a fourth resistor R212 and a fifth resistor R211, wherein one end of the fourth capacitor C211 is electrically connected to the output end of the signal electrode, the other end of the fourth capacitor C211 is respectively connected to one end of the fourth resistor R212 and one end of the fifth resistor R211, the other end of the fourth resistor R212 is directly grounded, and the other end of the fifth resistor R211 is respectively connected to one end of the fifth capacitor C212 and the input end of the rectifying unit 202, and the other end of the fifth capacitor C212 is directly grounded.
The low-pass filtering unit 203 comprises a sixth resistor R241, a seventh resistor R242, a sixth capacitor C241 and a seventh capacitor C242, wherein one end of the sixth resistor R241 is connected with the output end of the rectifying unit 202, the other end of the sixth resistor R241 is respectively connected with one end of the sixth capacitor C241 and one end of the seventh resistor R242, the other end of the sixth capacitor C241 and one end of the seventh capacitor C242 are directly grounded, and the other end of the seventh capacitor C242 and the other end of the seventh resistor R242 are connected with the input end of the microcontroller.
In an alternative embodiment, the rectifying unit 202 includes a first operational amplifier AMP1, a second operational amplifier AMP2, a third operational amplifier AMP3, an eighth resistor R222, a ninth resistor R221, a tenth resistor R231, an eleventh resistor R232, a twelfth resistor R233, a thirteenth resistor R234, a fourteenth resistor R235, a first diode D1, and a second diode D2;
The positive input end of the first operational amplifier AMP1 is connected to the output end of the band-pass filter unit 201, the negative input end of the first operational amplifier AMP1 is connected to one end of the eighth resistor R222 and one end of the ninth resistor R221, the other end of the eighth resistor R222 is directly grounded, the other end of the ninth resistor R221 is connected to the output end of the first operational amplifier AMP1, one end of the tenth resistor R231 and one end of the eleventh resistor R232, the other end of the tenth resistor R231 is connected to one end of the twelfth resistor R233, one end of the first diode AMP1 and the negative input end of the second operational amplifier AMP2, the positive input end of the second operational amplifier AMP2 is directly grounded, the output end of the second operational amplifier AMP2 is connected to one end of the first diode D1 and one end of the second diode D2, the other end of the twelfth resistor R233 is connected to the other end of the second diode D2 and one end of the thirteenth resistor R234, the other end of the eleventh resistor R232 is connected to the negative input end of the third operational amplifier 3, the thirteenth resistor R234 and the other end of the third operational amplifier 3 is connected to the positive input end of the fourth operational amplifier 235, and the positive input end of the third operational amplifier 3 is directly connected to the fourteenth filter unit 204.
In summary, the signal to be sampled in the embodiment of the present invention is directly output through the empty pipe sampling module 2, and is converted into the signal to be sampled which can be directly obtained by performing operations such as voltage division, band-pass filtering, rectification, low-pass filtering and the like on the voltage values Vx1 and Vx2 between the first signal electrode a and the second signal electrode B relative to the ground electrode, and the common mode interference in the signal to be sampled can be removed by averaging and making differences on the waveforms of the signal to be sampled, so as to obtain an empty pipe detection voltage without common mode interference, and at this time, according to the calibrated preset value and the empty pipe detection voltage, the accurate empty pipe detection for judging whether the electromagnetic flowmeter is the electrical conductivity of the empty pipe is obtained, so that the poor grounding or the accurate empty pipe detection of the electromagnetic flowmeter can be realized under the condition that the ground electrode is directly grounded.
In an alternative embodiment, the bandwidth of the bandpass filtering is 150Hz-50kHz.
Further functional descriptions of the above respective modules and units are the same as those of the above corresponding embodiments, and are not repeated here.
The embodiment of the invention also provides an electromagnetic flowmeter, which comprises a pipeline, a signal electrode, a grounding electrode and an excitation module, wherein the grounding electrode is connected with the signal grounding end, the excitation module is used for applying a magnetic field to a medium in the pipeline,
Secondly, the system also comprises an excitation module, an empty pipe sampling module and a microprocessor;
the excitation module is connected with the signal electrode and is used for applying an excitation signal to the signal electrode;
The system comprises a signal electrode, an empty pipe sampling module, a microprocessor, a first preset value, a second preset value and an empty pipe detection voltage, wherein the empty pipe sampling module is connected with the signal electrode and is used for acquiring an output signal of the signal electrode and generating a signal to be sampled according to the output signal of the signal electrode, the microprocessor is respectively connected with the excitation module and the empty pipe sampling module and is used for controlling the excitation module to apply an excitation signal to the signal electrode in a preset time period, the preset time period is the front section of each half excitation period of the excitation signal, the microprocessor is also used for acquiring the signal to be sampled in the preset time period and calculating the empty pipe detection voltage between the signal electrode and the grounding electrode according to the signal to be sampled, the conductivity of a medium in a pipe is calculated according to the first preset value, the second preset value and the empty pipe detection voltage, and whether the electromagnetic flowmeter is in an empty pipe state is detected according to the conductivity.
