A method and system for detecting empty pipe of an electromagnetic flowmeter and an electromagnetic flowmeter

Abstract

The application relates to the technical field of measuring instrument detection, and discloses an empty pipe detection method and system of an electromagnetic flowmeter and an electromagnetic flowmeter. The method comprises the following steps: applying an excitation signal to a signal electrode within a preset time period; wherein the preset time period is the front section of each half excitation period of the excitation signal; acquiring a to-be-sampled signal within the preset time period, and calculating an empty pipe detection voltage between the signal electrode and a grounding electrode according to the to-be-sampled signal; calculating the conductivity of a pipe medium according to a first preset value, a second preset value and the empty pipe detection voltage; and detecting whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity. The embodiment of the application can reduce the influence of common-mode signals on empty pipe detection, and further improves the empty pipe detection accuracy of the electromagnetic flowmeter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of measuring instrument detection, and particularly relates to an empty pipe detection method and system of an electromagnetic flowmeter and an electromagnetic flowmeter. BACKGROUND

[0002] The electromagnetic flowmeter is a flowmeter based on Faraday's law of electromagnetic induction, mainly composed of a pipe cavity, a pair of signal electrodes, an excitation coil, an excitation driving unit and a signal processing unit. The excitation driving unit drives the excitation coil to generate a magnetic field perpendicular to the flow direction of the fluid. When the fluid flows through the pipe cavity at an average flow rate, the signal electrode outputs an induced potential signal. At this time, the signal processing unit calculates the average flow rate of the fluid according to the received induced potential signal, and then calculates the flow rate through the pipe cavity according to the cross-sectional area of the pipe.

[0003] When the electromagnetic flowmeter is in an empty pipe state, i.e., the fluid in the pipe is not full, it is easy to be affected by strong electromagnetic interference, which causes the measurement signal received by the signal processing unit to be distorted, thereby affecting the accuracy of subsequent flow calculation. Therefore, one of the prerequisites for ensuring reliable measurement is to ensure that the pipe is in a full pipe state.

[0004] In related technologies, when the fluid does not fill the pipe, an alarm needs to be given. Most empty pipe alarm methods measure the solution resistance to determine the empty pipe state. However, the empty pipe signal often exists in the form of common mode. When the grounding is poor or the grounding electrode is used for grounding, common mode interference will be introduced at the same time. At this time, it is impossible to correctly identify whether the current pipe is in an empty pipe state, thereby causing false alarms or missed alarms. SUMMARY

[0005] Therefore, the present application provides an empty pipe detection method and system of an electromagnetic flowmeter and an electromagnetic flowmeter to solve the technical problem of false alarms or missed alarms of the empty pipe alarm caused by the introduction of common mode interference when the grounding is poor or the grounding electrode is used for grounding in related technologies.

[0006] In a first aspect, the present application provides an empty pipe detection method of an electromagnetic flowmeter, comprising:

[0007] applying an excitation signal to the signal electrode within a preset time period; wherein the preset time period is the front section of each half excitation period of the excitation signal;

[0008] obtaining a to-be-sampled signal within the preset time period, and calculating an empty pipe detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal;

[0009] calculating the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty pipe detection voltage;

[0010] detecting whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity.

[0011] In an alternative embodiment, the calculating the empty tube detection voltage between the signal electrode and the ground electrode according to the to-be-sampled signal comprises:

[0012] sampling the to-be-sampled signal in a preset time period in the positive half cycle of the excitation cycle, and calculating a first average voltage;

[0013] sampling the to-be-sampled signal in a preset time period in the negative half cycle of the excitation cycle, and calculating a second average voltage;

[0014] differencing the first average voltage and the second average voltage to obtain the empty tube detection voltage between the signal electrode and the ground electrode.

[0015] In an alternative embodiment, the length of the excitation cycle is T, the duration of the preset time period is t, and the duration t of the preset time period and the length T of the excitation cycle satisfy the following relationship: 0≤t≤T / 6.

[0016] In a second aspect, the present application provides an empty tube detection system of an electromagnetic flowmeter, comprising: a signal electrode, a ground electrode, an excitation module, an empty tube sampling module, and a microprocessor.

[0017] The signal electrode is fixedly connected to the pipeline of the electromagnetic flowmeter and contacts the medium in the pipeline of the electromagnetic flowmeter.

[0018] The ground electrode is connected to a signal ground end.

[0019] The excitation module is connected to the signal electrode and is configured to apply an excitation signal to the signal electrode.

