AU653516B2 - Magnetic resonance analysis in real time, industrial usage mode - Google Patents

Description

OPI DATE 21/10/92 APPLN. ID 75568 91 AOJP DATE 26/11/92

INTI

(51) International Patent Classification 5 G01R 33/20 PCT NUMBER PCT/US91/01859 (11) International Publication Number: Al (43) International Publication Date: "ION TREATY (PCT) WO 92/16851 1 October 1992 (01,10.92) (21) International Application Number: (22) International Filing Date: PCT/US91/01859 19 March 1991 (19.03.91) (81) Designated States: AT (European patent), AU, BE (European patent), CA, CH (European patent), DE (European patent), DK (European patent), ES (European patent), FR (European patent), GB (European patent), GR (European patent), IT (European patent), JP, LU (European patent), NL (European patent), SE (European patent).

(71)Applicant: AUBURN INTERNATIONAL, INC. [US/ US]; Eight Electronics Avenue, Danvers, MA 01923-5008 (US).

(72) Inventors: DECHENE, Ronald, L. SMITH, Thomas, B. MARINO, Scott, A. Auburn International, Inc., Eight Electronics Avenue, Danvers, MA 01923-5008 (US).

Published With (74)Agents: COHEN, Jerry et al.; Perkins, Smith Cohen, One Federal Street, Boston, MA 02110 (US).

iniernational search report.

653516 (54)Title: MAGNETIC RESONANCE ANALYSIS IN REAL TIME, INDUSTRIAL USAGE MODE (57) Abstract Pulsed NMR system for industrial purposes comprising sample throughput system LI, VI, V2) magnetic field adjustment (120, 124) and thermal adjustment (134-138 and 142-146). The resonance is established by a coil (100), excited by a transceiver (104) and interacting with the sample and the magnetic field at resonance to establish received and digitized free induction decay curve forms which are automatically analyzed into Gaussian and exponential components providing simplified high speed computation means with repetitive test sequence and thermal controls that systematically minimize errors to assure reliable determination of target nuclei quantities in successive samples from an industrial process and utilizing Hahn spin echo based equipment to automatically adjust the analysis of one or more of the analyzed components.

WO 92/16851 PCT/US91/01859 -1- M IaETIC RESONANCE ANALYSIS IN REAL TIME, INDUSTRIAL USAGE

MDCE

FIELD OF THE INVEIC The present invention relates to an instrument for measurement of the type and quantity of lattice bound and free magnetically active nuclei within successive samples of a process material flow through pulsed nuclear magnetic resonance (NMR) techniques and more particularly the application of such measurement to industrial process control of moisture content, poly-mr content, crystallinity fraction, and other percentages of components analysis and other paraieters.

BACHRDUND OF THE INVENTION Magnetic resonance imaging (MRI) and NMR techniques have grown extensively over the past forty years, most notably in the medical instrumentation areas where in vivo examination of various parts of the human body can be seen and in clinical research laboratory uses. In addition there has been some use WO 92/16851 PCT/US91/01859 -2arnd interest in the application of these techniques to industrial instrurmentation and control tasks. The present invention enables effective utilization (technically and econoically) of pulsed NMR techniques in industrial areas to replace or coplement existing optical and radiant energy-based instrumentation.

Pulsed NMR spectrosccpy uses a burst or pulse which is designed to excite all the nuclei of a particular nuclear species of a sample being measured (the protons, or the like, of such sample having first been precessed in an essentially static magnetic field); in other words the precession is modified by the pulse. After the application of the pulse there occurs a free induction decay (FID) of the magnetization associated with the excited nuclei. Traditional Fourier Transform analysis generates a frequency domain spectrum which can be used to advantage in studying the nuclei of interest. The duration of the pulses, the time between the pulses, the pulse phase angle and the composition of the sample are parameters which affect the sensitivity of this technique. These frequency domain techniques are not easily useable in i-dustrial applications, especially online applications.

An object of this invention is an improved measurnt system which leads to accurate, fast determination of the types and quantity of the nuclear species of interest.

A further object of the invention is to utilize time domain analysis in achieving such system.

Another object of this invention is its application to the inustrial, on-line' problem of measuring the controlling processes.

The principal variable of interest is moisture, with distinction between free and bound water in an organic or inorganic substance based on hydrogen nuclei precession analysis.

But other parameters can be measured based on hydrogen or other WO 92/16851 WO 9216851PCI! US9 1/01859 -3sensitive species including sodium. It is an object of this invention to accomodate a variety of such measuring tasks.

Another object is to accommodate the dynamics of industrial on-line applications including variations of density, temperature, packing and size factors, friction and static electricity, vibration and frequent, repetitive, cyclic and noncyclic measurements.

Another object of the invention is to use magnetic resonance NMR techniques in polymer analysis, including density melt index and/or isotatic index nmearent.

Another object is to enhianre accuracy and reliability of data obtained.

