CN106383364B - A kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument - Google Patents
A kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument Download PDFInfo
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- CN106383364B CN106383364B CN201610431261.8A CN201610431261A CN106383364B CN 106383364 B CN106383364 B CN 106383364B CN 201610431261 A CN201610431261 A CN 201610431261A CN 106383364 B CN106383364 B CN 106383364B
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
Abstract
The invention discloses a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument, the instrument includes control and communication module, impulse ejection module, response signal receiving module, frequency scanning control module and pulse frequency modulated module；The NMR response signal that the collection pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of response signal receiving module is excited, and it is sent to control and communication module；Control calculates current stimulating frequency with the frequency departure degree of true Larmor frequency to judge whether the response signal received is optimal response signal with communication module according to NMR response signal characteristic.The instrument can launch pseudorandom frequency sweep nuclear magnetic resonance excitation pulse, so as to be excited to the NMR response on multiple frequencies.
Description
Technical field
The invention belongs to geophysical exploration field, it is related to a kind of available for the prominent mud advanced prediction of tunnel gushing water and underground water
The pseudorandom frequency sweep nuclear magnetic resonance detection instrument detected.
Background technology
Nuclear magnetic resonance detection is a kind of can to verify the aqueous body position in underground and porosity and directly estimate its water
Geophysics new method.Its principle is the RENGONGSHE for being equal to Larmor frequency of the Hydrogen Proton under magnetic field of the earth in water using frequency
Frequency excites the free damping signal produced after field excitation directly to carry out quantitative judge to underground water content.At present, ground nuclear-magnetism
Resonance, drilling nuclear magnetic resonance and laboratory nuclear magnetic resonance have been widely used in underground water detecting, landslide detection, oil well logging
And rock sample detection etc. many geophysics fields.Due to nuclear magnetic resonance have can direct look for water the characteristics of, in tunnel
There are significant method advantage and important development meaning in the research and application of unfavorable geology and the prominent mud advanced prediction of gushing water.
In field work and hole in probe procedure, Larmor frequency is simultaneously obtained in the magnetic field of the earth that accurate measurement is surveyed in area, then
With instrument tranmitting frequency, equal nuclear magnetic resonance excitation pulse is the key that obtains reliable NMR response signal therewith.Due to
Magnetic field of the earth is changed over time and skewness, front geological body there may be the factors such as magnetic anomaly and instrument error；Excite
The frequency of pulse often deviates real Larmor frequency.The amplitude of resulting NMR response signal will be greatly reduced
So that causing that the phenomenon of NMR response signal can not be observed among being submerged in environment electromagnetic noise.At present, in nuclear-magnetism
On the problem of resonance instrument is designed with research and development, research emphasis is generally placed on signal condition, noise suppressed and antenna optimization etc.
Aspect.And to how to avoid stimulating frequency from deviateing true Larmor frequency aspect, lack enough research, it is not effective
Solution.
Specifically, with research and development there is following problem and deficiency in the design of nuclear magnetic resonance detection instrument：
(1) when in tunnel detect in hole, if front of tunnel heading country rock is the high magnetic such as mafic, Ultrabasic or metamorphic rock
Contain ferromagnetic mineral in property rock mass and country rock, the size of front of tunnel heading magnetic field of the earth magnetic induction intensity is with inclination angle due to upper
State magnetic anomaly and produce distortion, the stimulating frequency of nuclear magnetic resonance --- Larmor frequency does corresponding change therewith.Due to front
Magnetic field of the earth unknown parameters, now calculate stimulating frequency and front using the magnetic field of the earth measured in Tunnel room after face
There is deviation in true Larmor frequency, it is impossible to the reliable NMR response excited in the disaster water body of front.
(2) nuclear magnetic resonance excitation pulse uses single frequency sinusoidal pulse, and once transmitting is only capable of being total to a frequency progress nuclear-magnetism
Shake and excite.Constantly conversion stimulating frequency is needed when stimulating frequency and Larmor frequency have deviation and is excited after conversion can not be estimated
The numerical value of frequency.
