WWI‘H WWI“! 146 142 THS L9,” 1“. a. {$3th ”.33 :“ fii‘kzas‘.‘; ‘ 3t 1...} pug”; '91:“: 313‘- :EK .‘mi. S. tr? :3»; ‘J'Ltzfit' “MR1: .‘Rfi’ 3;: ~L’x;'...§\ ’E - - .- s 5,-1.’ no. ‘3:‘“:‘}‘1MC‘."3‘-’:‘.9§ “3. 22‘5“. i 35-254 _ ' 3.- ‘_ .‘JB: 0 isno‘ U;ua"svo-.J as“. u..- .u’ mi» :1 ‘11:. {figs A. 21 C”.- This is to certify that the thesis entitled "The Design of a Pressure Trsmducer Date 0-169 For Measuring Silage Pressures" presented by Wei-Wen Iu has been accepted towards fulfillment of the requirements for M. S. Agricultural Engineering degree in l _ ‘ /'I / : 'i'y'if I r ) " ’ )‘ ‘1 5 ’ (“a . s l - " " 1 Q I 7 7 Major professor " ' 8/18/60 Q‘Wfi‘t THEsu a4, a :3: m an .7; e (—3 THE DESIGN OF A.PRESSURE TRANSDUCER FOR MEASURING SILAGE PRESSURES by Wei-wen Yu AN ABSTRACT Submitted to the Colleges of riculture and Engineering or Hichigan State Uhiversi y of Agriculture and Applied Science in partial fulfillment of the requirements for the degree or MASTER OF SCIENCE IN AGRICULEURAL'ENOINEERINO Department of Agricultural Engineering 1960 Approved II Hm T“ 4L 2 warewss YU ABSTRACT The importance of silo structures has been recognized for years in cattle and livestock farming. The size of silo has changed greatly. The investigation of structural phases of vertical silos was insufficient to keep up with the change in size of silo. In the past five years more than ten silos have failed. The reasons for silo failures were investigated but most of them were left unverified. Various methods have been used to measure pressure. The transducer using wire strain gages was suitable for multiple point pressure measurement. Pressure transducers made of SR-h A-l8 gages were built and checked. The gages were cemented to the back of a thin stainless steel diaphragm which was rigidly clamped to a brass body.' The transducer was calibrated against known hydraulic pressure up to 36 psi; its stability observed with and without loading; calibrated against known pressure under different temperatures; calibrated against known pressure with silage in contact with the transducer diaphragm. Thirty-one transducers were made and installed in the an and on the bottom of a 30' x 60' silo. The characteristics of transducers were summarized as fellows: l. The curves obtained from the hydraulic pressure calibration were excellent. They were reproduced TH 5:315! WEI-WEN‘YU ABSTRACT with high accuracy in successive runs. The output of the transducer was insensitive to a change in temperature. The output measured with the silage in direct contact with the transducer diaphragm was found correct below 5 psi and 9 per cent higher at 10 psi than that measured from the hydraulic pressure calibration. Stability without loading was observed for six transducers over a period of two months. Four of them had a change less than 90 micro inches per inch in two months. The other two tended to creep. One transducer remained unloaded for 180 days and the strain readings observed continuously. The maximum variation in zero pressure readings was found to be 360 micro inches per inch over 180 days and was considered too high. Stability of a transducer under constant pressures of 10 and 20 ‘ psi is satisfactory. Change in readings tended to approach a constant decrease in output of 150 micro inches per inch. Measuring strains at a constant pressure as high as 30 psi was found unsatisfactory. HES}! THE DESIGN OF A PRESSURE TRANSDUCER FOR MEASURING SILACE PRESSURES by Wei-wen‘gu A THESIS Submitted to the Colleges of Agriculture and Engineering of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER 0‘! SCIENCE IN AGRICULTURAL ENGINEERING Department of Agricultural Engineering 1960 ACKNWLEDQIIEN'B The author wishes to express his sincere thanks and appreciation to all those who contributed to this investiga- tion. In particular, the contributions of the following: Dr. James S. Boyd, my major professor who continually provided guidance and inspiration throughout the entire investigation and preparation of this manuscript. Dr. Clement A. Tatro, professor in the Department of Applied Mechanics, who as minor professor provided valuable suggestions in designing the pressure transducer. Dr; Arthur‘w. Parrall, Dr. Merle L. Esmay, and other members of the guidance committee for administration of the . graduate program and assistantship. Members of the Research Co-ittee, National Silo Association, for the research grant which made this investi- gation possible. Hr. Ralph Baird, manager of C. a B. Silo Company, Charlotte, Michigan, for providing labor in install- ation of pressure transducers in the silo. Mr» James Cawood and his staff for providing assistance and facilities in constructing pressure transducers. 