V IN CONTRO£ 2%"! E1 “CTRBCAL BM“ [2 .‘l‘éCE MOISTU “‘ E515? RE METER Thais hr ‘ha Dames: {3% MS ‘53 5TH??? UNE‘JliPfiilTY ‘ému‘aa': Q Wang 19632 fish CHEGA {DE-133': :3 "'. ‘ " l'] ‘5 ;‘-‘\ I .1t»~" ' DRY'KILN CONTROL BY ELECTRICAL RESISTANCE MOISTURE METER BY Philip HWeig‘Wang A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Forest Products 1962 ACKNOWLEDGEMENT It is with great pleasure that the author expresses his gratitude to Dr. J. G. Haygreen for suggesting this study and for his constant supervision during all the operation stages of the experiment. The writer especially desires to acknowledge his indebtedness to Dr. Otto Suchstand for his direction. helpful criticism and continuing encouragement during the preparation and writing stages of this thesis. Philip H. Wang ii TABLE OF CONTENTS ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . LIST OF TABIIES O O O O O O O O O O O O O O O O O O 0 LIST OF Chapter I. II. III. IV. Iv. FIGUMS O O O O O O O 0 O O O O O O O O O 0 INTRODUCTION . . . . . . . . . . . . . . . DETERMINATION OF MOISTURE CONTENT OF WOOD WITH ELECTRICAL RESISTANCE METER . . . . The Electrical Resistance of Wood The Kil-Mo-Trol Moisture Meter EXPERIMENTAL PROCEDURE . . . . . . . . . . . Material Selection and Preparation for Kiln Operation Experimental Procedure “SETS 0 O O O O O O O O O O O O O O O O 0 ANALYSIS OF RESULTS . . . . . . . . . . . . 1. Correlation Between Two variables 2. Multiple Correlation Analysis 3. Nomograph CONCLUSIONS . . . . . . . . . . . . . . . . BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . iii Page ii iv 18 18 20 24 27 27 35 39 4O 41 LIST OF TABLES Table Page 1. Relationship between moisture content and electrical resistance of wood . . . . . . 5 2. Variations in the electrical resistance of wood in its different structural directions 0 O O O O O O O O O O O O O O O 11 3. Conversion table for strip chart recorder Esterline-Argus Modelka . . . . . . . . . 17 4. T8-C2 Moisture content schedule . . . . . . . 20 iv ll. 12. 13. LIST OF FIGURES Page Relation between moisture content and log of resistance for Douglas fir . . . . . . 6 Temperature corrections applicable to moisture content determined with resistance type electric moisture meters . . . . . . . . . 8 Temperature correction chart for resistance- type moisture meters for wood . . . . . . 9 Electrode assembly and its location on sample board I C O O O O O O O O O O O O O O O O 13 The control equipment for Kiln drying operation 16 Drying chamber . . . . . . . . . . . . . . . . 19 Method of cutting moisture section from the kiln sample . . . . . . . . . . . . . . . 22 Results of first kiln run. . . . . . . . . . . 25 Results of second kiln run . . . . . . . . . . 26 Correlation between electrical resistance moisture content and actual moisture content for shell . . . . . . . . . . . . 29 Correlation between electrical resistance moisture content and temperature for Shell 0 O O O O O O O O O O O O O O O O O 30 Correlation between electrical resistance moisture content and actual average moisture content for shell . . . . . . . . 31 Correlation between electrical resistance moisture content and actual moisture content for core . . . . . . . . . . . . . 32 Figure Page 14. Correlation between electrical resistance moisture content and temperature for core 0 O O O O O O O O O O O C O O O O O O 33 15. Correlation between electrical resistance moisture content and actual average moisture content for core . . . . . . . . 34 16. Nomography of the multiple correlation equation 36 17. Comparison between actual average moisture content and average moisture content (as a function of Ys' Y6. and X2) for first kiln run . . . . . . . . . . . . . . 37 18. Comparison between actual average moisture content and average moisture content (as a function of Ys' Y6. and X2) for second kiln run . . . . . . . . . . . . . 