Empty pipe detection method and system of electromagnetic flowmeter and electromagnetic flowmeter

Abstract

The invention relates to the technical field of measuring instrument detection, and discloses an empty pipe detection method and system of an electromagnetic flowmeter and the electromagnetic flowmeter. The method comprises the steps that an excitation signal is applied 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 in a preset time period, and calculating an empty pipe detection voltage between a signal electrode and a 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; according to the conductivity, whether the electromagnetic flowmeter is in a blank pipe state or not is detected. According to the embodiment of the invention, the influence of a common-mode signal on blank pipe detection can be reduced, and the blank pipe detection accuracy of the electromagnetic flowmeter is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring instrument detection, and in particular to an empty pipe detection method and system for an electromagnetic flowmeter and an electromagnetic flowmeter. Background Art

[0002] The electromagnetic flowmeter is a flow measuring instrument based on Farad's law of electromagnetic induction. It is mainly composed of a pipeline cavity, a pair of signal electrodes, an excitation coil, an excitation drive unit and a signal processing unit. The excitation drive unit drives the excitation coil to generate a magnetic field perpendicular to the direction of fluid flow. When the fluid passes through the pipeline 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 based on the received induced potential signal, and then calculates the flow rate flowing through the pipeline cavity based on the cross-sectional area of ​​the pipe body.

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

[0004] In the related technology, an alarm is required when the fluid does not fill the pipe. Most empty pipe alarm methods determine the empty pipe status by measuring the solution resistance. 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 pipeline is in the empty pipe state, which leads to false alarms or missed alarms. Summary of the invention

[0005] In view of this, the present invention provides an empty pipe detection method and system for an electromagnetic flowmeter and an electromagnetic flowmeter to solve the technical problem in the related technology that poor grounding or common mode interference is introduced when grounding with a grounding electrode, thereby causing false alarms or missed alarms of the empty pipe alarm.

[0006] In a first aspect, the present invention provides an empty pipe detection method for 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 first part of each half excitation cycle of the excitation signal;

[0008] Acquire a signal to be sampled within a preset time period, and calculate an empty pipe detection voltage between a signal electrode and a ground electrode according to the signal to be sampled;

[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] According to the conductivity, it is detected whether the electromagnetic flowmeter is in an empty pipe state.

[0011] In an optional implementation, the calculating the empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled includes:

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

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

[0014] The first average voltage is subtracted from the second average voltage to obtain an empty pipe detection voltage between the signal electrode and the ground electrode.

[0015] In an optional implementation, the duration 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 duration T of the excitation cycle satisfy the following relationship: 0≤t≤T / 6.

[0016] In a second aspect, the present invention provides an empty pipe detection system for an electromagnetic flowmeter, comprising: a signal electrode, a ground electrode, an excitation module, an empty pipe 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 the signal ground terminal;

[0019] The excitation module is connected to the signal electrode and is used to apply an excitation signal to the signal electrode;

[0020] The empty pipe sampling module is connected to the signal electrode and is used to obtain the output signal of the signal electrode and generate a signal to be sampled according to the output signal of the signal electrode;

[0021] The microprocessor is connected to the excitation module and the empty pipe sampling module respectively, and is used to control 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 cycle of the excitation signal; and is also used to obtain a signal to be sampled within a preset time period, and calculate an empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled; calculate the conductivity of the medium in the pipe according to a first preset value, a second preset value and the empty pipe detection voltage; and detect whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity.

[0022] In an optional embodiment, the microprocessor includes:

[0023] A first average voltage calculation unit, used for sampling the signal to be sampled within a preset time of a positive half cycle in an excitation cycle, and calculating a first average voltage;

[0024] A second average voltage calculation unit, used for sampling the signal to be sampled within a preset time of the negative half cycle in the excitation cycle, and calculating a second average voltage;

[0025] The empty pipe detection voltage calculation unit is used to obtain the empty pipe detection voltage between the signal electrode and the ground electrode by subtracting the first average voltage from the second average voltage.

[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 generating 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 generating chip are all connected to the microprocessor, the ground pin of the square wave generating chip is directly grounded, the power pin of the square wave generating chip is connected to the power supply, the output pin of the square wave generating 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, and 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 both connected to the signal electrode.

