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The development of a moisture detector Brown, Russel Keith 1949

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ft? Z)2  THE DEVELOBONT OF A MOISTURE DETECTOR  by RUSSEL KEITH BROWN  A thesis submitted i n partial fulfilment of the requirements for the degree of Master of Arts i n the Department of Physics, of the University of British Columbia.  ABSTRACT  The e l e c t r i c a l properties (equivalent shunt capacity and resistance) of f i v e samples of Douglas F i r plywood veneer were measured at moisture contents ranging from 0 to approximately 15 percent.  Results were plotted as capacity vs  and the r e c i p r o c a l of resistance vs  moisture content,  moisture content.  To compare  the results with those predicted by the theory a p l o t was made of tan 5 vs moisture content where % i s the phase difference between capacitive current and t o t a l current through the sample.  I t was  shown that, above c e r t a i n c r i t i c a l values of moisture content, both capacity and resistance can be used as an i n d i c a t i o n of moisture content.  Results indicated that moisture may be bound to the wood  in at l e a s t two d i f f e r e n t ways.  ACKNOWLEDGrEMENT  The experimental work described i n t h i s Thesis was carried out i n the laboratories of the B r i t i s h Columbia Research Council under project number Z-Ph~47-137B. The work was directed, i n i t i a l l y , by Dr. A.C. Young, then of the Research Council s t a f f and l a t e r by Dr. A. van der Z i e l of the Department of Physios of the university of B r i t i s h Columbia.  The author wishes t o express h i s thanks f o r the use of the f a c i l i t i e s a t the Research Council laboratories and the generous assistance of Dr. Young and Dr. van der Z i e l .  CONTENTS  Page I.  Object of the Investigation  1  II.  General Remarks  1  I I I . Apparatus and Materials  3  IV.  Experimental Procedure  4  V.  General Discussion of Results  9.  71.  Conclusions  11  THE DEVELOPMENT OF A MOISTJRE DETECTOR  I.  OBJECT OF THE INVESTIGATION To develop an instrument to measure the moisture content of plywood veneer.  I I . GENERAL REMARKS Dr. A.C. Young, formerly of the B r i t i s h Columbia Research Council s t a f f , had c a r r i e d out preliminary investigations of the e l e c t r i c a l properties of wood.  I t was expected that some simple and  r e l i a b l e r e l a t i o n between e l e c t r i c a l properties and moisture content could be found.  Results of the preliminary work indicated that i t  would be necessary t o investigate f u r t h e r the fundamental properties of the wood.  The work described i n t h i s paper i s concerned  entirely  with t h i s phase of the development.  The s i g n i f i c a n t e l e c t r i c a l properties of a d i e l e c t r i c such as wood are the capacity and equivalent shunt resistance which  result  when the wood i s used as the d i e l e c t r i c i n a p a r a l l e l plate condenser. The e l e c t r i c a l condition of a d i e l e c t r i c i s defined by two vectors, the e l e c t r i c vector E and the d i e l e c t r i c displacement D. In an i s o t r o p i c material these vectors are p a r a l l e l and related by the equation D  = £ E  2. where  6  i s the d i e l e c t r i c constant of the material.  sine function of the time, E  »  E  Q  When E i s a  cos wt, D changes s i n u s o i d a l l y  with time, but not necessarily i n the same phase.  Thus we may  write, D where e  K  »  £  E  x  cos (wt - S )  Q  (2)  i s a proportionality f a c t o r d i f f e r e n t from e (except i n the  s p e c i a l case where  3* =» 0 ) .  Using the symbolic calculus i n order to define a d i e l e c t r i c constant i n the case of an a l t e r n a t i n g f i e l d we write,  and  E  »  E  D  » eB  (3)  a**  Q  ( l ) becomes  (4)  0  S i m i l a r i l y (2) becomes D  » £*  E  Q  e^w*  -5 )  ( ) 5  Prom (3) and (5) i t follows that  £ » £*.- e"^ - 6  s  o&af - J£  K  sin X  This may be written i n the form  6 « £• - j £ The r e a l part part £  n  n  €.* i s c a l l e d the d i e l e c t r i c constant and the imaginary  i s connected with the phase angle S by c t f  ~  £ The quantity tan  - tan J ?  