38 vi I . INTRODUCTION Hardwoods are generally dried according to one of the moisture content schedules provided by the Forest Products Laboratory (1). A moisture content schedule prescribes the kiln condition as a function of the moisture content of the kiln charge. It is designed to dry the lumber in the shortest possible time with a minimum of degrade. This is accomplished by using mild conditions during the first part of the drying schedule when the moisture content of the lumber is high. and increasingly severe conditions as the moisture content approaches the final value. The control of kiln drying by the moisture content schedule makes it necessary to determine the moisture content of the kiln charge as a function of the drying time. The conventional method for determining the moisture content of the kiln charge as a function of drying time involves the use of kiln samples which are taken at uniform time intervals from various locations in the kiln charge. The number of kiln samples used depends on the characteristics of the stock to be dried. on the amount of lumber in the kiln and other factors. The average moisture content of all the kiln samples is generally assumed to represent the average moisture content of the kiln charge. The kiln sample method does not provide a continuous record of the moisture content of the kiln charge. It is a tedious procedure subject to errors on the part of the operator. Kiln samples must be accessible and cannot be placed in the interior of the lumber pile. The operator must enter the kiln every time a sample is taken. The kiln sample method is a destructive method causing a certain amount of loss. To improve the determination of moisture content during the drying operation. some commercial instruments have been developed and are available which are based on the correlation between moisture content and electrical resistance of wood. These instruments provide a continuous record of the moisture content of the kiln charge. The electrodes may be applied anywhere in the lumber pile. They provide a quick method for determining the moisture content just by turning on the Moisture Detector without entering the kiln. By using electrode needles of various lengths, it is possible to get some differentiation between the moisture content in the shell and the moisture content in the core of the board. Therefore. compared with the kiln sample method. electrical resistance type moisture meters provide a time and labor, as well as material saving method for the determination of moisture content. HOwever. the moisture content range. for which the moisture content-resistance relationship is usable as a basis for these instruments, is limited. Also, the electrical resistance of wood is not only a function of its moisture content. It is affected by temperature. species, grain directions. etc. Any moisture content gradient might also affect the reading. depending on the electrode arrange— ment. The following is a study of the performance of a commercial instrument under actual drying conditions. The conclusions are limited to the drying of 4/4 beech. II. DETERMINATION OF MOISTURE CONTENT OF WOOD WITH ELECTRICAL RESISTANCE METER The Electrical Resistance of wood Wood. when dry. is a very good insulator. Its resistance is about 25.000 Megohms (Douglas fir board thickness 3/8". pin electrodes driven perpendicularly to the surface. 1? apart). However. when the moisture content of wood increases. the electrical resistance decreases very rapidly. The sig— nificance of this great dependence of resistance upon moisture content has been investigated by C. G. Suits. and M. E. Dunlap (2) on 3/8 inch Douglas fir. pin electrodes spaced one inch apart. as shown on Table 1. It may be seen that between these limits: 1. The ratio of resistance is of the order of 105:1. 