[0028] In an optional implementation, the empty pipe sampling module includes: a bandpass filter unit, a rectifier unit, and a low-pass filter unit connected in sequence;

[0029] The bandpass filtering unit is used to obtain the output signal of the sampling electrode, and to perform bandpass filtering on the output signal of the sampling electrode to obtain an empty pipe detection AC signal;

[0030] The rectifier unit is used to rectify the empty pipe detection AC signal to obtain an empty pipe detection ripple signal;

[0031] The low-pass filtering unit is used to perform low-pass filtering on the empty pipe detection ripple signal to obtain a signal to be sampled.

[0032] In an optional implementation, the bandpass filtering 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 the 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 the input end of the rectifier unit, and the other end of the fifth capacitor is directly grounded;

[0033] The low-pass filtering unit includes: a sixth resistor, a seventh resistor, a sixth capacitor and a seventh capacitor; one end of the sixth resistor is connected to the output end of the rectifying unit, the other end of the sixth resistor is respectively connected to 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 to the input end of the microcontroller.

[0034] In an optional implementation, the bandwidth of the bandpass filter is 150 Hz-50 kHz.

[0035] In a third aspect, the present invention provides an electromagnetic flowmeter, comprising a pipeline, a signal electrode, a ground electrode and an excitation module, wherein the ground electrode is connected to the signal ground terminal, and the excitation module is used to apply a magnetic field to a medium in the pipeline, characterized in that it also includes: an excitation module, an empty pipe sampling module and a microprocessor;

[0036] The excitation module is connected to the signal electrode and is used to apply an excitation signal to the signal electrode;

[0037] The empty pipe sampling module is connected to the signal electrode and is used to obtain the output signal of the signal electrode and generate a signal to be sampled according to the output signal of the signal electrode;

[0038] The microprocessor is connected to the excitation module and the empty pipe sampling module respectively, and is used to control 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 cycle of the excitation signal; and is also used to obtain a signal to be sampled within a preset time period, and calculate an empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled; calculate the conductivity of the medium in the pipe according to a first preset value, a second preset value and the empty pipe detection voltage; and detect whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity.

[0039] The embodiment of the present invention applies an excitation signal to the signal electrode in the front section of each half excitation cycle of the excitation signal, collects the empty pipe detection voltage between the corresponding signal electrode and the ground electrode during the period of applying the excitation signal to eliminate common-mode interference, and then calculates the conductivity, thereby reducing the influence of the common-mode signal on the empty pipe detection and further improving the empty pipe detection accuracy of the electromagnetic flowmeter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 is a flow chart of an empty pipe detection method of an electromagnetic flowmeter according to an embodiment of the present invention;

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

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

[0044] Figure 4 This is a structural principle diagram of an empty pipe detection system of an electromagnetic flowmeter according to an embodiment of the present invention;

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

[0046] Figure 6 4 is a circuit schematic diagram of an empty pipe sampling module according to an embodiment of the present invention.

[0047] Reference numerals:

[0048] 1. Excitation module; 2. Empty pipe sampling module; 201. Bandpass filter unit; 202. Rectification unit; 203. Low-pass filter unit; A. First signal electrode; B. Second signal electrode; U1. Square wave generating 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, the sixth capacitor; C242, the seventh capacitor; C21, the eighth capacitor; C22, the ninth capacitor; R11, the first resistor; R12, the second resistor; R13, the third resistor; R212, the fourth resistor; R211, the fifth resistor; R241, the sixth resistor; R242, the seventh resistor; R222, the eighth resistor; R221, the ninth resistor; R231, the tenth resistor; R232, the eleventh resistor; R233, the twelfth resistor; R234, the thirteenth resistor; R235, the fourteenth resistor. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0053] According to an embodiment of the present invention, an empty pipe detection method for an electromagnetic flowmeter is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0054] Figure 1 FIG. 1 is a flow chart of an empty pipe detection method of an electromagnetic flowmeter according to an embodiment of the present invention. Figure 1 As shown, the process includes the following steps:

[0055] Step S101 , applying an excitation signal to a signal electrode within a preset time period; wherein the preset time period is the first part of each half excitation cycle of the excitation signal.