[0020] The empty tube sampling module is connected to the signal electrode and is configured to obtain an output signal of the signal electrode and generate a to-be-sampled signal according to the output signal of the signal electrode.

[0021] The microprocessor is connected to the excitation module and the empty tube sampling module, respectively, and is configured to control the excitation module to apply an excitation signal to the signal electrode in a preset time period, wherein the preset time period is the front part of each half excitation cycle of the excitation signal; the microprocessor is further configured to obtain a to-be-sampled signal in the preset time period and calculate an empty tube detection voltage between the signal electrode and the ground electrode according to the to-be-sampled signal; calculate the conductivity of the medium in the pipeline according to a first preset value, a second preset value, and the empty tube detection voltage; and detect whether the electromagnetic flowmeter is in an empty tube state according to the conductivity.

[0022] In an alternative embodiment, the microprocessor comprises:

[0023] The first average voltage calculation unit is configured to sample the to-be-sampled signal in a preset time in a positive half cycle of the excitation cycle and calculate a first average voltage;

[0024] The second average voltage calculation unit is configured to sample the to-be-sampled signal in a preset time in a negative half cycle of the excitation cycle and calculate a second average voltage;

[0025] The air tube detection voltage calculation unit is configured to subtract the first average voltage from the second average voltage to obtain an air tube detection voltage between the signal electrode and the ground electrode.

[0026] In an optional embodiment, the signal electrode includes a first signal electrode and a second signal electrode, and the excitation module includes a square wave generation chip, a first capacitor, a second capacitor, a third capacitor, a first resistor, a second resistor, and a third resistor.

[0027] The input pins of the square wave generation chip are connected to the microprocessor, the ground pin of the square wave generation chip is directly grounded, the power supply pin of the square wave generation chip is connected to a power supply, the output pin of the square wave generation chip is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the first resistor, the other end of the first resistor is respectively connected to one end of the second resistor and one end of the third resistor, the other end of the third resistor is directly grounded, the other end of the second resistor is respectively connected to one end of the second capacitor and one end of the third capacitor, and the other end of the second capacitor and the other end of the third capacitor are connected to the signal electrode.

[0028] In an optional embodiment, the air tube sampling module includes a band-pass filter unit, a rectifier unit, and a low-pass filter unit connected in sequence.

[0029] The band-pass filter unit 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 air tube detection alternating current signal.

[0030] The rectifier unit is configured to rectify the air tube detection alternating current signal to obtain an air tube detection ripple signal.

[0031] The low-pass filter unit is configured to perform low-pass filtering on the air tube detection ripple signal to obtain the to-be-sampled signal.

[0032] In an optional embodiment, the band-pass filter unit includes a fourth capacitor, a fifth capacitor, a fourth resistor, and a fifth resistor, one end of the fourth capacitor is electrically connected to an output end of the signal electrode, the other end of the fourth capacitor is respectively connected to 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 to one end of the fifth capacitor and an input end of the rectifier unit, and the other end of the fifth capacitor is directly grounded.

[0033] The low-pass filter unit comprises a sixth resistor, a seventh resistor, a sixth capacitor and a seventh capacitor; one end of the sixth resistor is connected with the output end of the rectifier unit, the other end of the sixth resistor is connected with one end of the sixth capacitor and one end of the seventh resistor respectively, the other end of the sixth capacitor and one end of the seventh capacitor are both directly grounded, and the other end of the seventh capacitor and the other end of the seventh resistor are both connected with the input end of the microcontroller.

[0034] In an alternative embodiment, the bandwidth of the band-pass filter is 150Hz-50kHz.

[0035] In a third aspect, the application provides an electromagnetic flowmeter, comprising a pipeline, a signal electrode, a grounding electrode and an excitation module, 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, characterized in that further comprising: an excitation module, an empty-pipeline sampling module and a microprocessor.

[0036] The excitation module is connected with the signal electrode and is used for applying an excitation signal to the signal electrode.

[0037] The empty-pipeline sampling module is connected with the signal electrode and is used for obtaining an output signal of the signal electrode and generating a to-be-sampled signal according to the output signal of the signal electrode.

[0038] The microprocessor is connected with the excitation module and the empty-pipeline sampling module respectively, is used for controlling the excitation module to apply an excitation signal to the signal electrode in a preset time period, wherein the preset time period is a front section of each half excitation period of the excitation signal; is further used for obtaining the to-be-sampled signal in the preset time period and calculating an empty-pipeline detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal; calculating the conductivity of the medium in the pipeline according to a first preset value, a second preset value and the empty-pipeline detection voltage; and detecting whether the electromagnetic flowmeter is in an empty-pipeline state according to the conductivity.