2. The maximum resistance is of the order of 1010 ohms. 3. An approximate determination of resistance is a relatively accurate determination of moisture content because of the extreme variation of resistance with moisture content. If the Log 10 resistance is plotted as a function of moisture content in percent. the curve in Figure 1 will be obtained. 4 5 * Table 1. Relationship between moisture content and electrical _ resistance of wood. Moisture content Resistance (per cent) (Megohms) 25000 8 5750 1720 10 ’ 630 11 257 12 120 13 58.2 14 33.0 15 19.0 16 11.6 17 7.37 18 4.50 19 3.1 20 2.18 21 1.58 22 1.15 23 0.85 24 0.63 25 0.473 26 0.35 *C. G. Suits and M. E. Dunlap. ”Determination of the Moisture Content of WOod by Electrical Means." General Electric Review. December. 1931. Figure 1.* Relation between moisture content and log of resistance for Douglas fir. *C. G. Suits and Dunlap. M. E. Determination of the moisture content of wood by Electrical Means. General Electric Review. Dec.. 1931. X \ \ O 3 . )«14))11.4 .4... 11.1.1.4. )1)11« O 2 1 can)... 25 20 15 10 " MOISTURE CONTENT (PERCENT) the .ect" Besides moisture content. such factors as temperature. the presence of electrolytes. high relative humidity. species of wood. direction of current flow relative to the grain. and moisture gradient also affect the resistance of wood. But compared with the moisture content. the above factors are of secondary importance. The effects of these factors may be described as follows: 1. Temperature--As the temperature of wood increases. the electrical resistance decreases and vice versa (3). The rate of change of resistance with temperature is higher at higher moisture contents. Because of this phenomenon. the readings of resistance-type moisture meters should be corrected if the temperature of the wood is different from the temperature at which the meter was calibrated. This correction can most easily be obtained graphically from a chart. such as shown on Figures 2 and 3. Figure 2 is drawn for temperatures below 90°F. Figure 3 extends to temperatures above 90°F (3). 2. Electrolytes--When wood is treated with salts for preservative or fire-retarding purposes. the wood becomes more conductive and consequently an electrical- resistance moisture meter may indicate a moisture Figure 2. Temperature corrections applicable to moisture content determined with resistance type electric moisture meters. Find the moisture content in- dicated by the moisture meter on the lower margin of the diagram. follow this line vertically to the horizontal temperature line approximating the temperature of the wood being tested. then follow the sloping lines to the 70°F. base line and read the corrected moisture content vertically- below. Example: measured moisture content. 12 percent. temperature of wood. 50°F.. corrected moisture content. 13.5 percent. If the meter was calibrated at a temperature different from 70°F.. the base line should be at the actual calibration temperature. not 70°F. mm Hm om mm mm mm mm mm vmmm NN Hm omma ma haoa ma .3” ma NH .3” OH m m ABvammmv EZmBZOU mmDEmHOZ h x/x/OO/V/ // / [V / 7.7 M / / y//. //M/ / ///A 2...”? . / . , , . / z. 1 ///// Ux/Qr 4. // / / //. x ///M/// // //// / M/ r x 7 /////// /H/// // // .////// ///// //// //// / Z ///r /// ./// ,7/5 ,9 . / //////// .7 // 6/ /V/./////.////%/ / /// flVH/x/CV/v/CO //7 // /x/ /9// JZvMVJ ('do) GOOM £0 HHOLVHHdWBI Figure 3. Temperature correction chart for resistance- type moisture meters for wood. Zoe mmosammafie own com 03 oma om ov o 3. o \ KlT \IIIL \ \ A. e t \ \ Czuuxmt 8o: .3 \ L. \ \ Lh m \ \ 3 3 on «m _ (LNEDHEd) ONICNHH HELEN HHMSIOW 10 content greater than the correct value. This is also true of some glue lines and measurements of moisture content of plywood specimens may. therefore. indicate higher values than the actual moisture content. 3. High relative humidity--When resistance-type meters are used in wet weather. their surfaces may become damp and provide leakage paths With low resistance. and thus preclude measurements at low moisture content (3). 