CN107782756A - The automatic search center frequency approach of nuclear magnetic resonance core analyzer - Google Patents
The automatic search center frequency approach of nuclear magnetic resonance core analyzer Download PDFInfo
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- CN107782756A CN107782756A CN201710886999.8A CN201710886999A CN107782756A CN 107782756 A CN107782756 A CN 107782756A CN 201710886999 A CN201710886999 A CN 201710886999A CN 107782756 A CN107782756 A CN 107782756A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
- G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
- G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
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Abstract
A kind of method that can search nuclear magnetic resonance core analyzer magnet field strength centre frequency automatically.It utilizes the Direct Digital Frequency Synthesizers AD9858 of Analog Devices companies of the U.S., do spectrometer frequency generator, in Automatic-searching centre frequency, a sample excitation is done according to nominal frequency first, then stimulating frequency is increased according to signal frequency, further increases stimulating frequency if signal frequency reduces, if signal frequency increases, then step-length is halved and remotivates sample and tracer signal frequency, until signal frequency is slightly larger than or equal to 0.25Hz.Accurate centre frequency is found, detection time can be shortened, improves the signal to noise ratio of single sweep operation.
Description
Art
, especially can be automatic the present invention relates to a kind of center operating frequency adjusting method of nuclear magnetic resonance core analyzer
Search the most strong corresponding Larmor's center operating frequency of signal amplitude corresponding to supporting magnet field strength.
Background technology
Crude oil, natural gas and water in stratum, rich in hydrogen nuclei, one-dimensional nuclear magnetic resonance logging technique measurement hydrogen nuclei
Signal, by inversion technique, obtain relaxation time T2 Spectral structure.By demarcation, relaxation time T2 spectrum amplitude and just etc.
In total porosity, wherein containing movable fluid and constraint fluid.When oil gas water is present in hole simultaneously, T2 spectrum signals are same
Shi Chengxian.
At present, known nuclear magnetic resonance core analyzer, it is to be operated in the proton resonance corresponding to the center field strength of magnet
In frequency.Because magnet temperature is affected by environment, the caused field strength variation with temperature in surrounding space and change, on the spot
After changing by force, the nominal resonance frequency value of instrument will be different from Larmor's resonant frequency corresponding to actual field strength, and
Difference when last time instrument resonant frequency set when using may also be with testing again, so as to be detected to each core fluids
Work brings error even error result.
At present, conventional nuclear magnetic resonance core analyzer, it is the side for taking simple comparison signal amplitude and frequency size
Method, to search for the centre frequency of the later magnet of start.After start, enter the excitation of water-filling mould and inspection first with the nominal frequency of instrument
Survey, record the initial amplitude and frequency of oscillation of signal, then comment experience randomly to increase or reduce the output signal of spectrometer again
Frequency, signal amplitude increase or reduction after adjustment, then random increase or the output frequency for reducing spectrometer, until satisfied letter
Number amplitude and frequency of oscillation occur.Current method, randomness is strong, and time-consuming, and the degree of accuracy of optimal centre frequency is low.
At present, in Chinese utility model patent《A kind of novel digital spectrum instrument for MRI system》（Authorize
Notification number CN2896299）In, devise one kind and be used for Magnetic resonance imaging（MRI）Novel digital spectrum instrument, mainly sent out by radio frequency
Penetrate module, receiver module, gradient modules composition.The spectrometer employs state-of-the-art Digital Signal Processing and modular
Design structure, total digitalization is realized, arbitrary pulse train can be produced, meet the need of nuclear magnetic resonance and its imaging method
Will, there is wider operating frequency range.But, the mode of search center frequency, not old after the patent is started shooting on spectrometer
State.
In addition in Chinese utility model patent《A kind of nuclear magnetic resonance impulse format conversion device》（Authorization Notice No.