c a l l e d the power f a c t o r , i s a measure of the  q u a l i t y of the d i e l e c t r i c .  Thus we may draw the equivalent  of the d i e l e c t r i c as shown i n P i g . 1. Note 1.  circuit  I t should be pointed out  More exactly sinS" i s the power f a c t o r but f o r tan $ <0.1 the difference i s n e g l i g i b l e .  3. that the angle % used here refers to phase difference between the oapaoiti\e current and the total current rather than between the applied voltage and the total current as i s frequently used. at an angular frequency T  »  The admittance of this circuit  is J  co 0  o  +  1/RQ  so that  In this investigation measurements were made of Ro and C  Q  as  described below. Many theories have been proposed to explain the mechanism of energy loss in a dielectric and to predict the variation of tan 8" with frequency.  These have been gathered together and disoussed in the  series of papers by M. Gevers "The Relation between Power Factor and Temperature Cbeffioient of the Dielectric Constant of Solid Dielectrics * 1  (see Bibliography) and w i l l not be discussed here.  However, one phase  of the theory of interest i s the predicted variation of tan 5* with frequency shown i n F i g . 1Q,  This w i l l be disoussed further i n the light  of the results of this investigation under Conclusions.  III.  APPARATUS AND MATERIALS Seventeen samples of Douglas F i r plywood veneer (Nos. 1, 4, and 10 to 24 inclusive), approximate dimension 10 i n . x 10 i n . x 0.1 in. thick. Twin T Bridge (see F i g . 1 for circuit) Hewlett Packard Oscillator Du Mont Oscillograph (5 in.) model 208B  4.  Humidity Cabinet Saturated solutions of Rochelle s a l t s , sodium n i t r a t e , magnesium chloride and calcium chloride  IV.  EXPERIMENTAL PROCEDURE In order to determine the e l e c t r i c a l properties of the plywood samples i t was necessary t o measure the equivalent capacity C  0  and the shunt loss resistance R Q .  The phase sensitive Twin T  bridge shown i n F i g . 2 was used f o r t h i s purpose.  Measurements  were made on a number of samples at frequencies of 20, 100, 1000 and  $000  cycles/second and over a range of moisture  from 0 to approximately 15  500,  contents  percent.  The work, as carried out, f a l l s into two parts; preliminary t e s t s and the main s e r i e s of measurements.  the  These w i l l  be discussed separately. A.  Preliminary Tests The veneer samples were placed, one at a time, between the  plates of the component A of the bridge. component i s shown i n F i g . 2(b).  The construction of t h i s  The upper plate was held by a  r i g i d support (not shown) about 3/8 i n . above the lower p l a t e . The remainder of the c i r c u i t , with the exception of the o s c i l l a t o r , transformer T, and the cathode ray oscilloscope was located on a separate chassis.  E l e c t r i c a l connection between the main chassis  and component A was with a braided shield c o a x i a l cable about 12 i n . long.  Seventeen samples of veneer were chosen from a large number  a v a i l a b l e and an e f f o r t was made to obtain the largest possible range i n density.  These samples had been stored f o r several months i n a  p i l e and the moisture content was unknown.  Each sample was weighed,  tested e l e c t r i c a l l y i n the bridge at a frequency of 100 cps and measured f o r thickness and area.  From the observed values of Oi  required f o r balance i t was decided that stray capacities i n the bridge c i r c u i t were too l a r g e .  In an attempt t o reduce these the  main chassis was mounted d i r e c t l y on top of the grounded shield box associated with the upper plate of A.  Considerable improvement was  noted. In order to a t t a i n the desired moisture contents i n the veneer samples they were placed i n a humidity cabinet at a constant temperature over various s a l t solutions as shown i n the table below.  Relative Humidity  Conditions 1.  2.  3. 4. 5.  Water a t ambient room temperature Roobelle s a l t s as 30 C Sodium n i t r a t e a t 30 C Sodium n i t r a t e at 58 C Magnesium chloride at 35 0  Approx. Moisture Content  95  87 75 63 32  13-15  11-12.5  8.5 - 10.5 3-6 6.5 - 7.5  The s a l t solutions were saturated and i n equilibrium with an exoess of s a l t .  