w. c. ANDERSON
Dec. 26, “I950
2,535,026
MOISTURE DETERMINATION Filed Feb. 21, 1947
OSCILLATOR
/
6
Cc
CHPHCITY &
EQUIVQLENT RES\ST'FINCE MEQSURING! HPPQRHTUS v
\ MEF-ISURING
INVENTOR W\LME_R CLHYTON HNDERSON PERCENT MO\$TURE CONTENT
(OR REG-am)
ATTORNEY "
Patented Dec. 26, 195(_)
2,535,026
UNITED STATES PATENT OFFICE 2,535,026
MOISTURE DETERMINATION Wilmer Clayton Anderson, Greenwich, Conn., as signor to Deering Milliken Research Trust, New York, N. Y., a nonpro?t trust of New York
1
Application February 21, 1947, Serial N0. 739,154 7 Claims. (Cl. 175-183)
My present invention relates to the measure ment of moisture content of materials such as
textile materials, paper, wood, grain or the like
2 ple, in the textile industry, once separate scales are made up for each composition of fabric or
yarn, for example, cotton, wool, rayon, etc., per
and comprises a new method of moisture content cent moisture content or per cent moisture regain measurement which is accurate and rapid and ii of any of these materials, irrespective of their may be used for measurements on continuously weight or thickness, can be readily determined. moving as well as on stationary material. As Similarly, in the case of measurement of mois compared to methods heretofore in use, the new ture content of paper, or the like, once a cali method is substantially independent of the bration is made for the various compositions of weight or thickness of the material being tested. 10 wood, paper, etc., the moisture content of any The following brief discussion will assist in un specimen can be quickly determined. derstanding the theory upon which the new For a better understanding of the invention, method of the invention is based. If a material, reference may be had to the accompanying such as yarn or the like, is inserted between the drawings of which: plates of an air condenser, the capacity of the 15 Fig. 1 illustrates diagrammatically the method condenser changes and this change in capacity of the invention as applied to the determination depends upon the particular material, its weight of percentage moisture content of material such and dimensions and upon its moisture content. as yarn, paper or the like; Insertion of the material between the condenser Fig. 1a illustrates as an example of one speci?c plates also changes the equivalent series resist 20 circuit suitable for use in measuring the values ance of the condenser and such change likewise involved, a Schering bridge; depends on the type of material, its weight and Fig. 2 illustrates the method of the invention dimensions and its moisture content. Some as applied to the determination of percentage methods heretofore suggested or practiced have moisture content of granular material; and utilized either changes in capacity or changes in 25 Fig. 3 is a diagram illustrating the types of re resistance or changes in total impedance in an lationship between moisture content and ARc/AC
attempt to obtain determinations of moisture
obtainable for various diiferent materials.
content. As indicated above, none of these vari In practicing the invention, the relationship ations are dependent solely upon the moisture between moisture content and A/Rs/AC for a par content of the material, and hence methods rely 30 ticular material and condenser is ?rst obtained ing upon either capacity measurement alone or empirically. The capacity Co and equivalent se resistance measurement alone or upon imped ries resistance R‘, of an air condenser, for exam ance measurement have not been satisfactory as ple that indicated diagrammatically in Fig. 1 by they necessitated equality in weight and dimen the plates 2 and 4, are ?rst measured by means sions of test and standard samples. As a result 85 of any suitable measuring apparatus as indicated
of theoretical considerations which have been at 6. A sample of the particular material for con?rmed experimentally, I have found that if which the relationship is to be determined and the change in equivalent series resistance, AR‘, the percentage moisture content of which is and the change in capacity,‘ AC, are measured known, is then inserted between the plates 2 and and their ratio taken, determinations of moisture 40 I and a new measure of equivalent series resist content may be made without requiring that the ance, say R._, and of capacity, C." is made. The weight and dimensions of test samples be equal to ratio those of a standard sample. This ratio, ARs/AC, is a measure of the per cent moisture content
Blur-RIO
over arelatively wide range of percentage mois 45 (LI-C, or ture content, provided the thickness of the sam AR . ple is relatively small as compared to the distance AC’ between the condenser plates. Thus, for any given type of material, once the relationship be is then plotted against the known percentage tween the percentage of moisture content and the 50 moisture content of the sample to give one point, ratio ARg/AC is obtained, a scale or table may be for example, the point a’ on a scale such as indi set up for that particular type of material and cated in Fig. 3. Additional points such as a", percentage moisture content of other samples of a'”, etc. are similarly determined and a smooth such material immediately determined from ca curve, the curve A of Fig. 3 drawn through the pacity and resistance measurements. For exam 56 point a’, a", a’”. If ‘the curve, as in the case of
2,035,026 3
.