11 HES“ J1. TABLE OF CONTENTS INTRODUCTION. . OBJECTIVES O O O O O O 0 REVIEW OF LITERATURE . . . . THEORY AND DESIGN OF PRESSURE TRANSDUCERS WheatstoneiDridge . . Stress and Strain . . . Design Procedure. . . . Design. . . . . . . DESCRIPTION OF EQUIPMENT. . Pressure Transducer . . Young's Strain Indicator. Calibration Equipment. . CALIBRATION PROCEDURES AND THE RESULTS . Hydraulic Pressure Calibration. Stability of the Transducer. Effects Due to the Change in Temperature Effects Due to the Materials in Contact with the Diaphragm. . . . APPLICATION OF PRESSURE TRANSDUCERS TO MEASURING SILAOE PRESSURES . . . . . SUMMARY AND CONCLUSION . . . RECOMMENDATIONS FOR.FURTHER STUDIES WMNCES O C C O O O O 111 P888 \OmmmMI-‘H 10 13 13 15 15 18 18 18 25 25 33 140 R1 Figure '0 0 damage: 13. 14. 15. 16. 17. 18. LIST‘OF FIGURES Wheatstone bridge. . . . . . . . . . A circular plate clamped at the edges with uniformly distributed load . . . . . . Strain and stress. . . . . . . . . . Pressure transducer . . . . . . . . . Transducer wiring diagram . . . . . . . Sketch of calibration equipment . . . . . Pressure transducer before the back cover sea]. 1“ O O I O O O I O O O O 0 Pressure transducer calibration apparatus. . Calibration curves . . . . . . . . . Calibration curves . . . . . . . . . Stability of transducers . . . . . . . Stability of the pressure transducer without loadim e 0 e O O O O 0 O O O O A transducer under constant pressure . . . Calibration set up for temperature effect on output of transducers with two-arm bridge . Calibration set up for temperature effect on output of transducers with four-arm bridge. Temperature effect . . . . . . . . . Calibration apparatus for pressure transducer with silage in contact with the diaphragm . Calibration curves with different depth of silage in contact with the transducer . iv Page 11 1h 16 16 17 17 19 20 21 22 24 26 26 27 3O Figure 19. 20. 21. 22. 23. 24. Calibration curves with different depth of silage in contact with the transducer . . Calibration curves with silages in contact with diaphragm compared with hydraulic pressure calibration . . . . . . . . Horizontal pressure . . . . . . . . . vertical pmasm O O O O O O O O O 0 Horizontal pressure measured on the wall of 30' x 60' silo with corn silage . . . . Summary of horizontal pressure measured on the wall of 30' x 60' silo with corn silage Page 31 32 34 34 36 37 INTRODUCTION It is well recognized that the storage silo is one of the most important structures in cattle farming. For over 80 years, silos have played an important and necessary part in livestock farming. The first silos were merely rectangular walled pits. Stone, brick, and concrete were commonly used. James Meilson of Mew'Brunswick (5) erected one of the first vertical silos of chestnut posts in 1881. The structure was no feet long, 20 feet wide, and 18 feet high. In spite of the increase in sizes of silos, investi- gation of structural phase were unfortunately very limited. In the past five years, more than ten silos from 1h' by 50' to 30' by 70' in size have collapsed. According to the remarks made by the National Silo Association, failures were due to inadequate hooping, improper filling, and improper site selection, yet the exact causes of failure for the most of them are unknown. OBJECTIVES The obJective of this investigation was to develop a device for measuring pressures exerted by silage in silos. REVIEW OF LITERATURE J. R. McCalmont (5) formulated silo design data from his experimental results obtained from the full scale silo in 1946. 