In the case of number 4 the solution dried out  before the end of the run.  This accounts f o r the r e s u l t i n g low  moisture content whiob should be approximately 7 - 8  percent.  As  a f i n a l step the samples were dried at 100 C f o r a minimum pf 48 hours.  Inspection of the values of R obtained showed that changes i n R f o r the same sample at two d i f f e r e n t moisture contents ( a f t e r storage and a f t e r holding over Rochelle s a l t s ) were of the same order of magnitude as the zero d r i f t .  The "zero" value of R used here was  f o r the condition of bridge balance with a i r only i n the space between the plates of A.  A f u r t h e r d i f f i c u l t y was experienced with c u r l i n g  of the samples (0.1 i n . t h i c k ) i n the space between the condenser plates, r e s u l t i n g i n variable readings f o r the sample under otherwise i d e n t i c a l conditions.  In order t o increase the s e n s i v i t y (change i n  R with changing moisture content) and reduce the c u r l i n g of the samples, the upper plate assembly was removed from i t s support, loaded with approximately 4 l b of lead and, i n a l l the f o l l o w i n g measurements, placed d i r e c t l y on the sample during t e s t .  This change caused an  increase i n capacity of the component A by a f a c t o r of about 3 and thus the condenser C had t o be replaced by one with greater range. A  25-250 micromicrofarad  a i r v a r i a b l e condenser with a National Velvet  Vernier d i a l was used.  Preliminary tests with the modified arrangement of the bridge showed that the s e n s i t i v i t y had been s a t i s f a c t o r i l y increased and that reasonably s a t i s f a c t o r y r e s u l t s might be expected from future tests.  I t was therefore decided t o balance the bridge at f i v e  frequencies -  8.  20, 100, 500, 1000, and 5000 ops f o r a l l  future t e s t s .  Main Series Prom the seventeen o r i g i n a l samples of veneer f i v e were  chosen t o represent the widest available range i n density (see Table 2).  This was  done because i t was  suspected  that changes i n e l e c t r i c a l  properties due to density differences might be as great or even greater than changes due to moisture content and i t was check t h i s .  desired to  These samples (Nos. 12, 14, 19, 22 and 24) were then  measured on the bridge at the f i v e frequencies given above and at moisture contents ranging from approximately 15 percent down to oven dry (0 percent).  Due to the modifications of the bridge assembly described above the upper plate of A was from the lower p l a t e .  no longer held at a f i x e d distance  I t was necessary therefore to set a  "zero" f o r the determination  of changes i n R.  chosen as the reading of R at balance with a 1/4 between the plates of A.  This was  new  arbitrarily  i n . piece of l u c i t e  When the bridge readings f o r wood of low  moisture content were examined i t was found that R  f  the power l o s s as w i l l be shown l a t e r ) was negative.  (a measure of This suggested  that the l o s s e s i n dry wood might be l e s s than those f o r l u c i t e . To check t h i s and e s t a b l i s h a true "zero" f o r R, the bridge  was  again balanced a t three frequencies 20, 100 and lOCOops with 0.25 spacing between the plates of A and a i r d i e l e c t r i c these measurements are shown i n Table  0  •  The r e s u l t s of  1.  In order to determine capacity 0 from the r e l a t i o n C  in.  o  of the veneer sample  (R2R3R4/RlR5R6)Cl (see F i g . 2) i t was  necessary to c a l i b r a t e C^.  This involved some d i f f i c u l t y since  c a l i b r a t i o n of C i when removed from the c i r c u i t was not s a t i s f a c t o r y because of s t r a y capacity within the c i r c u i t .  Accordingly C i was  8.  calibrated while connected i n the c i r c u i t as f o l l o w s : 1.  The c i r c u i t assembly containing R i , R3,  R4,  R5,  R6 and Oi  was removed from the upper plate of A and the contact wire disconnected from the ungrounded plate of A. 2.  