curve A of Fig. 3 is a straight line, relatively few points are necessary to determine the slope of the line. It so happens that the curves for vari ous textile materials are substantially straight lines, but the method of the invention is not de
pendent upon a linear relationship between per
cent moisture content and ARs/AC. The points a’. a”, and a'” of Fig. 3 may represent 5, 10 and 15 percent moisture content, respectively, of cot ton material and may have been determined
from the following values which represent typi cal measurements:
R.,,=o ohms 00:34.0 pal’.
4
mentalities for measuring capacities and equiva lent series resistance of condensers, have been specified, nor have instruments for automatically computing the desired ratio been speci?ed, as the present invention is directed only to the broad principles underlying the new method and not to
any speci?c apparatus for carrying out the ac tual measurements. Bridge or other type cir cuits for measuring these values are known in the art and the method as herein described can be practiced by the use 0! various types of meas
uring instruments. One such bridge type circuit suitable for measuring these values is described in an article by D. B. Sinclair on pages 310-18 15 of volume 28 of the Proceedings of the Institute
of Radio Engineers. As an example of One spe ci?c circuit suitable for use in measuring these
values, a Schering bridge is shown in Fig. 1a. In this circuit the resistors R’. and Rh may be 20 fixed and the capacities Cb and Cc‘ adjustable.
When the bridge is in balance, that is when no voltage is impressed on the detector D, the ca— pacity C of the test cell is equal to Co (Rs/R.)
and the equivalent series resistant R; is equal to
which yield the values of ARI/AC at point a’ of
36/.8 or 45, for point a" of 94/14 or 67, and for 25 Re (GI/Cc), (See Terman’s Radio Engineer’s point a'” of 175/15 or 90. Assuming, as above Handbook, ?rst edition, page 905, Fig. 6 (j)_.) It will be apparent that the new method has a wide indicated, that the material used in obtaining the applicability in various industries, for example, line A of Fig. 3 was cotton yarn, measurement of in the textile industry, the food industry, the percentage moisture content of other cotton yarns, whether of the same or different weight 30 paper industry, or the building industry. When used in the textile industry, the curves or lines and dimensions as the sample used for calibra for the various materials would be plotted so as to tion may now be readily determined. For exam give directly per cent moisture regain, rather ple; a length of yarn 8 from a reel It may be
continuously passed between the plates 2 and 4 and measurements of equivalent series resistance and capacity taken at intervals. The percentage
than per cent moisture content.
"
As heretofore indicated, the relationship be tween per cent moisture content and ARs/AC for any material holds true fora relatively wide range of per cent moisture content irrespectiveoi the weight or dimensions of the material, pro vided, however, that the thickness of the mate rial is relatively small compared to the distance between condenser plates. For example the thick ness of the material under test should be not more than ?Ity per cent of the distance between electrodes and preferably of the order of ten per cent or less. The humidity of the air between
moisture content of the part of the yarn between the plates 2 and 4 can then be read directly from the chart, as
AR is
where 1%., and C; are the respective measured values of eouivalent series resistance and capac
ity at the moment under consideration.
the condenser electrodes at the time measure For other material, such as wool or rayon, the ments are made of moisture content does not same procedure is followed. That is, a curve need to be the same as when the characteristic such as curve B may be obtained for woolen yarns, and one such as curve C, for rayon yarns. 60 curve for the particular material was determined but should not vary substantially between con Once these curves, or lines, are obtained for any
given apparatus, measurement of the moisture content of other samples of the corresponding materials may be directly determined as with the case of cotton yarn.
secutive measurements made with, and without, the material between the electrodes when the dif ference values are being found. Wide tempera 55 ture fluctuations sui?cient to affect resistance
When moisture content of granular material is to be determined, apparatus such as indicated di aarammatically in Fig, 2 may be employed. As shown in Fig. 2, an endless traveling belt l2 may be passed between plates 21 and 4. of a condenser, 00
measurement should be avoided.