CN202094857U）In, a kind of nuclear magnetic resonance impulse format conversion device is disclosed, including：Pulse input end；Format identification list
Member；Clock generating unit, for producing clock frequency signal according to the time pulse information；Etc..The utility model is changed
Device can be converted to the X amplitudes of pulse and Y amplitude list informations the amplitude and phase list information of pulse, can be directly used for core
The programming radio-frequency signal generator of resonance spectrometer uses.But on magnetic nuclear resonance radio frequency pulse frequency after powering, how to adjust
Save and match with the real-time field strength of magnet, without the statement of correlation technique.
The content of the invention
After overcoming existing nuclear magnetic resonance core analyzer spectrometer to start shooting, the degree of accuracy is not high during search center frequency
Problem, the invention provides a kind of method of automatic search center frequency, this method can be by the center frequency value of setting, successively
With tri- orders of magnitude of kHz, 0.1kHz, 0.01kHz and 1Hz, using 0.5Hz precision as target, automatic center frequency values are carried out
Adjustment.
The present invention, technical scheme is used by solving its technical problem：When nuclear magnetic resonance core analyzer magnet part
During in temperature constant state, after opening instrument, the accurate resonance frequency value corresponding to magnet field strength is not known first.According to core
The nominal resonance frequency value of magnetic resonance core analyzer, do a radio-frequency pulse excitation transmitting.If collect with certain
The free induction decay signal of amplitude and frequency of oscillation, driving frequency is then increased into 1kHz, then observe the vibration of detection signal
Frequency, if frequency reduces, it is correct that illustrating, which increases driving frequency, and records the frequency and initial amplitude of detection signal.Enter
One step 1kHz frequency steps increase driving frequency, if signal frequency increased with previous compare, driving frequency is increased
Step-length is adjusted to 0.5kHz, if signal frequency during than the 1st time increase 1kHz of corresponding signal is small, illustrates this step of 0.5kHz
And correctly.Then, driving frequency, then the change of observation signal frequency are increased by step-length of 0.25kHz.As it was previously stated, until
Driving frequency step-length is finally reduced into 0.5Hz magnitudes, and at this moment reception signal frequency of oscillation is close to 0.25Hz.So, then this
When driving frequency be exactly to search for obtained centre frequency automatically.There is accurate driving frequency value, carrying out core fluids
During analysis, it is possible to the accurate content for knowing each constituent of oil gas water collected, for instructing the probing of oil exploration
Direction.
The invention has the advantages that, according to the result of frequency comparator, it can be realized automatically rapidly by software
Accurate center frequency value is searched, centre frequency can be just found accurately without manual intervention, or by experience.
Brief description of the drawings
The present invention is further described with reference to the accompanying drawings and examples.
Fig. 1 is the automatic search center frequency algorithm schematic diagram of the present invention.
1. set initial frequency to walk in figure, and 2. record reception signal frequency of oscillation steps, 3. increases set frequency values to walk, and 4. such as
Fruit signal frequency increases condition, and 5. reduce setting frequency values, and 6., which continue increase, sets frequency values to walk, if 7. signal frequencies reduce
Condition, 8. adjust setting frequency values repeatedly again walks, and 9. find frequency difference 0.25Hz central resonance frequencies.
Embodiment
In Fig. 1, after the start of nuclear magnetic resonance core analyzer, the value and magnetic of spectrometer radio-frequency pulse output frequency to be adjusted
Body field strength correspond to resonance frequency value it is consistent when, the present invention contains following steps, including sets initial frequency（1）, note
Record receives magnetic resonance signal frequency of oscillation（2）, first increase set frequency values（3）, observe and record reception signal frequency of oscillation value
And if compared with last time signal frequency value, the judgement of signal frequency reduction condition（7）If, signal frequency increase condition criterion
（4）, continue with 1kHz, 2kHz, 4kHz or 8kHz step-length increase set frequency values walk（6）, reduce set frequency values walk（5）, again
Secondary adjustment repeatedly sets frequency values to walk（8）And find frequency difference 0.25Hz centre frequencies step（9）.