In order to reduce stray capacity between the common point or R5 and R5 and ground, a shield was placed around R5 and connected e l e c t r i c a l l y to the lead wire from R5 to R 2 . R6 was s i m i l a r l y shielded.  3.  A number of mica condensers of suitable capacity were measured on a Q meter and connected i n turn into the c i r c u i t i n place of A.  For each condenser the bridge was balanced at two  frequencies, 100 and 1000 4.  cps and the d i a l reading of C± noted.  From the expression f o r 0  O  above values of  were calculated  corresponding to each d i a l reading.  The r e s u l t i n g c a l i b r a t i o n curve i s shown i n F i g . 3.  In order to obtain a measure of the r e p r o d u c i b i l i t y of the capacity and resistance of a given sample a t various moisture contents i t was decided to carry sample No. 14 from high moisture content (approx. 15 percent) to low moisture content (approx. 4 percent) and back again. moisture content.  0  O  and R  0  were determined a t each  GENERAL DISCUSSION OF RESULTS The r e s u l t s of the bridge measurements showing R' vs moisture content and C vs moisture content f o r the f i v e frequencies 0  20, 100, 500, 1000 and 5000 cps are shown i n Tables 3 t o 13 and plotted i n F i g . 4 - 13 i n c l u s i v e .  The quantity R' i s , i n a l l cases,  the difference R2 (0) - R2 {sample) where R2 (0) i s the value of R2 at balance with the 0.25 i n . thick piece of l u c i t e between the plates of A, and R2 (sample) i s the corresponding value f o r the veneer sample The values of C were obtained using the expression shown under F i g . 2 c  The values of the various components of the Twin T Bridge shown i n F i g . 1 are nominal.  Exact values are: C  1  -  12 - 242 mmf d  -  see tables 2.2 megohms  -  R2 R3  R4  R5 R6  11,000 ohms  -  1.9  2.1 1.8  "  » w  Thus a t y p i c a l c a l c u l a t i o n of C would be as follows (see Table 3, Q  sample No. 24 f o r R2 and F i g . 3 f o r C i ) .  °°  (R1R5R6)  0  l  „ (10.960 x 2.2 x IO** x 1.9 x 10$)  (11,000 x 2.1 x 10° x 1.8 x 10°)  •  x  y  '  217 mmfd  The curve drawn on each plot i s f o r sample No. 22 and i t i s of i n t e r e s t to note that while i t i s the sample of highest density (dry) the points f o r other samples f a l l on both sides of the curves with  10.  those f o r the two lowest density samples (No. 1 9 and 1 2 ) f a l l i n g respectively above and below the curves. of both R' and 0 Q .  This i s true f o r the plots  I t would appear, therefore, that the scatter  was not due to density differences or at least that any variations i n R* or 0 O due to differences i n density were masked by other e f f e c t s . The nature of the "other effects" i s not understood. The results of the check on the losses i n l u c i t e as compared to dry wood show that the d i e l e c t r i c loss of dry wood i s indeed smaller than that of l u c i t e .  R* i s proportional to l/Ro the shunt  loss resistance and therefore the larger i s R', the smaller i s 1/RQ« Now the power loss i n material placed between the plates of A ( d i e l e c t r i c loss) i s P across A.  =  V^/RQ where V i s the R.M.S. voltage existing  Thus we see that power loss i s d i r e c t l y proportional to R*.  This cannot be negative.  The reason for the negative values of R* i s  the arbitrary choice of the losses i n the 0 . 2 5 - i n . piece of l u c i t e as reference.  A glance at Table 1 which shows R' f o r l u c i t e referred to  a i r indicates that the curves f o r R* would have been shifted up (toward larger values of R') by approximately 2 ohms at 2 0 oycles, 9 ohms at 1 0 0 cycles and 6 4 ohms at 1 0 0 0 cycles i f a i r , f o r which the d i e l e c t r i c loss i s 0 , had been used as a reference.  Such a s h i f t would make a l l  values of R' f o r these three frequencies, equal to or greater than 0 within the experimental error. curves f o r the frequencies  500  I t seems reasonable to expect that the and  5000  cps would be shifted s i m i l a r l y .  The f a i r l y definite knee on the R* curves at a l l frequencies i s of particular interest i n this investigation.  The position of this  11. knee s h i f t s from approximately 4*5 percent moisture a t 20 cycles t o approximately  8 percent  at  5000  cycles.  