CN110703343A - Wide-matching-resonance magnetic resonance detection device and detection method based on PWM (pulse-Width modulation) regulation and control technology - Google Patents
Wide-matching-resonance magnetic resonance detection device and detection method based on PWM (pulse-Width modulation) regulation and control technology Download PDFInfo
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/14—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electron or nuclear magnetic resonance
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- G05F1/10—Regulating voltage or current
- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
- G05F1/565—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor
- G05F1/569—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for protection
- G05F1/571—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for protection with overvoltage detector
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- H—ELECTRICITY
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- H03K—PULSE TECHNIQUE
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- H03K7/08—Duration or width modulation ; Duty cycle modulation
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- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
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Abstract
The invention relates to a wide-matching resonance detection device and a detection method based on a PWM (pulse-width modulation) regulation and control technology, which comprises the steps that a PC (personal computer) upper computer sends transmission parameters to an STM32+ FPGA (field programmable gate array) transceiving main control module, displays the working state and stores the acquired magnetic resonance signal data; the transmitting system comprises a storage battery, an energy storage capacitor is charged after the conversion of the storage battery by a DC-DC converter, and the storage battery is connected with an H-bridge transmitting module through a high-power diode, and the H-bridge transmitting module is connected to a controllable constant voltage source through a low-power diode; the STM32+ FPGA transceiving main control module drives the H-bridge transmitting module through the PWM driving module; the PWM driving module is connected to the receiving and transmitting switching device through a bidirectional diode; the receiving system is controlled by the receiving and transmitting switching device to be connected with the receiving and transmitting integrated coil; and according to the instruction of the main control module, the transmitting and receiving switching device controls the connection between the transmitting system or the receiving system and the transmitting and receiving integrated coil. The problem of the turn-off time of traditional tuning when adopting the transmission of receiving and dispatching integrative coil is long is solved, the dead time of magnetic resonance detection device has been reduced.
Description
Technical Field
The invention relates to the field of geophysical exploration equipment, in particular to a wide-band resonance detection device and method based on a PWM (pulse-width modulation) regulation and control technology.
Background
The ground Magnetic Resonance (MRS) technology is an effective geophysical detection method and is widely applied in the fields of shallow groundwater detection, disaster water source detection and the like. When magnetic resonance detection is carried out, the transmitting system transmits excitation pulses through the transmitting coil to excite hydrogen protons in water, and then the receiving system collects magnetic resonance signals induced by the receiving coil. The current magnetic resonance detection technology adopts an LCR series resonance mode for transmission, a transmitting coil can be equivalent to the series connection of an inductor and a resistor, and then is connected in series with a capacitor with a proper value to match resonance, so that the resonance is carried out at a Larmor frequency point, the equivalent impedance of a load can be reduced, and the detection depth is larger under the condition of the same transmission voltage. However, after the LCR series resonance is transmitted, the current oscillates and attenuates, which causes slow transmission shutdown, so that the acquired signal is delayed, and since the magnetic resonance signal is in an e-exponential attenuation form, an early large amplitude signal cannot be acquired. Especially, when the water-bearing stratum is a sandy clay stratum, the average relaxation time is less than 30ms, the signals are acquired after the emission is completely turned off, the attenuation of the signals is serious, a large amount of signals are lost, effective magnetic resonance signals can hardly be detected, and the detection effect is seriously influenced.
Disclosure of Invention
In view of the above-mentioned problems in the prior art, the technical problem to be solved by the present invention is to provide a wide-band resonance detection apparatus based on PWM control technology, which solves the problems of serious signal attenuation, large signal loss, and almost no detection of effective magnetic resonance signals.
The invention also aims to provide a wide-harmonic magnetic resonance detection method based on the PWM regulation and control technology.
The invention is realized in this way, a wide-matching magnetic resonance detection device based on PWM regulation and control technology is used for shallow magnetic resonance detection, the device includes: PC host computer, STM32+ FPGA receiving and dispatching main control module, transmitting system, receiving and dispatching switching device, receiving and dispatching integrated coil and receiving system, wherein,
the PC upper computer is used for man-machine interaction, sending transmission parameters to the STM32+ FPGA transceiving main control module, displaying the working state and storing the acquired magnetic resonance signal data;
the transmitting system comprises a storage battery, an energy storage capacitor, a high-power diode and an H-bridge transmitting module, wherein the storage battery is charged after being converted by a DC-DC converter and is connected with the H-bridge transmitting module through the high-power diode; the STM32+ FPGA transceiving main control module drives the H-bridge transmitting module through the PWM driving module; the H-bridge transmitting module is connected to the receiving and transmitting switching device through a bidirectional diode;
the receiving system is controlled by the receiving and transmitting switching device to be connected with the receiving and transmitting integrated coil;
and the receiving and transmitting switching device controls the connection of the transmitting system or the receiving system and the receiving and transmitting integrated coil by receiving the instruction of the STM32+ FPGA receiving and transmitting main control module.