'Ee used a calibrated bar as the sensing element. The deflection due to the pressure exerted by the silage in the silo was measured. The pressure panel was built of two layers of l- by 6- inch lumber as an ordinary silo door. To this were attached vertically two steel 3-inch T-sections 12 inches apart. Each panel was supported on two 5/8-inch round alloy steel bars that passed through holes in the T—sections and were secured in corresponding channels along each side of the doorway. The panels were hung in each door opening in column and the measurements taken from the out- side. Eis results show that the diameter of the silo affects the unit lateral pressure exerted on its wall. The formulas calculated from these experimental results recognize the critical relationship between diameter and pressure as follows: Design pressures for the silos in feet and less in diameter: d h“” R = 265th Design pressures for silos 16 feet and more in diameter: d h"‘5 Pu. “" 5 where, Ph uiflorizontal pressure, pounds per square foot d - Diameter, feet. h . Depth of the silage, feet. Density measurements were carried out by Otis and Pomroy (7) to evaluate silage pressure. They used the layer method, the surface sampling method, and the horizontal core sampling method at various elevations. The density was measured and the curves drawn. The samples used for the density measurement were placed in airtight plastic bags and brought into the laboratory. A portion of each sample was placed in a cylinder and compressed to the density in the silo at the time the core sample was taken. Comparison of the pressure and density diagram (7) showed good agreement with high density material located in high pressure area. During 1940 in connection with the construction of siols in France and Algeria, a large scale investigation of pressure in silos was initiated. The results of investi- gations have been published by Reimbert (195A), Caquot (1957), and Despeyroux (1958). They found that, in grain silos, when filling, the wall pressure was almost in accordance with the Janssenrxonen formula and with Caquot's modified formula. Reimbert carried out an experiment on a steel silo 13-feet 6-inch square and 33-feet in height. The pressures were determined by measuring the strains in the walls at various depth with electric wire strain gages. Dergau (1951-1952) made two test arrangements for measuring grain silo pressures, one in a reinforced concrete silo he used hydraulic earth pressure cells developed by Kallstenius and.Dergau, to make the measurement. The hydraulic earth pressure cell has built-in electrical con- tacts for checking cell compression. In 1951, he obtained one complete cycle of pressure measurements and found that during emptying the pressure of the grain was almost twice as large as that during filling. as suggested further investigation be made as the above resudts were merely from one point measurement and doubtful as being representative of the distribution of pressures over the entire surface. Por the steel silo, similar results were found by using electrical wire strain gages. The strain gages were cemented on the steel plate in pairs both horizontal and vertical. The compensation circuit was also employed by placing the dummy gages on an angle profile fixed between the points of measurement. Pressure cells have been successfully used in measuring soil pressures. The united States waterway Experimental Station report (11) gives a complete description of types of soil pressure cells developed for'measurements of pres- sure in the soil under walls, footings, and tunnels. They considered it very probable that the criteria established for cells mounted in a rigid wall were as follows. The ratio of the diameter to the proJection of the cell must be greater than 30 and the ratio of the diameter to the deflection must be greater than 1000. The ratios do provide the limit within which the cells indicate approximately the 5 pressures which act on the wall in their absence. The MES soil pressure cell consists of a circular face plate welded at its perimeter to a thicker base plate. The face plate has a peripheral slot which forms a flexible Joint between two plates. A diaphragm is formed in the base plate by a lathe. A connecting cable enters the gage chamber through a packing gland at the side of the base plate. The