[0056] Among them, Figure 2As shown, a conventional electromagnetic flowmeter includes: a pipeline, an excitation coil (coil 1 and coil 2), a signal electrode (a first signal electrode A and a first signal electrode B), a grounding electrode, an excitation module and a flow sampling module. The signal electrode and the grounding electrode are both arranged on the pipeline. The fluid in the pipeline is connected to the signal grounding terminal through the grounding electrode, and the flow sampling module is connected to the grounding electrode. The excitation module is used to output an excitation signal to the excitation coil so that it generates a magnetic field perpendicular to the flow direction of the pipeline fluid. When the fluid passes through the pipeline cavity at an average flow rate, it cuts the magnetic flux lines, thereby generating an induced electromotive force. At this time, the induced electromotive force is collected by the signal electrode, and the signal electrode transmits the induced potential signal to the flow sampling module. At this time, the flow sampling module calculates the average flow velocity of the fluid based on the received induced potential signal, and then calculates the flow through the pipeline cavity based on the cross-sectional area of ​​the pipe body.

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

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

[0059] In one example, the excitation signal may 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 cycle. 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 for grounding reduces the accuracy of subsequent flow calculation. Therefore, the embodiment of the present invention performs empty pipe detection on the electromagnetic flowmeter at the beginning of the change in the direction of the magnetic field, which can better eliminate common mode interference and further improve the accuracy of empty pipe detection.

[0061] 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, thereby reducing the impact of the excitation signal on the flow calculation during empty pipe detection.

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

[0063] In one example, the excitation signal and the stimulation signal are synchronized, and the time when the excitation module outputs the excitation signal can be controlled by a program so that the excitation signal is synchronously applied to the signal electrode in the front section of each half excitation cycle of the excitation signal.

[0064] In an optional implementation, the duration 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 duration T of the excitation cycle satisfy the following relationship: 0≤t≤T / 6.

[0065] In one example, if Figure 3 As shown, assuming that the excitation period of the excitation signal is 160 ms, for each excitation period, the excitation signal can be synchronously applied to the signal electrode during the period from 0 ms to 20 ms and from 80 ms to 100 ms of the excitation period.

[0066] Of course, after the first part of each half excitation cycle, the excitation signal may be synchronously applied to the signal electrode, and at this time the excitation signal is at a low level.

[0067] Step S102, obtaining a signal to be sampled within a preset time period, and calculating an empty pipe detection voltage between a signal electrode and a ground electrode according to the signal to be sampled.

[0068] In step S102, the signal to be sampled can be directly acquired, and the empty pipe detection voltage after eliminating the common mode signal can be directly calculated based on the acquired signal to be sampled. The empty pipe detection voltage is one of the parameters for calculating the conductivity of the medium in the pipe.

[0069] Step S103, 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.

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

[0071] Step S104: Detect whether the electromagnetic flowmeter to be tested is in an empty pipe state according to the conductivity.

[0072] In step S104, the empty pipe detection voltage after eliminating the common mode signal is used as one of the parameters of conductivity, which can reduce the influence of the common mode signal on the empty pipe detection and improve the accuracy of the empty pipe detection. When the fluid conductivity of the pipeline is lower than the set threshold, the induced electromotive force generated will be very weak or even undetectable, causing the flow meter to fail to work properly, thereby triggering an empty pipe alarm.

[0073] The embodiment of the present invention applies an excitation signal to the signal electrode in the front section of each half excitation cycle of the excitation signal, collects the empty pipe detection voltage between the corresponding signal electrode and the ground electrode during the period of applying the excitation signal to eliminate common-mode interference, and then calculates the conductivity, thereby reducing the influence of the common-mode signal on the empty pipe detection and further improving the empty pipe detection accuracy of the electromagnetic flowmeter.

[0074] In an optional implementation, the step S102 further includes:

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

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

[0077] Step S1023: Subtract the first average voltage from the second average voltage to obtain an empty pipe detection voltage between the signal electrode and the ground electrode.

