CN116667888B

CN116667888B - Very low frequency electromagnetic signal transmitter

Info

Publication number: CN116667888B
Application number: CN202310960126.2A
Authority: CN
Inventors: 张军; 曾艳丽; 宋华东; 关洁升; 江歌; 张成石
Original assignee: Shenyang Academy of Instrumentation Science Co Ltd; Sinomach Sensing Technology Co Ltd
Current assignee: Shenyang Academy of Instrumentation Science Co Ltd; Sinomach Sensing Technology Co Ltd
Priority date: 2023-08-02
Filing date: 2023-08-02
Publication date: 2023-10-20
Anticipated expiration: 2043-08-02
Also published as: CN116667888A

Abstract

The invention discloses an extremely low frequency electromagnetic signal transmitter, which relates to the technical field of pipeline detection, and comprises: the magnetic field transmitter comprises a singlechip, a magnetic field transmitting loop, a receiving coil and an iron core; the magnetic field emission loop comprises a series resonant loop and a driving circuit, wherein the series resonant loop comprises an emission coil, a capacitor network, a resistor network and a current sampling resistor which are connected in series, the driving circuit is respectively connected with the emission coil and the singlechip, and the driving circuit generates SPWM waveforms to drive the series resonant loop; the singlechip is used for adjusting parameters of the SPWM waveform; the method comprises the steps that in the working time period of a magnetic field emission loop, a receiving coil receives an external signal, a singlechip identifies an external control signal from the external signal, and in the next working time period of the magnetic field emission loop, the magnetic field emission loop is controlled to send a response signal in a set signal modulation mode; the singlechip adjusts parameters of the SPWM waveform according to external control signals. The invention improves the power utilization efficiency and the application flexibility.

Description

Very low frequency electromagnetic signal transmitter

Technical Field

The invention relates to the technical field of pipeline detection, in particular to an extremely low frequency electromagnetic signal transmitter.

Background

The buried steel long oil and gas pipeline needs to regularly carry out in-pipeline detection operation and pipe cleaning operation; to achieve positioning of the running equipment inside the pipeline, it is necessary to install a transmitter on it, which emits a low frequency (Extremely Low Frequency, ELF) electromagnetic wave signal that can be detected by a positioning detection device (a ball passing indicator or marker) installed at a designated location outside the pipeline, the device recording the time of passage. When the running equipment in the pipeline is blocked, the strength of the ultra-low frequency electromagnetic wave signal is inspected along the pipeline through the handheld receiver, and the signal peak point corresponds to the blocking position.

The small-sized transmitter is easy to install and maintain, but is limited by the battery capacity and the number of turns of the size of the transmitting coil, and it is difficult to maintain a certain continuous transmitting power, so that it is very critical to improve the electromagnetic wave radiation efficiency and the power utilization.

At present, the main reasons for low power efficiency of the transmitter are: the existing scheme generally adopts unipolar or bipolar square waves to directly excite the transmitting coil, and the power supply utilization efficiency is low although a driving circuit is simple. The reason is that: 1. the large amount of direct current component contained in the square wave consumes electric energy, but cannot be detected by a receiver, and belongs to invalid components; 2. the harmonic components with higher frequencies contained in the square wave can be absorbed by the pipeline and soil and cannot be detected by a receiver; 3. the transmitting coil is a multi-turn coil, has larger inductance, forms inductive reactance in the transmitting loop, and limits exciting current and magnetic field radiation intensity.

The intensity of the radiation of the magnetic field of the transmitter is proportional to the product of the excitation current and the inductance. In the existing scheme, the battery voltage is directly used as exciting voltage, and the influences of battery voltage change, battery internal resistance and transmitting coil direct current resistance along with temperature are not considered, so that the stability of the radiation intensity of the magnetic field cannot be ensured.

When the transmitter does not enter the pipeline, the power switch is turned on by mistake, so that the electric quantity of the battery can be consumed or exhausted, and the normal operation of the transmitter is affected.

The working parameters of the circuit part of the transmitter cannot be changed from the outside after encapsulation; after entering the pipe, the control and the acquisition of the running state cannot be performed.

Disclosure of Invention

The invention aims to provide an extremely low frequency electromagnetic signal transmitter, which improves the utilization efficiency and the application flexibility of a power supply.

In order to achieve the above object, the present invention provides the following solutions:

the invention discloses an extremely low frequency electromagnetic signal transmitter, comprising: the magnetic field transmitter comprises a singlechip, a magnetic field transmitting loop, a receiving coil, an analog-digital converter and an iron core; the magnetic field emission loop comprises a series resonant loop and a driving circuit, wherein the series resonant loop comprises an emission coil, a capacitor network, a resistor network and a current sampling resistor which are sequentially connected in series, the driving circuit is respectively connected with the emission coil and the singlechip, and the driving circuit is used for generating Sine Pulse Width Modulation (SPWM) waveforms to drive the series resonant loop;

The singlechip is used for adjusting parameters of the SPWM waveform; parameters of the SPWM waveform include duty cycle;

the receiving coil and the transmitting coil are wound on the iron core, and the receiving coil is connected with the singlechip through the analog-digital converter; the receiving coil is used for receiving an external signal in a working time period of the magnetic field emission loop, the singlechip is also used for identifying an external control signal from the external signal and controlling the magnetic field emission loop to send a response signal in a set signal modulation mode in the next working time period of the magnetic field emission loop; the singlechip is also used for adjusting parameters of the SPWM waveform according to the external control signal.

Optionally, the very low frequency electromagnetic signal transmitter further comprises a first multi-path analog switch and a second multi-path analog switch; the first multi-path analog switch is respectively connected with the capacitor network and the singlechip, and the second multi-path analog switch is respectively connected with the resistor network and the singlechip;

the singlechip is also used for judging whether the current of the current sampling resistor is in a set range, and if not, the resistance value of the resistor network is regulated through the second multipath analog switch;

The singlechip is also used for comparing the phase of the acquired current of the current sampling resistor with the input signal of the H-bridge driving circuit, and when phase deviation occurs, the capacitance value of the capacitance network is adjusted through the first multipath analog switch.

Optionally, the very low frequency electromagnetic signal transmitter further comprises a temperature sensor and a motion sensor which are connected with the singlechip; the temperature sensor is used for detecting the ambient temperature, and the motion sensor is used for detecting the acceleration of the very low frequency electromagnetic signal transmitter;

the singlechip is used for collecting the ambient temperature and the acceleration, when the ambient temperature is greater than a first threshold value and the acceleration is greater than a second threshold value, the magnetic field emission loop is started through the driving circuit, and otherwise, the magnetic field emission loop is controlled to be in a stop working state.