In the embodiment shown in fig. 1, the frequency synthesizer chip used in nuclear magnetic resonance core analyzer spectrometer, it is
The AD9858 Direct Digital Frequency Synthesizers chips of Analog Devices companies, it is characterized in that clock frequency is 1GHz when operating
When, output signal frequency precision is 0.23Hz.After the start of nuclear magnetic resonance core analyzer spectrometer, first according to analyzer magnetic
The nominal field strength of body, and the nominal resonant frequencies of analyzer, first time sample excitation is done using nominal frequency.If collect
The magnetic resonance signal for the certain frequency that can be identified, and obviously stimulating frequency used has certain difference from target center frequency,
Adjusted with regard to carrying out second of sample excitation, and to stimulating frequency.Increase stimulating frequency 1kHz, at this moment, if magnetic resonance is believed
Number quality improves, and records the frequency of oscillation value of signal, is then further added by stimulating frequency 1kHz, if signal quality is deteriorated, or
Person says that signal oscillating frequency values become big, then retracts a step, stimulating frequency increase step-length is adjusted into 0.5kHz, signal is write down and shakes
Swing frequency values, if with compared just now, frequency values further reduce, then again using 0.25kHz as step-length increase frequency.So circulate
Back and forth go down, be equal to 0.23Hz until the frequency of oscillation of magnetic resonance signal is slightly larger than, then sample excitation frequency now is just
It is the center stimulating frequency to be looked for.
Claims (3)
- A kind of 1. automatic search center frequency approach of nuclear magnetic resonance core analyzer spectrometer, by back and forth progressively reducing frequency step Method, the difference of driving frequency and target center frequency is narrowed down into hertz from KHz, it is characterized in that：One is set first Driving frequency initial value, then judge magnetic resonance signal frequency of oscillation size and record, change one one step of driving frequency, then Observation determines the frequency of magnetic resonance signal, determines to be in next step increase by the frequency of oscillation value or reduces driving frequency.
- 2. the automatic search center frequency approach of nuclear magnetic resonance core analyzer spectrometer according to claim 1, it is characterized in that： After first time, which increases, sets frequency values 1kHz, if signal frequency reduces, continue to increase driving frequency value；And if when the After once increase sets frequency values 1kHz, if signal frequency increases, being changed to increases 0.5kHz driving frequency values excites again Sample.
- 3. the automatic search center frequency approach of nuclear magnetic resonance core analyzer spectrometer according to claim 1, it is characterized in that： The frequency synthesizer of spectrometer used is the AD9858 Direct Digital Frequency Synthesizers of Analog Devices companies of the U.S..
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| CN201710886999.8A CN107782756A (en) | 2017-09-27 | 2017-09-27 | The automatic search center frequency approach of nuclear magnetic resonance core analyzer |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2009034152A (en) * | 2007-07-31 | 2009-02-19 | Toshiba Corp | Mri apparatus |
| CN101744616A (en) * | 2008-12-19 | 2010-06-23 | Ge医疗系统环球技术有限公司 | Transmitting frequency calibration method for chemical saturation in MRI and MRI system |
| CN106383364A (en) * | 2016-06-16 | 2017-02-08 | 山东大学 | Pseudo-random frequency-sweeping nuclear magnetic resonance detection instrument |
| CN106597557A (en) * | 2016-11-03 | 2017-04-26 | 长安大学 | Fundamental frequency controllable broadband nuclear magnetic resonance and optimal response extraction method |
-
2017
- 2017-09-27 CN CN201710886999.8A patent/CN107782756A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2009034152A (en) * | 2007-07-31 | 2009-02-19 | Toshiba Corp | Mri apparatus |
| CN101744616A (en) * | 2008-12-19 | 2010-06-23 | Ge医疗系统环球技术有限公司 | Transmitting frequency calibration method for chemical saturation in MRI and MRI system |
| CN106383364A (en) * | 2016-06-16 | 2017-02-08 | 山东大学 | Pseudo-random frequency-sweeping nuclear magnetic resonance detection instrument |
| CN106597557A (en) * | 2016-11-03 | 2017-04-26 | 长安大学 | Fundamental frequency controllable broadband nuclear magnetic resonance and optimal response extraction method |
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Application publication date: 20180309 |