(3) generation of single frequency sinusoidal pulse need to be using RLC resonance circuits and high-voltage capacitance charge-discharge modules.Excitation pulse
FREQUENCY CONTROL needs the capacitive reactance by adjusting external capacitor to be allowed to match to reach resonance with the induction reactance of coil and circuit.Choosing
It is current that realization of the frequency with humorous process is combined and through detection electronic feedback by multiple connection in series-parallel of the switching with humorous electric capacity of relay
The quality factor of circuit are exported with pulse.Therefore frequency-selecting is quite time-consuming with humorous process.And due to main group of resonance circuit
It is to match somebody with somebody humorous inductance and electric capacity into part, therefore emitter needs circumscribed volume huge and heavy capacitive (matches somebody with somebody humorous inductance one
As by transmitting coil induction reactance provide).
The content of the invention
In order to solve the shortcoming of prior art, the present invention provides a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument.This hair
Bright pseudorandom frequency sweep nuclear magnetic resonance detection instrument can be used for tunnel gushing water to dash forward mud advanced prediction and underground water detecting, and can be with
In once observing multiple frequencies are carried out with nuclear magnetic resonance to excite and obtain optimal response by adjusting excitation pulse frequency scanning.
To achieve the above object, the present invention uses following technical scheme：
A kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument, including control and communication module, it gathers the ground in measurement zone
Signal magnetic field parameter and the frequency modulation(PFM) function for calculating the pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of transmitting for the first time, and by frequency
Modulation function is sent to pulse frequency modulated module；
Pulse frequency modulated module, it produces frequency modulated signal according to the frequency modulation(PFM) function of reception and is sent to pulse hair
Penetrate module；
Impulse ejection module, it is generated and transmitted by one group of pseudorandom frequency sweep nuclear magnetic resonance and excited according to frequency modulated signal
Multiple frequencies are carried out nuclear magnetic resonance and excited by pulse；
Response signal receiving module, it gathers the NMR response that pseudorandom frequency sweep nuclear magnetic resonance excitation pulse is excited
Signal, and it is sent to communication module；The control is additionally operable to be calculated according to NMR response signal characteristic with communication module works as
Preceding stimulating frequency judges whether the response signal received is optimal response with the frequency departure degree of true Larmor frequency
Signal：
If optimal response signal, it is determined that optimum excitating frequency simultaneously records optimal response；
Otherwise, frequency departure degree is sent to frequency scanning control module, the frequency scanning control module is according to frequency
Rate departure degree carries out calculating frequency scanning direction and step-length carrys out regulating frequency modulation function signal, and input to pulse frequency is adjusted
Molding block；Pulse frequency modulated module controls the impulse ejection module to make it according to the frequency modulation(PFM) function signal received
The pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of another group of different frequency is generated and transmitted by, optimum excitating frequency is determined.
The pulse frequency modulated module, its frequency modulated signal produced is used in directly control impulse ejection module
The conducting and shut-off of each bridge arm of IGBT bridge circuit, are realized to pseudorandom frequency sweep nuclear magnetic resonance excitation pulse frequency and pulse persistance
The control of time.
The response signal receiving module using Ditital multichannel frequency-selecting reception by the way of, by it is set in advance it is multiple not
The NMR response signal excited with the signalling channel collection pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of centre frequency.
The frequency scanning control module has automatically scanning and two kinds of working methods of manual scanning.
The frequency scanning control module is under automatically scanning mode, according to the NMR response signal being currently received
The automatic direction for judging frequency scanning and regulating frequency modulation function.
The frequency scanning control module passes through host computer incoming frequency scanning direction and scanning under manual scanning mode
Step-length regulating frequency modulation function.
The frequency scanning control module is by constantly changing frequency modulation(PFM) function so that pseudorandom frequency sweep nuclear magnetic resonance swashs
The spectral characteristic of hair pulse is slided with fixed form along frequency axis, and realization is entered to a series of NMR response on frequencies
Row scanning is excited.
The impulse ejection module includes the bridge circuit and associated trigger circuit being made up of switching tube.
The control is in communication with each other with communication module with host computer.
Beneficial effects of the present invention are：
(1) present invention can not reliably swash for disaster water body (underground reservoir) in the detection of tunnel (and ground) nuclear magnetic resonance
The problem of hair, is there is provided feasible scheme, so as to preferably solve the quantitative judge and forecasting problem at the prominent mud disaster water source of gushing water；
In terms of impulse ejection, abandon transferring to use what is be made up of the bipolarity cycle square wave of multigroup different frequency using sinusoidal wave pulse
Pseudorandom frequency sweep nuclear magnetic resonance excitation pulse；The generation of pulse no longer needs RLC resonance circuits.Therefore, impulse ejection module is not
Needing external huge and heavy to match somebody with somebody humorous electric capacity.Because bridge circuit can be integrated in solid state module, with small volume,
Lightweight, easy to control the characteristics of；Therefore be as the radiating circuit of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse using it
Instrument realizes miniaturization and lighting.