Optionally, the very low frequency electromagnetic signal transmitter further comprises a parameter memory connected with the singlechip; the parameter memory is used for storing working parameters, wherein the working parameters comprise working current and parameters of the SPWM waveform, and the working current is current passing through the current sampling resistor.

Optionally, the parameters of the SPWM waveform further include frequency, and the duty cycle of the SPWM waveform is 0.5/1.5.

Optionally, the driving circuit is an H-bridge driving circuit.

Optionally, the current sampling resistor is connected with the singlechip through the analog-digital converter.

Optionally, the very low frequency electromagnetic signal transmitter further comprises a battery pack and a voltage stabilizing circuit, wherein the battery pack is connected with the voltage stabilizing circuit, and the voltage stabilizing circuit is connected with the singlechip.

Optionally, an extremely low frequency electromagnetic signal transmitter still includes shell, insulating cylinder, first coil dog, second coil dog, end cover and circuit board, the shell with end cover threaded connection, the welding of the shell outside has disk mounting flange, the insulating cylinder the transmitting coil the receiving coil the first coil dog the second coil dog with the circuit board is located the shell with in the cavity that the end cover constitutes, the group battery is located in the insulating cylinder, the insulating cylinder is located cylindric iron core, the circuit board is located in the end cover, first coil dog with the second coil dog is located the both ends of iron core, the receiving coil with the transmitting coil is limited to be located between first coil dog and the second coil dog, the receiving coil with the transmitting coil all with the circuit board is connected.

Optionally, the very low frequency electromagnetic signal transmitter further comprises a crystal oscillator circuit connected with the singlechip, wherein the crystal oscillator circuit is used for calibrating the frequency of the RC oscillation circuit in the singlechip.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

the invention adopts SPWM waveform driving, the emitted magnetic field waveform is approximate sine wave, other invalid frequency component values are reduced to the maximum extent in the emitted signal, and the power utilization efficiency is improved; a receiving coil is installed to enable bi-directional communication with an external control device.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic circuit diagram of an extremely low frequency electromagnetic signal transmitter according to an embodiment of the present invention;

fig. 2 is a schematic mechanical structure diagram of an extremely low frequency electromagnetic signal transmitter according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a magnetic field emission circuit according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a monolithic circuit according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a crystal oscillator circuit according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a temperature sensor circuit provided by an embodiment of the present invention;

FIG. 7 is a schematic diagram of a motion sensor circuit provided by an embodiment of the present invention;

FIG. 8 is a schematic diagram of a power circuit according to an embodiment of the present invention;

fig. 9 is a schematic diagram of a voltage stabilizing circuit according to an embodiment of the present invention.

Symbol description:

the device comprises a 1-shell, a 2-battery pack, a 3-insulating cylinder, a 4-iron core, a 5-flange, a 6-receiving coil, a 7-transmitting coil, an 8-first coil stop, a 9-second coil stop, a 10-circuit board, an 11-end cover, a 12-driving circuit and a 13-sensor.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.

Term interpretation:

1) Long-distance oil and gas pipeline: the long-distance oil-gas conveying pipeline refers to an oil-gas conveying system for conveying oil gas to a user through underground, surface or a pipeline combining the underground and the surface, and the long-distance oil-gas conveying pipeline is a main part of the whole oil-gas conveying system.

Oil and gas long-distance pipelines are divided into two types: one for transporting crude oil and finished oil and another for transporting natural gas.

2) In-line operation equipment (PIG): generally refers to a pig, and also generally refers to all equipment that is run within the pipeline, such as various detectors, etc.

3) PIG blocking and positioning: in the process of cleaning a pipeline by using the pipeline PIG, a blocking phenomenon is easy to occur, and thus the stay position of the pipeline PIG is easy to be difficult to determine. An Extremely Low Frequency (ELF) transmitter is mounted on the PIG and the signal can be detected by a detector external to the pipeline to determine where the PIG is located.

4) A transmitter: an electromagnetic wave transmitting device arranged on the PIG adopts a battery to supply power and transmits electromagnetic field signals to the space under the control of a circuit. A circuit within the transmitter applies an excitation signal to the transmitting coil, which generates an alternating electromagnetic field and radiates it into space. The transmitter operates at very low frequencies, and the antenna size used is much smaller than the wavelength, so that only the magnetic field radiation can be considered by neglecting the electric field radiation, the radiation power is proportional to the magnetic field strength generated by the transmitting coil, and the magnetic field strength is proportional to the product of the exciting current and the inductance of the coil.

The soft magnetic material is added into the solenoid type transmitting coil, so that the intensity of a radiation magnetic field can be effectively improved, the radiation power of the magnetic field is improved, and the inductance value of the transmitting coil are improved.

5) Total efficiency (energy efficiency ratio) of the transmitter: defined as the ratio of the total magnetic field strength radiated by the transmitter to space to the electrical power consumed.

6) Extremely Low Frequency (ELF) and frequency bin selection: the 3Hz to 30Hz is defined as Extremely Low Frequency (ELF) electromagnetically, and engineering practice shows that a transmitting machine installed on the PIG has the strongest capability of penetrating through the pipe wall and soil at the working frequency of 22-23 Hz.

7) Vortex effect: the alternating magnetic field may generate an eddy current effect in the metal material, and the magnetic field generated by the eddy current effect may weaken the original magnetic field. The eddy current effect generates heat, which reduces the transmission efficiency of the magnetic field, and should be avoided as much as possible. By adopting a high-resistivity magnetic core or a multilayer iron core, the resistance of the eddy current flowing path can be increased, thereby reducing the influence of the eddy current.

8) Sinusoidal pulse width modulation (Sine pulse width modulation, SPWM): the SPWM method is a relatively mature, widely used PWM method. When narrow pulses with equal impulses and different shapes are applied to links with inertia, the effect is basically the same. The SPWM method is based on the theory, and the PWM waveform, which is the equivalent pulse width to sine wave, is used to control the on-off of the switching device in the inverter circuit, so that the area of the output pulse voltage is equal to the area of the sine wave in the corresponding interval, and the frequency and amplitude of the output voltage of the inverter circuit can be regulated by changing the frequency and amplitude of the modulating wave.

The SPWM variable frequency speed regulation technology is widely applied to speed regulation control of an alternating current motor, and the conversion efficiency can reach more than 95%.