[0078] Among them, the signal to be sampled is obtained through a series of processing based on the excitation signal and the stimulation signal, and its waveform is synchronized with the excitation signal and the stimulation signal. At this time, the waveform of the signal to be sampled within 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 signal to be sampled corresponding to the time period is calculated. When the preset time period is in the negative half excitation cycle of the excitation signal, the average voltage of the signal to be sampled corresponding to the time period is calculated. Finally, the two are subtracted to eliminate the common mode signal interference, thereby obtaining the empty pipe detection voltage between the signal electrode and the ground electrode.

[0079] The embodiment of the present invention can eliminate common-mode interference by averaging and subtracting the sampled signals, and finally calculate the conductivity based on the empty pipe detection voltage after the common-mode interference is eliminated, so as to achieve accurate empty pipe detection of the electromagnetic flowmeter in the case of poor grounding or direct grounding through a grounding electrode.

[0080] In this embodiment, an empty pipe detection system for an electromagnetic flowmeter is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and the descriptions that have been made will not be repeated. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0081] This embodiment provides an empty pipe detection system for an electromagnetic flowmeter, such as Figure 4 As shown (microprocessor omitted), including signal electrode, ground electrode, excitation module 1, empty pipe sampling module 2 and microprocessor ( Figure 4 not shown).

[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 ground electrode is connected to the signal ground terminal;

[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 may have a certain impact on the accuracy of empty pipe detection. The more electrodes there are, 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 circumstances and is not specifically limited here.

[0084] Secondly, the excitation module 1 is connected to the signal electrode, and the excitation module 1 is used to apply the excitation signal to the signal electrode; the empty pipe sampling module 2 is connected to the signal electrode, and the empty pipe sampling module 2 is used to obtain the output signal of the signal electrode, and generate the signal to be sampled according to the output signal of the signal electrode; the microprocessor is connected to the excitation module 1 and the empty pipe sampling module 2 respectively, and the microprocessor is used to control 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 part of each half excitation cycle of the excitation signal; it is also used to obtain the signal to be sampled within the preset time period, and calculate the empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled; calculate the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty pipe detection voltage; and detect whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity.

[0085] In some optional implementations, the microprocessor includes: a first average voltage calculation unit, a second average voltage calculation unit, and an empty pipe detection voltage calculation unit.

[0086] Specifically, the first average voltage calculation unit is used to sample the signal to be sampled within a preset time of the positive half cycle in the excitation cycle, and calculate the first average voltage; the second average voltage calculation unit is used to sample the signal to be sampled within a preset time of the negative half cycle in the excitation cycle, and calculate the second average voltage; the empty pipe detection voltage calculation unit is used to subtract the first average voltage from the second average voltage to obtain the empty pipe detection voltage between the signal electrode and the ground electrode.

[0087] In an optional embodiment, if Figure 5 As shown, 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;

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

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

[0090] In one example, assuming that the power supply voltage is 2.5V, a 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 be used as a reference voltage.

[0091] Of course, the output pins of the square wave generating chip U1 are not limited to two. When multiple signal electrodes are provided, the output pins can be increased.

[0092] It should be noted that Figure 5 Where Vx1 and Vx2 correspond to the voltage values ​​between the first signal electrode A and the second signal electrode relative to the ground electrode, which can be directly obtained by the empty pipe sampling module. Rx1 and Rx2 correspond to the equivalent resistance between the first signal electrode A and the second signal electrode relative to the ground electrode, that is, the fluid resistance.

[0093] In an optional implementation, the first preset value and the second preset value may be calibrated according to Vx1 and Vx2, the resistance values ​​of each resistor of the excitation circuit and the reference voltage using Kirchhoff's law.

[0094] In an optional embodiment, if Figure 6 As shown, the empty pipe sampling module 2 includes a bandpass filter unit 201, a rectifier unit 202 and a low-pass filter unit 203 connected in sequence;

[0095] Specifically, the bandpass filter unit 201 is used to obtain the output signal of the sampling electrode, and to perform bandpass filtering on the output signal of the sampling electrode to obtain an empty pipe detection AC signal; the rectifier unit 202 is used to rectify the empty pipe detection AC signal to obtain an empty pipe detection ripple signal; the low-pass filter unit 203 is used to perform low-pass filtering on the empty pipe detection ripple signal to obtain a signal to be sampled.