To the l e f t of t h i s knee  the curves show r e l a t i v e l y small changes i n R ' with moisture content. So that t h i s phenomenum might be examined further and a l s o to compare the r e s u l t s of t h i s i n v e s t i g a t i o n with M. Gevers* prediction of the v a r i a t i o n of tan cT with frequency c a l c u l a t i o n was made of the quantity RVOo* *  O  T  the f i v e frequencies used and f o r moisture contents of 0, This quantity i s proportional t o tan Jf as i s  4, 8 and 12 percent. shown below. tan  cf  » OOCQRO  Substituting the values f o r C  and R Q (see. F i g . 2) we have  0  tan 5 - i|3-±^4l . -51 1 5 6 °o R  R  R  c  R»  -  0 f  K  o  where f i s the frequency at which the bridge i s operated  K  »  j. * 2 II R3H5R6 R  i s a constant of the bridge  Data f o r these calculations was taicen from the curves of C vs moisture content f o r sample No. 22.  Q  and R  F  The r e s u l t i n g plots are":  shown i n F i g s . 14 and 15.  V I . CONCLUSIONS Examination of the curves of R * vs moisture content ( F i g s . 4 - 8 ) and C following:  0  vs moisture content ( F i g s . 9 - 13) y i e l d s the  12.  1.  For moisture contents lower than those corresponding to the knee of curves, R* does not appear to be a reliable indication of moisture content.  2.  I f R were used as an indication of moisture content f  the maximum expected error would be i 2 percent moisture content. 3. Use of C as an indication of moisture content gives 0  approximately the same error. 4*  Difference i n density of the dry wood samples i s not the chief cause of the scatter observed.  For the same sample on repeated runs, points on the R* curves are reproduced with an error of ± 1 percent moisture content (see Figs. 16 and 17). Comparison of Fig. 18, which shows the predicted variation of tan Z with frequency, and the curves of Fig. 15, suggests the possibility that the moisture i n the wood may be held i n at least two forms. (  One form seems to predominate at low moisture contents  8 percent).  At higher moisture contents ( 1 0 - 1 2 percent) a  large hump appears i n the tan X curve which does not exist at lower moisture contents.  This seems to indicate that i n this case part  of the water i s bound to the wood i n a different way such that a very definite relaxation time results.  REFERENCE 1.  Gevers,  M . , Philip's Vol.  1,  Research N o . 3-6  Reports inclusive  BIBLIOGRAPHY  1.  Dunlop,  M J 2 . . ,  Proc  A.S.T.M.  45:269  Committee  Reports  1945  2.  Stamm, A . J . , I n d . E n g . C h e m . 1 9 ( a ) : 1 0 2 1 i l l u s .  3*  Stamm. A . J . , A n a l y t i c a l E d . , I n d . & E n g . C h e m .  2:240 4*  Suits,  Suits,  2877:42  1930  C . G . and Dunlop, M . E . , Instruments 1930  6.  1930  C . G . and Dunlop, M . E . , Amer. Lbrman, illus.  5.  illus.  1927  3:(8):548  illus.  Maheu, C . F . , Technique  V22-nl0,  Dec.  1947  p.  649.52  September 9?  Y-Fh-47"137B  Table 1 R  9  f o r L u c i t e Referred t o A i r  R ohms  ohm.3  Lucite  474  +2  Air  472  Lucite  483  Air  474  Lucite  550  Dielectric  FrequencyCycles  20 20  +9  100 100  +64  1000 1000  486  Table 2  RKB/kmSo  R»  September 9» 3-949°  Y-Ph-47-137B Table J3 A f t e r 120 Hr Over Water a t Room Temp. Fixed Part of Ro = 10S50  Sample Number  Weight g  L 1 2  7 9  o2  1 4  9 3 c 8  1 9  8 3  2 2 2 4  9 9  R Ohma !  » 2  1 0 0 . 2  8 9 . 0  7 0  4 7  1 3 4  5 8 1 2 2  10.8  1 4 8  2 4 . 8  1 2 c 2  2 0 5  off d i a l  7 4 c  =•  1 2 . 3  1 0 2  9 0  2 7 . 2  8 9 - 0  1 1 . 5  9 9  2 0  8 8  1 3 . 2  2 1 7  8 9  3 1 0  289  08  7106  3 6 5  3 4 4  4 4 o 0  4 3 0  1 9  3 2 2  08  3 0 1  4 3 o O  3 1 0  360  1 0 0  o2  3 3 1  1 2  7 9  o 0  1 4 3 0  1 3 4 8  82»1  1 4  9 3 ° 8  3 2 2 5  3 1 4 3  7 2 „ 8  1 9  82  . 5.  1 0 0  6 2 . 0  4 5 1  8 9 » 0  5  9 0 » 5  8 3 „ 1  .5036  4 9 5 4  7 1 o 0  2 2  9 9 = 7  3 0 8 3  3 0 0 1  760O  2 4  1 0 0 . 2  3 7 1 0  3 6 2 8  7 1 c  RKB/kmSo  0  1 1 1  8 3 o l  L  %  Co Calcul= ated mmf d  71.6  9 3 = 8  2 4  Moi sture Content  8 3 . 6  1 9  9 9 o 4  Oven Dry g  2 0  = 0  1 4  2 2  Frequency cps  1 9 8  2 1 7 9 o l  C Dial  1 2  ol  L 1 2  R Ohms  1 0 o 5  1 1 2  1 2 , 2  1 5 9  1 2 . 3  2 2 5  1 1 . 7  1 6 1  1 3 . 