9) H-bridge drive: an H-bridge is an electronic circuit that inverts the voltage/current across a load or output to which it is connected. The circuit can be used for forward and reverse control of a direct current motor, rotation speed control, stepping motor control, most direct current-alternating current converters (such as an inverter and a frequency converter) in electric energy conversion, part of direct current-direct current converters (push-pull converters) and the like, and other power electronic devices.

10 Series resonance): in the series circuit formed from resistor, inductor and capacitor a resistor R and a capacitive reactance X are existed _C Sum inductance X _L Wherein R is the pure resistance value in the loop, and the capacitance resistance X _C The calculation formula is:

；

inductance X _L The calculation formula of (2) is:

；

the calculation formula of the total loop impedance Z is:

；

wherein:for angular frequency, f denotes frequencyThe ratio j represents an imaginary symbol, and R, L and C are a resistance value, an inductance value, and a capacitance value, respectively.

When X is _L And X _C When the absolute values of (a) are equal, the circuit presents pure resistance, which is called series resonance, and at the moment, the circuit presents pure resistance, namely:

Z=R；

the voltage U in the circuit is the same as the phase of the current I, the total impedance in the circuit is the smallest, and the current will reach the maximum.

11 Analog switch): the analog switch mainly completes the signal switching function in the signal link. The signal link is turned off or turned on by adopting a switching mode of an MOS tube; since its function is similar to a switch, it is implemented with the characteristics of an analog device, called an analog switch. Analog switches mainly function as on-signals or off-signals in electronic devices. The analog switch has the characteristics of low power consumption, high speed, no mechanical contact, small volume, long service life and the like.

12 Adjustable regulated power supply): the working principle of the adjustable stabilized voltage supply is that the purpose of adjusting the output voltage of the power supply is achieved by controlling the output voltage of the stabilized voltage circuit. The operating point of a regulating element (such as a zener diode, a transistor, an operational amplifier, etc.) of the regulator circuit can be controlled by the regulating circuit, so as to regulate the magnitude of the output voltage.

13 Digital modulation scheme): the digital modulation modes of the signals are various, and the following are common ones.

On-Off Keying (OOK). The modulation principle of OOK is to control taking one amplitude to be 0 and the other amplitude to be non-0, OOK. Also known as binary amplitude keying (2 ASK), which uses a unipolar non-return-to-zero code sequence to control the turning on and off of a sinusoidal carrier.

Amplitude shift keying (amplitude shift keying, ASK). The carrier wave may have 4 amplitudes after modulation, v0=00, v1=01, v2=10, v3=11, respectively, each amplitude may represent 2 bits. So that its transmission rate is 2 times that of OOK.

Frequency shift keying (Frequency shift keying, FSK). Information is carried by changing the frequency of the carrier wave.

Phase shift keying (Phase Shift Keying, PSK). Information is carried by changing the phase of the carrier wave.

14 The technical principle of the transmitter is as follows.

When the transmitter pipeline installed in the PIG runs, an alternating magnetic field is generated through a circuit or a mechanical mode, penetrates through the pipeline wall and soil and is transmitted to the ground, and the alternating magnetic field is detected by the alternating current receiving device.

The transmitter is preferably used for frequencies near 22 Hz-23 Hz, and magnetic field signals of other frequencies are seriously attenuated after being absorbed by steel pipelines and soil. Because the magnetic field strength of the magnetic field emitted by the transmitter at the ground surface is in the nT magnitude, the current detection device mostly adopts a detection coil as a sensor, and the sensor is only sensitive to alternating current signals, so that the direct current magnetic field cannot be detected by an alternating current receiver.

An ideal transmitter transmits only a single frequency (e.g., 22Hz or 23 Hz) sine wave signal with a transmission efficiency of 100%. If the signal contains both DC magnetic field and magnetic field signal components of other frequencies, the emissivity will be less than 100%.

The output of the detection coil is proportional to the change rate of the space magnetic flux, and the output of the detection coil depends on the total magnetic flux generated by the transmitting coil under certain conditions such as frequency, distance, external dimension and the like. The total magnetic flux is equal to the product of the coil inductance and the excitation current.

Example 1

As shown in fig. 1, the present invention provides an extremely low frequency electromagnetic signal transmitter comprising: the magnetic field transmitter comprises a singlechip, a magnetic field transmitting loop, a receiving coil and an iron core; the magnetic field emission loop comprises a series resonant loop and a driving circuit, wherein the series resonant loop comprises an emission coil, a capacitor network, a resistor network and a current sampling resistor which are sequentially connected in series, the driving circuit is respectively connected with the emission coil and the singlechip, and the driving circuit is used for generating SPWM waveforms to drive the series resonant loop.

The driving circuit is an H-bridge driving circuit and can be realized by a circuit formed by discrete elements such as a triode and a MOS tube.

The H-bridge driving circuit is used for generating an SPWM waveform, and the singlechip is used for adjusting parameters of the SPWM waveform; parameters of the SPWM waveform include duty cycle.

The H-bridge driving circuit and the SPWM waveform form a magnetic field emission driving circuit, 2 input signals of the H-bridge driving circuit come from a digital output port of the singlechip, and the output signals of the H-bridge driving circuit are connected to two ends of the series resonance loop. The singlechip can form 4 driving states including a bidirectional driving state, a standby state and a braking state by controlling 2 input signals of the H-bridge driving circuit.

The receiving coil and the transmitting coil are wound on the iron core, and the receiving coil is connected with the singlechip; the receiving coil is used for receiving an external signal in a stop period (stop period) of the magnetic field emission loop, the singlechip is also used for identifying an external control signal from the external signal, and controlling the magnetic field emission loop to send a response signal in a set signal modulation mode in a next operation period (emission period) of the magnetic field emission loop (after the external control signal is identified); the singlechip is also used for adjusting parameters of the SPWM waveform according to the external control signal.

The very low frequency electromagnetic signal transmitter further comprises a first multi-path analog switch and a second multi-path analog switch; the first multi-path analog switch is respectively connected with the capacitor network and the singlechip, and the second multi-path analog switch is respectively connected with the resistor network and the singlechip.

The first multi-path analog switch and the second multi-path analog switch can be replaced by other switch elements, such as various relays, transistors, field effect transistors, and the like. The first multi-path analog switch and the second multi-path analog switch comprise a plurality of or a plurality of groups of chips and switch contacts. The switch type is not limited to the single pole single throw type, and other types of switches can realize more various combinations of element parameters by reasonably selecting the element parameters connected with the switch contacts.