(2) in terms of pulse frequency characteristic is launched, the sequence circuit that instrument is made up of integrated digital chip is flexibly controlled
The cycle number of repetition of different frequency square wave excites multiple frequencies so as to realize to obtain different spectral characteristic in once observing
On NMR response.
(3) on the mode of excitation of nuclear magnetic resonance, pulsatile once transmitting can ring to the nuclear magnetic resonance on multiple frequencies
It should be excited.According to current NMR response feature, it is determined that frequency scanning direction, changes pseudorandom frequency sweep nuclear magnetic resonance and swashs
Send out the frequency of pulse；Excited so as to realize to be scanned in certain frequency band and NMR response.
(4) in terms of NMR response signal acquisition, receive to realize by Ditital multichannel frequency-selecting and pseudorandom is swept
The collection for the response signal on multiple frequencies that frequency nuclear magnetic resonance excitation pulse is excited.NMR response letter on different frequent points
Number it can be gathered and be recorded respectively for judging, so as to find out optimal NMR response signal.Signal receiving channel
Centre frequency by program setting and can be adjusted.This digital processing mode has that precision is high, strong antijamming capability with
And can by it is programme controlled a little.
(5) excite aspect in the reliable of nuclear magnetic resonance, this instrument realized " multi-frequency waves are launched, and frequency sweep is excited, digital
Multichannel frequency-selecting is received " excite and acquisition method can effectively avoid detecting in hole with field work due to looking for inaccurate Rameau
Off resonance response produced by your frequency.The optimal NMR response obtained, is follow-up data processing, inverting and solution
Release the observation signal there is provided high-quality.
Brief description of the drawings
Fig. 1 is the overall system structure of pseudorandom frequency sweep nuclear magnetic resonance apparatus.
Fig. 2 is the impulse ejection and frequency sweep control principle of pseudorandom frequency sweep nuclear magnetic resonance apparatus.
Fig. 3 is the operation principle of pseudorandom frequency sweep NMR response signal receiving module.
Fig. 4 is the contrast of nuclear magnetic resonance optimal response signal and off resonance response signal.
Fig. 5 is the workflow in the specific implementation process of pseudorandom frequency sweep nuclear magnetic resonance apparatus.
Embodiment
The present invention will be further described with embodiment below in conjunction with the accompanying drawings：
As shown in figure 1, the pseudorandom frequency sweep nuclear magnetic resonance detection instrument of the present invention includes impulse ejection module, pulse frequency
Modulation module, frequency scanning control module and control and communication module.Wherein, control and communication module and host computer phase intercommunication
Letter.
Power module is that pulse frequency modulated module, frequency scanning control module and control and communication module are carried out respectively
Power supply.
Power module is realized to the transformation of external power supply, rectification and voltage stabilizing to provide work for the disparate modules of whole instrument
Make power supply.The component in overvoltage, excessively stream and dump energy absorbing circuit guarantee instrument in power module is in rated condition
Lower steady operation, by the loop to different voltage class and module impose reliable electrical isolation ensure instrument work safety with
And the acquisition precision of signal.To ensure signal acquisition precision and personal equipment safety, power module provides numeral for whole instrument
Ground, simulation ground and reliable ground protection.
Wherein, pseudorandom frequency sweep nuclear magnetic resonance detection instrument also includes transmitting and reception antenna (or probe), launches and connects
It is the main peripheral hardware for exciting and gathering NMR response signal to receive antenna (or probe).Carrying out the field work of underground water detecting
When making NMR response signal is received using receiving coil.In tunnel carry out gushing water dash forward mud advanced prediction when remove receiving coil
It is outer to be also acquired using the magnetic probe with bigger equivalent received area.
The number of turn of transmitting coil is selected as needed with the length of side.For the underground water detecting work carried out in earth's surface, transmitting
The number of turn of coil is 1~2 circle, and 50m and 100m may be selected according to investigation depth using coil length of side during square loop line.For
4~8 circles are may be selected according to investigation depth in the prominent mud advanced prediction work of gushing water carried out in hole, the number of turn of transmitting coil, and coil is hung
On face, girth is suitable with exploration face girth.Receiving coil is utilized when carrying out the field work of underground water detecting
Receive NMR response signal.In tunnel carry out gushing water dash forward mud advanced prediction when in addition to receiving coil also using have more
The magnetic probe of big equivalent received area is acquired.Carry out multipoint array-type observation to increase observation number in face using probe
It is that follow-up inverting and data interpretation provide more observation data according to amount.The scale of array observation according to face size and
The length of side of excitation variable winding is determined.