[0039] The embodiment of the application applies an excitation signal to the signal electrode in a front section of each half excitation period of the excitation signal and collects the empty-pipeline detection voltage between the signal electrode and the grounding electrode for eliminating common-mode interference during application of the excitation signal, and then calculates the conductivity, thereby reducing the influence of the common-mode signal on the empty-pipeline detection and further improving the empty-pipeline detection accuracy of the electromagnetic flowmeter. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0041] Figure 1 is a flowchart of an empty tube detection method of an electromagnetic flowmeter according to an embodiment of the present application;

[0042] Figure 2 is a structure principle diagram of a conventional electromagnetic flowmeter according to an embodiment of the present application;

[0043] Figure 3 is a waveform diagram of an excitation signal and an excitation signal according to an embodiment of the present application;

[0044] Figure 4 is a structure principle diagram of an empty tube detection system of an electromagnetic flowmeter according to an embodiment of the present application;

[0045] Figure 5 is a circuit principle diagram of an excitation module according to an embodiment of the present application;

[0046] Figure 6 is a circuit principle diagram of an empty tube sampling module according to an embodiment of the present application.

[0047] Reference signs:

[0048] 1, excitation module; 2, empty tube sampling module; 201, band-pass filter unit; 202, rectifier unit; 203, low-pass filter unit; A, first signal electrode; B, second signal electrode; U1, square wave generation chip; AMP1, first operational amplifier; AMP2, second operational amplifier; AMP3, third operational amplifier; D1, first diode; D2, second diode; C13, first capacitor; C11, second capacitor; C12, third capacitor; C211, fourth capacitor; C212, fifth capacitor; C241, sixth capacitor; C242, seventh capacitor; C21, eighth capacitor; C22, ninth capacitor; R11, first resistor; R12, second resistor; R13, third resistor; R212, fourth resistor; R211, fifth resistor; R241, sixth resistor; R242, seventh resistor; R222, eighth resistor; R221, ninth resistor; R231, tenth resistor; R232, eleventh resistor; R233, twelfth resistor; R234, thirteenth resistor; R235, fourteenth resistor. DETAILED DESCRIPTION

[0049] The technical solutions of the present application will be described clearly and completely in connection with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of the present application.

[0050] In the description of the present application, it should be noted that the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0051] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication between two elements, or it can be wireless connection, or it can be wired connection. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0052] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0053] According to the embodiments of the present application, a kind of empty tube detection method of electromagnetic flowmeter is provided, it should be noted that the steps shown in the flowchart of the drawing can be executed in computer system such as a group of computer executable instructions, and although logical sequence is shown in flowchart, in some cases, the steps shown or described can be executed in different order from here.

[0054] Figure 1 It is a flowchart of the empty tube detection method of electromagnetic flowmeter according to the embodiments of the present application, as shown in Figure 1 The flowchart includes the following steps:

[0055] Step S101, excitation signal is applied to signal electrode within a predetermined time period;Wherein, the predetermined time period is the front section of each half excitation period of excitation signal.

[0056] Wherein, as Figure 2As shown, the conventional electromagnetic flowmeter comprises a pipeline, excitation coils (coil 1 and coil 2), signal electrodes (first signal electrode A and first signal electrode B), a grounding electrode, an excitation module and a flow sampling module, the signal electrodes and the grounding electrode are arranged on the pipeline, the 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 excitation module is used for outputting an excitation signal to the excitation coils, so that a magnetic field perpendicular to the fluid flow direction of the pipeline is generated. When the fluid flows through the pipeline cavity at an average flow rate, the magnetic induction lines are cut, thereby generating an induced electromotive force. At this time, the induced electromotive force is collected by the signal electrodes, and the signal electrodes transmit the induced electromotive force signal to the flow sampling module. At this time, the flow sampling module calculates the average flow rate of the fluid according to the received induced electromotive force signal, and then calculates the flow rate through the pipeline cavity according to the cross-sectional area of the pipeline.

[0057] In step S101, the excitation signal is an alternating signal applied to the excitation coil by the excitation module of the electromagnetic flowmeter, which periodically changes so that the excitation coil generates an alternating magnetic field. This alternating magnetic field causes the fluid to cut the magnetic induction lines when flowing through the pipeline, thereby generating an induced electromotive force. For an 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.