And the singlechip is also used for judging whether the current of the current sampling resistor is in a set range, and if not, regulating the resistance value of the resistor network through the second multipath analog switch.

The singlechip is also used for comparing the phase of the acquired current of the current sampling resistor with the input signal of the H-bridge driving circuit, and when phase deviation occurs, the resistance value of the resistor network is regulated through the second multipath analog switch.

The very low frequency electromagnetic signal transmitter also comprises a temperature sensor and a motion sensor which are connected with the singlechip; the temperature sensor is used for detecting the environment temperature of the very low frequency electromagnetic signal transmitter, and the motion sensor is used for detecting the acceleration of the very low frequency electromagnetic signal transmitter.

The singlechip is used for collecting the ambient temperature and the acceleration, when the ambient temperature is greater than a first threshold value and the acceleration is greater than a second threshold value, the magnetic field emission loop is started through the H-bridge driving circuit, and otherwise, the magnetic field emission loop is controlled to be in a stop working state.

The first threshold is an environmental temperature threshold for the magnetic field emission loop to work, that is, the magnetic field emission loop works when the environmental temperature of the very low frequency electromagnetic signal transmitter is greater than the first threshold; the second threshold value is an acceleration threshold value at which the magnetic field emission circuit operates, that is, the magnetic field emission circuit operates when the acceleration of the very low frequency electromagnetic signal transmitter is greater than the second threshold value. If the transmission pipeline transmits crude oil, the first threshold value is 40 ℃, and the second threshold value is 0.1g, g is gravity acceleration.

The combination of the thresholds of the temperature sensor and the motion sensor can reduce the power consumption in the non-working state, and can avoid the power consumption caused by the false electrification (because the working condition in the pipeline is not reached, the transmitter still keeps the standby state).

The temperature sensor adopts a discrete element such as a thermistor, a thermocouple, a diode and the like or an integrated chip, and can also adopt a temperature measuring element internally integrated with other functional chips (such as a singlechip, an analog-digital converter and the like).

The very low frequency electromagnetic signal transmitter also comprises a parameter memory connected with the singlechip; the parameter memory is used for storing original information and working parameters of the transmitter, and can also store a certain working record, wherein the working parameters comprise working current and parameters of the SPWM waveform, and the working current is current passing through the current sampling resistor.

The parameter memory adopts an electrically erasable programmable read-only memory (Electrically Erasable Programmable read only memory, EEPROM) or a ferroelectric memory (Ferroelectric Random Access Memory, FRAM) with static current close to zero (less than or equal to 1 mu A), and also can adopt EERPOM or FLASH memory in the singlechip, and the capacity is from tens of bytes to several megabytes.

Parameters of the SPWM waveform also include frequency and amplitude.

The duty cycle of the SPWM waveform is 0.5/1.5.

The ultra-low frequency electromagnetic signal transmitter further comprises an analog-digital converter, and the current sampling resistor and the receiving coil are connected with the singlechip through the analog-digital converter.

The transmitting coil is cylindrical, and the center of the transmitting coil is a round hole. The outer side of the round hole is a cylindrical magnetic core made of soft magnetic materials. And enamelled wires are uniformly wound outside the magnetic core. And determining the size of the battery pack and the size of the transmitting coil according to the mechanical specification parameters of the transmitter, and selecting an enameled wire winding coil with proper specification. The transmitting coil has a DC resistance R _DC ，R _DC And changes with temperature.

The position relation between the receiving coil and the transmitting coil adopts an inner layer and outer layer layout or a front-back layout mode.

The capacitor network is composed of a plurality of capacitors, each capacitor is controlled by an independent switch of the first multipath analog switch to form a capacitor branch, and the plurality of branches are in parallel connection. The capacitance value can meet the regulation requirement in a certain range, generally, the relation of 1, 2, 4 and 8 multiplying power can be adopted, and the capacitance regulation range of 1-15 times can be formed through combination use.

The resistor network is composed of a plurality of resistors, each resistor is controlled by an independent switch of the second multipath analog switch to form a resistor branch, and the plurality of branches are in parallel connection. The resistance value can meet the regulation requirement in a certain range, generally, the relation of 1, 2, 4 and 8 multiplying power can be adopted, and the resistance value regulation range of 0.53-8 multiplying power can be formed through combination use.

The current sampling resistor is used for monitoring the current of the magnetic field emission loop in real time, and is 0.1Ω -1Ω in order not to significantly influence the working state of the emission loop. The current sampling resistor is connected at both ends to an analog-to-digital converter (ADC) for measuring the terminal voltage of the resistor and thus the emission excitation current and for regulation.

The receiving coil is formed by an independent multi-turn coil, and is wound on the iron core together with the transmitting coil. When the transmitting coil is energized, the output signal of the receiving coil is ignored. During the period when the magnetic field transmitting loop is inactive, a magnetic field signal (external signal) from an external device to the transmitter can be received by the receiving coil and an output signal can be transmitted to the ADC. The ADC converts the analog signal and sends the result data to the singlechip. The singlechip analyzes the data and extracts the control instruction contained in the data. Upon receiving a control command (external control signal), the transmitter will either complete the transmitter parameter configuration or feed back the transmitter information to the external device via the transmitting coil, according to the command requirements. The signal modulation modes of the two-way communication can adopt a plurality of modes such as ASK, PSK, FSK, OOK and the like.

The bidirectional communication realized through the receiving coil and the transmitting coil can realize the adjustment of the working parameters of the singlechip.

The singlechip is used for realizing the functions of logic control, waveform generation, communication, parameter storage and the like of the transmitter.

The general single chip microcomputer is adopted, and the specific selection is to give priority to the low-power consumption model.

The outside of the singlechip is provided with a crystal oscillator circuit of 32.768kHz, which is used for calibrating the frequency of an RC oscillating circuit in the singlechip. An accurate 22Hz or 23Hz magnetic field radiation frequency can be generated after calibration. The crystal oscillator circuit adopts a low-frequency crystal oscillator of 32.768kHz, has the advantage of low quiescent current, and is beneficial to reducing standby power consumption.

The singlechip is connected to the control pins of all channels in the first multipath analog switch through a digital control port, so that the total capacitance of the resonant capacitor network can be switched. The connection points of each capacitor of the capacitor network and the analog switch are in a series connection mode. When the analog switch of a certain channel is turned on, the capacitor connected in series with the analog switch is connected, and the total capacitance of the capacitor network is correspondingly increased.