Host computer realizes instrument manipulation, instrument self checking, signal acquisition and the data note of interfacial type by upper computer software
Record.The daily record of work when working condition of instrument, the NMR response signal sampled and measurement can be with the shape of file
Formula is recorded and stored.
The master system is made up of an industry control notebook and pc control procedure.Master system passes through upper
Machine software realizes instrument manipulation, instrument self checking, signal acquisition and the data record of interfacial type.The self-detection result of instrument, work
Daily record of work when state, the NMR response signal of sampling and measurement can be recorded and stored in the form of a file.
(1) control and communication module
Control and communication module realize overall control, detection and the instruction with master system of each module of instrument with
Data transfer.In addition, the sensor in module can measure the magnetic field of the earth parameter in area, including earth's magnetic field magnetic induction is strong
Degree, geomagnetic inclination and geomagnetic declination.
Control and communication module according to its gather the magnetic field of the earth parameter in measurement zone and calculate transmitting for the first time it is pseudo- with
The frequency modulation(PFM) function signal of machine frequency sweep nuclear magnetic resonance excitation pulse, and by frequency be adjusted to function signal be sent to pulse frequency adjust
Molding block.
Control mainly has three functions with communication module：
One is each module is controlled and detected by embedded chip；
Secondly the signal being responsible between instrument and host computer is transmitted with instruction.Control with communication module and core is
ARM chips, are responsible for realizing the bottom control of instrument host.Analog sensor, Boolean value output sensor, electricity are provided with this module
Current transformer etc. is used for the working condition and working environment of detecting instrument.The instruction of instrument host and host computer is led to data transfer
Cross the realization of RS-232 serial communications.
Third, magnetometer built-in in this module is responsible for the magnetic induction intensity in the magnetic field of the earth that collection is surveyed in area, magnetic dip angle
And magnetic declination.Magnetic field data of Earth ARM chips according to being obtained are calculated launches desired pseudorandom frequency sweep nuclear-magnetism for the first time
The frequency modulation(PFM) function of resonance excitation pulse.Pulse frequency modulated module is adjusted in function control impulse ejection module according to frequency
The transmitting of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse is realized in the generation that switching tube is triggered with cut-off signals.
(2) impulse ejection module
Impulse ejection module, its frequency modulation(PFM) function signal exported according to control with communication module is generated and transmitted by the
One group of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse.
In specific implementation process, the bridge that impulse ejection module is made up of high-power insulated gate bipolar IGCT (IGBT)
Formula circuit and associated trigger control circuit are produced and pseudorandom frequency sweep nuclear magnetic resonance excitation pulse.Pseudorandom frequency sweep nuclear magnetic resonance
Excitation pulse is made up of the cycle square wave of multiple different frequencies within a period of time.The frequency of each square wave, cycle repeat secondary
The number of number and square wave is controlled by pulse frequency modulated module.Voltage stabilizing in impulse ejection module ensures stable with clamp circuit
Voltage output and pulse rapidly switch off.
Impulse ejection module is responsible for realizing the transmitting of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse.As shown in Fig. 2 pulse is sent out
The core for penetrating module is the bridge circuit and trigger control circuit of high-power insulated gate bipolar IGCT (IGBT) composition.Q1~
Q4Four IGBT pipes are located on four bridge arms of bridge circuit respectively, D1~D4It is fly-wheel diode, ZLRepresent the resistance of excitation variable winding
It is anti-.When excitation pulse is forward direction, Q1With Q4Two IGBT pipes conductings；When excitation pulse is reverse, Q2With Q3Two IGBT pipes
Conducting.In Q1With Q4(conducting) is turned off to Q2With Q3In the transit time for turning on (shut-off), sustained diode2With D3(D1With D4) lead
Logical (shut-off) is that the electric current in oad freewheels proof load will not abrupt transients.D5And D6The pincers of two anti-paralleled diode compositions
Position circuit is automatically shut down when load terminal voltage is less than its conduction voltage drop, and terminal voltage is clamped into zero；Ensure pulsed emission current
Rapidly switch off.During whole impulse ejection, IGBT trigger signal comes from pulse frequency modulated module.To avoid electricity
Triggers circuit in source short circuit, impulse ejection module, which is removed, ensures that IGBT reliably can be triggered and turned off, and also assures the same side two
Two pipes on individual bridge arm will not be simultaneously turned on.