It is an object of the invention to achieve the necessary practical economies consistent with the foregoing objects,, A further object of the invention is to integrate all the features of accurate, fast determination of the types and quantity of the nuclear species of interest, the use of time domain analysis in such a system, its application to the industrial, on-line problems of monitoring and controlling processes, e.g. measuring free and bound water in organic or inorganic substances (based on hydrogen nuclei modifiedprecession analysis) or other parameter measurement (based on hydrogen or other sensitive species including sodium-23 cz carbon-13), acarmmdating the dynamics of industrial on-line applications including variations of density, temperature, packing and size factors, friction and static electricity, vibration and frequent, repetitive, cyclic and non-cyclic measurements.

A further object of the invention is to use such magnetic resonance techniques in polymer analysis, including density, all with enhanced accuracy and reliability of data obtained and while achieving the necessary practical economies.

A further object of the present invention is to extend those achievements further in relation to industrial on-line processing, and the like, as applied to mixed species (or mixed phases) of NMR-active materials and more particularly foodstuffs and plastics materials (and being applicable to many other NMR-active materials) with a third component such as oils/fats or solvents in addition to two main components (moisture/solids, crystalline/amorphous).

SUMMARY OF THE INVENTION The present invention provides a materials measurement system using magnetic resonance hardware, controls (and related data capture and data reduction means and steps) and techniques, preferably in the time domain.

The system is utilizable in connection with capture of data from a continucus production line or like repetitive measurement system.

According to a broad aspect of the invention there is provided a nuclear magnetic resonance system for industrial process monitoring comprising: means for assessing successive samples from an industrial process, placing them in a sample measuring region and discarding successive such samples from said sample measuring region, -4ameans for applying a base magnetic field to the sample measuring region to effect precession of sample nuclei therein and for applying a resonant excitation pulse to the sample measuring region to modify the precession with means defining receive antenna coil means and signal translating means interacting with a sample in said region and relaxation detected at the coil means as a free induction decay signal which is measurable as a free induction decay curve via said signal translating means, means for digitizing the free induction decay curve and automatically analysing the digitized curve to zero-axis intercepts of Gaussian and exponential components of the decay curve, summing and extracting a ratio of the intercept of one of said components to the sum of the intercepts of said components, and wherein: said means are constructed and arranged: to stabilize base field application, excitation and signal translation conditions in response to variations of one or more parameters of actual condition of a sample in the sample measuring region; to effect such extraction of ratio and related stabilization on a repeating, high speed basis for successive samples from the industrial process; and translating at least a thousand data points in each decay curve and effecting reduction as to at least a 100 points thereof whereby sample component proportions are reliably and repeatedly measurable from sample to sample in rapid succession for on-line real time monitoring.

L

C,

-4b- The NMR system effects a reliable extraction of free induction decay data in a way that is practical in an industrial on-line context and economically practical.

The system is characterized by provision of a base magnetic field homogeneity to a reasonable degree and offset of inhomogeneity effects, temperature stabilzation to a reasonable degree and offsets of thermal drift effects and use of multiple runs (50-500) for each measurement with digital data reduction and use of statistical methods or other data manipulation for industrially effective measurement.

These data can be represented, for discussion/ '.9 fi4

A

WO 92/16851 PCI/US91/01859 analysis, as a free induction decay curve (FID) with attention to time sequence canponents of a first, very fast, essentially Gaussian portion followed by a slower, essentially exponential region representative of proton relaxation after an initial excitation by a pulse of transmitted and resonantly coupled radio frequency energy that induces a modification of the precession of protons in the sample being measured in a high static magnetic field.

The Gaussian FID portion is based on masuremnt data points of magnetization decay of immobile or highly constrained protons present in the sample and picked up at the NMR system's receiver; this portion is usually based on the response of bound proton species such as the hydrogen or hydrate content of chemical compounds (or similarly for many other NMR-active species, sodium-23 or carbon-13, which are chemically bonded). The exponential FID portion is usually based on loosely constrained or unconstrained NMR-active species such as moisture physically present in a sample but essentially chemically unbonded thereto. The Gaussian and exponential FID portions and the FID as a whole can be extrapolated to a decay origin usually set at the timie center of the excitation pulse. Zero time intercepts of these curves FID and one or more of its cmponent curve portions) provide ratio data using the FID intercept and/or intercepts of one or more of the curve portions to determine e.g. free vs. bound water in a moist material (e.g.

for process control of industrial chemicals, minerals and metals, agricultural commodities, processed foods by deterning moisture content for upstream or downstream correction or for acceptance/rejection purposes). Instead of determining moisture in, say a food product the object may be to determine ratio of relatively crystalline and non-crystalline components of a material, e.g. hard and scft cmponents of a plastic material and that. is accompliAhed in a fashion analogous to the moisture WO 92/16851 PC/US91/01859 -6measurement. Density can also be determined through the invention because the FID varies predictably as a function of density.

Within a given such measurement, a source of error can arise if the material has a fat or oil or organic solvents component that has an exponential response similar to that of moisture content or the like. Such fats or oils or solvents may appear in foods. In sce instances, it may be desirable to actually determine such fat, oil or solvent content not merely separate it out from determination of moisture or the like.