4. Species of wood--At any moisture content the electrical resistance of wood depends on the species. The apparent variation between species may be due partly to differences in the electrolyte content of various species. 5. Direction of current with respect to grain—-The resistance of several cubes 5 x 5 x 5 cm; were determined. by A. J. Stamm (4). in each of the three structural directions of the wood. Namely. the longitudinal. the tangential and the radial direction. The results are shown in Table 2. The resistance in the tangential direction is only slightly greater than in the radial direction but about twice as great as in the longitudinal direction. Similar variations were found by Hiruma (5). 11 Table 2.* Variations in the electrical resistance of wood in its different structural directions. Electrical resistance (in.Megohms) Moisture Longitudi- Species Density Content (%) nal Radial Tangential western red cedar 0.336 14.0 9 22 24 Sitka spruce 0.417 15.7 10 18 20 Alaska cedar 0.547 15.6 18 27 27 Douglas fir 0.584 15.3 11 21 23 *A. J. Stamm. ”The Electrical Resistance of WOod as a Measure of Its Moisture Content." Industrial and Engineering Chemistry. Sept.. 1927. The practical equality of radial and tangential resistance is of interest because it eliminates the "grain" factor in two directions as a variable in making resistance- moisture determinations. 6. Moisture gradient--Measurements were made by A. J. Stamm (4) to determine the effect of variations in the moisture distribution through a section. Four pieces of veneer 0.2 cm thick at moisture contents of 15.0. 27.7. 6.4 and 6.2 per cent. respectively. and averaging 13.8 per cent. were clamped together between the electrodes. with the first and second 12 veneers located at the outside. The resistance was 450 Megohms; with the first and second veneers at the inside it was 560 Megohms. These results show that the surface layers affect the moisture content determination considerably. When the surface layers are drier than the core. a lower moisture content will be obtained. and vice versa. In the present study the electrodes were driven to a depth of 1/4 inch and 1/2 inch respectively. This arrangement will allow some differentiation between core and shell moisture content. Generally. the core will always have a higher moisture content than the shell. The Kil-Mo-Trol Moisture Meter The Kil-Mo-Trol is an electrical system designed to measure the moisture content of lumber in different parts of the kiln charge at any time while the kiln is in operation. With this instrument it is not necessary for the operator to enter the kiln. Sample boards are not used but tests are made directly on the lumber without degrading the quality. Moisture content in either the shell or the core can be measured when desired in any part of the kiln where a station has been set up by driving an electrode assembly into the board (Fig. 4). Any station can be selected by a station Figure 4. Electrode assembly and its location on sample board. 13 dezmmmd deom 20 maomBUMAm ho ZOHB 40 130 4 126 1 2 40 130 5 125 1 3 35 130 8 123 2 4 30 140 14 126 3 5 25 150 30 120 4 6 20 160 50* 110* 5 6 15 180 50* 130* *Temperature used in this table is °F. Experimental Procedure During each of the two kiln runs. eight sample boards were used as mentioned previously. They were put in the 36 cubic feet drying chamber. The installation of the Kil-Mo- Trol was according to the 9operating Instructions for Kil-Mo- Trol? published by the manufacturer--Delmhorst Instrument Co.. Boonton. New Jersey. Two stations were set up on each of the five station boards. Each station consisted of two long- insulated, stainless steel contact pins driven to the center of the board for core moisture determination. and one short. uninsulated. stainless steel pin driven to a depth of 1/4 inch a‘ {"3352 “A" 21 for shell moisture determination. Two stations were located at one foot distance from each end of the