2  1 8 0  1 0 0 0 7 1  c 6  1 0 o 3 1 2 , 2  1 5 8  1 2 . 3  3  8 9 » 0  1 2  o  6 5 c 3 1 3 4  0  1 3 c 2  9 5 c 2 1 4 3  September 9, 1949°  Y=Ph°47°137B  Table 4 i i 2 S L QggJL Sodium Nitrate at ^ 0 G Fixed Part of 22 = 10880  ample umber  Weight g  L 1 2  77=6  14  9 0 . 9  19  8 0 , 2  R Ohms  R" Ohms  c Dial  Frequency cps  Oven Dry g  Moisture Content  %  Co C a l c u l ated mmfd  2 0  = 1 0  8 9 . 0  34  44  7 0 o O  55  56=0  8o7  1 2 4  1 1 4  48o0  8  45  8=4  •  8 8 o 9  4  1 4 5  2 2  96<,6  42  52  6 2 = 0  8 o 5  109  2 4  9 7 . 0  60  7 0  4 4 . 0  9o6  1 5 5  L  1 0 4  8 9 . 8  0  0  05  1 0 0  1 2  7 7 . 6  114  1 1 4  80o8  7106  8=4  14  90c9  2 4 2  242  7 4 . 5  8 3 „ 6  8c7  7 9 . 4  19  80o2  2 9 0  2 9 0  7 6 cO  7 4 c 0  8o4  7 5 . 0  2 2  9606  1 9 6  1 9 6  76*5  8 9 =0  8o5  7 3 . 3  2 4  9 7 . 0  3 5 0  3 5 0  9 7 . 0  8 8 = 5  9c6  97=1  7 7 . 6  2 5 0  188  8 4 . 5  8 c 4  53=7  9 0 o 9  5 6 0  498  8 4  02  8 c 7  55=1  L 1 2  14 19  62  9 0 . 5  6 1 . 7  1 0 0 0  80c2  540  478  83 = 5  8=4  56=3  2 2  9606  4 4 0  378  8 4  8 c 5  55=8  2 4  9 7 . 0  9 0 3  841  9c6  58=0  ©  RKB/kmSo  oO  8 3 = 5  •  Y~Ph°47~137B  September 9, 1949. Table 5 A f t e r 4 8 Hr Over Magnesium Chloride at 3 5 C Fixed Part of Rp <= 10850  Sample Number  Weight  L  R Ohms  R« Ohms  Dial  12  83<>2  71=6  6o4  54=6  35  78oO  89=0  7=1  69=0  18 76o2  12 22  95o3  I  89 = 8  14  30 53  89<,0  18 67  C  Frequency cps  Oven Dry  Moisture Content  Co Calcul= ated mmfd  20  89o0 49  73=5  8 3 , 6  7 » 4  8 0 o l  52  7 4 » 8  74=0  6,3  76o8  32  79 = 3  88o5  7 = 5  64=6  19  7 9 . 0  70  24  ••95.1  50  12  76c2  42  14  85 = 0  6=4  50o8  22  95=3  82  54  83=4  7=1  54=9  14  89=8  123  96  8 2 c 0  7=4  58=4  19  79=0  107  80  8 2 oO  608  5 8 . 9  95=1  73  46  8 3 c 8  7 =5  53=8  L  28  L  89 = 5  89=8  27  24  L  90  12  76o2  22  95=3  L  82  100  90 = 5  1000  =18  85 = 8  6 , 4  49=4  =54  85=0  7=1  50=,8  51=6  90c5  87  ,14  89=8  227  8 5 , 0  7=4  19  79=0  186  99  84=0  608  54=4  24  95=1  124  37  85=0  7=5  50=6  RKB/kms  0  140  September  Y~Pb.°47°137B  9 ,  1 9 4 9 <  Table 6 A f t e r _4j0 Hr Over. Sodium Mtrote^ at J 3 G_ Fixed Part of % = IQgJO  Weight S  R Ohms  R» • Ohms  9 3 = 8  L 1 4 1 9 2 4  2 2  3 5  7 6 . 3 8 9 = 9  3 0  28 28  9 3 = 8  3 4 4 1  L  4 0  1 4  3 4  1 9 2 4  8 6 o 9 7 6 = 3 8 9 = 9  L  2 0 4 = 5  4 7 = 0  =1  8 5 = 5  3 = 9  4 9 = 1  =3  8 6  3 = 1  4 8 = 1  1 . 6  4 6 = 9  5 = 4  5 0 . 2  8 9 = 5  =3  „0  8 6 , 5  8 9 . 8 - 5 +2  1 0 0 71.-6  4 = 5  4 7 = 0  8 9 = 0  5 = 4  4 9 = 2  8 6 . 0  8 3 . 6  3 = 9  8 6 . 2  7 4 = 0  3 = 1  4 7 = 5  8 6 . 8  8 8 . 5  1 . 6  4 5 = 8  8 6 . 5 8 5 = 5  9 0 . 0 =6 =7  3 1  =9  9 0 = 5  1 2  7 4 = 8  5 5  =44  2 2  9 3 = 8  7 0  =29  8 7 = 0 8 6 . 0  4 8 . 0  1 0 0 0 4 = 5  4 6 . 0  5 = 4  4 8 = 3  3 = 9  4 7 = 1  3 . 1  4 7 = 1  1 . 6  4 6 . 0  9 0 = 5  9 3  1 4  36*9  5 7  =36  8 6 o 5  1 9  7 6 = 3  5 6  =37  8 6 o 5  2 4  89=9^  RKB/kmSo  Co Calcul= ated mmfd  5  3 3  5 1  Moisture Content  8 5 = 0  9 9  L  Oven Dry  8 6 c 3  3 9 7 4 = 8  Frequency eps  =1  3 1 8 6 * 9  L 1 2  2 9  Dial  8 9 = 0  3 0 7 4 o 8  0  =42  8 7 = 0  September  9 „  1 9 4 9 °  Table 7 A f t e r 3^ Hr at 1 0 0 £ i n a Drying Oven Fixed Fart of = 10800  Sample Number  Weight g  L 1 2 1 4 1 9  C  R  Ohms  Ohms  3 7  8 9 o 0  2 0  3 5  8 3 . 6  3 6  =1  8 7  7 4 = 3  3 6  =1  8 6 = 8 8 9 = 0 8 7 o 5  7 1 = 6  2 2  8 9 = 0  3 5  2 4  8 8 = 8  3 6  - 1  L  1 4  Frequency cps  =2  =2  1 2  Dial  8 9  4 7 7 1 . 6 8 3 o 6  3 8 3 9  8 7 c 5 o9  = 5  Moisture Content  Cc Calcul ated mmf d  0  4 4 » 2  w  4 2 . 5  n w n  4 0 o 3  4 5 c 8  4 4 » 2  1 0 0  =9  8?c8  0  4 2 c 5  =8  8 8 . 0  ft  4 2 c  ft  4 5 c 8  5  1 9  7 4 » 3  3 9  =8  8 7 o 0  2 2  8 9 c 0  3 8  - 9  8 9 . 0  ft  4 0 c 3  2 4  8 8 » 8  - 9  8 7 . 