Similarly, residial solvents ay appear in plastics or other industrial materials as an error factor to be resolved and/or as a target parameter to be measured. The NMR response of such solvent or fat/oil portion can be isolated by use of Hahn spin echo technique as an extension of each of several measurement cycles. When a FID has progressed from initial excitation and Gaussian and exponential response portions, a iew secondary refocussing pulse (usually a 1800 or pi rotation compared to the ixiitial excitation 900 or pi/2 pulse) is applied to produce an echo and then a third pulse (also pi) is applied to obtain a second echo which is reflective entirely of the solvent or oil/fat content. That second echo can be treated independently of stored data of the first FID and then subtracted from the first FID to provide a valid first FID intercept (exclusive of oil/fat effects) which is reduceable via ratio analysis with that FID's Gaussian portion intercept to derive valid solids/liquid content (or crystallinity, or moisture) data.

The invention also coprises the direct extraction of data, with appropriate calibration, fram the tertiary FID to show the solvent or fat/oil content. Such technique can be extended, to some degree, to distinguish among sidb-canonents of such solVents or fats/oils.

WO 92/16851i WO 9216851PCTr/US9I/01859 -7- The measuring system of the invention comprises economically scaled down and industrially hardened portions, relative to the widely used laboratory systems. A magnetic essentially fixed field is produced by closely spaced pole pieces with a 4,000 8,000 Gauss field (about 4,700 Gauss, nominally).

Helmholtz coils are provided which are adjustable to provide rapid adjustments for the precise, correct field and overlaid with coarse, slower adjustments to -thermal environment. This is to assure that the product of a materials related constant (gama) multiplied by the magnetic field strength, which is resonant frequency, will match excitation frequency. Still further fine adjustment is made in signal processing as described below.

The system of the present invention accommodates great streams of data in practical ways through features, described below, which are inter-related to the thermal controls to provide a measuring system meeting the foregoing objects. The materials of construction are also integrated into the reliability considerations, as described below. Measurent of a sample is often accamlished in less than a few minutes (in contrast to hours-long measur~ents of many prior art systems).

he measurements made through the present invention based on ratios of intercepts and/or integrated areas under curves and/or peak analysis are independent of weight or volume of sample in a measuring region whereas precise weight measurement is a necessary featre, and limitation of, rany prior art systems.

Prior art efforts at industrial on-line measurement of the same parameters as are treated herein have involved non-NMR gravimetric, radioactive, acoustic, optical and WO 92/16851 PCT/US91/01859 -8electrostatic/capacitive systems, none wholly satisfactory for present purpose and NMR usage in support of continuous industrial processes has been a forcing of off-line laboratory instruments into service [at great expense and nevertheless with inadequate sampling] or some early efforts of the 1980s at industrially hardened pulsed NMR instruments making use of only one or two data points for FID analysis.

Laboratory methods of frequency domain NMR analysis are described for crystallinity content determination in, e.g., Spiess, "Molecular Dynamics of Solid Polymers As Revealed By Deuteron NMR", 261 Colloid Polymer Science 193-209 (1983) and Kauffman et al., "Determination of Transition Temperatures and Crystalline Content of Linear High Molecular-Weight Polyethylene by Proton NMR Spectroscopy", 27 Jl. of Polymer Science 2203-2209 (1989). Time domain analysis using pulsed and multiple pulsed NMR/free induction decay in coals for detection of free radicals therein is shown in the laboratory systems of Gerstein et al.

(Iowa State University Ames Laboratory) reported in "Utility of Pulse Nuclear Magnetic Resonanra In Studying Protons In Coals", 81 Jl. of Ehys. Chem. 566-571 (1977) and "IH Nuclear Magnetic Resonance Studies of Dmain Structures In Polymers", 52(9) J.

Appl. Phys. 5517-5528 (1981). The instruments or former instruments of 7SM Federal Systems Division model and Brucker GmQibH model P201 and the description in U.S. patent 4,430,719, granted February 7, 1984, to Pearson are the earlier attempts referred to above at industrial use of NMR methods. The Pearson work was embodied in 1985 industrial plant control work of Kaiser Aluminum Chemical Corp. It was not effective as a reliable quantitative device. Auburn International, Inc. offered the Pearson/Kaiser product for sale in 1987-1988 and it could not meet the needs of irdustrial on-line monitoring.