thin disc chamber between the face and base plate is filled with oil (recently modified cells are filled with mercury). Pressure applied to the face plate is averaged and trans- mitted by the oil to the diaphragm. The radial strain produced in the diaphragm by the pressure is measured by SR-h electric wire strain gages. A linear relation between applied pressure and resistance change can be obtained with appropriate connection of gages to give the complete temper- ature compensation. Cooper (2) developed another type of pressure cell which had two SR-h electric wire strain gages cemented on the underside of the 0.025-inch thick circular stainless steel plate. The circular plate was rigidly soldered to a brass body. The strain gages used were l/B-inch in gage length, l20-ohm in resistance and had a gage factor of 1.73. Two gages of the same lot were cemented to the side of the brass body to complete the‘Wheatstone Bridge as well as perfect temperature compensation. The cells were placed at various depths in the soil perpendicular to the direction of travel, and pressures were measured. The results were very satisfactory. TREOR! AND DESIGN OF PRESSURE TRANSDUCERS The electric wire strain gage was adopted in designing pressure transducers. The gages will be cemented on a stainless steel diaphragm firmly clamped on the cell body. The theory related to this design will be discussed here. Wheatstone Bridge The output of the wheatstone bridge in Figure 1 can be found by the following equations. where 6 - total output of the bridge. R. R2, R. and R4 - resistances of the gage l, 2, 3, and 4. AR’ARI’AR,’ and 4R4- changes of resistances in gage l, 2, 3, and 4. If the gages of the same resistance were used, the equation becomes, 6 . -|R_ (ARI +AR3‘AR2" 4R4) As from the relation between strain and resistance change ‘AR L F F the change in resistance can be measured by a strain meter directly in strain (micro inches per inch). In order to get the maximum output by Wheatstond Bridge, gage 1 and gage 3 6 ELLOW Z til Ill RED 3 l 3 I I I 4 I YELLOW 3 4 C) .J LIJ (D 0: FIGURE I. WHEATSTONE BRIDGE f q I I I I I I I in T FIGURE 2. A CIRCULAR PLATE CLAMPED AT THE EDGES WITH .UNIFORMLY DISTRIBUTED LOAD 8 should be cemented at a point subject to tension and gage 2 and A should be cemented at a point subjected to compression. Stress and Strain For a circular plate clamped all around the edges with uniformly distributed load of intensity q pounds per square inch applied, the radial and tangential moment, stress and strain can be calculated from the following formulas (Fig. 2). Mr :- |ié[a‘(l +U) -- r‘(3+u)] M. - %[a'(l+v)- r'(l+3V)] 0', :- 6—Mrr‘ = -:—E',[a'(l+V)- rt(3+v)] h 0'. - €513 = fir [a‘Ui-V)‘ r'(l+3v)] 6. - {gun-w.) 6t - .'E(o-t-vo-r) where, Mn M, . radial and tangential moment, in pound-inch 0., 0'. a radial and tangential stresses, in pound per square inch 6. - radial and tangential strain, in micro inches per inch q - unit uniform load, in pound per square inch . thickness of the diaphragm, in inch E - Young's modulus of elasticity, in pound per square inch v - Poison's ratio a r . radii of the diaphragm, in inch Design Procedure Diameter of digphgggm, General consideration should be given to the nature of the silage and the situation during pressure measurements. The transducers were cali- brated against hydraulic pressure, while during the field measurement, the diaphragm was in direct contact with silage. Because of silage cut size and its non-homogeneous property, a diameter sufficiently large as to avoid possible concen- trated loading was selected. On the other hand, from the technique in strain gage application the diameter of the diaphragm will directly affect the thickness of the diaphragm as well as its sensitivity. Silage stored on Michigan farms, usually was chopped from 3/8 to 5/8 inch in length. Hence, a diameter of 2 inches was selected for this study. Thickness of dm. After the diameter of the diaphragm was determined, the limiting factor was the diaphragm thickness. As the thickness of the diaphragm was inversely proportional to its extreme fiber stresses, a thin diaphragm was more desirable for sensitivity. The high reproductibility and