The singlechip is connected to the control pins of all channels in the second multipath analog switch through a digital control port, so that the total resistance value of the resistance network can be switched. The contacts of each resistor of the resistor network and the analog switch are in a parallel mode. When the analog switch of a certain channel is turned on, the resistor connected in parallel with the analog switch is shorted, and the total resistance value of the resistor network is correspondingly reduced.

The analog-digital converter converts the analog signal output by the receiving coil into a digital signal for processing and identification by the singlechip.

The ultra-low frequency electromagnetic signal transmitter further comprises a power supply circuit, wherein the power supply circuit comprises a battery pack and a voltage stabilizing circuit, the battery pack is respectively connected with the H-bridge driving circuit and the voltage stabilizing circuit, and the voltage stabilizing circuit is connected with the singlechip.

As a specific implementation mode, the battery pack is formed by connecting a single battery or a plurality of batteries in series and parallel, and is used for supplying power to all circuits in the very low frequency electromagnetic signal transmitter.

As another embodiment, the battery pack is formed by serially connecting disposable lithium batteries, and the lithium batteries have a higher energy density than rechargeable batteries. After the specification of the battery pack is determined, the rated voltage U and the rated capacity parameter Q of the battery pack can be obtained; the battery pack is placed at the axial center of the transmitter, so that the external dimension of the battery pack is also determined.

The battery pack provides power for the magnetic field emission circuit. In order to match the parameters of the magnetic field emission loop, the duty cycle of the SPWM waveform output needs to be dynamically adjusted to achieve maximum power stability and efficiency.

The voltage stabilizing circuit outputs 3.3V voltage, and the 3.3V voltage provides power for the digital circuit and the analog circuit.

To improve the power utilization efficiency, a 3.3V voltage regulator source typically employs a switching regulator scheme.

The voltage stabilizing circuit part adopts a 3.3V switching voltage stabilizing chip, and the conversion efficiency is generally over 90 percent. The circuit parts except the H-bridge driving circuit are powered by a 3.3V power supply.

According to the requirement of continuous working time t of transmitter, calculating average working current I according to rated capacity of battery pack _{Average of} =q/t. In order to reduce power consumption, the magnetic field emission circuit is operated in an intermittent manner, and the emission period and the stop period are set to be integral multiples of the excitation period. Let the duty cycle of the transmitter be K _d The theoretical emission current should be: i _{Emission of} =I _{Average of} /K _d Since other circuits consume a part of the power, the actual emission current needs to be smaller (typically 80% of the theoretical calculation). And then calculating the direct current resistance of the transmitting coil: r is R _DC =U/I _{Emission of} 。

According to the upper limit value (60 ℃ for example) of the working medium temperature, the corresponding upper limit resistance value R is calculated at the moment _DCH 。

An insulating sleeve is arranged outside the battery pack, and the thickness is generally 0.5 mm-1 mm; the insulation sleeve is provided with a soft magnetic iron core, and the thickness of the soft magnetic iron core is 2 mm-4 mm; the soft magnetic cores are isolated by winding an insulating film, and the thickness is 0.1 mm-0.2 mm; the above constitutes the coil former. And winding a transmitting coil and a receiving coil on the coil framework.

Next, R is as described above _DCH And calculating coil parameters in combination with the limit condition of the size of the transmitting coil to obtain the specification and the number of turns of the wire of the wound coil, and calculating the inductance through an empirical formula or a simulation mode.

The receiving coil is wound by a wire which is as thin as possible so as to wind more turns, and the receiving sensitivity can be improved.

The iron core can also be made of other soft magnetic materials such as permalloy, silicon steel, ferrite and the like, and the forming form can be an axial lamination type, cylindrical winding type or cylindrical axial slotting type.

The invention adopts the scheme of single transmitting coil and H bridge driving, improves the space utilization rate of the double-coil positive and negative excitation mode coil by one time, can wind more turns and provides higher magnetic field radiation capability. The SPWM waveform driving is adopted, the waveform of the emitted magnetic field is approximately sinusoidal, other invalid frequency component values are reduced to the maximum extent in the emitted signal, and the power utilization efficiency (energy efficiency ratio) is improved.

And (3) calculating resonance parameters of the transmitting coil: after the transmitting coil is wound, inductance at 22Hz and direct current resistance at normal temperature are measured by an LCR meter. And comparing the measurement result with the theoretical value, and fine-tuning the specification of the lead to obtain an ideal value.

According to the inductance value L of the transmitting coil and the capacitance value C of the capacitance network, the resonant frequency f of the resonant circuit can be calculated by the following formula:

。

wherein the inductance of the coil in the loop isCapacitive reactance of capacitive network in loop>。

In series resonance, the inductive reactance of the transmitting coil and the capacitive reactance of the capacitor network cancel each other out, the vector sum is zero, the loop impedance is minimum, and the loop impedance z=r=coil direct current resistance R _DC +resistor network R _N The circuit exhibits pure resistance and the loop current is maximum.

By adjusting the capacitance value of the capacitance network, the magnetic field emission loop can generate series resonance at a preset frequency point, and at the moment, the emission current is the largest and the magnetic field radiation is the strongest. The capacitive network is regulated by a first plurality of analog switches. The first multipath analog switch is composed of a plurality of independent single-channel switches, and each channel is correspondingly connected with one capacitor. By combining multiple channels, multiple capacitance values can be combined.

Once the transmitting coil is wound, the inductance is basically constant, and the corresponding resonance capacitance value can be calculated by the above resonance frequency calculation formula. Since the initial accuracy of the capacitor is low and the temperature characteristic is poor, a case where the resonance frequency point is shifted is liable to occur. A group of capacitors are selected in the circuit according to the theoretical calculated value, and the capacitors are combined through an analog switch, so that the capacitors can be maximally close to the theoretical value, and the stability of the resonance frequency point is ensured.

The total direct current resistance of the loop can be changed by adjusting the resistance value of the resistance network, so that the purposes of adjusting the emission current and the radiation intensity of the magnetic field are achieved.

The transmitting coil, if wound with an enameled copper wire, has a positive temperature coefficient of about 0.4%/DEG C. When the temperature is changed from room temperature 20 ℃ to 60 ℃, the resistance value will increase by about 16%, which will result in an increase in the direct current resistance value of the coil in the transmitting loop and the total resistance value of the transmitting coil loop, while the emitted excitation current and the intensity of the magnetic field radiation correspondingly decrease. The resistance value of the resistance network is dynamically adjusted to compensate the resistance change of the copper wire, so that the constant emission current and the constant radiation intensity of the magnetic field can be realized.