Other objects, features, and advantages will be apparent WO 92/16851 WO 92/6851 cr/us9i/01859 -9from the following detai led description of pr,:ferred emb~odiments tuken in conjunction with the accompanying drawing in which: E= E SCRIPTICt OF. UMl EIPAWNG(S) FIGS. 1 andi 2 axe lateral and cross-sections of a preferred embodiment of the invention including electrical block diagramn comonents with FIG. 1A showing a variant of the saiple tubte carponent thereof; FIG.* 3 shows the voltage-time waveforms of tree induction decav (FID) of the emoiment of FIGS. 1-2 in the course of operation; FIG. 4 is a flow chart of me~asuring steps utilizing the FIGS. 1-2 apparatus including its signal processing elements, (the activity of which is il1lustrated by the FIG. 3 wc.'vef orLs) FIG. 5 is a voltage-time waveform. for free induction decay (FID) of the embodiment of FIGS, 1-2 modified for Hahn spin echo utilization; FIG. 6 is a flow chart of measuring steps utilizing the FIG. 1-2 embodient, mo~dified for Hahn spin echo utilization, includn its signal processing elemnts (the activity of which is described by the FIG. 5 wavefonn) and also indiicating density as well as imiture measurmnt; FIG. 7 is voltage (or other varied intensity paramreter) ti trace for FID curves derived from sanples of different densi-ties using the above cited mocdified enodiarent of the present invention affording relative and abrzlute density measurezents of samples; WO 92/16851 WO 9216851PCT/tS91/01859 FIG. 8 is a 6alibration curve for absolute density iieasuremnent using the above cited e~mbouents of the present invention a-L applied to polyethylene; and FIGS.- 9A, 9B, 9C are intensity -vs. time decay curves illustrating the operation of the modJified emoiment according to further aspects thereof for establishing decay tims constant shifts and scalinaj pre-set factors and for measuring a solvent or oil/fat or like further cc&ponent of a sample by simp~le peak readings (averaged) instead of (reuse of) full FID analysis.

MD=U~ DSCRIPTIC2K OF PFERRED EMBODIMENTUS FIGS. 1-2 show transverse and cross sections with block diagram inserts of a first emiment of the invention. An industrial process line IPL has material flow'ing. as indicated by arrow A. Some of the material is captured by a probwe P and fed throu1gh an inlet. line LI to a sanple region Sl. The said region is defined by a tube 98 typically a foot long made of an essentially non-magnetic, nonconducting material which does not itself generate -Mbstantially interfering FID signals (glass, certain ceramiacs, certain plastics or hybrids).- The sample region is defined between inlet and outlet valves V1 and V2. Gas jets J are also prvided. These are pulsed on/off repeatedly to agitate fluent sarple materials during sample admission and expulsion. The region S2 is the critical portion of the saniple.

It is surround.ed by a sample coil 100 tuned to resonance and driven by a tuning circuit 102 and related t-ranszitter/receiver controller 104. Grounded 1CCps 101 are active Lenz law shields which are provided above and below~ coil 100 to help shape the field of coil 100 contain the field established by an excitation pulse. The controller 104 includes an on-board microprocessor and required power supply elements, memory, WO 92/16851 PCI/US91/01859 -11program and I/O decoding suitable to interonnect to the hardware shown and to an ex&ernal microccmptern 106 with keyboard 108, monitor (or other display) 110, recorder 112 and/or process ,controller 114 (to control the process at TPL). The operator initiates and controls operation from the display keyboard 108 and the resulting data and signals are subsequently shown on the display 100 and utilized in. 110, 112 and/or 114. The computer 106 also controls instrument operation coritions.

The region S2 of tube 98 and coil 100 are in a static but adjustable crossing magnetic field defined by a magnetic assembly 116 which ccmprises a yoke 118, pole pieces 120, surrounding Helmholtz coils 124, and a coil current generator 122. The critical sample region S2 of the type 98 and magnet are contained in a metallic (but non-ferromagnetic) box 126 with highly thermally conductive face-plates 128 and internal partitions 130 aid over-all mass related to each otner to minimize harmnics and other interferences with a microwave signal emitted from coil 100 to a sample and/or returned from the sample for pick-up by coil 100 and its tuned circuit 102 and transmit/receive corntroller 104.

The magnetic assembly 116 including yoke 118, and other parts therein as shown on FIGS. 1-2, is in turn contained in an environmental control chamber 132 with gas fill and purge controls (not hown), an interral gas heater 134, a motor M driving fan 136, and a temperature sensor 138 which can be applied to the yoke or other detection region whose temperature is reflective of the temperature at pole pieces 120 and in the s mple region therebetween. A thermal controller 140 processes temperature signals from 138 to adjust heating/circulation at 134/136 as a coarse control and to adjust current through the Helmholtz coils 124 at magnet pole pieces 120 as a sensitive and fast fine control, as well as implementing general control instructions of camputer 106. Further thermal stabilization is provided by a closed loop heat exchanger 142 having pump 144 and WO 92/16851 PCT/US91/01859 -12coils 146 attached to yoke 118 and coils 148 attached to the plates 128 of box 126. Further or alternative thermal stabilization may be obtained by a closed loop heat exchanges or heatcd air stream annules as shown in FIG. 1A where the annulus ANN is defined between concentrix cylinders Wl and W2 running the full length of sample tube SIA with a heated. air stream fed through the annulus length.