[0096] In an optional embodiment, the bandpass 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 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, 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 rectifier unit 202, 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 respectively connected to 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 to the input end of the microcontroller.

[0098] In an optional implementation, 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 terminal of the first operational amplifier AMP1 is connected to the output terminal of the band-pass filter unit 201, the negative input terminal of the first operational amplifier AMP1 is respectively 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 respectively connected to the output terminal 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 respectively connected to one end of the twelfth resistor R233, one end of the first diode D1, and the negative input terminal of the second operational amplifier AMP2, the second operational amplifier AMP The positive input terminal of the second operational amplifier AMP2 is directly grounded, the output terminal of the second operational amplifier AMP2 is respectively 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 respectively 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 respectively connected to the negative input terminal of the third operational amplifier AMP3, the other end of the thirteenth resistor R234, and one end of the fourteenth resistor R235, the positive input terminal of the third operational amplifier AMP3 is directly grounded, and the output terminal of the third operational amplifier AMP3 and the other end of the fourteenth resistor R235 are both connected to the low-pass filtering unit 204.

[0100] 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 a signal to be sampled that can be directly acquired by performing voltage division, band-pass filtering, rectification, low-pass filtering and other operations on the voltage values ​​Vx1 and Vx2 between the first signal electrode A and the second signal electrode B relative to the ground electrode. The common-mode interference in the signal to be sampled can be removed by averaging and subtracting the waveform of the signal to be sampled, and an empty pipe detection voltage without common-mode interference can be obtained. At this time, according to the calibrated preset value and the empty pipe detection voltage, the conductivity for judging whether the electromagnetic flowmeter is an empty pipe is obtained, so that accurate empty pipe detection of the electromagnetic flowmeter can be achieved when the grounding is poor or directly grounded through the grounding electrode.

[0101] In an optional implementation, the bandwidth of the bandpass filter is 150 Hz-50 kHz.

[0102] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0103] The embodiment of the present invention further provides an electromagnetic flowmeter, including a pipeline, a signal electrode, a ground electrode and an excitation module, wherein the ground electrode is connected to the signal ground terminal, and the excitation module is used to apply a magnetic field to the medium in the pipeline.

[0104] Secondly, it also includes: an excitation module, an empty pipe sampling module and a microprocessor;

[0105] The excitation module is connected to the signal electrode, and is used to apply an excitation signal to the signal electrode;

[0106] The empty pipe sampling module is connected to the signal electrode, and the empty pipe sampling module is used to obtain the output signal of the signal electrode and generate a signal to be sampled according to the output signal of the signal electrode; the microprocessor is connected to the excitation module and the empty pipe sampling module respectively, and the microprocessor is used to control 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 part of each half excitation cycle of the excitation signal; the microprocessor is also used to obtain the signal to be sampled within the preset time period, and calculate the empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled; calculate the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty pipe detection voltage; and detect whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity.

[0107] The above-mentioned method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium and downloaded through a network, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above-mentioned types of memory. It can be understood that a computer, a processor, a 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 a computer, a processor or hardware, the method shown in the above embodiment is implemented.

[0108] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. An empty pipe detection method for an electromagnetic flowmeter, characterized in that: include: Applying an excitation signal to the signal electrode within a preset time period; wherein the preset time period is the first part of each half excitation cycle of the excitation signal; Acquire a signal to be sampled within a preset time period, and calculate an empty pipe detection voltage between a signal electrode and a ground electrode according to the signal to be sampled; 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; According to the conductivity, it is detected whether the electromagnetic flowmeter is in an empty pipe state.

2. The method according to claim 1, characterized in that The step of calculating the empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled comprises: Sampling the signal to be sampled within a preset time of a positive half cycle in an excitation cycle, and calculating a first average voltage; Sampling the signal to be sampled within a preset time of the negative half cycle in the excitation cycle, and calculating and obtaining a second average voltage; The first average voltage is subtracted from the second average voltage to obtain an empty pipe detection voltage between the signal electrode and the ground electrode.