The specific driving control of the transmitting coil circuit is as follows:

the transmitting coil circuit is driven by the SPWM waveform generated by the H-bridge driving circuit, and the singlechip controls parameters such as frequency, amplitude, duty ratio and the like of the SPWM waveform.

The SPWM waveform is generated by a timer of the singlechip. First determining the frequency f of the exciting current ₀ (e.g. 22 Hz), and obtaining the modulation frequency f of the SPWM waveform according to the waveform modulation factor M _M =Mf ₀ The value of M is preferably 32-128, which is favorable for limiting the duty ratio of high-frequency harmonic components and ensuring the timing precision of the timer. In the initialization stage of the program, duty ratio coefficient D corresponding to the period of each modulation frequency is calculated _n (n= 1~M) and stored in an array; the overflow period of the timer is additionally set equal to the modulation period. After the program is run, the overflow interrupt of the starting timer is matched with the comparison. The overflow interrupt of the timer corresponds to the beginning of each modulation period, and is taken after the overflow interruptStarting driving current in the service program, and setting the comparison matching value as the current duty ratio value D _n (n= 1~M); after a period of time, the timer count value is equal to the duty cycle value D _n And generating a comparison match, and shutting down the drive current in a comparison match interrupt service routine. The above process is repeated until one excitation current period ends, and then n=1 is set to restart a new excitation control period.

The maximum excitation voltage corresponding to the conventionally calculated duty ratio value is the power supply voltage or the battery pack voltage, and in order to realize the adjustment of the emission excitation current, an SPWM adjustment mode can be adopted. The specific method comprises the following steps: multiplying each duty cycle coefficient of the modulated frequency waveform by a power coefficient K _P （0<K _P <1) Obtaining a new coefficient (K _P D _n ) Using this factor, the excitation current can be adjusted to K, the maximum current _P Multiple times.

As shown in fig. 2, the very low frequency electromagnetic signal transmitter further comprises a shell, an insulating cylinder, a first coil stop, a second coil stop, an end cover and a circuit board, wherein the shell is in threaded connection with the end cover, a sealing ring can be installed between the shell and the end cover according to the working pressure and sealing requirements, and a disc-shaped mounting flange is welded on the outer side of the shell, so that the very low frequency electromagnetic signal transmitter can be conveniently mounted on other equipment.

The battery pack is located in the insulating cylinder, the insulating cylinder is located in the cylindrical iron core, the circuit board is located in the end cover, the first coil stop and the second coil stop are located at two ends of the iron core, the receiving coil and the transmitting coil are limited between the first coil stop and the second coil stop, and the receiving coil and the transmitting coil are connected with the circuit board. The outer side of the iron core is wound with an insulating film or an insulating tape, and then the transmitting coil and the receiving coil are wound.

The housing is made of non-magnetic materials such as various metals (e.g. 304 stainless steel), plastics, and the like, wherein the plastics comprise polyether ether ketone (PEEK), polyoxymethylene (POM), acrylonitrile-butadiene-styrene (ABS) and the like.

The shape of the shell comprises a cylinder, a cuboid and a cube.

As a specific implementation mode, the shell and the end cover are made of 304 stainless steel materials, the magnetic permeability is close to 1, and the radiation of the magnetic field is not obviously affected. The insulating cylinder, the first coil stop block and the second coil stop block are made of plastic materials.

An electronic hardware circuit other than the transmitting coil and the receiving coil is mounted on the circuit board.

The invention can compensate the inductance in the transmitting coil loop through the capacitance network with adjustable parameters, so that the loop is in a state similar to series resonance, the transmitting current under the same coil is close to the theoretical maximum value, and the space utilization rate and the power supply utilization efficiency are improved.

The invention can compensate under the condition of the resistance change of the transmitting coil caused by temperature change through the resistance network with adjustable parameters, and can keep the stability of transmitting power.

The invention can carry out bidirectional communication with an external control device through the receiving coil.

According to the invention, the temperature sensor can detect the ambient temperature and compensate the working parameters.

The invention can detect and judge the state of the transmitter through the motion sensor and control the working mode of the transmitter.

The circuit hardware of the very low frequency electromagnetic signal transmitter is as follows. Fig. 4-9 constitute a schematic circuit diagram of an extremely low frequency electromagnetic signal transmitter.

As shown in fig. 8, in the power supply circuit, BT1 is a battery pack; the battery pack adopts 3 batteries of ER14505M power type lithium batteries, and has the rated voltage of 10.8V and the rated capacity of 2200mAh.

As shown in FIG. 9, the voltage stabilizing circuit UP1 is a voltage stabilizing chip, the model is TPS54302, and is set by an external resistor R8 and a resistor R7The output voltage is V _CC =3.3v. The resistor R5 and the resistor R6 form a voltage dividing circuit, and the voltage value of the voltage dividing value VPEN is about 2.7V and is connected to the 5-pin enabling end of the voltage stabilizing chip. The other elements CA1, C7 and C9 in the power supply circuit are all filter capacitors, C8 is a switch capacitor, and L3 is a 10uH inductor. The battery pack BT1, the filter capacitor CA1 and the filter capacitor C7 are connected in parallel, a resistor R5 and a resistor R6 are connected in series at two ends of the filter capacitor C7, and a voltage division value VPEN is arranged between the resistor R5 and the resistor R6. The voltage value of the battery BT1 is VBAT.

The singlechip U1 is a 32-bit ARM inner core singlechip, and as shown in fig. 4, the singlechip U1 is AT32F403ACGT7, and the highest working frequency is 200MHz. Power pins, crystal oscillator pins, and part of General Purpose Input Output (GPIO) pins are used. The crystal oscillator Y1 is a 32.768kHz low-frequency crystal oscillator, C5 and C6 are load capacitors, and two ends of a crystal oscillator circuit are connected to pins OSC32A and OSC32B of the singlechip.

As shown in FIG. 3, the H-bridge driving circuit U2 is DRV8870, the output terminal pin 8 and the pin 6 are connected to the magnetic field excitation loop, the pin 2 and the pin 3 are driving control terminals, and are connected to the GPIO of the singlechip. Pin 5 is the drive power input, which is connected to the battery pack positive voltage VBAT.