The strength, consistency and constancy of the magnetic field between poles 120 in the region S2 of the sample is thus controlled by a uniform base magnetic field in the entire region S2. The Helmholtz coils 124 are energized by the coil current controller 140 to accurately trim the final agnitude of the field in which the sample is placed. This field is the vector addition of the fields due to the magnet poles 120 and the Helmholtz coils 124 Tbe controller 140 sets the current through the Helmholtz coils 124 using current generators. The coils 124 are wound around the magnet 110 such that the magnetic field created by the current in the coils 114 can add to or subtract from the field created by the magnet pole pieces 120. The magnitude of the current through the coils 124 determines the strength of the field added to or subtracted from the field due to the magnet pole pieces 120 (and related yoke structure) alone.

The actual determination of the current through the Helmholtz coils is accmplished by carrying out the magnetic energy and resonance techniques hereinafter described in preliminary runs and adjusting Helmholtz current until the maximm sensitive resonance is achieved.

The major elements of electrical controls are in tuner 102, including coils 100 and 101 and variable capacitors 102-1 and 102-2, resistor 102-3 and diodes 102-4 and constructed for tuning to Q of twenty to fifty to achie,'e coil 100 resonance, and WO 92/16851 WO 9216851Pcr/US91/01859 -13control 104 including a transmit/ receive switch 104-1 a transmitter 104-2 and receiver 104-3, a crystal. oscillator 104-4, gated pulse generator (PPG) 104-5, and phase shifter 104-6. The crystal provides a nominal twenty Megahertz carrier which is pohase modulated or demochlated by the NOD, DMD elonnts of transmftter 104-2 and receiver 104-3. The receiver includes variable gain airplifier elements 104-31 andi 104-32 for operation.

The armlog signals received are fed to a high speed flash converter 105-1 and internal (to the instrument) CPU element 105- 2, which provides data to an external carqater 106 Which has a keyboard 108, mo~nitor 109, niodem 110, recording elements 112 and.

process controller elerezits 114, for control of valves Vl, V2 via valve controls 115 and/or to coil current controls 122, all via digital-analog converters (not showqn).

The excitation of coil 100 and excitation-precession of the sample' s proton content and subsequent relaxation/decay produces a received FM signal that, after demodulation, controlled gain amplification, A/D cornversion and plotting~ of points has the free inuction decay (FID) curve shape C shown in FIG. 3.

FIG. 3, voltage-tinie trace, show.s the elennts of a "1cycle" (with and~ sub-cycles) of excitation of a saxiple and3. free ir4uction decay. In each sub-cycle a pulse of excitation energy is applied. The excitation pulse center is takeni as to.

The transceiver 104 electronic components do not receive effectively untilI saturation effects are overcame at t1. Th en a~ useable cuzve or is developed. The signal processing equimnt can &.dd or subt--act consrcitive C+ and C- form for useful adjusbrent as described below.

The FID curve data is stored in the external camputer 106 where a proram finds the best curve to fit each stored FID WO 92/16851 PCT/US91/01859 -14curve. The FID curve C has two component parts shown as A and B in FIG. 3. The A curve which dominates the first part of the FID curve is a Gaussian curve while the B curve which dominates that later part of the FID curve is an exponential decay. The Gaussian and eqormmtial portions are respectively controlled by bound and unbmxnd proton content of the samples water or hydration miwlecules and other water (moisture) content of the sample mass, crystalline and amorphous contents where they both occur, including mixtures of highly and lightly polymerized materials and caoponents a mixed elastomer-polyirer). The determination of the type of carve which makes up the FID curve C is important because once the curves are known they can be extended back to a time origin (shown as to-1, excitation of a Cycle which is at the theoretical center of the transmitted burst signal. This is important since there are saturation effects of the instrmntnt' s electronic gear which occur from the end of the burst signal to tl. During this time measrements cannot be accurately taken, yet the area of interest under the curve, which is a measure of the nmber of nuclei in the sample, extends from tO to t4 beyond which the curve is too small to matter and the electronics need recovery time to prepare for the next cycle (beginning with a pulse centered at tO-2).

Each (sub) cycle goes on to t5 to allow for recovery essentially full relaxation of the protons of the sample before beginning a new transmit signal burst Typically, an excitation pulse interval is five to ten microseconds, the to tl time is five to fifteen microseconds (the shorter the better), tl-t2, where effects due to bound nuclei (Gaussian) are prsdominayat is five to fifteen microseconds duration (with critical measurement taken at a narrmer region tin); t2-t3 is an unclear transiti;, Legion of fifteen to twenty-five microseconds duration, t3-t4 is a region where the unbound (exponential) component predominates and it is three hundred to five hunred WO 92/168S I PCT/US91/01859 miczosecords duration during that part of the decay. The closest exponential curve is fitted to the C curve in the t3 t4 region where the C and B curves are essentially equal and this B curve is extrapolated back to to, establishing a curve B and its phantom B' component and BO intercept at to. This exponential curve is subtracted fran the C c %rve in the area (t2-t3) where the A (Gaussian) curve is doxminant. The resulting curve is then fitted with the best least squar-s Gaussian curve. This best Gaussian curve is then extrapolated back to tO to establish A including its phantom A' omponent and AO intercept at tO.