stability would provide the lower limit for the design of its thickness. For a circular diaphragm clamped all around the edges with uniform loading, the outer edge has the higher fiber stress and remains as the reference point for the chosen working stress in design. Sensitivity. After the diameter and thickness of the diaphragm were determined, the total output of the transducer 10 could be calculated by formulae in terms of the strain. The smallest gradient of Young's Strain Indicator is 10 micro inches per inch and the strain reading can be estimated accurately to 5 micro inches per inch. The best design would be to make the diaphragm of such a thickness to give the desired sensitivity at the smallest gradient of the Strain Meter. m It was required to design the transducer for the measurement of the wall pressure in a silo with silage cut 3/8 to 5/8 inches in length. use stainless steel plate as the diaphragm material. Working stress - 20,000 psi Maximum load - 20 psi Poison's ratio - 0.3 Modulus of elasticity - 30 x 106 psi Diameter of diaphragm. D - 2 inches Thickness of diaphragm. (h) Prom the formulae for the maximum radial stresses in Figure 3. Thickness required at the center of diaphragm h - 3"”) 0' q .. 0.022 inch 8 I, Thickness required at the edge of diaphragm 3 h . __.222T3__ - 0.027 inch So, choose h a 0.025 inch plate (corresponding to 22 gage plate). 11 EdmoSo wwwom own—.2440 I._.;> Sm1=>EOn=ZD no m35 mmmmkw $83818 024 Zackm .m manor... wwwom Qua—241.0 It; demraSo mQISUEO omens]. 558.2: 20 2:25 459:. no 20:35.55 BUB? (2A - I Izobe L o NIVHIS (zA-IIZDDS 12 Sensitivity. Sensitivity implies the output of the pressure transducer due to the uniform load of unit intensity” The total output can be calculated by swing the output of four gages. a-l‘" :h-0.025" 3v-O.3;q-1psi 08301: PIC; E «30x106 psi. ”r ' §s%‘[°‘('*")"z<3+v)]- mt”) .. 780 Psi a; 3%[a1(l+V)_r’(‘+3V)J- ETC-02.5253: [[_3]-= 780 psi 6' .- ‘é—(Vr - v 0;) n 18.2 x 10"6 inches per inch 0880 3: I' I 3/16" I 0.1875" 0; - 710.? not a; - “(no.1 psi 5: .- 16.3 x 10'6 inches per inch Gage 2 and ll: r m 7/8" - 0.875" 0'' - 735-9 931 (Tt I 92.8 psi 6, - 23.6 x 10'6 inches per inch Sensitivity .. z e,. (18.2 + 16.3 + 23.6 + 23.6) x 10"6 .- 81.? micro inches per inch per psi. DESCRIPTION OF EQUIPMENT Pressure Transducer Strain gage transducers were built to make silage pressure measurements. Each transducer had four SR-4 A-18 electric resistance wire strain gages cemented to the under- side of the stainless steel plate 0.025 inches in thickness and 2.25 inches in diameter. Two gages were cemented at the center of the circular plate perpendicular to each other and the other two gages were cemented close to the fixed edge in the radial direction. The four gages were connected so as to compose a wheatstone bridge with all four gages active and providing a complete temperature com- pensation. A-18 gages were 1/8 inch in length 120 ohms in resistance and had gage factors of 1.80 1,.3. Dupont Mo. 5458 Cement and Petrosene Wax were used for cementing and moisture-proofing the gages. Belden 8424 four lead rubber shielded cable was used for the connection of the transducer to the strain indicator. Each transducer was made water tight with a brass back cover screw-fastened to the body. A special gasket made of the tube patch and aluminum foil was used in sealing. The design of the transducer is shown in Figures 4 and 7. 13 14 6- NO. 6- 32 RH BRASS % SCREWS .L I 4|" "[1 Jy'gr BACK COVER - GASKET I/Il/I/Il/Illllllg; BRASS BODY 5;: . ~ In vow- SOLDERED JOINT \n g '3 STAINLESS 2.00 a? T3- STEEL PLATE r' 2,245 “'39?" SECTION A—A NO. 20-4 BELDEN B424 SHIELDED TURN OFF 7|- THREADS ‘I-‘a'é T0 PRESS FIT m___ u- BRASS NUT AND SOLDER -T- DETAIL OF MODIFIED STANDARD BRASS WITH TAPERED FITTING THREADS I— _l A A SR-4 STRAIN GAGES R= RED WIRE G= GREEN WIRE 88 BLACK WIRE Y8 YELLOW WIRE SCALE | : | FIGURE 4. PRESSURE TRANSDUCER 15 Yoggg's Strain Indicator The type A M strain indicator was used to measure the change in resistance of electric strain gages. The indicator was calibrated to interpret those resistance changes directly in micro inches of strain. The indicator was useable both for two arm bridges and four