The capacitor network comprises capacitors C1-C4 and a first multipath analog switch U3. The capacitors C1-C4 are shown in FIG. 3, 22uF, 10uF, 4.7uF and 2.2uF are respectively X7R material capacitors, and have smaller temperature coefficients. The model of the first multipath analog switch U3 is TS3A4751, and 4 paths of independent Single Pole Single Throw (SPST) analog switches are arranged inside the first multipath analog switch U. Each switch comprises a control end INx and two switch ends COMx and NOx, and x takes on the value of 1 to 4. The COM ends of the 4-way switch are connected together, and the other ends of the 4-way switch are respectively connected to the capacitors C1-C4. The on-off of each switch is controlled through input signals CSEL 1-CSEL 4, the connection of the capacitor can be controlled independently, the minimum value of the capacity adjusting range of the capacitor is 2.2uF, and the maximum value of the capacity adjusting range of the capacitor is 38.9uF. The values of the capacitors C1-C4 are required to be based on the inductance value of the coil, so that the capacity adjustment range of the capacitor network can effectively compensate the inductance in the transmitting coil loop, and the loop is in an approximately series resonance state.

The resistor network comprises resistors R1-R4 and a second multi-path analog switch U4. As shown in FIG. 3, the resistors R1-R4 are respectively 100 omega, 51 omega, 25 omega and 12 omega, which are the resistors with the precision better than 1% and the temperature coefficient less than or equal to 50ppm. The model of the second multi-path analog switch U4 is TS3A4751, and 4 paths of independent Single Pole Single Throw (SPST) analog switches are arranged inside the second multi-path analog switch U. Each switch comprises a control terminal INx and two switch terminals COMx and NOx. The COM ends of the 4-way switch are connected together, and the other ends of the 4-way switch are respectively connected to the resistors R1-R4. The on-off of each switch is controlled through input signals RSEL 1-RSEL 4, the connection of the resistors can be controlled independently, the minimum value of the resistance adjusting range of the resistors is about 6.3 omega, and the maximum value of the resistance adjusting range of the resistors is 100 omega. The resistor network may use digital potentiometers in addition to passive resistor elements. The digital potentiometer internally comprises an integrated resistor network and a programmable switch, and the resistance value of the digital potentiometer can be changed through a control interface of the digital potentiometer, so that the effect of variable resistance can be achieved. The resistors can also be connected in series, and the adjusting effect can be achieved. The values of the resistors R1-R4 are required to be based on the direct current resistance value of the coil and the working current condition of the transmitter, so that the resistance value adjusting range of the electric resistance network can effectively compensate the temperature change of the resistance value in the loop of the transmitting coil, and the exciting current of the loop is kept stable and meets the preset continuous working time.

As shown in fig. 3, a transmitting coil L1, a capacitor network, a resistor network, and a current sampling resistor R _sen After being connected in series, the transmitter coil resonant circuit (series resonant circuit) is formed.

U5 in the ADC circuit is a 16-bit dual-channel analog-digital converter (ADC), and the model is ADS1112. Analog signal input terminals AIN0 and AIN1 of the two-channel converter U5 are respectively connected to a current sampling resistor R _sen For measuring the transmit loop current; analog signal input terminals AIN2 and AIN3 of the two-channel converter U5 are respectively connected to two ends of the receiving coil L2, for detecting communication signals.

As shown in fig. 6, the temperature sensor U6 is a TMP100, and is used for measuring the system temperature, and the temperature acquisition result can be used for system function control and temperature compensation by adopting I2C bus communication.

As shown in FIG. 7, the motion sensor U7 is ADXL345, and is used for measuring acceleration and motion conditions, I2C bus communication is adopted, and a pin 8 of the U7 has an interrupt output function, so that motion can be detected in a low power consumption state, and a singlechip and a system can be awakened through the pin.

The chip model of the parameter memory is BL24C16F, is an EEPROM chip with 2 kbyte capacity and is used for storing system parameters and working parameters.

The working flow of the very low frequency electromagnetic signal transmitter is as follows.

After power-on, the singlechip reads the content of the parameter memory, configures working parameters, and completes the initialization of internal resources and peripheral devices of the singlechip.

And calibrating an RC oscillation clock signal in the singlechip through an external 32.768kHz crystal oscillator signal.

The singlechip reads the data of the temperature sensor and the motion sensor at regular time, and adjusts the resonant capacitor network and the resistor network through the first multi-path analog switch and the second multi-path analog switch according to the current working parameter setting and the sensor data so as to enable the resonant capacitor network and the resistor network to meet the preset transmitting power setting.

And comparing the data of the temperature sensor and the motion sensor with a set starting threshold value, and starting a transmitting function after the data meets the working conditions.

According to the set working period, in the working period of the transmitter, a timer in the singlechip is used for timing waveforms, and a digital port is used for outputting a signal to control an H-bridge driver to excite a series resonant circuit comprising a transmitting coil, so that the magnetic field radiation is effective; in the stop time period of the transmitter, a standby signal is output at the digital port, the H bridge stops working, the transmitting coil has no exciting current, and the magnetic field radiation stops. Taking excitation frequency of 22Hz as an example, taking 1.5 seconds as a period, wherein the working period is 0.5 seconds, corresponding to 11 excitation periods, the stop time is 1 second, corresponding to 22 excitation periods, and the duty ratio of a transmitting loop is 0.5/1.5=33.3%. With the above treatment, the battery operating time is correspondingly prolonged to 3 times.

The current sampling resistor of the magnetic field emission loop is used for monitoring the emission current value, and the resistance value of the resistor network is regulated through the second multipath analog switch, so that the emission current in a certain range is regulated, and the requirements of different working conditions can be met. In addition, the direct current resistance of the transmitting coil is changed due to the temperature change of the medium in the pipeline, and the direct current resistance can be compensated through a resistance network.

The singlechip compares the phase of the acquired current signal with the phase of the excitation signal, and when phase deviation occurs, the singlechip shows that the series resonant circuit contains reactance components (X is not equal to 0), and the second multipath analog switch is used for adjusting the capacitance network, changing the access capacitance value of the series resonant circuit, reducing the reactance components of the resonant circuit and enabling the series resonant circuit to approach to a pure resistive state.

In the communication process, the external device detects the state of the transmitting signal of the transmitter. In the period of stopping the transmitting signal of the transmitter, the external device transmits a control signal to the transmitter, the control signal can be received by a detection coil in the transmitter, the control signal is converted into a digital signal through an ADC (analog-to-digital converter), the digital signal is input into a singlechip, the singlechip identifies the external control signal according to a preset signal demodulation mode and responds to the external control signal in the next transmitting stage through a specific signal modulation mode, and the signal is received by the external device, so that a complete bidirectional communication process is formed.