The resulting data utilized in the computer 106 (FIGS.

1-2) is the A curve and the B curve and ultimately their intercepts at to and the BO/AO+BO ratio thereof. Each of these curves (and their intercepts) has been experimentally and theoretically related to the same nuclei of interest, but with the group of the nuclei which yield the A curve (Gaussian) bound in a lattice structure. The nuclei which yield the B curve (exponential) are unbound or relatively unbound.

The data can be used as a QC type measurement or as an on-line control parameter which is fed back to control a process, back in line IPL (FIG. 1) or related equipment in drying or baking a food product, corducting a continuous chemical or metallurgical reaction process, etc.) The form of the input operating parameters of the system can be wide reaching to include previously stored parameters in PRTs or RIs or nputs sent in over telephone line and modem 110. The generation of the RF signal can be accomplished with many techniques including a coil or antennr arrangement. The steady magnetic field can be generated by electromagnets, perimanent magnets, electrmagnetics with superconducting winding or other standard techniques of gererating magnetic fields.

WO 92/16851 PCT/US91/01859 -16- FIG. 4 is an expanded flow chart showing the steps of measurement to establish effective industrial measurement. First a single free induction decay curve C is established to see if the sample area is clear (Quick FID) in an abbre iated cycle of attempting to establish a curve C. If the sample region is not clear measurement is interrupted to allow valve V2 (re)opening and operation of jets J and gravity to clear the region. A new Quick FID step establishes clearance. Then a sample is admited by closing valve V2, opening valve Vi and making such adjustments of probe P and line LI as may be necessary (if any) to assure sample acquisition. Jets J adjust and stabilize the new sample.

Temperature controls 134-138 and 142-146, described above, establish very coarse and less coarse thermal controls countering sample temperature variations.

An electronic signal processing apparatus baseline is eatablished in 30-40 cycles (each having and sub-cycles with addition of and to detect an offset and coapensate for it). Further adjustment is established by coils 24 to adjust HO and this is enabled by ten to twenty field check cycles of FID curve generation. The FID is subtracted from the FID, tne absolute C values are added to obtain a wrkable FID derivative which has a ieaxim value at resonance. HO is adjusted via coil current generator 122 and coils 124 until such maximum is achieved. These measurements are taken in a reliable region for such purpose, the exponential region of t3--t4 [the above baseline measurements are also taken there]. Adequate field adjustment is usually made in less than seven cycles.

Then fifty to five hundred cycles are conducted to obtain a useable measurement. Each of those fifty to five hundred cycles involves a modulate' FM WO 92/16851 PC'/ US91/01859 -17transmission/reception/flash A-D conversion, and storage of data.

The curves are then averaged for curve fitting, to intercept and BO/AO+BO ratio establishment. Similar cycles, but somewhat abbreviated can be applied for Quick FID, field check and baseline correction purposes. Each of the sub-cycles and of each such cycle involves a capture of thousands of FID points and utilization of hundreds of such points in data reduction.

Where multiple cycles are applied for a single measurement, the amplitudes of (digitized) curve C points are stored and a least squares fit to such data points is established. Further, plus and minus values are taken in alternation to eliminate zeroing errors as noted above.

The area under a squaring derivation of the FID curve is integrated and the area under a squared derivative of the desired exponential is integrated and a ratio is established, the square root of which is I/(KS+L) where L is liquid (moisture) value derived from the exponential, K a constant and S is a solid (or bound proton) related quantity related to the Gaussian, KS+L being total protons affected by resonance (and capable of being so affected).

It has also been discovered as greater accuracy and reliability is obtained that sample tube composition can distort readings. If glass is not used (and it is preferred to avoid glass in industrial usage), then the replacement should not be a hydrocarbon plastic. But flurocarbons can be effective in several applications since signals from fluorine act out of resonance (with conditions tuned to resonance for hydrogen in moisture measurements) and can be distinguished from moisture related readings at the levels of sensitivity required for such readings ani if desired can be filtered (or distinguished). In WO 92/16851 /CT/US91/01859 -18other cases of higher sensitivity measurements, for gauging relative proportions of amorphous and crystalline species in mixtures thereof t' e container shnould be glass or nonprotonic ceramic. all such cases the point is to avoid sample containers with species that can couple with transmitted energy and generate a FID decay curve misreading the samples. This invention includes a system response to discovery of certain such cases not heretofore recognized.

FIG. 5 shows another NMR decay waveform with repetition of terminology of identical components of the FIG. 3 NMR decay waveform discussed above. In a modification of operation of the FIG. 1-2 method and apparatus (and in modification of the structure and control settings thereof to effect such modified operation), each waveform is triggered by further pulses centered at mo' and mo" to cause Hahn spin echo responses to occur. The falling portions of the echoes (henceforth called D and E) have the same general patterns as the original FID C, excepting that D and E, particularly the latter are based primarily on response of the sample with nil response of non-fat solids and non-oil and non-solvent liquid components, whereas FID C is a measure of significant response to pulse excitation by all of solids, moisture and oil/fat or solvent caxpnents.