board. The data were recorded automatically four times a day. namely at 7 a.m.. 12 a.m.. 5 p.m.. and 12 p.m. (these readings will be designated as K.M.T. moisture content later). However. one can take readings at any time and on any station for both the shell and the core as desired by throwing the toggle switch to the "on” position and turning the station selector dial clockwise to "test” position. After chart readings had been taken. conversion was made according to Table 3. The moisture content of the kiln samples was deter- mined twice a day (at 8:30 a.m. and 2:00 p.m.. these results will be designated as actual moisture content later). Moisture content determinations were conducted by both weighing one of the kiln samples as a whole and by cutting moisture content sections from one of the other two kiln sample boards. The latter was done in this way: each time five inches along the length of the board were trimmed off from the end. a one-inch section was cut (Fig. 7) and then each section was cut across its length into three layers with the exterior layers being 1/4 inch thick (representing the shell) and the center layer being 1/2 inch thick (representing '- '3». .~ 3' ‘_"1‘v! '\ , .__.__ Figure 7. 22 Method of cutting moisture section from the kiln sample. mZOHBumm MMDBWHOZ w w w w . $3.8 23m SHE. F m m w m $8.8 886 I I II N m n 6 7.3.8 395 v 1:1 1:.- 1:1 = m = H = m = H .-m = .H :9» ll! 23 the core). These layers were put into the oven, and the shell and core moisture content was obtained according to oven-dry method. After both ends had been re-coated, the board was put back to its original position in the drying chamber. The moisture content obtained in such a way can be taken as a guidance for the kiln operation. When the moisture content of the driest kiln sample board reached a value 2% below the desired final moisture content (7% in this case). an equalization treatment was provided. The equalization process continued until all boards in the drying chamber reached 7%.moisture content. After the equalization period. a conditioning treatment followed. The purpose of this treatment was to relieve all the stresses within the board. Therefore, a stress test was made at the start of the conditioning treatment. Severe case hardening was found. The conditioning temperature was the same as the dry bulb temperature at the end of the drying period. The wet-bulb was set at such a temperature that the conditioning equilibrium moisture content was 4%»above the desired final moisture content (in this case lBOOF dry bulb and 165°F wet bulb temperature). The conditioning treatment covered 24 hours. At the end of this treatment. a stress test was made again. and at this time all stresses were relieved. F" ‘ w ._.ip1:y;i’* IV. RESULTS The results of the two experimental kiln runs are shown in Figures 8 and 9 for the first and the second kiln run respectively. It seems that there is a considerable discrepancy between the moisture contents obtained by Kil-Mo-Trol and those determined by oven-drying method. The following symbols are used in the graphs: Shell (K.M.T.) Core (K.M.T.) Ave. M.C. (K.S.) Core (K.S.) Shell (K.S.) shell moisture content determined by Kil-Mo-Trol. Core moisture content determined by Kil-Mo-Trol. Average moisture content of the kiln sample determined by oven-dry method. Core moisture content of the kiln sample determined by oven-dry method. Shell moisture content of the kiln sample determined by oven-dry method. 24 W “P w_- .. J,“ ' I _.._.‘.__..|--.f_-F u T um” I: TflESlS . ‘Ir|ll ‘ _. l q.‘ { L'i'i :01...“ Figure 8. 25 Results of first kiln run. .—.—— SHELL (K.M.T.) .__..___.-—— CORE (K.M.T.) ._'_.._.._ CORE (K.S.) -—-o-—-o-—- AVE. M.C. (K.S.) .o .. SHELL (K.S.) VT ‘3 1,80 170 ,L. ..... l 160 .___J u ' 150 DRY a BULB ' r 140 I l -41----4 130 }-L F“: : \ WET -- "k u BULB * i ._ r r 120 g! I l p b-b-l L-Jb----J . 110 50 100 I 45 - 1 ’ 90 40 q*::- \i' K 8% 80 . K. . ~,\.. .