The methods according to embodiments of the present invention described above may be implemented in hardware, firmware, or as computer code which may be recorded on a storage medium, or stored originally in a remote storage medium or a non-transitory machine-readable storage medium and to be stored in a local storage medium, downloaded over a network, so that the methods described herein may be stored on such software processes on storage media using general purpose computers, special purpose processors, or programmable or special purpose hardware. The storage medium may be a magnetic disk, an optical disk, a read-only memory, a random-access memory, a flash memory, a hard disk, a solid state disk, or the like, and further, the storage medium may further include a combination of the above types of memories. It will be appreciated that a computer, processor, microprocessor controller or programmable hardware includes a storage element that can store or receive software or computer code that, when accessed and executed by the computer, processor or hardware, implements the methods illustrated by the above embodiments.
Although embodiments of the present invention have been described in connection with the accompanying drawings, various modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope of the invention as defined by the appended claims.
Claims (8)
1. A method for empty pipe detection of an electromagnetic flowmeter, comprising:
Applying an excitation signal to the signal electrode in a preset time period, wherein the preset time period is the front section of each half excitation period of the excitation signal;
Acquiring a signal to be sampled in a preset time period, and calculating an empty pipe detection voltage between a signal electrode and a grounding electrode according to the signal to be sampled;
Calculating the conductivity of the medium in the tube according to the first preset value, the second preset value and the empty tube detection voltage;
detecting whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity;
wherein, the calculating the empty pipe detection voltage between the signal electrode and the grounding electrode according to the signal to be sampled includes:
Sampling a signal to be sampled in a preset time of a positive half period of an excitation period, and calculating to obtain a first average voltage;
Sampling a signal to be sampled in a preset time of a negative half period in an excitation period, and calculating to obtain a second average voltage;
The first average voltage and the second average voltage are subjected to difference to obtain an empty pipe detection voltage between the signal electrode and the grounding electrode;
The duration of the excitation period is T, the duration of the preset time period is T, and the duration T of the preset time period and the duration T of the excitation period meet the following relation that T is more than or equal to 0 and less than or equal to T/6.
2. The empty pipe detection system of the electromagnetic flowmeter is characterized by comprising a signal electrode, a grounding electrode, an excitation module, an empty pipe sampling module and a microprocessor;
The signal electrode is fixedly connected to a pipeline of the electromagnetic flowmeter and is in contact with a medium in the pipeline of the electromagnetic flowmeter;
The grounding electrode is connected with the signal grounding end;
the excitation module is connected with the signal electrode and is used for applying an excitation signal to the signal electrode;
the empty pipe sampling module is connected with the signal electrode and used for acquiring an output signal of the signal electrode and generating a signal to be sampled according to the output signal of the signal electrode;
the system comprises an excitation module, a microprocessor, a blank pipe detection voltage calculation module, a first preset value, a second preset value and a blank pipe detection voltage, wherein the microprocessor is respectively connected with the excitation module and the blank pipe sampling module and is used for controlling the excitation module to apply excitation signals to signal electrodes in a preset time period, the preset time period is the front section of each half excitation period of the excitation signals, the microprocessor is also used for obtaining signals to be sampled in the preset time period, calculating the blank pipe detection voltage between the signal electrodes and the ground electrodes according to the signals to be sampled, calculating the conductivity of media in the pipe according to the first preset value, the second preset value and the blank pipe detection voltage, and detecting whether the electromagnetic flowmeter is in a blank pipe state according to the conductivity, wherein the blank pipe detection voltage between the signal electrodes and the ground electrodes is calculated according to the signals to be sampled, and the method comprises the following steps:
Sampling a signal to be sampled in a preset time of a positive half period of an excitation period, and calculating to obtain a first average voltage;
Sampling a signal to be sampled in a preset time of a negative half period in an excitation period, and calculating to obtain a second average voltage;
The first average voltage and the second average voltage are subjected to difference to obtain an empty pipe detection voltage between the signal electrode and the grounding electrode;
The duration of the excitation period is T, the duration of the preset time period is T, and the duration T of the preset time period and the duration T of the excitation period meet the following relation that T is more than or equal to 0 and less than or equal to T/6.
3. The system of claim 2, wherein the microprocessor comprises:
The first average voltage calculation unit is used for sampling a signal to be sampled in a preset time of a positive half cycle of an excitation period and calculating to obtain a first average voltage;
The second average voltage calculation unit is used for sampling the signal to be sampled in the preset time of the negative half period in the excitation period and calculating to obtain a second average voltage;
and the empty pipe detection voltage calculation unit is used for carrying out difference on the first average voltage and the second average voltage to obtain the empty pipe detection voltage between the signal electrode and the grounding electrode.