Further, receiving system includes preamplification circuit, signal conditioning circuit, programme-controlled amplification module, LPF module and AD conversion module, receiving system's preamplification circuit is connected to receiving and dispatching auto-change over device, amplifies the signal through preamplification circuit, transmits to STM32+ FPGA receiving and dispatching host system after passing through signal conditioning circuit, programme-controlled amplification module, LPF module and AD conversion module in proper order.
Furthermore, the receiving and dispatching switching device comprises a switch driving module and a receiving and dispatching switching switch, wherein the switch driving module controls the connection between the transmitting system or the receiving system and the receiving and dispatching integrated coil through the receiving and dispatching switching switch according to the instruction of the receiving STM32+ FPGA receiving and dispatching main control module.
Furthermore, the STM32+ FPGA transceiver main control module is used for interacting with an upper computer, calculating parameters and controlling the detection working sequence; controlling the DC-DC converter to store the energy in the storage battery to the energy storage capacitor; adjusting the voltage value of the controllable constant voltage source; generating two paths of PWM control signals through a PWM driving module; the receiving and transmitting switch is controlled to select the connection of the receiving and transmitting integrated coil and the H-bridge transmitting module or the pre-amplification circuit through the control switch driving module; and controlling the A/D conversion module to collect the signals sensed by the receiving-transmitting integrated coil, amplifying the signals through the preamplification circuit, conditioning the signals through the signal conditioning circuit, amplifying the signals again through the program control amplification module, filtering the magnetic resonance signals through the LPF module, and adjusting the gain of the program control amplification module.
Furthermore, an energy storage capacitor of the transmitting system is a high-voltage large-capacitance capacitor and is used for providing energy during transmitting; the high-voltage pulse at the moment of turn-off is clamped by a controllable constant-voltage source with the voltage value higher than the voltage of the energy storage capacitor, so that an IGBT (insulated gate bipolar translator) of a switching device forming the H-bridge transmitting module is protected, and the energy of a guide coil is quickly released in the dead time of the transmitting pulse.
Furthermore, the high-power diode is a reverse high-voltage fast recovery diode with a unidirectional conduction characteristic, and blocks a discharge loop formed by an energy storage capacitor and an H-bridge emission module within the dead time of an excitation pulse; and prevent the controllable constant voltage source from discharging to the energy storage capacitor; isolating instantaneous pulses generated by coil discharge within the dead time of the excitation pulse and protecting the capacitor;
the low-power diode is a reverse high-voltage fast recovery diode with a unidirectional conduction characteristic, and prevents the controllable constant voltage source from discharging to the energy storage capacitor, the H-bridge transmitting module, the bidirectional diode and the coil; the controllable constant voltage source is only used for clamping in the dead time of the excitation pulse and does not release energy through the transmitting loop;
the bidirectional diode comprises two diodes which are connected in parallel in an opposite direction and used for transmitting residual energy absorption.
Further, in the transmitting phase: when a PWMA signal or a PWMB signal sent by the PWM driving module is effective, a group of IGBTs in the H-bridge transmitting module are conducted, an energy storage capacitor, a high-power diode, a group of IGBTs, a bidirectional diode and a receiving and transmitting integrated coil which is equivalent to a series connection of an inductor L and a resistor R form a loop, and the controllable constant voltage source Ur is equivalent to open circuit due to the unidirectional conductivity of the low-power diode; when the PWMA signal and the PWMB signal are invalid, the excitation pulse dead time is entered, because of the one-way conductivity of the high-power diode, the energy storage capacitor is equivalent to open circuit in the period, and the energy release loop of the receiving and transmitting integrated coil is composed of an H-bridge transmitting module, a low-power diode and a controllable constant voltage source, so that the purposes of equal-amplitude high-quality waveform transmission and quick turn-off are realized.