Times tl', t2', t3', t4' and tl t2", t3", t4" are defined for D 'nd E, respectively, as rough analogs of the tl, t2, t3, t4 points of FID C discussed above. However, there are significantly different effects in echoes (arising from 1800 rotation) compared to C (arising from 900 rotation). FID C has a duration of about one millisecond order of magnitude and each of the echoes has a duration, typically of about two milliseconds order of magnitude as controlled by selective timing of P" in relation to P; but these intervals can be set as substantially more or less for different materials to be sampled and different WO 92/16851 PCT/US91/01859 -19sets of instrument electronics specification. Almost all the time of C is occupied in the decay process, ccmpared to the latter half of each of the echoes. The effective beginning of decay for D and E is tO' and tO" at the actual peaks of these curves (whereas tO for C is set at the middle of the excitation pulse. The decays +C/D/E are alternruted with -C/D/E sub-cycles for the same purposes as sub-cycles in FIG. 3, discussed above. The pulses which initiate FID's effect (pi/2) rotation of protons while the pulses for -E respectively effect 180° (pi) rotation.

The block diagram of operations of FIG. 6 for such a modified system includes the sse artifacts as are described above in connection with FIG. 4, i.e. sarmple region clearance check by a Quick FID, multiple cycles of baseline correction and field checking (using simply P- excitation) with consequent adjustments and then measurement substantively in accordance with the use of Hahn spin echo as described in connection with FIG. above.

The signal processing of this measurement involves storage of digitized data points of the C and E decays, subtraction of E from the C and then processing of an adjusted FID C essentially as described above in connection with FIGS. 3-4, with use of time-zero intercepts and/or integrals of Gaussian and exponential subsidiary curves derived from adjusted FID C. In some cases the peak of the E decay is used to quantify the solvent or oil/fat component(s).

Additionally the data of FID C before or after adjustment by subtraction of E is utilizable as a determinant of density on an absolute or relative basis. FIG. 7 shows FID' s taken for polyethylene samples 7-1, 7-2, 7-3 of highest, less and least density. The curves are sufficiently distinct so that the WO 92/16851 PCT/US91/01859 differences are detectable by the signal processing means described above.

The appropriate tO" time setth-S of the E peak itself is determined as a presettable calibration factor for the instrument as applied to a certain type of material to be analyzed on-line over subsequent days (or weeks or months) of measurement. FIGS.

9A, 9B, 9C illustrate how this is done. FIG. 9A shows the C and E curves as developed by running the curves C, D, E of FIG. with a roughly calculated tO" under non-resonance coupling conditions (deliberately induced at coil 100, FIGS. 1-2 as ccnpared to a resonant decay curve shown in FIG. 9B) and superimposed. The difference of x-axis intercepts (Delta t, determined by shifting the curves until the zero crossings of C and E coincide) provides a correction factor to apply to the rough tO" to provide an adjusted t0"-a relative to tO for use in later runs at resonance of FID decay with Hahn spin echo (FIG.

9C). That is, in such later runs the digitizer/flash converter (105-1, FIG. 1) is gated open at a time toa" after the time to.

The last peaks (LP) of C and E in FIG. 9 ae also analyzed to obtain a ccrrection factor f, as the ratio C/E, to apply to later E readings to compensate for attenuation of tl coupared to what it would be if tO" coincided with tO in reality, rather than as an arbitrary superimposition. This is a valid correction because C at LP is wholly due to solvent or oil/fact effects and thn measured E is smaller than the masured C at LP only because of the attenuation.

Further, the intensity I parameter voltage) is measured over a range includir the nminal lwcation of tO and averaged to provide an average I usable with greater reliability.

Finally, due account must be taken of the relative quantity of protons (or other NMR-active species) per gram in each phase solid, water, oil/fat) of interest. Appropriate WO 92/16851 WO 9216851PCT/US91/01859 -21calibration constants can be developed for determining concentrations of those phases or comonents or other percentages data, e.g. crystallinity, in a mixture. For example, the proportion P of, say, oil/fat is determined by: YaEo IK.Eo KaAo KODBo where Ke,Ka ,lb are calibration factors derived from standard materials and Ao, Bo, Eo are the to intercepts afte, -application of the above correction factors. Density of a samnple material as a whole can be determined either tlmmugli ct~we analysis discussed above in connection with FIGS. 7-1, 7-2, 7-3 or for plastics (and other materials) through the equation: M [KaAo] d= N [KaAo 14bBo Y4-gF'Eoj itina the bracketed fraction is the cmystallinity proortion and Xand N are eirically derived calibration factors (usmally constAnts for the materials, consistently applied after initial detexminaticn) Densities of the components would normally be additional terms in the equation; but for plastics 'the crystalline and amorphous components have closely related fundamental densities aid density terms can drop out (except isofar as built into the 14, N factors) WO 92/16851 PCT/US91/01859 -22- For other materials the equation would be: [K]oda d= +N [KAoda KBodb KEode] where da, db and de are component densities.