(3) response signal receiving module
Response signal receiving module, it gathers the NMR response that pseudorandom frequency sweep nuclear magnetic resonance excitation pulse is excited
Signal, and it is sent to control and communication module；The control is calculated with communication module according to NMR response signal characteristic works as
Preceding stimulating frequency judges whether the response signal received is optimal response with the frequency departure degree of true Larmor frequency
Signal：
If optimal response signal, it is determined that optimum excitating frequency simultaneously records optimal response；
Otherwise, frequency departure degree is sent to frequency scanning control module, the frequency scanning control module is according to frequency
Rate departure degree carries out calculating frequency scanning direction and step-length carrys out regulating frequency modulation function signal, and input to pulse frequency is adjusted
Molding block；Pulse frequency modulated module controls the impulse ejection module to make it according to the frequency modulation(PFM) function signal received
It is generated and transmitted by another group of new pseudorandom frequency sweep nuclear magnetic resonance excitation pulse；The frequency spectrum of new pulse and the pulse of last transmitting
Frequency spectrum is different, can cover the frequency that last time transmitting is not covered with, it is thus possible to be scanned and excite；Afterwards, response signal
Receiving module, control and communication module, frequency scanning module, pulse frequency modulated module and impulse ejection module are simultaneously repeated
Collection, analysis are stated with scanning the process of transmitting until receiving optimal response signal；All signals collected are equal during this period
By controlling to store and record with the master system that communication module is uploaded.
Wherein, response signal receiving module passes through difference set in advance by the way of Ditital multichannel frequency-selecting reception
The signalling channel of centre frequency is realized to enter the NMR response signal that pseudorandom frequency sweep nuclear magnetic resonance excitation pulse is excited
Row collection and record., can be to multiple frequencies because pseudorandom frequency sweep nuclear magnetic resonance excitation pulse contains abundant frequency component
NMR response excited.Therefore, the collection of NMR response signal should be excited with pseudorandom frequency sweep nuclear magnetic resonance
The frequency component of pulse is corresponding, so as to ensure that all NMR responses being excited on frequency are all observed.Sweep every time
Retouch the frequency spectrum during exciting according to the pseudorandom frequency sweep excitation pulse launched and set the centre frequency of program control frequency-selective network.
Finally, optimal NMR response signal is judged by human-computer interaction function.
The core component of response signal receiving module is dsp chip.Institute's signalling channel set in advance in DSP by having
The digital filter (program) of different center frequency is realized.Receiving coil and probe received by response signal through over-sampling,
Dsp chip is inputted after preposition frequency-selective filtering and analog-to-digital conversion.There is programme controlled digital filter in dsp chip to receiving
Signal be further processed.Frequency range according to where NMR response signal, the passband of preamplifier is
1.2kHz to 3.5kHz.
As shown in figure 3, the digital filter program in dsp chip uses parallel processing manner, pre-set n signal
Passage.The passband non-overlapping copies of n signalling channel, it is ensured that the phenomenon of mixing is not present in filtered signal.Each signal
The centre frequency of passage is set according to the spectrum signature for the pseudorandom frequency sweep nuclear magnetic resonance excitation pulse currently launched, it is ensured that current
The NMR response signal on each frequency being excited is extracted.Locked in each signalling channel by digital quadrature
Surely the filter amplified carries out chip select amplification and denoising Processing to the response signal being digitized into.After final process
Signal is uploaded to master system with communication module by control and stored.It is each logical under the working method that automatically scanning is excited
The centre frequency in road is set and is sent to dsp chip automatically by frequency scanning control module.The Working mould excited in manual scanning
Under formula, the centre frequency of each passage is inputted by host computer or is set automatically by frequency scanning control module and be sent to dsp chip.