A wide-band resonance detection method based on a PWM (pulse-width modulation) regulation and control technology comprises the following steps:
step 301: the STM32+ FPGA transceiving main control module identifies parameters and working start signals sent by a PC upper computer and comprises an excitation current ImThe number M of the emission currents, the number k of the superposition times and the excitation pulse frequency f are calculated, the emission pulse time t and the number n of pulse periods are calculated, and the actual excitation time t is transmitted back to the PC upper computer, wherein M and n are positive integers;
step 302: the STM32+ FPGA transceiving main control module controls a transceiving switch to switch a transceiving integrated coil to be connected with a pre-amplification circuit of a receiving system by controlling a switch driving module in the transceiving switching device so as to prepare to enter a gain adjustment and noise acquisition stage;
step 303: the STM32+ FPGA transceiving main control module controls the receiving system to collect noise signals through the transceiving integrated coil, and adjusts the gain of the program control amplification module according to the amplitude of the collected signals;
step 304: judging whether the gain adjustment of the program control amplification module is finished, if so, continuing to enter the step 305, otherwise, returning to the step 303, and judging the basis for finishing the gain adjustment is as follows: the signal amplitude acquired by the A/D conversion module is between 1/2 full scale and full scale of A/D;
step 305: the STM32+ FPGA transceiving main control module controls a transceiving selector switch through a transceiving selector device to switch a transceiving integrated coil to be connected with an H-bridge transmitting module of a transmitting system to prepare for entering a bipolar pulse excitation stage;
step 306: STM32+ FPGA transceiving master control module rootAccording to the excitation current ImAnd calculating the excitation voltage U according to the constraint conditionSDuty cycle d of excitation pulse and clamping voltage UDC；
Step 307: the STM32+ FPGA transceiving main control module adjusts the voltage value of the controllable constant voltage source according to the calculated clamping voltage value UDC;
step 308: judging whether the clamping voltage reaches a clamping voltage value UDC, if so, continuing to enter a step 309, otherwise, returning to the step 307;
step 309: the STM32+ FPGA transceiving main control module controls the DC-DC converter to charge the energy storage capacitor according to the excitation voltage value;
step 310: judging whether the charging is finished or not, if the judgment basis of finishing the charging is that the excitation voltage value is reached, entering step 311 if the charging is finished, otherwise returning to step 309;
step 311: STM32+ FPGA receives and dispatches the master control module control PWM drive and produce two routes of duty ratio and be d, time interval T/2's drive signal, through H bridge transmitting module, bidirectional diode and the integrative coil transmission n cycles of receiving and dispatching, the excitation pulse of frequency is f. The purpose of emitting pulses of n cycles instead of fixed duration is to turn off the excitation pulses at the whole cycle, thereby reducing the dead time;
step 312: delaying for 800us after the transmission is turned off to ensure that all transmission actions are completed, switching the receiving and transmitting integrated coil to be connected with a pre-amplification circuit of a receiving system, and preparing to enter a signal acquisition stage;
step 313: the STM32+ FPGA transceiving main control module controls the A/D conversion module to sample signals and store the signals to the PC upper computer, and the received signals correspond to the transmitting time t in the step 301 during storage;
step 314: judging whether current detection is finished, if so, continuing to enter step 315, otherwise, returning to step 309;
step 315: and judging whether to detect the next current value or not, finishing the detection, and returning to the step 305 if not.
Further, step 306: STM32+ FPGA transceiver main control module according to excitation current ImAnd calculating the excitation voltage according to the constraint conditionUSDuty cycle d of excitation pulse and clamping voltage UDCAnd satisfies the following conditions:
wherein, T is the transmission pulse cycle, satisfies T1/f, and R is coil equivalent resistance value, and L is coil equivalent inductance value, and each volume all adopts SI unit system in the formula, and the constraint condition is:
UDC≤1000
0.25≤d≤0.45
the aim is to make
And C is the capacitance value of the energy storage capacitor.
Further, step 310: the charging is performed after the constant voltage source adjustment.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention provides a transmitting mode adopting wide harmonic matching, which effectively solves the problem of long turn-off time of the traditional harmonic matching when transmitting by adopting a transmitting-receiving integrated coil and reduces the dead time of a magnetic resonance detection device; the problem of because lead to the transmission turn-off slower for the signal delay of collection, can't acquire the large amplitude signal in early stage is solved.
(2) The invention adopts the constant voltage clamping circuit formed by the controllable constant voltage source and the diode, shortens the dead time, simultaneously inhibits the transient pulse and prolongs the service life of the instrument;
(3) the invention realizes the constant-amplitude emission in a wide-tuning emission mode by changing the emission duty ratio, and improves the emission waveform quality.
Drawings
Fig. 1 shows a schematic structural diagram of a wide-resonance magnetic resonance detection device based on a PWM control technique according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating a controllable active clamp transmit loop provided by an embodiment of the present invention;
fig. 3 is a schematic diagram illustrating a working flow of wide-band resonance detection based on a PWM control technique according to an embodiment of the present invention;
fig. 4 shows a wide-resonance magnetic resonance detection excitation current and a wide-resonance magnetic resonance detection excitation current waveform diagram based on the PWM control technique according to the present invention, in which (a) is the wide-resonance magnetic resonance detection excitation current waveform diagram, and (b) is the excitation current waveform diagram provided by the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, a wide-matching magnetic resonance detection apparatus based on PWM control technique for shallow magnetic resonance detection includes: PC host computer 1, STM32+ FPGA receiving and dispatching main control module 2, transmitting system, the receiving and dispatching auto-change over device that constitutes by switch drive module 12, receiving and dispatching change over switch 13, receiving and dispatching integrative coil 14 and receiving system.
According to the instruction of the STM32+ FPGA transceiving master control module, the transceiving switching device controls the connection condition of the receiving system, the transmitting system and the transceiving integrated coil.