For same materials, statistical methods may be applied to manually or automatically by computer programs) superimpose more complex, and intrinsically more accurate, non-linear functions on sets of data points (plots of density and/or proportion [or other parameter] determinations according to the process and apparatus of this invention vs. laboratory determinations of the same parameters for the same samples) and thus derive a second-or-third-order fit calibration function.

Later determinations via the invention can be adjusted by such calibration function.

FIG. 8 shows a calibration curve of such polyethylene density measurements by the present invention (y axis) vs.

standard method oil bath flotation) density measurements (x axis), illustrating the efficacy of the present invention. Other standard methods include acoustic transmissivity.

It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, ccnstrued in accordance with the patent law, including the doctrine of equivalents.

What is claimed is:

Claims (19)

1. Nuclear magnetic resonance system for industrial process monitoring comprising: means for assessing successive samples from an industrial process, placing them in a sample measuring region and discarding successive such samples from said sample measuring region, means for applying a base magnetic field to the sample measuring region to effect precession of sample nuclei therein and for applying a resonant excitation pulse to the sample measuring region to modify the precession with means defining receive antenna coil means and signal translating means interacting with a sample in said region and relaxation detected at the coil means as a free induction decay signal which is measurable as a free induction decay curve via said signal translating means, means for digitizing the free induction decay curve and automatically analysing the digitized curve to zero-axis intercepts of Gaussian and exponential components of the decay curve, summing and extracting a ratio of the intercept of one of said components to the sum of the intercepts ot said components, and wi.erein: said means are constructed and arranged: to stabilize base field application, excitation and signal translation conditions in response to variations of one or more parameters of actual condition of a sample in the sample measuring region; 7 N T*C~ -24- to effect such extraction of ratio and related stabilization on a repeating, high speed basis for successive samples from the industrial process; and translating at least a thousand data points in each decay curve and effecting reduction as to at least a 100 points thereof whereby sample component proportions are reliably and repeatedly measurable from sample to sample in rapid succession for on-line real time monitoring.

2. A NMR system as claimed in Claim 1 wherein said base magnetic field appliition coil means comprise Helmholtz coil means with coarse thermal stabilisation of an outer sample processing region and an intermediate stabilisation of an interior sample containing region which is adjacent to pole faces of the coil and wherein the said construction arrangement for stabilisation comprises coarse thermal environment coil means for the sample region, and means for fine adjustment via electromagnetic field variation to maintain resonance ina the sample region.

3. A NMR system as claimed in Claim 2 comprising means for effecting a further countermeasure to thermally induced drift by adjustment of extracted decay signal.

4. A NMR system as claimed in Claim 3 wherein the said means for adjustment of extracted decay signals comprise means for affecting said analysis of the free induction decay curve by areal integration of at least a discrete-function component thereof.

A NMR system as claimed in Claim 1 wherein said means for effecting said analysis effect an extension of bound and unbound components of the decy curve to a reconstructed time-zero intercept coinciding with or related to the time of excitation leading to the decay.

6. A NMR system as claimed in Claim 1 comprising a sample container essentially free of sample decay inducing ingredients in relationship to the sensitivity of measurement to be made.

7. A NMR system as claimed in Claim 6 wherein the sample container is a fluorocarbon tube.

8. A NMR system as claimed in Claim 6 wherein the sample container is a ceramic tube.

9. A NMR system as claimed in Claim 6 wherein the sample container is a glass tube.

A NMR system as claimed in Claim 1 constructed and arranged for measurement of moisture content.

11. A NMR system as claimed in Claim 1 constructed and arranged to detect proportions of amorphous and crystalline components of mixtures thereof.

12. A NMR system as claimed in claim 1 and further comprising the provision therein of means for extending each of multiple decay curves by Hahn spin-echo re-focus/decay to capture data related to a further sub-component(s) oi tns sample for enhancing the accuracy of the ratio determination of above and/or to identify proportion of the further sub-component(s). -26-

13. A NMR system as claimed in claim 12 wherein two pi re-focus pulses are applied for generation of the Hahn spin echoes.

14. A NMR system as claimed in claim 12 and further comprising means for determining a time window for gating spin echo detection at a correct zero-axis intercept relatable to an original intercept of the free induction decay curve.

A NMR system as claimed in claim 14 and further comprising means to effect such time window determination and also to compensate for attenuation of the spin echo response relative to initial response of the free induction decay by off-resonance comparisor.

16. A NMR system as claimed in claim 12 constructed and arranged to provide output identifying said proportion of the further sub-components.

17. A NMR system as claimed in claim 12 constructed and arranged to provide crystallinity output.

18. A NMR system as claimed in claim 12 constructed and arranged to provide moisture output.

19. A NMR system as claimed in claim 12 constructed and arranged to provide density output. Dated this 29th day of July 1994 AUBURN INTERNATIONAL INC By their Patent Attorneys HALFORD CO j 4.