(4) control module is frequency scanned
Frequency scanning control module has automatically scanning and two kinds of working methods of manual scanning.Automatically scanning mode is according to current
The NMR response signal received judges the direction of frequency scanning and regulating frequency modulation function, manual scanning mode automatically
Pass through upper computer software incoming frequency scanning direction and scanning step regulating frequency modulation function.Will be current under automatically scanning mode
The NMR response signal received is inputed to after the processing of response signal receiving module in control and communication module
ARM chips.Meanwhile, current frequency is adjusted to function and feeds back to ARM chips by Tx ports.ARM chips will be special according to response signal
Whether levy the response received by judging is that off resonance responds and qualitatively judges current stimulating frequency and true Larmor frequency
Departure degree.Judge the response signal that receives whether be optimal response signal according to NMR response signal it is initial
Relation curve between amplitude and excitation pulse square.
Nuclear magnetic resonance optimal response signal and different degrees of off resonance response signal are illustrated in accompanying drawing 4.Such as Fig. 4 institutes
Show, compared with optimal response signal, the tracing pattern of off resonance response signal is distorted, and initial amplitude is greatly reduced, signal
Phase shifts.Resulting judged result is inputted to frequency scanning control module by Rx ports, frequency scans control module
Scanning direction and step-length are drawn by calculating processing, regulating frequency modulation function and is inputted control signal by WR ports afterwards
Give pulse frequency modulated module.Pulse frequency modulated module according to abovementioned steps control impulse ejection module in IGBT conducting with
Shut-off.Under manual scanning mode, the NMR response signal that operator records and shown according to host computer judges received
Response whether be that off resonance responds and qualitatively judges the departure degree of current stimulating frequency and true Larmor frequency.
The instruction is passed through serial communication by direction and scanning step that operator is scanned in host computer incoming frequency, host computer
It is sent to the main frame of instrument.The control of instrument host is with communication module receives frequency surface sweeping direction with step-length and by it by Rx ports
Input frequency scans control module regulating frequency modulation function and control signal is passed through into WR ports to frequency scanning control module
Input to pulse frequency modulated module.Afterwards, pulse frequency modulated module is controlled in impulse ejection module according to abovementioned steps
IGBT is turned on and shut-off.
(5) pulse frequency modulated module
Pulse frequency modulated module directly controls the IGBT bridge circuit in impulse ejection module according to frequency modulation(PFM) function
The conducting and shut-off of each bridge arm, realize to pseudorandom frequency sweep nuclear magnetic resonance excitation pulse frequency, the pulse duration and control.
The sequence circuit that the frequency modulation(PFM) of excitation pulse is made up of integrated digital chip is realized.In certain pulse duration scope
Interior exported pseudorandom frequency sweep nuclear magnetic resonance excitation pulse contains the square wave of multiple different cycles, containing abundant frequency into
Point.Frequency modulation(PFM) function controls the building form of these square-wave pulses and the cycle number of repetition of each frequency square wave.Therefore, change
Frequency modulation function can make output pulse have different frequency contents, and then meet to the nuclear magnetic resonance on different frequent points
Excite requirement.
Specific practice is：In a square-wave cycle, when excitation pulse is forward direction, pulse frequency modulated module is sent out to pulse
Penetrating module and sending trigger signal makes Q1With Q4Conducting, meanwhile, negater circuit in impulse ejection module is to Q2With Q3Send cut-off letter
Number ensure that its is turned off；When excitation pulse is reverse, pulse frequency modulated module sends pick-off signal to impulse ejection module makes Q1
With Q4Shut-off, meanwhile, negater circuit in impulse ejection module is to Q2With Q3Send trigger signal and ensure that it is turned on.Frequency modulation(PFM)
The functional value of function is the period frequency of pulse-triggered (cut-off) signal, is also side in pseudorandom frequency sweep nuclear magnetic resonance excitation pulse
The frequency of ripple.The time divided by current corresponding functional value that the fixed value that frequency modulation(PFM) function takes is undergone are pseudorandom frequency sweeps
The cycle number of repetition of square wave in nuclear magnetic resonance excitation pulse.Therefore control of pulse-triggered (cut-off) signal in frequency modulation(PFM) function
The frequency and cycle number of repetition of square wave in the pseudorandom frequency sweep nuclear magnetic resonance excitation pulse that the lower change instrument of system is launched.Again by
In the spectrum signature of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse, that is, frequency content contained by it is with constituting its side
The change of wave frequency rate and cycle number of repetition and change.Therefore, pulse frequency modulated module can be according to frequency modulation(PFM) function control
Frequency content contained by the pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of instrument output processed, so as to realize to many in certain frequency band
NMR response on individual frequency is excited.