In this embodiment, the transmitting system includes a storage battery 3, a DC-DC converter 4, an energy storage capacitor 5, a controllable constant voltage source 6, a PWM driving module 7, a high-power diode 8, a low-power diode 9, an H-bridge transmitting module 10 and a bidirectional diode 11, where the DC-DC converter 4 is connected to the STM32+ FPGA transceiver main control module, receives the control of the STM32+ FPGA transceiver main control module, the storage battery 3 charges the energy storage capacitor 5 through the DC-DC converter 4, the energy storage capacitor 5 is connected to the H-bridge transmitting module 10 through a high-power diode 8, and transmits current to the transceiver integrated coil through the H-bridge transmitting module 10.
The controllable constant voltage source 6 is connected with an H-bridge transmitting module 10 through a low-power diode 9, the H-bridge transmitting module 10 is connected with a receiving and transmitting switching device through a bidirectional diode 11, the H-bridge transmitting module 10 controls a switching device IGBT through a PWM driving module 7, and the PWM driving module 7 receives an instruction of STM32+ FPGA receiving and transmitting main control module.
The receiving system comprises a preamplification circuit 15, a signal conditioning circuit 16, a program control amplification module 17, an LPF (Low pass filter) module 18 and an A/D conversion module 19, wherein in the receiving stage, the receiving and transmitting switching device is conducted with a receiving and transmitting integrated coil, signals are collected by the preamplification circuit 15, the signal conditioning circuit 16, the program control amplification module 17, the LPF (Low pass filter) module 18 and the A/D conversion module 19 to an STM32+ FPGA receiving and transmitting main control module in sequence.
The PC upper computer 1 is used for man-machine interaction, sending transmitting parameters to the STM32+ FPGA transceiving main control module 2, displaying the working state and storing the acquired magnetic resonance signal data;
the STM32+ FPGA transceiving master control module 2 is used for interacting with an upper computer, calculating parameters and controlling the detection working time sequence;
the STM32+ FPGA transceiving master control module 2 is also used for controlling the DC-DC converter 4 to store the energy in the storage battery 3 to the energy storage capacitor 5;
the STM32+ FPGA transceiving master control module 2 is also used for adjusting the voltage value of the controllable constant voltage source 6;
the STM32+ FPGA transceiving master control module 2 is also used for generating two paths of PWM control signals through the PWM driving module 7;
the STM32+ FPGA transceiving master control module 2 is further used for controlling the transceiving switch 13 to select the transceiving integrated coil 14 to be connected with the bidirectional diode 11 or the preamplification circuit 15 by controlling the switch driving module 12;
the STM32+ FPGA transceiving master control module 2 is also used for controlling the A/D conversion module 19 to collect magnetic resonance signals induced by the transceiving integrated coil 14, amplified by the preamplification circuit 15, conditioned by the signal conditioning circuit 16, amplified again by the program control amplification module 17 and filtered by the LPF module 18;
the STM32+ FPGA transceiving master control module 2 is further configured to adjust the gain of the program-controlled amplification module 17.
Further, in the present embodiment, the energy storage capacitor 5 is a high-voltage large-capacitance capacitor, and is used for providing energy during transmission; in the transmitting system in the embodiment, the voltage value of the controllable constant voltage source 6 is higher than the voltage of the energy storage capacitor, so that high-voltage pulses at the moment of turn-off are clamped, a switching device IGBT forming an H-bridge transmitting module is protected, and the energy of a guide coil is quickly released within the dead time of transmitting pulses;
the high-power diode 8 is a reverse high-voltage fast recovery diode and has a unidirectional conduction characteristic. A discharge loop formed by the energy storage capacitor 5 and the H-bridge emission module 10 in the dead time of the excitation pulse is blocked; the controllable constant voltage source 6 is prevented from discharging to the energy storage capacitor 5; and transient pulses generated by coil discharge within the dead time of the excitation pulse are isolated, so that the capacitor is protected.
The low-power diode 9 is a reverse high-voltage fast recovery diode and has a unidirectional conduction characteristic. The controllable constant voltage source 6 is prevented from discharging to the energy storage capacitor 5, the H-bridge transmitting module 10, the bidirectional diode 11 and the transceiver integrated coil 14; it is ensured that the controllable constant voltage source 6 is only used for clamping during the dead time of the firing pulse and not for releasing energy through the firing loop.
And the bidirectional diode 11 is composed of two diodes connected in reverse parallel and used for transmitting residual energy absorption.