5  tt  4 4 = 2  L 1 2  3 8  1 0 6 7 1  c 8  5 8  9 0 c  5  1 0 0 0  0  = 4 8  8 8 = 0  n  4 2 c 5  tt  4 2 = 5 4 5 c 2  1 4  8 3 = 5  5 7  = 4 9  8 8 = 0  1 9  7 4 o 3  6 2  =42  8 7 c l  tt  2 2  8 9 o 2  5 4  = 5 2  8 9 c l  ft  3 6 = 0  8 7  tt  4 2 c 6  2 4  RKB/kms=  8808  6 1  = 4 5  c 8  September  9,  1949°  Table 8 A f t e r 41 Hr Over jfater at 23 G Fixed Part of R2 = 10400  Sample Number  Weight g  H " Ohms  1 2  78.0  1880  L 4  9 3 = 8  2 1 7 0  L  •R« " Ohms  4 9 6  06  G Dial  Frequency ops  9 0 o 0  5 0 0  1 3 8 4  6 7  Oven Dry g  Moisture Content  Co Calcul= ated mrafd  08  7106  1 2 = 9  1 0 7  0  8 3 = 6  1 2  108  j j  c 2  1 6 7 4  6 8 c  3 3 9 0  7 4 = 0  1 3 = 0  1 9 3  1 9  8 3  2 8 9 4  4 4 c 8  2 2  9 9 c 9  2 0 5 0  1 5 5 4  6 8 = 0  8 9 = 0  1 0 = 9  1 0 7  2 4  9 9 o 9  2 2 6 0  1 7 6 4  6 4 o 0  8 8 = 5  1 2 = 9  1 2 1  1 2  7 7 c 6  6 1 5 0  8 8 „ 5  7 1 = 6  1 2 = 3  1 4  93*5  5 8 3 0  8 8 c 5  8 3 = 6  1 1 = 8  6 2 = 0  1 2 = 6  8 4 = 0  L  5 0 0 0  6 9 0 6 0 8 1 5 7 6 1  6 3 = 2  1 9  8 3 = 3  1 3 8 6 0  9 0 o 0  7 4 = 0  2 2  9 9 c 8  5 6 0 0  5 5 3 1  8 8 . 0  8 9 = 0  1 2 = 2  62.7  2 4  9 9 o 4  6 8 5 0  6 7 8 1  8 8 = 5  8 8 = 5  1 2 . 3  6 5 = 8  EKB/kms.  1 3 7 9 1  September  9 ?  1 9 4 9 °  Table 9 A f t e r 6 0 Hr Oyer Rochelle Salts a t 2 9 G of R2 = 1 0 4 0 0 P  a  r  t  "1 Sample Number L 12 1 4 1 9 2 2 2 4  Weight g  R Ohms  R Ohms 8  5 0 8  C Dial  1 9 4 0  1 4 3 2  7 1  9 3 . 5  2080  1 5 7 2  6 8  3 3 7 0  2862  9 9 9 9  o 4  0  L  5  2 1 5 0 1 8 7 0  •57  1 6 4 2  6 5  1 3 6 2  6 6  7 3 0  9 1  Oven Dry g  Moisture Content  %  -  Co Calcul= ated mmfd  5 0 0  9 0  7 7 = 5  82 06  Frequency cps  69a  0  5  1 0 , 7  9 8  8 3 = 6  1 1 . 8  1 0 7  7 4  =0  cO  1106  1 5 2  8 9  l i e ?  1 1 7  1 2 . 4  1 1 2  8 8 c  5  5 0 0 0  1 2  7 7 = 3  4 8 0 0  4 0 7 0  8 8  6 9 o l  1 1 = 9  6 0 . 1  1 4  9 3 = 3  5 9 4 0  5 2 1 0  8 9  8 3 . 6  1 1 . 6  6 0 . 7  7 5 3 0  8 9  7 4 = 0  1 1 . 5  6 8 . 9  5 6 6 0  8 8  8 9 = 0  1 1 . 4  6 6 . 5  5 7 5 0  8 9  8 8 . 5  1 2 . 3  6 2 . 6  1 9  82.5  2 2  9 9 o l  8260 639O  2 4  9 9 = 4  6 4 8 0  RKB/kmsc  Y-Pn~47=137B  September?, 1949, Table 1 0 A f t e r 44 g r Oyer Sodium M t r a t e n g t r 2 8 G  Sample Number  Weight g  L 1 2  R Ohms  R Ohms  C Dial  6 9 . 1  1 1  8 3 . 6  1 0 . 7  8  4 9 6  9 0 . 5  7 6 . 8  1 6 1 5  1 1 1 9  7 5 o 0  1 4  9 2 o 5  1820  1 3 2 4  7 3 o 0  1 9  8 2 . 3  2 3 9 7  1 9 0 1  6 4  2 2  98 o 7  1 8 6 5  1 3 6 9  2 4  9 8 . 6  2 0 3 5  1 5 3 9  L  7 2 0  Frequency cps  Oven Dry g  Moisture Content %  5 0 0  oO  o l  7 4 c 0  1 1 . 2  7 0 . 3  8 9 . O  1 0 . 9  7 0 . 0  8 8 . 5  1 1 . 4  9 1 « 3  5 0 0 0  1 2  7 6 . 9  3 4 8 5  2 7 6 5  8 7 . 8  69.I  1 1 . 3  1 4  9 2 . 5  4 0 5 5  3 3 3 5  8 8 . 0  8 3 . 6  1 0 . 7  1 9  8 2 . 1  7 0 7 0  6 3 5 0  8 9 . 0  7 4 . 0  1 1 . 0  2 2  9 8 . 7  4 6 2 5  3 9 0 5  8 8 . 0  8 9 . 0  1 0 . 9  2 4  9 8 . 6  5 0 4 5  4 3 2 5  8 8 . 0  8 8 . 5  1 1 . 4  RKB/kms.  Co Calcul= ated mmfd  Table 11 A f t e r 4 8 Hr Over Maqaesium Ohloride at 3 8 C Fixed Part of_ Rg = 1 0 4 0 0  Sample Number  Weight g  L 12  R Ohms  791  1 4  90o2  775  19  80,4  24  9  C Dial  ' 1 0 1 0  9 6 . 5  730  9 6 , 2  780  L  Frequency cps  Oven Dry  Moisture Content  Co Calcul= ated mmfd  500  519 7 5 . 1  22  R Ohms  272 256  69 o l  8 4 . 0 84o5  8 , 7  55c0  8 3 , 6  7 . 9  53=3  8 , 6 5  58,5  491  83o0  7 4 . 0  211  8 4 . 0  89c0  8 , 4 5  54=8  8 8 , 5  8 , 7  55=0  6 9 . 1  8,96  261  8 4 . 0  91o0  730 361  860  0  5000  50,7  12  7 5 . 3  1091  14  9 0 , 2  1065  546  8 6 , 0  8 3 , 6  19  80o4  1440  710  8 5 , 5  7 4 oO  7.9 8065  50,7  96o3  950  2 2 0  8 6 , 0  8 9 , 0  8,2  50,1  22 2 4  96c2  1020  501  8 6 , 0  880  RKB/kms,  5  8,7  53 = 5  50=5  Y-Ph-47=137B Table 12 A f t e r ?2 Hr Over Sodium Nitrate at $0 0 Fixed Part of Ro = 10400  Sample Number  19  22 24  72=9 86=9 77.7 92.9 93.-0  509 485 484 501 483 486  =24 -25 =8 =26 =23  86.4  72.9 86.9 77.7 92.9 93.0  710 587 580 632 574 585  =123 =130 =78 =136 =125  91=2 87=0 87=0 96=0 87=3 87=0  L  12 14 19 22 24  9  R Ohms  L  12 14  R • Ohms  Weight g  C Dial  90 86.5 86=5 85 = 5  Frequency cps  Oven Dry g  Moisture Content  fo  Go C a l ated mmfd  69=1 83.6 74=0 89.0 88.5  5=5 3.9 5.0 4=4 5=1  47=0 47 = 0 49=9 45=4 47=0  83=6 74=0 89.0 88.5  69.I  5=5 3=9 5=0 4=4 5=1  45=8 45 = 8 29.9 44=6 45=8  69=1 83.6 74=o 89.0 88.5  7=7 5=9 6=3 6.7 6=3  49 = 8 52o8 53=0 48o 5 49o5  69=1 83.6 74=0 89=0 88 = 5  7°7 5=9 6=2 6=7 6.3  500  87.O  5000  A f t e r 48 Hr Over Sodium Nitrate at 55 G L  12 14 19 22 24  74.4 88.5 78.7 95=0 94=1  L  12 14 19 22 24  RKB/kms=  74=4 880 5 78.6  95=0 94=1  512 601 534 585 554 533 725 765 650 761 661 644  89 22 73 42 21  90=3 85 = 5 84=5 84=5 86.0 85 = 5  . 