In specific implementation process, the workflow of pseudorandom frequency sweep nuclear magnetic resonance detection instrument is as shown in Figure 4.Tie below
Fig. 5 is closed to elaborate to it.
Before start-up operation, measuring coil and receiving transducer are laid surveying in area.Open master system, main frame system
Power-on self-test is carried out after system, system boot.The result of instrument self checking is uploaded to by the control of instrument host with communication module
Position machine is simultaneously shown in upper computer software.When instrument has failure, self-inspection does not pass through, and carries out self-inspection after fixing a breakdown again.Instrument
Do not have failure then self-inspection by and carry out next step operation.
The control of master system order instrument host measures the magnetic field of the earth parameter in area, including ground with communication module
Magnetic field magnetic induction intensity, geomagnetic inclination and geomagnetic declination；Afterwards, the pseudorandom frequency sweep nuclear magnetic resonance of generation transmitting for the first time is excited
The frequency modulation(PFM) function of pulse is simultaneously sent to pulse frequency modulated module.Afterwards, by upper computer software by associated transmissions parameter
Instrument host is sent to by serial communication.
Emission parameter includes：The current strength of excitation pulse, excitation pulse duration, pseudorandom frequency sweep nuclear magnetic resonance swash
Send out the frequency of pulse and the number and intensity of excitation pulse square.
Instrument host completes relevant configuration after the emission parameter of host computer transmission is connected to and waits firing order.Firing order
Control and the communication module of instrument host are assigned and are sent to by host computer.
Control is received after firing order with communication module, and pulse frequency modulated module is given birth to frequency according to frequency modulation(PFM) function and adjusted
The generation of switching tube trigger signal in signal processed, control impulse ejection module.Transmitter module is according to by pulse frequency modulated module
The frequency modulated signal of input, is generated and transmitted by first group of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse.
After transmitting terminates for the first time, the IGBT used of impulse ejection module is turned off rapidly in the presence of clamp circuit.Together
When, response signal receiving module receives and handles response signal.NMR response on each frequency passes through Ditital multichannel
The n signalling channel that frequency-selecting is received is filtered and amplified, and host computer control will be handled with communication module by serial communication afterwards
The signal data in n passage afterwards, which is uploaded to after host computer, to be stored and is shown on screen.By launching a series of excite
Pulse square, the process that instrument repeats above-mentioned transmitting with observing finally gives each and excites the first of frequency coker Magnetic Resonance
Relation between beginning amplitude and excitation pulse square.Excitation pulse square is the current strength of excitation pulse and multiplying for pulse duration
Product.Under the control of same impulse modulation function, after emission parameter is inputted by host computer, the pulse duration no longer changes
Become.Instrument host control calculates corresponding with the ARM chips in communication module according to the intensitometer of the excitation pulse square to be launched
Emission current intensity.Impulse ejection module changes voltage to launch different amplitudes according to the emission current intensity calculated
Electric current.
After all transmittings of pulse square and response signal collection are finished.Upper computer software initially shakes signal in each passage
The relation of width and excitation pulse square is depicted as curve and is shown on screen respectively.If some passage in n receiving channel
Optimal response signal is have received, then observation terminates.Needed if none of channel reception to optimal response signal into
Row scanning is excited.Judge the response signal that receives whether be optimal response signal according to NMR response signal it is initial
Relation curve between amplitude and excitation pulse square.
As shown in figure 4, compared with optimal response signal, the initial amplitude of off resonance response signal is greatly reduced, signal phase
Position changes.Described in Fig. 4 change impulse modulation function after be scanned the mode excited have it is automatic with manual two kinds.Instrument
The process performed a scan as previously described, is repeated no more here.Specified otherwise is needed, the process excited in scanning
In, the centre frequency of n passage of digital filter and passband are by host computer input or certainly in response signal receiving module
Dynamic scan function setting.Ensure that excited NMR response can be received with this.The process that multiple scanning is excited is known
Optimal response signal is have received in a certain signalling channel, observation just can terminate.All equal energy of explanation signal in observation process
Enough it is uploaded to host computer in real time by serial communication and stores and be shown on screen.
Although above-mentioned the embodiment of the present invention is described with reference to accompanying drawing, not to present invention protection model
The limitation enclosed, one of ordinary skill in the art should be understood that on the basis of technical scheme those skilled in the art are not
Need to pay various modifications or deform still within protection scope of the present invention that creative work can make.