In the transmitting stage:
a schematic diagram of a controllable active clamp transmitting loop is shown in fig. 2, when a PWMA signal (or a PWMB signal) is effective, a group of IGBTs in an H-bridge transmitting module are conducted (two IGBTs controlled by the same control signal are in a group), an energy storage capacitor, a high-power diode, a group of IGBTs, a bidirectional diode and a receiving and transmitting integrated coil equivalent to a series connection of an inductor L and a resistor R form a loop, and due to the unidirectional conductivity of the low-power diode, a controllable constant voltage source is equivalent to an open circuit in the period; when the PWMA signal and the PWMB signal are invalid, the dead time of the excitation pulse is entered at the moment, due to the unidirectional conductivity of the high-power diode, in the period, the energy storage capacitor is equivalent to open circuit, the energy release loop of the receiving and transmitting integrated coil is composed of an H bridge circuit, a small-power diode and a controllable constant voltage source Ur, and because the voltage of the controllable constant voltage source Ur is constant, the loop current meets the following requirements:
As shown in fig. 3, a wide-resonance magnetic resonance detection method based on the PWM control technique includes the following steps:
step 301: STM32+ FPGA transceiver main control module 2 identifies parameters and working start signals sent by PC upper computer 1, including excitation current ImThe number M of emission currents, the number k of superposition times and the excitation pulse frequency f, the emission pulse time t and the number n of pulse periods are calculated, and the actual excitation time t is transmitted back to the PC upper computer 1, wherein M and n are positive integers;
step 302: the STM32+ FPGA transceiving main control module 2 controls the transceiving switch 13 to switch the transceiving integrated coil 14 to be connected with the preamplifier circuit 15 of the receiving system by controlling the switch driving module 12 in the transceiving switching device so as to prepare to enter a gain adjustment and noise acquisition stage;
step 303: the STM32+ FPGA transceiving main control module 2 controls the receiving system to collect noise signals through the transceiving integrated coil 14, and adjusts the gain of the program control amplification module 17 according to the amplitude of the collected signals;
step 304: judging whether the gain adjustment of the program control amplification module is finished, if so, continuing to enter the step 305, otherwise, returning to the step 303, and judging the basis for finishing the gain adjustment is as follows: the amplitude of the signal collected by the A/D conversion module 19 is between 1/2 full scale and full scale of the A/D conversion module, so as to make the precision of the A/D conversion module reach the highest, and avoid the saturation of the amplifier;
step 305: the STM32+ FPGA transceiving main control module 2 controls the transceiving selector switch 13 to switch the transceiving integrated coil 14 to be connected with the H-bridge transmitting module 10 of the transmitting system through the transceiving selector switch 12 to prepare for entering a bipolar pulse excitation stage;
step 306: STM32+ FPGA transceiving main control module 2 according to excitation current ImAnd calculating the excitation voltage U according to the constraint conditionSDuty cycle d of excitation pulse and clamping voltage UDCIt should satisfy:
wherein, T is the transmission pulse cycle, satisfies T1/f, and R is coil equivalent resistance value, and L is coil equivalent inductance value, and each volume all adopts SI unit system in the formula. The constraint conditions are as follows:
UDC≤1000
0.25≤d≤0.45
the aim is to make
C is the capacitance value of the energy storage capacitor;
step 307: the STM32+ FPGA transceiving main control module 2 calculates the clamping voltage value U according toDCAdjusting the voltage value of the controllable constant voltage source 6;
step 308: judging whether the clamping voltage reaches the clamping voltage value UDCIf yes, go on to step 309, otherwise go back to step 307;
step 309: the STM32+ FPGA transceiving main control module 2 controls the DC-DC converter 4 to charge the energy storage capacitor 5 according to the excitation voltage value;
step 310: and judging whether the charging is finished or not, wherein the judgment basis of finishing the charging is that the excitation voltage value is reached, if the charging is finished, the step 311 is carried out, and if the charging is not finished, the step 309 is carried out. It should be noted that charging needs to be performed after the constant voltage source is adjusted, otherwise energy loss is caused by capacitor leakage;
step 311: the STM32+ FPGA transceiving main control module 2 controls PWM driving to generate two paths of driving signals (PWMA, PWMB) with duty ratio d and time interval T/2, so that n periods of excitation pulses with frequency f are transmitted through the H-bridge transmitting module 10, the bidirectional diode 11 and the transceiving integrated coil 14. The reason for emitting pulses of n cycles instead of pulses of fixed duration is to turn off the excitation pulses at the whole cycle, thereby shortening the dead time;
step 312: delaying for 800us after the transmission is turned off to ensure that all transmission actions are completed, switching the receiving and transmitting integrated coil 14 to be connected with a pre-amplifying circuit 15 of a receiving system, and preparing to enter a signal acquisition stage;
step 313: the STM32+ FPGA transceiving main control module 2 controls the A/D conversion module 19 to sample signals and store the signals to the PC upper computer 1, and the received signals correspond to the transmitting time t in the step 301 during storage;
step 314: judging whether current detection is finished, if so, continuing to enter step 315, otherwise, returning to step 309;