[0058] The excitation signal is preferably a square wave signal with a duty cycle of 50%.

[0059] In an example, the excitation signal can be a low-frequency square wave excitation signal of 6.25 Hz.

[0060] It should be noted that under the action of the excitation signal, the alternating magnetic field generated by the excitation coil changes direction once in each half excitation period. The magnetic field is unstable at the beginning of the change, and the common mode interference caused by poor grounding or the use of a third electrode grounding affects the subsequent flow calculation accuracy. Therefore, the embodiment of the present application detects the empty pipe of the electromagnetic flowmeter at the beginning of the change of the magnetic field direction, which can better eliminate the common mode interference and further improve the accuracy of the empty pipe detection.

[0061] In an example, for the flow sampling module, the induced electromotive force sampling and flow calculation are not performed at the beginning of the change of the magnetic field direction, and the influence of the excitation signal on the flow calculation is reduced during the empty pipe detection.

[0062] The preset time period can be set according to actual needs, and is not limited here.

[0063] In an example, the excitation signal and the excitation signal are synchronized, and the time when the excitation signal is output by the excitation module can be controlled by a program, so that the excitation signal is synchronously applied to the signal electrode at the beginning of each half excitation period of the excitation signal.

[0064] In an alternative embodiment, the length of the excitation period is T, the duration of the preset time period is t, the duration of the preset time period t and the length of the excitation period T satisfy the following relationship: 0≤t≤T / 6.

[0065] In an example, as shown in FIG. 1, assuming that the excitation period of the excitation signal is 160 ms, then for each excitation period, the excitation signal can be synchronously applied to the signal electrode during the 0th ms to 20th ms and the 80th ms to 100th ms of the excitation period. Figure 3

[0066] Of course, the excitation signal can also be synchronously applied to the signal electrode after the first half of the excitation period, at which time the excitation signal is at a low level.

[0067] In step S102, the signal to be sampled in the preset time period is obtained, and the empty tube detection voltage between the signal electrode and the ground electrode is calculated according to the signal to be sampled.

[0068] In step S102, the signal to be sampled can be directly obtained, and the empty tube detection voltage after the common-mode signal is eliminated can be directly calculated according to the obtained signal to be sampled. The empty tube detection voltage is one of the parameters for calculating the conductivity of the medium in the tube.

[0069] In step S103, the conductivity of the medium in the tube is calculated according to the first preset value, the second preset value and the empty tube detection voltage.

[0070] In step S103, the first preset value and the second preset value can be calibrated in advance, and the specific values can be set according to actual needs, which are not limited here.

[0071] In step S104, whether the electromagnetic flowmeter to be measured is in an empty tube state is detected according to the conductivity.

[0072] In step S104, the empty tube detection voltage after the common-mode signal is eliminated is used as one of the parameters for calculating the conductivity, which can reduce the influence of the common-mode signal on the empty tube detection and improve the accuracy of the empty tube detection. When the fluid conductivity of the pipeline is lower than the set threshold, the induced electromotive force will be very weak, and even cannot be detected, which causes the flowmeter to fail to work normally, thereby causing the empty tube alarm.

[0073] The embodiment of the present application applies the excitation signal to the signal electrode in the first half of the excitation period of the excitation signal, and collects the empty tube detection voltage after the common-mode interference is eliminated between the corresponding signal electrode and the ground electrode during the application of the excitation signal, and then calculates the conductivity, which reduces the influence of the common-mode signal on the empty tube detection and further improves the accuracy of the empty tube detection of the electromagnetic flowmeter.

[0074] ​In an alternative embodiment, the step S102 further comprises:

[0075] Step S1021, sampling the to-be-sampled signal in the preset time in the positive half cycle of the excitation cycle, and calculating a first average voltage;

[0076] Step S1022, sampling the to-be-sampled signal in the preset time in the negative half cycle of the excitation cycle, and calculating a second average voltage;

[0077] Step S1023, subtracting the first average voltage from the second average voltage to obtain the empty tube detection voltage between the signal electrode and the grounding electrode.

[0078] The to-be-sampled signal is obtained by processing the excitation signal and the excitation signal, and the waveform thereof is synchronized with the excitation signal and the excitation signal. At this time, the waveform of the to-be-sampled signal in the preset time period is obtained, the average voltage of the corresponding to-be-sampled signal in the preset time period is obtained when the preset time period is in the positive half excitation cycle of the excitation signal, the average voltage of the corresponding to-be-sampled signal in the preset time period is obtained when the preset time period is in the negative half excitation cycle of the excitation signal, and finally the common-mode signal interference is eliminated by subtracting the two, so that the empty tube detection voltage between the signal electrode and the grounding electrode is obtained.