3. The method according to claim 1 or 2, characterized in that: The duration 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 duration T of the excitation cycle satisfy the following relationship: 0≤t≤T / 6.

4. An empty pipe detection system for an electromagnetic flowmeter, characterized in that: include: Signal electrode, ground electrode, excitation module, empty pipe sampling module and 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 ground electrode is connected to the signal ground terminal; The excitation module is connected to the signal electrode and is used to apply an excitation signal to the signal electrode; The empty pipe sampling module is connected to the signal electrode and is used to obtain the output signal of the signal electrode and generate a signal to be sampled according to the output signal of the signal electrode; A microprocessor is connected to the excitation module and the empty pipe sampling module, respectively, and is used to control the excitation module to apply an excitation signal to the signal electrode within a preset time period; wherein the preset time period is the first section of each half excitation cycle of the excitation signal; and is also used to obtain a signal to be sampled within the preset time period, and calculate an empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled; and calculate the conductivity of the medium in the pipe according to the first preset value, the second preset value and the empty pipe detection voltage; According to the conductivity, it is detected whether the electromagnetic flowmeter is in an empty pipe state.

5. The system according to claim 4, characterized in that The microprocessor comprises: A first average voltage calculation unit, used for sampling the signal to be sampled within a preset time of a positive half cycle in an excitation cycle, and calculating a first average voltage; A second average voltage calculation unit, used for sampling the signal to be sampled within a preset time of the negative half cycle in the excitation cycle, and calculating a second average voltage; The empty pipe detection voltage calculation unit is used to obtain the empty pipe detection voltage between the signal electrode and the ground electrode by subtracting the first average voltage from the second average voltage.

6. The system according to claim 4 or 5, characterized in that: The signal electrode includes a first signal electrode and a second signal electrode, and the excitation module includes: 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 all connected to the microprocessor, the ground pin of the square wave generating chip is directly grounded, the power pin of the square wave generating chip is connected to the power supply, the output pin of the square wave generating 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, and 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 both connected to the signal electrode.

7. The system according to claim 4, characterized in that The empty pipe sampling module comprises: a bandpass filter unit, a rectifier unit and a low-pass filter unit connected in sequence; The bandpass filtering unit is used to obtain the output signal of the sampling electrode, and to perform bandpass filtering on the output signal of the sampling electrode to obtain an empty pipe detection AC signal; The rectifier unit is used to rectify the empty pipe detection AC signal to obtain an empty pipe detection ripple signal; The low-pass filtering unit is used to perform low-pass filtering on the empty pipe detection ripple signal to obtain a signal to be sampled.

8. The system according to claim 7, characterized in that The bandpass 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 the 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 the input end of the rectifier unit, and the other end of the fifth capacitor is directly grounded; The low-pass filtering unit includes: a sixth resistor, a seventh resistor, a sixth capacitor and a seventh capacitor; one end of the sixth resistor is connected to the output end of the rectifying unit, the other end of the sixth resistor is respectively connected to 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 to the input end of the microcontroller.

9. The system according to claim 7, characterized in that The bandwidth of the bandpass filter is 150 Hz-50 kHz.

10. An electromagnetic flowmeter, comprising a pipeline, a signal electrode, a ground electrode and an excitation module, wherein the ground electrode is connected to the signal ground terminal, and the excitation module is used to apply a magnetic field to a medium in the pipeline, characterized in that: It also includes: an excitation module, an empty pipe sampling module and a microprocessor; The excitation module is connected to the signal electrode and is used to apply an excitation signal to the signal electrode; The empty pipe sampling module is connected to the signal electrode and is used to obtain the output signal of the signal electrode and generate a signal to be sampled according to the output signal of the signal electrode; The microprocessor is connected to the excitation module and the empty pipe sampling module respectively, and is used to control 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 cycle of the excitation signal; and is also used to obtain a signal to be sampled within a preset time period, and calculate an empty pipe detection voltage between the signal electrode and the ground electrode according to the signal to be sampled; calculate the conductivity of the medium in the pipe according to a first preset value, a second preset value and the empty pipe detection voltage; and detect whether the electromagnetic flowmeter is in an empty pipe state according to the conductivity.

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