\ '\ 35 :\~°Mn\ ' 3‘ .\ 70 W F\°. \‘\ \‘ 3o _\ “ ~‘°‘ \ 6O 25 .«"\ . Q. 50 20 R 40 15 ~. 0 _JJ . . 3 1 ____l— L‘ t. 1 10 - ‘ . _ 20 5 _ L, 1 g u l.— 10 1 0 Aug. 5 6 7 8 9 10 11 TIME I 9 f1) ‘- ‘w— “erv—— . . I, Figure 9. Results of second kiln run. 26 SHELL (K.M. T.) CORE (K.M.T.) M.C. (K.S.) AVE. .___’"__.u__. CORE (K.S.) ._.-_.._ SHELL (K.S.) P blush. 1.3 0 0 0 O O O 0 0 0 0 0 0 0 O 0 0 0 O 7 .b '3 4 3 n4 1 AU Q. RV 7 ,0 R4 4 «J 7. 1 1 l .I. l .1 l l .l. . . " .fi . r... flu Q .m = "l-'L"J E 1 - : i» i _, m . H Lf'-'4 ON w- YB . B \. .. J“; E “Tm \ __ B IILWB ‘\.N N = \‘ K.bo\ . \ L\ _..\\ l .q Q» . POI .i .i x x. .- , .1 . _ .L i . . . . 4 1 . _.. \ . . % . q . 1‘ g # , , L 0 5 O 5 0 5 0 5 0 5 O 5 4 4 3 3 2 2 .I. l «BZWUIHNS .U.E «KHZBUMNWV .U.E.m 2 1 Sept. Aug. 31 TIME {iiéifiih ‘5 "q V. ANALYSIS OF RESULTS As has been mentioned previously. due to the effects of temperature. high moisture content. and moisture content gradient. etc.. the moisture content determined by Kil-Mo—Trol does not represent the true average moisture content of the wood. In order to include and consider the effects of these factors. a multiple correlation analysis was conducted according to K. A. Brownlee's ”Industrial Experimentation" (6). The analysis was done in the following three steps: 1. Correlation Between Two Variables A correlation problem considers the joint variation of two measurements. neither of which is restricted by the experimenter. In the present case there are the following variables: yS = Moisture content of shell determined by Kil-Mo-Trol. Yc = Moisture content of core determined by Kil-Mo-Trol. (x1)S = Moisture content of shell determined by kiln sample (oven-dry method). 27 28 (x ) = Moisture content of core determined by kiln sample (oven-dry method). x = Average moisture content determined by kiln sample (oven-dry method). x2 = Kiln temperature 0F. For the shell moisture content yS = 4.1027 + 0.6812 (X1)S (Figure yS = 54.9076 - 0.2706 X2 (Figure yS = 2.8603 + 0.5729 X3 (Figure For the core moisture content = . + . - yc 2 4427 0 6593 (X1)c (Figure yC = 78.0769 — 0.3946 X2 (Figure yc = 3.0164 + 0.8113 x3 (Figure These equations have been derived from the combined 10) 11) 12) 13) 14) 15) data obtained from both kiln runs. The equations are limited to a moisture content range below 30%.M.C. All other values 'were eliminated because the linear relationship between the electrical resistance of the wood and moisture content only exists when the wood moisture content is below 30% (see Figures 10. ll. 12. l3. l4. and 15). .5 J Ruth “I \._ a—A Correlation between electrical resistance moisture ' content and actual moisture content for shell. ‘———— Figure 10. __.—_ ___—.. 29 ——-—-\V.—l‘ 3O 25 20 15 10 . +'. 4 1027 O 6812 (X1)S V . . C C O 0 O at} A O Q . O 0 «0° .00 10 15 20 25 30 35 (X1)S (ACTUAL MOISTURE CONTENT) IN PERCENT “ h J.'- A. . :iSQH-‘I..vn.-.:' 9.. . 431.3% I' V ! .Y': 0‘. 7"! ‘1' Figure 11. 30 Correlation between electrical resistance moisture content and temperature for shell. 1,.e_~_- ,. Y s = 54.9076 - 0.2706,X2 3O \ U 0 O 9O 10 O 110 120 130 140 x2 (TEMPERATURE IN OF) 150 160 170 .._u___n1 ”-—v- H, . _ . ‘ ' ‘ a ' a.tv~'* _s ) Figure 12. Correlation between electrical resistance moisture content and actual average moisture. 31 Y = 2.8603 + 0.5729 x s 3 30 P. ’;/’ 25 T I Q g. 0 / O O O 20 p O / . 15 . /,. . O . O O 10 ' O 5 .00 0 O 10 15 20 ' 25 30 35 40 x (AVERAGE MOISTURE CONTENT IN PERCENT) 3 ~fl~C‘Mt.-fi . .' f! gas. -‘-.".A . ‘ (_ nuae ., “A Figure 32 13. Correlation between electrical resistance moisture content and actual moisture content for core. 2.4427 + 0.6593 (x ) Y c 1 c 30 . 1’ 0 0+ / 2 j . / O 2 ’L/’//} o ' f - O L O 1- ‘1/ ' O O O I O O . / . D 10 0 fi . ’7. O I O 5 1’ t ' O 1 5 10 15 20 2 5 30 35 40 (X ) (ACTUAL MOISTURE CONTENT IN PERCENT) 1c '1! '35.. a , «‘w—~—_, ‘i. z.‘ :u'-~"--- Figure 14. 