[0079] The embodiment of the present application can eliminate common-mode interference by averaging and subtracting the to-be-sampled signal, and can realize precise empty tube detection of the electromagnetic flowmeter in the case of poor grounding or direct grounding through the grounding electrode by calculating the conductivity according to the empty tube detection voltage after eliminating the common-mode interference.

[0080] In the embodiment, an empty tube detection system of an electromagnetic flowmeter is also provided, which is used to realize the above-mentioned embodiments and preferred embodiments, and will not be described again. As used below, the term "module" can be a combination of software and / or hardware that realizes a predetermined function. Although the devices described in the following embodiments are preferably realized in software, hardware or a combination of software and hardware is also possible and is conceived.

[0081] The embodiment provides an empty tube detection system of an electromagnetic flowmeter, as shown in Figure 4 The system includes a signal electrode, a grounding electrode, an excitation module 1, an empty tube sampling module 2 and a microprocessor (not shown). Figure 4

[0082] The signal electrode is fixedly connected to the pipeline of the electromagnetic flowmeter and contacts the medium in the pipeline of the electromagnetic flowmeter; the grounding electrode is connected to the signal grounding end;

[0083] ​Of course, the number of signal electrodes includes but is not limited to 2, and can also be 3, 4, 6, etc. The number of electrodes can have a certain influence on the accuracy of the empty tube detection. The more the number of electrodes, the higher the measurement accuracy. Multiple signal electrodes can improve the stability and accuracy of the measurement signal. The number of signal electrodes can be set according to specific conditions, which is not specifically limited here.

[0084] Secondly, the excitation module 1 is connected with the signal electrode, and the excitation module 1 is used for applying an excitation signal to the signal electrode; the empty tube sampling module 2 is connected with the signal electrode, and the empty tube sampling module 2 is used for obtaining an output signal of the signal electrode, and generating a to-be-sampled signal according to the output signal of the signal electrode; the microprocessor is connected with the excitation module 1 and the empty tube sampling module 2 respectively, and the microprocessor is used for controlling the excitation module to apply the excitation signal to the signal electrode within a preset time period; wherein the preset time period is the front section of each half excitation period of the excitation signal; and is also used for obtaining the to-be-sampled signal within the preset time period, and calculating an empty tube detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal; calculating the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty tube detection voltage; and detecting whether the electromagnetic flowmeter is in an empty tube state according to the conductivity.

[0085] In some optional embodiments, the microprocessor comprises: a first average voltage calculation unit, a second average voltage calculation unit and an empty tube detection voltage calculation unit.

[0086] Specifically, the first average voltage calculation unit is used for sampling the to-be-sampled signal within the preset time in the positive half cycle of the excitation period, and calculating a first average voltage; the second average voltage calculation unit is used for sampling the to-be-sampled signal within the preset time in the negative half cycle of the excitation period, and calculating a second average voltage; and the empty tube detection voltage calculation unit is used for subtracting the first average voltage from the second average voltage to obtain an empty tube detection voltage between the signal electrode and the grounding electrode.

[0087] In an optional embodiment, as shown in Figure 5 the signal electrode comprises a first signal electrode A and a second signal electrode B, and the excitation module 1 comprises: a square wave generation 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.

[0088] The input pins (A pin and B pin) of the square wave generation chip U1 are connected with the microprocessor, the ground pin (GND pin) of the square wave generation chip is directly grounded, the power supply pin (VCC) of the square wave generation chip U1 is connected with the power supply, the output pin (Y pin) of the square wave generation chip U1 is connected with one end of the first capacitor C13, the other end of the first capacitor C13 is connected with one end of the first resistor R11, the other end of the first resistor R11 is connected with one end of the second resistor R12 and one end of the third resistor R13 respectively; the other end of the third resistor R13 is directly grounded, the other end of the second resistor R12 is connected with one end of the second capacitor C11 and one end of the third capacitor C12 respectively, and the other end of the second capacitor C11 and the other end of the third capacitor C12 are both connected with the signal electrode.

[0089] The two input pins (A pin and B pin) of the square wave generation chip U1 are connected with the microprocessor, for receiving the PWM signal sent by the microprocessor, so that the excitation module 1 can output the square wave signal to the first signal electrode A and the second signal electrode B. The power supply pin (VCC) of the square wave generation chip U1 is connected with the power supply, to determine the amplitude of the positive and negative voltage of the square wave signal output by the excitation module 1.