The invention achieves the following technical effects:

1. the power supply efficiency is high and stable: the invention adopts low-impedance H-bridge driving and SPWM wave to output sine wave excitation signals, and the transmitting coil is wound by a single wire, so that the structure is simple; the alternating current fundamental frequency component in the magnetic field excitation signal accounts for most of the components, the direct current component and the harmonic component are weak, and the power supply efficiency is high.

2. And the working parameters are automatically adjusted in real time: the invention monitors the battery voltage, the ambient temperature, the emission current and the emission frequency in real time, and automatically adjusts the circuit parameters according to the data so that the intensity of the radiation magnetic field is kept constant. The method comprises the following steps: 1) Series resonance parameter adjustment: and the resonant capacitance parameters are adjusted (the multi-path analog switch is used for switching the resonant capacitance to be connected in) to adapt to different pipelines (the pipeline parameters influence the inductance and then change the resonant frequency to influence the efficiency). 2) Transmit power adjustment: the excitation current can be adjusted by adjusting the duty ratio coefficient of the SPWM waveform, so that the transmitting power is changed, and the power utilization rate can be improved; 3) Temperature compensation: the operating current is compensated based on the resistivity changes of the copper wire at different temperatures. 4) Dynamic adjustment: the excitation current is monitored and subjected to closed-loop regulation, and the average power is consistent with the target value in a multi-period average mode.

3. Two-way communication function: the invention can carry out half duplex bidirectional communication with an external device, can receive external instructions to configure working parameters, and can upload the state of a transmitter. By setting working parameters, the transmitter can meet different pipeline working condition requirements, and one machine is multipurpose.

4. Transmitter state real-time monitoring: the emitter is provided with a temperature sensor and a motion sensor, and the position and the state of the emitter are judged according to the temperature and the acceleration, and the starting of a power supply is controlled. When the set working threshold is not reached, the power supply is automatically turned off, and misoperation is avoided.

When blocking occurs, the working parameters of the transmitter are adjusted in real time according to the residual electric quantity of the battery and the detection data of the motion sensor, so that the energy-saving effect is realized, and the premature exhaustion of the electric quantity of the battery is avoided.

In summary, the extremely low frequency electromagnetic signal transmitter provided by the invention has a high-efficiency transmitting circuit structure, improves the energy efficiency ratio of the transmitter and prolongs the continuous working time; the stability of the intensity of the radiation magnetic field can be ensured by automatically adjusting the working parameters; the stability and the continuity of signal emission can be ensured through the detection of working conditions; the applicability of the transmitter can be improved and the transmitter state can be obtained by carrying out parameter configuration on the transmitter through bidirectional communication.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.

The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.

Claims

1. An extremely low frequency electromagnetic signal transmitter, comprising: the magnetic field transmitter comprises a singlechip, a magnetic field transmitting loop, a receiving coil, an analog-digital converter and an iron core; the magnetic field emission loop comprises a series resonant loop and a driving circuit, the series resonant loop comprises an emission coil, a capacitor network, a resistor network and a current sampling resistor which are sequentially connected in series, the driving circuit is respectively connected with the emission coil and the singlechip, and the driving circuit is used for generating SPWM waveforms to drive the series resonant loop;

the receiving coil and the transmitting coil are wound on the iron core, and the receiving coil is connected with the singlechip through the analog-digital converter; the receiving coil is used for receiving an external signal in a working time period of the magnetic field emission loop, the singlechip is also used for identifying an external control signal from the external signal and controlling the magnetic field emission loop to send a response signal in a set signal modulation mode in the next working time period of the magnetic field emission loop; the singlechip is also used for adjusting parameters of the SPWM waveform according to the external control signal;

the extremely low frequency electromagnetic signal transmitter further comprises a temperature sensor and a motion sensor which are connected with the singlechip; the temperature sensor is used for detecting the ambient temperature, and the motion sensor is used for detecting the acceleration of the very low frequency electromagnetic signal transmitter;

2. The very low frequency electromagnetic signal transmitter of claim 1, further comprising a first multi-path analog switch and a second multi-path analog switch; the first multi-path analog switch is respectively connected with the capacitor network and the singlechip, and the second multi-path analog switch is respectively connected with the resistor network and the singlechip;

the singlechip is also used for comparing the phase of the acquired current of the current sampling resistor with the input signal of the driving circuit, and when phase deviation occurs, the capacitance value of the capacitance network is adjusted through the first multipath analog switch.

3. The very low frequency electromagnetic signal transmitter of claim 1, further comprising a parameter memory coupled to the single chip microcomputer; the parameter memory is used for storing working parameters, wherein the working parameters comprise working current and parameters of the SPWM waveform, and the working current is current passing through the current sampling resistor.

4. The very low frequency electromagnetic signal transmitter of claim 1, wherein the parameters of the SPWM waveform further comprise frequency, the duty cycle of the SPWM waveform being 0.5/1.5.

5. The very low frequency electromagnetic signal transmitter of claim 1, wherein the drive circuit is an H-bridge drive circuit.

6. The very low frequency electromagnetic signal transmitter of claim 1, wherein the current sampling resistor is connected to the single chip microcomputer through the analog-to-digital converter.

7. The very low frequency electromagnetic signal transmitter of claim 1, further comprising a battery pack and a voltage stabilizing circuit, wherein the battery pack is connected to the voltage stabilizing circuit, and wherein the voltage stabilizing circuit is connected to the single chip microcomputer.

8. The very low frequency electromagnetic signal transmitter of claim 7, further comprising a housing, an insulating cylinder, a first coil block, a second coil block, an end cap, and a circuit board, wherein the housing is in threaded connection with the end cap, a wafer-shaped mounting flange is welded on the outer side of the housing, the insulating cylinder, the transmitting coil, the receiving coil, the first coil block, the second coil block, and the circuit board are positioned in a cavity formed by the housing and the end cap, the battery pack is positioned in the insulating cylinder, the insulating cylinder is positioned in the cylindrical iron core, the circuit board is positioned in the end cap, the first coil block and the second coil block are positioned at both ends of the iron core, the receiving coil and the transmitting coil are positioned between the first coil block and the second coil block, and the receiving coil and the transmitting coil are all connected with the circuit board.

9. The very low frequency electromagnetic signal transmitter of claim 1, further comprising a crystal oscillator circuit connected to the single chip microcomputer, the crystal oscillator circuit being configured to calibrate a frequency of an RC oscillating circuit within the single chip microcomputer.