Claims (8)
1. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument, it is characterised in that including control and communication module, it gathers measurement
Magnetic field of the earth parameter in area and the frequency modulation(PFM) function for calculating the pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of transmitting for the first time,
And frequency modulation(PFM) function is sent to pulse frequency modulated module；
Pulse frequency modulated module, it produces frequency modulated signal according to the frequency modulation(PFM) function of reception and is sent to impulse ejection mould
Block；
Impulse ejection module, it is generated and transmitted by one group of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse according to frequency modulated signal,
Nuclear magnetic resonance is carried out to multiple frequencies to excite；
Response signal receiving module, it gathers the NMR response letter that pseudorandom frequency sweep nuclear magnetic resonance excitation pulse is excited
Number, and it is sent to communication module；The control is additionally operable to calculate current according to NMR response signal characteristic with communication module
Stimulating frequency judges whether the response signal received is optimal response letter with the frequency departure degree of true Larmor frequency
Number：
If optimal response signal, it is determined that optimum excitating frequency simultaneously records optimal response；
Otherwise, frequency departure degree is sent to frequency scanning control module, the frequency scanning control module is inclined according to frequency
Carry out calculating frequency scanning direction from degree carrying out regulating frequency modulation function signal with step-length, and input to pulse frequency modulated mould
Block；Pulse frequency modulated module controls the impulse ejection module to produce it according to the frequency modulation(PFM) function signal received
And launch the pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of another group of different frequency, determine optimum excitating frequency；
The response signal receiving module is by the way of Ditital multichannel frequency-selecting reception, by multiple differences set in advance
The NMR response signal that the signalling channel collection pseudorandom frequency sweep nuclear magnetic resonance excitation pulse of frequency of heart is excited.
2. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 1, it is characterised in that the pulse frequency
Modulation module, each bridge arm of IGBT bridge circuit that its frequency modulated signal produced is used in directly control impulse ejection module
Conducting and shut-off, are realized to pseudorandom frequency sweep nuclear magnetic resonance excitation pulse frequency and the control in pulse duration.
3. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 1, it is characterised in that the frequency scanning
Control module has automatically scanning and two kinds of working methods of manual scanning.
4. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 3, it is characterised in that the frequency scanning
Control module judges the side of frequency scanning according to the NMR response signal being currently received automatically under automatically scanning mode
To simultaneously regulating frequency modulation function.
5. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 3, it is characterised in that the frequency scanning
Control module modulates letter under manual scanning mode by host computer incoming frequency scanning direction and scanning step regulating frequency
Number.
6. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 3, it is characterised in that the frequency scanning
Control module is by constantly changing frequency modulation(PFM) function so that the spectral characteristic of pseudorandom frequency sweep nuclear magnetic resonance excitation pulse is with solid
Fixed form is slided along frequency axis, and realization is scanned to a series of NMR response on frequencies to be excited.
7. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 1, it is characterised in that the impulse ejection
Module includes the bridge circuit and associated trigger circuit being made up of switching tube.
8. a kind of pseudorandom frequency sweep nuclear magnetic resonance detection instrument as claimed in claim 1, it is characterised in that the control is with leading to
Letter module is in communication with each other with host computer.
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| CN106871993B (en) * | 2017-04-14 | 2023-05-19 | 西安翼飞软件科技有限公司 | External longitudinal section detection wave liquid level water-containing detector |
| CN107782756A (en) * | 2017-09-27 | 2018-03-09 | 中国科学院电工研究所无锡分所 | The automatic search center frequency approach of nuclear magnetic resonance core analyzer |
| CN107898460A (en) * | 2018-01-05 | 2018-04-13 | 河北坤宇物探科技有限公司 | A kind of ion calculus remote sensing instrument |
| CN109031433A (en) * | 2018-07-18 | 2018-12-18 | 卢氏县地质勘查研究所 | A kind of nuclear magnetic resonance remote-sensing detector |
| CN109031434A (en) * | 2018-07-18 | 2018-12-18 | 卢氏县地质勘查研究所 | A kind of frequency-sweeping apparatus of nuclear magnetic resonance remote-sensing detector |
| CN110989009B (en) * | 2019-11-27 | 2021-04-06 | 吉林大学 | High-sensitivity compensation type underground metal unexplosive object detection device and detection method |
| CN114487954B (en) * | 2022-04-14 | 2022-07-01 | 中国科学院精密测量科学与技术创新研究院 | Multichannel transmitting-receiving NMR method for accurately measuring field intensity and distribution of electromagnet |
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