[0090] In an example, assuming that the power supply voltage is 2.5V, then the square wave signal of ±2.5V is output to the first signal electrode A and the second signal electrode B. The power supply voltage can also serve as a reference voltage.

[0091] Of course, the output pin of the square wave generation chip U1 is not limited to two, and when multiple signal electrodes are set, the output pin can be increased accordingly.

[0092] It should be noted that, Figure 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, which can be obtained directly by the air tube sampling module, and Rx1 and Rx2 correspond to the equivalent resistances of the first signal electrode A and the second signal electrode relative to the ground electrode, i.e. the fluid resistance.

[0093] In an optional embodiment, according to Vx1 and Vx2, the resistance values of the resistors of the excitation circuit and the reference voltage, the first preset value and the second preset value can be calibrated by Kirchhoff's law.

[0094] In an optional embodiment, as Figure 6 shown, the air tube sampling module 2 includes a band-pass filter unit 201, a rectifier unit 202 and a low-pass filter unit 203 connected in sequence;

[0095] Specifically, the band-pass filter 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 tube detection alternating current signal; the rectifier unit 202 is configured to rectify the empty tube detection alternating current signal to obtain an empty tube detection ripple signal; and the low-pass filter unit 203 is configured to perform low-pass filtering on the empty tube detection ripple signal to obtain a to-be-sampled signal.

[0096] In an optional embodiment, the band-pass filter unit 201 includes a fourth capacitor C211, a fifth capacitor C212, a fourth resistor R212 and a fifth resistor R211; 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 connected to one end of the fourth resistor R212 and one end of the fifth resistor R211 respectively, the other end of the fourth resistor R212 is directly grounded, the other end of the fifth resistor R211 is connected to one end of the fifth capacitor C212 and the input end of the rectifier unit 202 respectively, and the other end of the fifth capacitor C212 is directly grounded.

[0097] The low-pass filter unit 203 includes a sixth resistor R241, a seventh resistor R242, a sixth capacitor C241 and a seventh capacitor C242; one end of the sixth resistor R241 is connected to the output end of the rectifier unit 202, the other end of the sixth resistor R241 is connected to one end of the sixth capacitor C241 and one end of the seventh resistor R242 respectively, the other end of the sixth capacitor C241 and one end of the seventh capacitor C242 are both directly grounded, and the other end of the seventh capacitor C242 and the other end of the seventh resistor R242 are both connected to the input end of the microcontroller.

[0098] In an optional embodiment, the rectifier 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.

[0099] The positive input end of the first operational amplifier AMP1 is connected with the output end of the band-pass filter unit 201, the negative input end of the first operational amplifier AMP1 is connected with one end of the eighth resistor R222 and one end of the ninth resistor R221 respectively, the other end of the eighth resistor R222 is directly grounded, the other end of the ninth resistor R221 is connected with the output end of the first operational amplifier AMP1, one end of the tenth resistor R231 and one end of the eleventh resistor R232 respectively, the other end of the tenth resistor R231 is connected with one end of the twelfth resistor R233, one end of the first diode D1 and the negative input end of the second operational amplifier AMP2 respectively, the positive input end of the second operational amplifier AMP2 is directly grounded, the output end of the second operational amplifier AMP2 is connected with one end of the first diode D1 and one end of the second diode D2 respectively, the other end of the twelfth resistor R233 is connected with the other end of the second diode D2 and one end of the thirteenth resistor R234 respectively, the other end of the eleventh resistor R232 is connected with the negative input end of the third operational amplifier AMP3, the other end of the thirteenth resistor R234 and one end of the fourteenth resistor R235 respectively, the positive input end of the third operational amplifier AMP3 is directly grounded, the output end of the third operational amplifier AMP3 and the other end of the fourteenth resistor R235 are connected with the low-pass filter unit 204.

[0100] To sum up, the to-be-sampled signal of the embodiment of the present application is directly output by the empty tube sampling module 2, and through voltage value Vx1 and Vx2 between the first signal electrode A and the second signal electrode B relative to the ground electrode are divided, band-pass filtered, rectified, low-pass filtered and the like, the to-be-sampled signal is converted into a to-be-sampled signal which can be directly obtained, and through averaging and difference of the waveform of the to-be-sampled signal, common-mode interference in the to-be-sampled signal can be removed, and an empty tube detection voltage without common-mode interference is obtained, at this time, according to the preset value and the empty tube detection voltage, the conductivity for judging whether the electromagnetic flowmeter is an empty tube is obtained, that is, the precise empty tube detection of the electromagnetic flowmeter in the case of poor grounding or direct grounding through the grounding electrode can be realized.