4. The system of claim 2 or 3, wherein the signal electrodes comprise a first signal electrode and a second signal electrode, and the excitation module comprises a square wave generating chip, a first capacitor, a second capacitor, a third capacitor, a first resistor, a second resistor, and a third resistor;
The input pins of the square wave generating chip are connected with the microprocessor, the ground pins of the square wave generating chip are directly grounded, the power supply pins of the square wave generating chip are connected with a power supply, the output pins of the square wave generating chip are connected with one end of a first capacitor, the other end of the first capacitor is connected with one end of a first resistor, the other end of the first resistor is respectively connected with one end of a second resistor and one end of a third resistor, the other end of the third resistor is directly grounded, the other end of the second resistor is respectively connected with one end of a second capacitor and one end of a third capacitor, and the other end of the second capacitor and the other end of the third capacitor are respectively connected with a signal electrode.
5. The system according to claim 2, wherein the empty pipe sampling module comprises a band-pass filtering unit, a rectifying unit and a low-pass filtering unit which are connected in sequence;
The band-pass filtering unit is used for obtaining the output signal of the sampling electrode and carrying out band-pass filtering on the output signal of the sampling electrode to obtain an empty pipe detection alternating current signal;
the rectification unit is used for rectifying the empty pipe detection alternating current signal to obtain an empty pipe detection ripple signal;
The low-pass filtering unit is used for carrying out low-pass filtering on the empty pipe detection ripple signal to obtain a signal to be sampled.
6. The system of claim 5, wherein the band-pass filter unit comprises a fourth capacitor, a fifth capacitor, a fourth resistor and a fifth resistor, wherein one end of the fourth capacitor is electrically connected with the output end of the signal electrode, the other end of the fourth capacitor is respectively connected with one end of the fourth resistor and one end of the fifth resistor, the other end of the fourth resistor is directly grounded, the other end of the fifth resistor is respectively connected with one end of the fifth capacitor and the input end of the rectifying unit, and the other end of the fifth capacitor is directly grounded;
The low-pass filter unit comprises a sixth resistor, a seventh resistor, a sixth capacitor and a seventh capacitor, wherein one end of the sixth resistor is connected with the output end of the rectifying unit, the other end of the sixth resistor is respectively connected with one end of the sixth capacitor and one end of the seventh resistor, the other end of the sixth capacitor and one end of the seventh capacitor are directly grounded, and the other end of the seventh capacitor and the other end of the seventh resistor are connected with the input end of the microcontroller.
7. The system of claim 5, wherein the band pass filter has a bandwidth of 150Hz-50kHz.
8. The electromagnetic flowmeter comprises a pipeline, a signal electrode, a grounding electrode and an excitation module, wherein the grounding electrode is connected with a signal grounding end, and the excitation module is used for applying a magnetic field to a medium in the pipeline;
the excitation module is connected with the signal electrode and used for applying an excitation signal to the signal electrode;
the empty pipe sampling module is connected with the signal electrode and used for acquiring an output signal of the signal electrode and generating a signal to be sampled according to the output signal of the signal electrode;
The system comprises an excitation module, a microprocessor, a blank pipe detection voltage calculation module, a first preset value, a second preset value and a blank pipe detection voltage, wherein the microprocessor is respectively connected with the excitation module and the blank pipe sampling module and is used for controlling the excitation module to apply excitation signals to signal electrodes in a preset time period, the preset time period is the front section of each half excitation period of the excitation signals, the microprocessor is also used for acquiring signals to be sampled in the preset time period, calculating the blank pipe detection voltage between the signal electrodes and the ground electrodes according to the signals to be sampled, calculating the conductivity of media in the pipe according to the first preset value, the second preset value and the blank pipe detection voltage, and detecting whether the electromagnetic flowmeter is in a blank pipe state according to the conductivity, wherein the blank pipe detection voltage between the signal electrodes and the ground electrodes is calculated according to the signals to be sampled, and the method comprises the following steps:
Sampling a signal to be sampled in a preset time of a positive half period of an excitation period, and calculating to obtain a first average voltage;
Sampling a signal to be sampled in a preset time of a negative half period in an excitation period, and calculating to obtain a second average voltage;
The first average voltage and the second average voltage are subjected to difference to obtain an empty pipe detection voltage between the signal electrode and the grounding electrode;
The duration of the excitation period is T, the duration of the preset time period is T, and the duration T of the preset time period and the duration T of the excitation period meet the following relation that T is more than or equal to 0 and less than or equal to T/6.
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