step 315: judging whether to detect the next current value or not, finishing the detection, and returning to the step 305 if not;
examples
Now, according to actual detection, it is determined that the coil equivalent parameter is L ═ 0.8mH, and R ═ 1 Ω, and the actual detection is specifically performed by the following steps:
step 301: STM32+ FPGA transceiver main control module 2 identifies parameters and working start signals sent by PC upper computer 1, including excitation current ImThe emitting pulse time t is approximately equal to 39.914ms and the number of pulse periods n is 93, and the actual excitation time t is transmitted back to the PC upper computer 1;
step 302: the STM32+ FPGA transceiving main control module 2 controls the transceiving switch 13 to switch the transceiving integrated coil 14 to be connected with the preamplifier circuit 15 of the receiving system by controlling the switch driving module 12 in the transceiving switching device so as to prepare to enter a gain adjustment and noise acquisition stage;
step 303: the STM32+ FPGA transceiving main control module 2 controls the receiving system to collect noise signals through the transceiving integrated coil 14, and adjusts the gain of the program control amplification module 17 according to the amplitude of the collected signals;
step 304: and judging whether the gain adjustment of the program control amplification module is finished or not, if the gain adjustment is finished, continuing to step 305, and otherwise, returning to step 303. The judgment basis for completing the gain adjustment is as follows: the amplitude of the signal collected by the A/D conversion module 19 is between 1/2 full scale and full scale of A/D, so as to make the precision of the A/D conversion module reach the highest, and avoid the saturation of the amplifier;
step 305: the STM32+ FPGA transceiving main control module 2 controls the transceiving selector switch 13 to switch the transceiving integrated coil 14 to be connected with the H-bridge transmitting module 10 of the transmitting system through the transceiving selector switch 12 to prepare for entering a bipolar pulse excitation stage;
step 306: STM32+ FPGA transceiving main control module 2 according to excitation current ImAnd calculating the excitation voltage U according to the constraint conditionSDuty cycle d of excitation pulse and clamping voltage UDCIt should satisfy:
wherein, T is the transmission pulse cycle, satisfies T1/f, and R is coil equivalent resistance value, and L is coil equivalent inductance value, and each volume all adopts SI unit system in the formula. The constraint conditions are as follows:
UDC≤1000
0.25≤d≤0.45
the aim is to make
And C is the capacitance value of the energy storage capacitor.
Under the condition that the energy storage capacitor is 0.132F, the clamping voltage is 1000V, the duty ratio of the excitation pulse is 40.91%, and the excitation voltage is 253.76V;
step 307: the STM32+ FPGA transceiving main control module 2 calculates the clamping voltage value U according toDCAdjusting the voltage value of the controllable constant voltage source 6;
step 308: judging whether the clamping voltage reaches 1000V, if so, continuing to step 309, otherwise, returning to step 307;
step 309: the STM32+ FPGA transceiving main control module 2 controls the DC-DC converter 4 to charge the energy storage capacitor 5 according to the excitation voltage value;
step 310: and judging whether the charging is finished or not, wherein the judgment basis of finishing the charging is that the excitation voltage value is reached, if the charging is finished, the step 311 is carried out, and if the charging is not finished, the step 309 is carried out. It should be noted that charging needs to be performed after the constant voltage source is adjusted, otherwise energy loss is caused by capacitor leakage;
step 311: the STM32+ FPGA transceiving main control module 2 controls PWM driving to generate two paths of driving signals (PWMA, PWMB) with duty ratio d and time interval T/2, so that 93 periods of excitation pulses with frequency of 2330Hz are transmitted through the H-bridge transmitting module 10, the bidirectional diode 11 and the transceiving integrated coil 14;
step 312: delaying for 800us after the transmission is turned off, ensuring that all transmission actions are completed, wherein the transmission turn-off time is only 1ms, and switching the receiving and transmitting integrated coil 14 to be connected with a pre-amplifying circuit 15 of a receiving system to prepare for entering a signal acquisition stage;
step 313: the STM32+ FPGA transceiving main control module 2 controls the A/D conversion module 19 to sample signals and store the signals to the PC upper computer 1, and the received signals correspond to the transmitting time t in the step 301 during storage;
step 314: judging whether the current detection is finished, and continuing to enter step 315 because the superposition time k is 1;
step 315: judging whether to detect the next current value, wherein the number M of the excitation currents is 1, so that the current detection is finished;