[0101] In an alternative embodiment, the bandwidth of the band-pass filter is 150Hz-50kHz.

[0102] Further function descriptions of the above-mentioned various modules and units are the same as those of the above-mentioned corresponding embodiments, and will not be described here again.

[0103] The embodiment of the present application further provides an electromagnetic flowmeter, which comprises a pipeline, a signal electrode, a grounding electrode and an excitation module, the grounding electrode is connected with a signal grounding end, the excitation module is used for applying a magnetic field to a medium in the pipeline,

[0104] Secondly, it further comprises an excitation module, an empty tube sampling module and a microprocessor.

[0105] The excitation module is connected with the signal electrode, and is configured to apply an excitation signal to the signal electrode.

[0106] The air tube sampling module is connected with the signal electrode, and is configured to acquire an output signal of the signal electrode, and generate a to-be-sampled signal according to the output signal of the signal electrode; the microprocessor is connected with the excitation module and the air tube sampling module respectively, and is configured to control the excitation module to apply the excitation signal to the signal electrode in a preset time period; wherein the preset time period is a front section of each half excitation period of the excitation signal; the microprocessor is further configured to acquire the to-be-sampled signal in the preset time period, and calculate an air tube detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal; calculate the conductivity of the in-pipe medium according to the first preset value, the second preset value and the air tube detection voltage; and detect whether the electromagnetic flowmeter is in the air tube state according to the conductivity.

[0107] The method according to the embodiments of the present application can be implemented in hardware, firmware, or as computer code recorded on a storage medium, or stored in a remote storage medium or non-transitory machine-readable storage medium and downloaded through a network and stored in a local storage medium, so that the method described herein can be processed by such software using a general purpose computer, a special purpose processor, or programmable or special purpose hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only memory, a random access memory, a flash memory, a hard disk or a solid state disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that the computer, processor, microprocessor controller or programmable hardware includes a storage component that can store or receive software or computer code, when the software or computer code is accessed and executed by the computer, processor or hardware, the method shown in the above embodiments is implemented.

[0108] Although the embodiments of the present application are described in conjunction with the drawings, various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and changes fall within the scope defined by the appended claims.

Claims

1. A method of empty pipe detection for an electromagnetic flowmeter, the method comprising: The method comprises the following steps: applying an excitation signal to the signal electrode within a preset time period; wherein the preset time period is the front section of each half excitation period of the excitation signal; obtaining a to-be-sampled signal within the preset time period, and calculating a empty-pipe detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal; calculating the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty-pipe detection voltage; detecting whether the electromagnetic flowmeter is in the empty-pipe state according to the conductivity; wherein the calculating of the empty-pipe detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal comprises: sampling the to-be-sampled signal within the preset time in the positive half cycle of the excitation period, and calculating a first average voltage; sampling the to-be-sampled signal within the preset time in the negative half cycle of the excitation period, and calculating a second average voltage; differencing the first average voltage and the second average voltage to obtain the 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 satisfy the following relationship: 0≤t≤T / 6.

2. An empty pipe detection system for an electromagnetic flowmeter, characterized by, The method comprises the following steps: a signal electrode, a grounding electrode, an excitation module, an empty-pipe sampling module and a microprocessor; the signal electrode is fixedly connected to the pipeline of the electromagnetic flowmeter and contacts the medium in the pipeline of the electromagnetic flowmeter; the grounding electrode is connected to the signal grounding end; the excitation module is connected to the signal electrode and is used for applying an excitation signal to the signal electrode; the empty-pipe sampling module is connected to the signal electrode and is used for obtaining an output signal of the signal electrode and generating a to-be-sampled signal according to the output signal of the signal electrode; the microprocessor is connected to the excitation module and the empty-pipe sampling module respectively, is used for controlling the excitation module to apply an excitation signal to the signal electrode within a preset time period; wherein the preset time period is the front section of each half excitation period of the excitation signal; is further used for obtaining a to-be-sampled signal within the preset time period, and calculating an empty-pipe detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal; calculating the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty-pipe detection voltage; detecting whether the electromagnetic flowmeter is in the empty-pipe state according to the conductivity; wherein the calculating of the empty-pipe detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal comprises: sampling the to-be-sampled signal within the preset time in the positive half cycle of the excitation period, and calculating a first average voltage; sampling the to-be-sampled signal within the preset time in the negative half cycle of the excitation period, and calculating a second average voltage; differencing the first average voltage and the second average voltage to obtain the 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 satisfy the following relationship: 0≤t≤T / 6.