33 Correlation between electrical resistance moisture content and temperature for core. X 2 78.0169 - 0.3946 Y \ O \ O 3 .4 7.1UJJHQM 744. 5 O 5 0 5 2 2 l 1 ‘474a474)\l 2340.135Q «HHJchd. 04.02 3J4/H4JQ-J‘QJ 130 140 150 160 170 180 120 U H 0 X2 (TEMPERATURE IN F) PO 'I- .! .h ‘ ..".-~_... Figure 15. Correlation between electrical resistance moisture content and actual average moisture content for core. 34 man 51]-? ; Euiutlil REIM- O C C O / I O / . 3 C X 3 1 Q l 8 M / O + O 4 O 6 o l O O o 3 C = o o C (01.! o C O O / O Y O C C O O O O C 5 O 5 O 5 O 3 2 2 1 1 Bsz/mmm ZH Aezmezoo mNDEmHoz mozm.u Nq.m + Ammae mmoo.o + immv mmmo.o + 1048 wmom.o Nq.m + NR mmoo.o + 05 mmmo.o + m» mmmm.o :H m :N QZ¢ :H WZHA NWQZH .m Q24 .a MZHA XszH m 024 a MZHA XmQZH Lfl .0m mm .01 1.. w 'i'ur'ui 1‘ Figure 17. 37 Comparison between actual average moisture content and average mositure content (as a function of Ys' Y6. and X2) for first kiln run. SHELL (K.M.T.) O CORE (K.M.T.) Q M.C. (K.S.) AVE. ———o-——o~— AVE. M.C. (AS A FUNCTION OF Y8. YC. AND x2) easemmiewm . 33 0 0 0 0 0 11 10 TIME 0 0 0 0 nu 0 0 0 0 0 0 0 O m“ mu ”m ”D M. «J, «z .1 nu q, R. .I ,6 .5 .4 1. «z .1 . . . o L. 1111.11 B 1 m .1 T 1 w. B _1.11f11.1 1 .3 1* mm 1 .1 \ _L1 D B . f " \.\% ‘N H11 J“Wu\. 1|— _ 1. 1 1 1. 1L L .1 \ .Illrl1ll— . IF— . x _ N 1.1.. 1,. 1.. 3. r 1 1.1. 11 a \ _ 0 5 0 5 0 5 0 5 0 5 0 5 4 4 3 3 2 2 1... 1 Aezmommmv .o.z.m Aszmummmv .U.£ “Czuuummv .u.:.u Aug.5 -_ ---4~_‘A._. A .. gain. 4 rvnv— 4 Figure 18. Comparison between actual average moisture content and average moisture content (as a function of Y . Y . and X ) for second . s c 2 kiln run. 38 ° ° SHELL (K.M.T.) ——-o—o— CORE (K.M.T.) .1__.-__,.__ AVE. M.C. (K.S.) ._o.—-o.~— AVE. M.C. (AS A FUNCTION OF Y , Y . AND x2) S C 180 "1 170 J L__1— 160 l\ \ DRY 150 BULB 140 — r_--_h——>«'——Flpm 130 “mm-4"". {"1 : 1 1 b-—-1 L-.JL 4-1-1 -44 I”! . 120 : WET : l L", BULB: '1 110” . I a: 5 ' E 45 . - . -1: 90 E . E: 40 80 O 35 70 2". 30 60 E E 25 50 8% 2 33 0 40 7: 15 . 30 O . ‘ ' 5:: 10 . .~%— 20 m , ’3 b. 5 . 10 0 1 0 Aug. 31 Sept. 1 2 3 4 ' 5 6 7 TIME 39 3. Nomograph The Equation 6 is represented in the form of a nomograph as shown in Figure 16. If values are given for Ys' Y6. and X2. the corresponding value of X3 is found as follows: Set index line 1 to values of Ys and Y6. marking the resulting value of Q on the Q—line; set index line 2 on this mark for Q and also on the given value of X2 and read the corresponding value of X3 on the XB-scale. Several checks for the accuracy of this nomograph were made on Figure 16. and accurate answers were obtained as shown on said figure. “—1 1. ‘ "’11:. -, VI. CONCLUSIONS The use of an electrical resistance moisture meter like the Kil-Mo-Trol as a means for controlling the kiln drying of lumber makes it necessary to apply certain corrections to the readings in order to compensate the error due to high M.C.. temperature. and other factors. The present study is an example of how such corrections are obtained for a particular drying situation. The presented equations and the nomograph cannot be considered to be of value in different conditions. They are limited to two kiln runs drying 4/4 beech. The multiple correlation analysis seems to yield satisfactory results. 40 THESIS BIBLIOGRAPHY Forest Products Laboratory Kiln Schedules and Drying Time. Report No. 1900-5. March. 1960. C. G. Suits and Dunlap. M. E. Determination of the Moisture Content of Wood by Electrical Means. General Electric Review. December. 1931. James. W. L. Electrical MOisture Meters for Wood Forest Products Laboratory Report No. 1660. January. 1958. Stamm. A. J. The Electrical Resistance of WOod as a Measure of Its Moisture Content. Industrial and Engineering Chemistry. September. 1927. Hiruma. Extracts Bulletin. Forest Experiment Station. Meguro (TOkyo). 1915. Brownlee. K. A. Industrial Experimentation. 1949. 41 v- ,u. .. i THESIS 3‘93 J "h‘JK’QJW“ ‘ . "11171111111111! [1113111111118111111111111155