in addition, in order to further show the influence of the technology provided by the invention on the quality of the emission waveform, a wide-harmonic magnetic resonance detection excitation current waveform based on a PWM (pulse width modulation) regulation technology and a magnetic resonance detection excitation current waveform only with wide harmonic are provided, as shown in FIG. 4. Fig. 4a is a waveform diagram of excitation current for wide-harmonic magnetic resonance detection, and it can be seen that the problem of long detection dead time can be solved by a wide-harmonic excitation mode, but only by using the wide-harmonic excitation mode, the waveform in the early stage of emission tends to be attenuated, the quality of the excitation waveform is poor, and effective excitation is affected; fig. 4b is a wide-resonance detection excitation current oscillogram based on the PWM control technique, and after the active clamp fast turn-off technique and the PWM control technique are adopted, the problem of poor quality of the excitation waveform in the early stage is effectively solved, the quality of the magnetic resonance excitation waveform is improved, and the detection effect is improved.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A wide-matching magnetic resonance detection device based on a PWM (pulse-width modulation) regulation and control technology is used for shallow magnetic resonance detection, and is characterized by comprising: PC host computer, STM32+ FPGA receiving and dispatching main control module, transmitting system, receiving and dispatching switching device, receiving and dispatching integrated coil and receiving system, wherein,
the PC upper computer is used for man-machine interaction, sending transmission parameters to the STM32+ FPGA transceiving main control module, displaying the working state and storing the acquired magnetic resonance signal data;
the transmitting system comprises a storage battery, an energy storage capacitor, a high-power diode and an H-bridge transmitting module, wherein the storage battery is charged after being converted by a DC-DC converter and is connected with the H-bridge transmitting module through the high-power diode; the STM32+ FPGA transceiving main control module drives the H-bridge transmitting module through the PWM driving module; the H-bridge transmitting module is connected to the receiving and transmitting switching device through a bidirectional diode;
the receiving system is controlled by the receiving and transmitting switching device to be connected with the receiving and transmitting integrated coil;
and the transmitting and receiving switching device controls the connection of the transmitting system or the receiving system and the transmitting and receiving integrated coil according to the instruction of the STM32+ FPGA transmitting and receiving main control module.
2. The device of claim 1, wherein the receiving system comprises a pre-amplifying circuit, a signal conditioning circuit, a program-controlled amplifying module, an LPF module and an A/D conversion module, the pre-amplifying circuit of the receiving system is connected to the transceiving switching device, and the signal is amplified through the pre-amplifying circuit and is transmitted to the STM32+ FPGA transceiving main control module after sequentially passing through the signal conditioning circuit, the program-controlled amplifying module, the LPF module and the A/D conversion module.
3. The device according to claim 3, wherein the transceiving switching device comprises a switch driving module and a transceiving switching switch, and the switch driving module controls the connection between the transmitting system or the receiving system and the transceiving integrated coil through the transceiving switching switch according to the instruction of the receiving STM32+ FPGA transceiving master control module.
4. The apparatus of claim 4,
the STM32+ FPGA transceiving master control module is used for interacting with an upper computer, calculating parameters and controlling the detection working time sequence; controlling the DC-DC converter to store the energy in the storage battery to the energy storage capacitor; adjusting the voltage value of the controllable constant voltage source; generating two paths of PWM control signals through a PWM driving module; the receiving and transmitting switch is controlled to select the connection of the receiving and transmitting integrated coil and the H-bridge transmitting module or the pre-amplification circuit through the control switch driving module; and controlling the A/D conversion module to collect the magnetic resonance signals sensed by the receiving and transmitting integrated coil, amplifying the magnetic resonance signals through the preamplification circuit, conditioning the signals through the signal conditioning circuit, amplifying the magnetic resonance signals again through the program control amplification module and filtering the magnetic resonance signals through the LPF module, and adjusting the gain of the program control amplification module.
5. The apparatus of claim 1, wherein the energy storage capacitor of the transmitting system is a high voltage high capacitance capacitor for providing energy during transmission; the high-voltage pulse at the moment of turn-off is clamped by a controllable constant-voltage source with the voltage value higher than the voltage of the energy storage capacitor, so that an IGBT (insulated gate bipolar translator) of a switching device forming the H-bridge transmitting module is protected, and the energy of a guide coil is quickly released in the dead time of the transmitting pulse.
6. The apparatus of claim 1,
the high-power diode is a reverse high-voltage fast recovery diode with a unidirectional conduction characteristic and blocks a discharge loop formed by an energy storage capacitor and an H-bridge emission module in the dead time of an excitation pulse; and prevent the controllable constant voltage source from discharging to the energy storage capacitor; isolating instantaneous pulses generated by coil discharge within the dead time of the excitation pulse and protecting the capacitor;
the low-power diode is a reverse high-voltage fast recovery diode with a unidirectional conduction characteristic, and prevents the controllable constant voltage source from discharging to the energy storage capacitor, the H-bridge transmitting module, the bidirectional diode and the coil; the controllable constant voltage source is only used for clamping in the dead time of the excitation pulse and does not release energy through the transmitting loop;
the bidirectional diode comprises two diodes which are connected in parallel in an opposite direction and used for transmitting residual energy absorption.