arm bridges. The gage should have a resistance of 60 to 500 ohms to use this indicator. The wiring diagram of the transducer and indicator is shown in Figure 5. Calibration Eguipggnt The appratus for calibrating the transducer against the hydraulic pressure is shown schematically in Figures 6 and 8. The calibration equipment consists of a constant hydraulic pressure tank, Bourdon tube pressure gage, regulator valve, pressure chamber, transducer fastener, and a release valve. At the upper part of the pressure chamber an entraped air-release valve was installed to obtain more stable and uniform pressure on the transducer diaphragm. The Bourdon Tube pressure gage was calibrated with the Ashcroft dead weight tester. Each transducer was calibrated separately up to a gage pressure of 36 pounds per square inch. 16 RED WIRE A GREEN WIRE __O_ s ,l' K “HR -—o-C I' GAGE 3 rlvgggw WIRE D \1 . FOUR ARM BRIDGE ‘ SQRJA‘FRS METER FIGURE 5. TRANSDUCER WIRING DIAGRAM HYDRAULIC PRESSURE TANK PRESSURE GAGE FASTENER PLATE . . I ' I I z /////////4 a ENTRAPPED- , r F TRANS. “—12 AIR PRESSURE 7 3:33:85 CHAMBER REGULATOR VALVE RELEASE VALVE FIGURE 6. SKETCH OF CALIBRATION EQUIPMENT 17 Figure 7. Pressure transducer before the back cover sealing. Figure 8. Pressure transducer calibration apparatus CALIBRATION PROCEDURES AND THE RESULTS gydraulic Pressure Calibration Each transducer was placed on the calibration apparatus and calibrated against the known hydraulic pressure indicated by the Bourdon Tube pressure gage. The pressure was first applied to about 30 psi and released from the valve to eliminate entrapped air. Loading and unloading was then repeated several times before the data were taken. The strain output was taken for each 2 psi pressure increment up to 36 psi. Typical calibration curves are shown in Figure 9 and 10. Theoretically the curve should be a straight line yet it has a slight curvature with an increase of applied pres- sure. The calibration results were excellent, and were reproducible without error in successive runs. Sensitivity of the transducers ranged from 100 to 1&0 micro inches per inch per psi. The difference in sensitivity was due to the variation in diaphragm thickness and inexact alignment of the gages. Stability of the Transducers Stability without loading, Six transducers were placed in the laboratory after they were calibrated. The zero pressure readings were taken continuously for two months 18 19 — TRANSDUCER B- 3 —o——o—- TRANSDUCER B - 5 --+—_+_ I SOOO ZOOO MICRO INCHES PER INCH IOOO STRAIN l I l I I l l l I | l 00 FIGURE 9. l 4 8 I2 PRESSURE C A LI BRATION I6 1 20 P. S. I. CURVES 24 28 32.36 INCH MICRO INCHES PER STRAIN I I I TRANSDUCER C- 7 —--—-e—-._- 250 TRANSDUCER C- 8 ——+—-—+_ TRANSDUCER C- II f a 200% I500 ' IOOOI 500 I I I. I II I I I I I I I I I O 2 4 6 8 IO l2 I4 I6 I8 PRESSURE I? S. I. FIGURE IO. CALIBRATION CURVES 21 mo C3545 mmmoaomz.:..:m<._.m .N_ mmaoi I .825 m2: M. om. ow. ON. 00. om oo ow ow w o e 1~4a_4 ___J_~ fi__a IJIJI. N .. m 00.? 3 S .. \\\. mo. 08.... _ 29.3.5.2 z. a - Tv 39... 2 Km... w comm] H .93 z. 226% I/I . - _ m “III _ u Ib\v/\\MO¢D _ ozaqmm .3352 _ A— 23 and results shown (Figure 11). It was found that four of the transducers had a limited range of change (70 micro inches per inch) in output while unstressed. Two transducers were found unsatisfactory. The failure of two transducers was attributed to poor>moisture-proofing. Transducer D-h was also checked for long-time stability. This transducer was left at the H a B»Farm.in Mulliken, Michigan for three months and then brought to the laboratory completely unloaded. The change in strain readings was continuously observed for six months. The results, both normal and reversed readings, were shown in Figure 12. It indicates that the variation in strain readings was not due to zero drift or temperature effect (this will be verified later) but from creep and other unknown sources. The maximum range of this variation was 360 micro inches per inch which would correspond to 3.0 psi of calibrated sensitivity. This variation was considered too high. Stability with constant loading. One transducer was used for testing the effects due to constant loading. The