The calibra
tion curve for a given material should be made at the same frequency as that used thereafter for
moisture content measurement. any suitable fre quencies such as ordinarily used in measuring equivalent series resistance may be used. the capacity and equivalent series resistance of Obviously, the method of the invention could which is to be measured. For calibration. that is be employed for control of moisture content as well to obtain a curve, such as curve D of Fig. 3, for as for measurement thereoiI and could be‘ used for any particular granular material, the capacity and equivalent series resistance of the condenser 65 moisture content measurements of other than ?at and granular materials. Although flat con with the two stretches of the belt I2 therein, but denser plates have been diagrammatically indi without granular material on the belt, are taken cated in the drawings, their use is not essential as the reference values. Points on the curve are as I have successfully practiced the invention then obtained by measurements taken when ma terial of known moisture content is between the 70 with condensers having other types of electrodes. Although the ratio ARs/AC has been described plates, as described in connection with cotton as a measure of the moisture content, and such yarn. ratio has been indicated in the chart of Fig. 3, In the description so far given of the new obviously, the inverse ratio AC/ARs could as read method of determining percentage moisture con ily be employed. tent of material, no particular type of instru
I claim:
8
2,688,096
1. The method of determining moisture con tent of a de?nite type of material which com prises, ?rst obtaining a relationship for that type of material between the per cent moisture 5 content and the ratio of change in equivalent series resistance to change in capacity of a con
denser occasioned by insertion of such material
determining the ratio of the change in these val ues to obtain per cent moisture content of the
material by reference to predetermined rela tionship between such ratio and known moisture contents for material of the same type. 6. The method of measuring per cent moisture content or regain of a material which comprises
first preparing a graph for that material by
between the condenser electrodes, and thereafter measuring, at a constant frequency, the equiva using such relationship for determining moisture m lent series resistance and capacity of a condens
content of material of the same type but not nec er with and without samples of the material of essarily of the same dimensions or weight from known moisture content or regain between the ratios of equivalent series resistance and capacity plates of the condenser, and plotting the ratio 01' measurements of the condenser with the latter change of equivalent series resistance to change material between the electrodes. I5 in capacity as a function of per cent moisture 2. The method of continuously determining the content or regain, then inserting like material of percentage moisture content of a material which unknown per cent moisture content or regain be includes passing the material between spaced tween the plates of the same condenser, measur plates of a condenser comparing the equivalent ing at the same frequency the equivalent series series resistance of the condenser and the ca 20 resistance and capacity of the condenser, to de pacity thereof when the material is between the termine the change in these values as compared plates with the corresponding values when no ma to those without the material between the con
terial is between the plates to obtain the changes
denser plates, and ?nally taking the ratio of
in these values due to the presence of the mate
these changes to determine the per cent moisture rial and determining the ratio of these changes 25 content or regain from the graph. to obtain percentage moisture content by refer 7. The method of determining per cent mois ence to predetermined relationship between such ture content or regain of a material which com ratios and known moisture contents for material prises measuring the equivalent series resistance of the same type. and capacity of a condenser the distance be 3. The method of preparing a graph for use ” tween the plates of which is large compared to in moisture content measurements which com the thickness of the material, inserting the ma prises measuring both the equivalent series resist terial between the condenser plates and measur ance and the capacity of a condenser with and ing the change in equivalent series resistance and the change in capacity of the condenser and ?nal without material of known moisture content be tween the plates of the condenser and plotting 35 ly determining the ratio of these changes to ob the ratio of change in these values as a function tain per cent moisture content or regain deter of moisture content. minations by reference to predetermined rela 4. The method of preparing a graph for use in tionship between such ratio and known moisture content or regain for material of the same type. per cent moisture content or regain measure ment which comprises measuring the equivalent 4° _ WILMER CLAYTON ANDERSON. series resistance and capacity of an air condens REFERENCES CITED er, inserting material of known moisture content or regain between the plates of the condenser The following references are of record in the and measuring the changed equivalent series re die of this patent: sistance and capacity of the condenser, repeating 45 UNITED STATES PATENTS these measurements for different per cent mois Number Name Date ture content or regain, and ?nally plotting the ratio of the changes in equivalent series resist 1,978,904 Terman .......... __ Oct. 16, 1934 ance to the changes in capacity as a function of the per cent moisture content or regain. 5. The method of measuring moisture in a ma
terial which includes determining both the equiv alent series resistance and capacity of a condens er at a given frequency with and without the ma
0 I
2,217,626 2,349,992 2,373,846
Strang et a1. ______ .... Oct. 8, 1940 Bchrader _______ -- May 30, 1944 Olken ___________ .._ Apr. 17, 1945
OTHER REFERENCES
Alternating Current Bridge Methods by Hague,
terial between the plates oi’ the condenser, and 5 5 fourth edition. pages 352 and 353.