3. The system of claim 2, wherein, The microprocessor comprises: The first average voltage calculation unit is configured to sample the to-be-sampled signal in a preset time in a positive half cycle of the excitation cycle and calculate a first average voltage; The second average voltage calculation unit is configured to sample the to-be-sampled signal in a preset time in a negative half cycle of the excitation cycle and calculate a second average voltage; The empty tube detection voltage calculation unit is configured to subtract the first average voltage from the second average voltage to obtain an empty tube detection voltage between the signal electrode and the ground electrode.

4. The system of claim 2 or 3, wherein, The signal electrode includes a first signal electrode and a second signal electrode, and the excitation module includes a square wave generation 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 generation chip are connected to the microprocessor, the ground pin of the square wave generation chip is directly grounded, the power supply pin of the square wave generation chip is connected to a power supply, the output pin of the square wave generation chip is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the first resistor, the other end of the first resistor is connected to one end of the second resistor and one end of the third resistor respectively, the other end of the third resistor is directly grounded, the other end of the second resistor is connected to one end of the second capacitor and one end of the third capacitor respectively, and the other end of the second capacitor and the other end of the third capacitor are connected to the signal electrode.

5. The system of claim 2, wherein, The empty tube sampling module includes a band-pass filter unit, a rectifier unit, and a low-pass filter unit connected in sequence. The band-pass filter unit 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 tube detection alternating current signal. The rectifier unit is configured to rectify the empty tube detection alternating current signal to obtain an empty tube detection ripple signal. The low-pass filter unit is configured to perform low-pass filtering on the empty tube detection ripple signal to obtain the to-be-sampled signal.

6. The system of claim 5, wherein, The band-pass filter unit includes a fourth capacitor, a fifth capacitor, a fourth resistor, and a fifth resistor. One end of the fourth capacitor is electrically connected to an output end of the signal electrode, the other end of the fourth capacitor is connected to one end of the fourth resistor and one end of the fifth resistor respectively, the other end of the fourth resistor is directly grounded, the other end of the fifth resistor is connected to one end of the fifth capacitor and an input end of the rectifier unit respectively, and the other end of the fifth capacitor is directly grounded. The low-pass filter unit includes a sixth resistor, a seventh resistor, a sixth capacitor, and a seventh capacitor. One end of the sixth resistor is connected to an output end of the rectifier unit, the other end of the sixth resistor is connected to one end of the sixth capacitor and one end of the seventh resistor respectively, the other end of the sixth capacitor and one end of the seventh capacitor are both directly grounded, and the other end of the seventh capacitor and the other end of the seventh resistor are both connected to an input end of the microcontroller.

7. The system of claim 5, wherein, The bandwidth of the band-pass filtering is 150 Hz-50 kHz.

8. An electromagnetic flowmeter comprising a conduit, a signal electrode, a ground electrode connected to a signal ground, and an excitation module for applying a magnetic field to a medium within the conduit, characterized by, The system further includes an excitation module, an empty tube sampling module, and a microprocessor. The excitation module is connected to the signal electrode and configured to apply an excitation signal to the signal electrode. The empty tube sampling module is connected to the signal electrode and configured to obtain an output signal of the signal electrode and generate a to-be-sampled signal based on the output signal of the signal electrode. The microprocessor is connected with the excitation module and the air tube sampling module respectively, and is used for controlling the excitation module to apply an excitation signal to the signal electrode in a preset time period; wherein, the preset time period is a front section of each half excitation period of the excitation signal; is further used for acquiring a to-be-sampled signal in the preset time period, and calculating an air tube detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal; calculating the conductivity of the medium in the pipe according to a first preset value, a second preset value and the air tube detection voltage; and detecting whether the electromagnetic flowmeter is in an air tube state according to the conductivity, wherein, the calculating the air tube detection voltage between the signal electrode and the grounding electrode according to the to-be-sampled signal comprises: sampling the to-be-sampled signal in the preset time in the positive half cycle of the excitation period, and calculating a first average voltage; sampling the to-be-sampled signal in the preset time in the negative half cycle of the excitation period, and calculating a second average voltage; subtracting the first average voltage from the second average voltage to obtain the air tube 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 satisfy the following relationship: 0≤t≤T / 6.

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