7. The apparatus of claim 6, wherein during the transmit phase: when a PWMA signal or a PWMB signal sent by the PWM driving module is effective, a group of IGBTs in the H-bridge transmitting module are conducted, an energy storage capacitor, a high-power diode, a group of IGBTs, a bidirectional diode and a receiving and transmitting integrated coil which is equivalent to a series connection of an inductor L and a resistor R form a loop, and the controllable constant voltage source Ur is equivalent to open circuit due to the unidirectional conductivity of the low-power diode; when the PWMA signal and the PWMB signal are invalid, the excitation pulse dead time is entered, because of the one-way conductivity of the high-power diode, the energy storage capacitor is equivalent to open circuit in the period, and the energy release loop of the receiving and transmitting integrated coil is composed of an H-bridge transmitting module, a low-power diode and a controllable constant voltage source, so that the purposes of equal-amplitude high-quality waveform transmission and quick turn-off are realized.
8. A wide-band resonance detection method based on a PWM (pulse-width modulation) regulation technology is characterized by comprising the following steps of:
step 301: the STM32+ FPGA transceiving main control module identifies parameters and working start signals sent by a PC upper computer and comprises an excitation current ImThe number M of the emission currents, the number k of the superposition times and the excitation pulse frequency f are calculated, the emission pulse time t and the number n of pulse periods are calculated, and the actual excitation time t is transmitted back to the PC upper computer, wherein M and n are positive integers;
step 302: the STM32+ FPGA transceiving main control module controls a transceiving switch to switch a transceiving integrated coil to be connected with a pre-amplification circuit of a receiving system by controlling a switch driving module in the transceiving switching device so as to prepare to enter a gain adjustment and noise acquisition stage;
step 303: the STM32+ FPGA transceiving main control module controls the receiving system to collect noise signals through the transceiving integrated coil, and adjusts the gain of the program control amplification module according to the amplitude of the collected signals;
step 304: judging whether the gain adjustment of the program control amplification module is finished, if so, continuing to enter the step 305, otherwise, returning to the step 303, and judging the basis for finishing the gain adjustment is as follows: the signal amplitude acquired by the A/D conversion module is between 1/2 full scale and full scale of A/D;
step 305: the STM32+ FPGA transceiving main control module controls a transceiving selector switch through a transceiving selector device to switch a transceiving integrated coil to be connected with an H-bridge transmitting module of a transmitting system to prepare for entering a bipolar pulse excitation stage;
step 306: STM32+ FPGA transceiver main control module according to excitation current ImAnd calculating the excitation voltage U according to the constraint conditionSDuty cycle d of excitation pulse and clamping voltage UDC；
Step 307: the STM32+ FPGA transceiving main control module adjusts the voltage value of the controllable constant voltage source according to the calculated clamping voltage value UDC;
step 308: judging whether the clamping voltage reaches a clamping voltage value UDC, if so, continuing to enter a step 309, otherwise, returning to the step 307;
step 309: the STM32+ FPGA transceiving main control module controls the DC-DC converter to charge the energy storage capacitor according to the excitation voltage value;
step 310: judging whether the charging is finished or not, if the judgment basis of finishing the charging is that the excitation voltage value is reached, entering step 311 if the charging is finished, otherwise returning to step 309;
step 311: STM32+ FPGA receives and dispatches the master control module control PWM drive and produce two routes of duty ratio and be d, time interval T/2's drive signal, through H bridge transmitting module, bidirectional diode and the integrative coil transmission n cycles of receiving and dispatching, the excitation pulse of frequency is f. The purpose of emitting pulses of n cycles instead of fixed duration is to turn off the excitation pulses at the whole cycle, thereby reducing the dead time;
step 312: delaying for 800us after the transmission is turned off to ensure that all transmission actions are completed, switching the receiving and transmitting integrated coil to be connected with a pre-amplification circuit of a receiving system, and preparing to enter a signal acquisition stage;
step 313: the STM32+ FPGA transceiving main control module controls the A/D conversion module to sample signals and store the signals to the PC upper computer, and the received signals correspond to the transmitting time t in the step 301 during storage;
step 314: judging whether current detection is finished, if so, continuing to enter step 315, otherwise, returning to step 309;
step 315: and judging whether to detect the next current value or not, finishing the detection, and returning to the step 305 if not.
9. The method of claim 8, wherein step 306: STM32+ FPGA transceiver main control module according to excitation current ImAnd calculating the excitation voltage U according to the constraint conditionSDuty cycle d of excitation pulse and clamping voltage UDCAnd satisfies the following conditions:
wherein, T is the transmission pulse cycle, satisfies T1/f, and R is coil equivalent resistance value, and L is coil equivalent inductance value, and each volume all adopts SI unit system in the formula, and the constraint condition is:
UDC≤1000
0.25≤d≤0.45
the aim is to make
And C is the capacitance value of the energy storage capacitor.
10. The method of claim 8, wherein step 310: the charging is performed after the constant voltage source adjustment.
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