500  40 =75 36 =64  91 5 86, • 3 86, 3 85< 5 86, 9 86c 3  5000  =81  September  Y-Ph-47-137B  9  a  1 9 4 9 °  Table 1 3 4 8 Hr at 1 0 0 C i n a Drying Oven Fixed Part of = 10400  Sample Number  Weight g  L  R Ohms  R« ' Ohms  G  Dial  9 0 c 5  5 1 2 6 9 » 1  4 8 7  = 2 5  1 4  8 3 » 5  4 8 5  = 2 7  7 4 o 0  4 8 8  = 2 4  8 7 » 5  8 9 - 3  4 8 5  = 2 7  8 8 . 5  8 8 o 8  4 8 6  = 2 6  8 8 . 0  2 2 2 4  L  8 8 . 0  1 2  6 9 . 6  5 7 7  = 1 2 3  1 4  8 3 . 7  5 6 5  = 1 3 5 = 1 1 0  8 8 . 0  7 4 . 5  5 9 0 5 6 0  = 1 4 0  8 9 . 0  5 7 6  = 1 2 4  1 9 2 2 2 4  RKB/kmSc  8 9 . 3 8 9  oO  6 9 . 1  8 8 . 0  8 8 . 0  Moisture Content  _£ 0  Co Calcul= ated mmfd  4 3 . 6  7 4 . 0 8 9 . 0  0 o 3 4  8 8 . 5  0 , 3 4  5 0 0 0 6 9 . 1 8 3 . 6 7 4 . 0 8 9 . 0 8 8 . 5  4 2 o 6 4 2 c 6  8 3 . 6  8 8 . 0  9 1 . 0  7 0 0  Oven Dry  5 0 0  8 8 . 0  1 2  1 9  Frequency cps  4 1 . 5 4 2 . 6  0 . 7 2  4 2 . 6  0 . 1 2  4 2 . 6  0 . 6 8  4 2 . 6  0 . 3 4  4 0 . 4  0  4 2 . 6  APPENDIX  Twin  T  Bridge  Type .578  T  -  General Radio  Cj  -  25-250 mrafd  R^  -  1.0K ohms (approx.)  R2  =  10K *  R3, R^j R^j HQ  Circuit  a i r variable  General Radio resistance -  2.2  R  megohms  CRO  -  Dumont Cathode Ray Oscilloscope (5 in.)  A  -  test specimen assembly (see below)  FIGURE  I  January 19,  DEVELOPMENT OF MOISTURE DETECTOR  1949  D e t a i l s of Component A: (a)  Electrical  equivalent c i r c u i t  »Ro  Co  (b)  -  Co - e f f e c t i v e  capacity  Ro -  shunt l o s s resistance  "  Mechanical  1 C ^  Shield  (at ground potential-  77T  Upper plate  -iucite i n s u l a t i n g r i n g 3^-lower plate (at ground potential) FIGURE  2  Ccnditions at balance:  1  „  R  2  (R3 • R  Ro  )  -  R  R5 R6  4  x  R±  (R  5  + R  )  6  Assuming Ro i s i n f i n i t e f o r a i r  /R3 +  1 Ro  (for veneer sample)  W  =  fR  2  Co  4  R  R 5  R3 R^  v i 85 R  R X 6 /  Z~Ph-47-137B  DIAL READING  Fig. 3  Z~Ph-47-137B  ;.:OISTUEE O O T E T  R'..T 20 cpa  Z-Fh-47-137B  i!  1  t  4  "  a  a  Moisture  10  content  ia %  Figo 4  Z-Ph-47°137B  Z-Ph-47-137B  KOTSTDHE CONTENT 78  -i' AT 510 ops !  !  1  Z-Jfc-47-lSTB Ol.o. i a • NO. 14 A No. i a • No. 22 A No. 24  •  —  Drawn AJUg. 29, 1949  j  ,  • • ;  A  •  —I-  A  ' :  .  1  j  • •  /  /• T* s~ -  1  /  •  -  4  — i  •! 1  P  /  / - No. 22  —  <  A  1  •  •  0  i .  0  * j 2  ! 4  6  8 10 12 Moisture content %  U  t  Z-Ph~47-137B  Fig* 7  z~Ph-47-i37B  MOISTUHE O O K m i VS  it AT 5000 cpa  -»I : 0  8  4  6  8 10 12 Moisture Content %  Fig.. 8  14  Z-Ph-47-137B  KOISTDHE COKTE1T VS Co AT 20 ops  j  1 :  •  2-1•h-4' -13' B wa  aet i  '•'4 C  220  • -  • A  i M|  29, 194 1  i 0, I4 no. i o. 1 9 I g. «. 1 o, £  > 2 4 3 mmfd.  . i  1  *  1  BOO  16C  •a  1  •  / - N I.  L O U  A  /  A  i  /  o 140  •/  120  ! Si  G  /  ...  /  100  j/  60  60  40'  SO  .I ;  1  4  6  8 10 UoiBture content %  F i g o  9  12  14  z-Ph-.47-.137J  MOISTURE CONTEM VS Co AT 100 ops !  ' 1 , 1.  41.  Dl awn Aug 1 o. 0. nHo. No.  M  i  A  , —  i  • 1  PbH 7-1 7B i  "T~  9  . 14 ia as 24  1 A.  j ISO  MM  •  14 0 Ttn 120  •  O 1  OC  so  J  i  •  60  40  1 —  I  -  —  t  •  9  -  j  -  1  20 Moisture  content  Figo  10  0  •N •  1 n  »  Z~Ph-47-137B  MOISTURE CONTEKT VS Co AT 500 cpe  Moisture content %  F i g - 11  Z-Ph~47-13?B  KOISTURE CONTENT VS Co AT 1000 cpa r-1 h-4 Ecn WI  124 C  o  • a  280  2<  A  u  NO. IS 50. «  ! —!  m t 2  1•4  i  ...  u  ?:-. 24  1  -  131  :  1GI  A  l-i-  •  12t  —  ' 1  IOC  •~-r  / 60  , I*  1  20 Moisture content %  Figo 12  Z-Ph-47-137B  MOISTURE CONTENT VS Co AT 5000 ops —f  I  -47-137B trim  drawn Aug. 2S  240  »  1949  ±t4±  12  * ._ KB  220  a  -  —  •w 14 19  I mii BO Mo  _  ?,?. 24  200  I  ISO  *  160  l"-0  ISC  -4 _L  0  ;,  o  60 A  40  20  — L I I  -L.  A  I.2  1•1. 3  z  4  s  •  e  Moisture  10  •  content  Figo 13  12 %  1<  a  Z-Ph-47-137B  F i g . 14  Z-Ph-47-137B  F i g . 15  Z-.Ph-47-137B  Moisture Content TS H* et 100 ope  Moisture Content <  F i g . 16  P i g . 17  In iJO  (a)  vary  (b)  r e l a t i v e l y inhomogeneous d i e l e c t r i c s  homogeneous d i e l e c t r i c s  Figo 18  

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