transducer was assembled on the hydraulic pressure calibra- tion apparatus and pressures of lO, 20, and 30 pounds per square inch were applied separately over a period of 25 days. The change in strain readings was continuously observed. This result was shown in Figure 13. It was found that for pressure up to 20 psi, the change was small and tended to approach the constant decrease in output of 150 micro inches 21+ wmmammwma P2455200 mmoz: mwonomza‘m... 4 .m. mmaoi «:8 ms; mm m m. o. - m 0 +4 a A _ _ _ _ _ a _ _ — 4 08. W W i I N / M 1000.. m we. ./I h I. If. 00¢: O E N I: I U I ._ mm o. cow m a Z .I I I I v I - .mmIoN/ir - 007mm 9 I II III IIIII o 25 per inch after 25 days of continuous loading. From the constant pressure of 30 psi the strain reading decreased rapidly during the first few days and then decreased almost constantly at the rate of 10 micro inches per inch per day after sixth day of loading. The reason for this variation might be due to the relaxation of the bond of the cement between the gages on the diaphragm. Effects Due to the Changg_in Temperature The same hydraulic pressure calibration apparatus was used in this test except that the temperature of the water was changed. The setup of this test was shown in Figure 14 and 15. The temperature of the water was measured by a thermocouple placed under the diaphragm in the pressure chamber and indicated by a potentiometer. iBoth a two arm bridge and a four'arm‘bridge were calibrated under water pressure with changes in water temperature. The result from the four arm bridge transducer was shown in Figure 16. The designed transducer proved to be insensitive to changes in temperature. Effects Due to the Materials in Contact with the Diaphragm As silage is a non-uniform, non-homogeneous material, the relation between hydraulic pressure calibration and silage in direct contact with the diaphragm was desired. The test apparatus is shown in Figure 17. Six.transducers were firmly placed at the bottom of the circular tank. The inner tube of a h x 8 inch trailer tire was placed on the 26 Figure 14. Calibration set up for temperature effect on output of transducers with two-arm bridge. Figure 15. Calibration set up for temperature effect on output of transducers with four-arm bridge. 27 TEMPERATURE 98—IO4°F e e 75°F : e 62—68°F e : 300 I O E D: LIJ O. (I) LIJ it) 000 Z2 0 o: 2 2 2 I000 <1 0: p. (D 0 0 5 FIGURE I6. I0 I5 20253035302520 I5 PRESSURE F? S.|. TEMPERATURE EFFECT I050 28 - COMPRESSED AIR SUPPLY LINE | PRESSURE GAGE (HYDRAULIC PRESS I 0 .PI - 4 e I * I REGULATOR g, f r VALVE I. ,STEEL . RELEASE / LT'I'I PLATE PLYWOOD VALVE , ' .mgaue'saeazaew CIRCULAR CABLE To STRAIN AIR 2 94.13": MR PLATE INDICATOR PRES' :-‘:5..\'-.1{=. PRES INNER TUBE L‘ '.."'.'\;:-.‘-.'._~."j:l OF 4X8" TIRE PRESSURE TRANSDUCER' SILAGE SILAGE FIGURE I7. CALIBRATION APPARATUS FOR PRESSURE TRANSDUCERS ,WITH SILAGE IN CONTACT WITH THE DIAPHRAGM 29 transducers under the circular plate held firmly in place by the hydraulic press. Silage was placed in all the open spaces, before the circular plate was put on. Different depths of corn and grass silage between the diaphragm and the tube was tested. A known pressure was applied to the tube from the compressed air supply line, and the strain was measured. The results were shown in Figure 18 and 19. It was found that the slope of the curve was greater than that of the hydraulic pressure calibration, for silage of one inch depth was placed between the diaphragm and the pressure source. When the depth of the silage was increased, the strain output decreased. This was due to the fluffy condition of the silage, which continued to condense without much pressure transmitted to the diaphragm of the transducer at first. It was found that the output of the pressure transducer with corn or grass silage of one inch depth in contact with the diaphragm was higher than that without them. The comparison of the calibration curves obtained form the hydraulic pressure calibration and the calibration with silage in contact with the diaphragm was shown in Figure 20. INCHES PER 3000 2500 I I I I I I ..___. HYDRAULIC PRESSURE CALIBRATION H N0 SILAGE .__. I " GRASS S I LAG E .__. 2" G RASS SI LAGE o——- 4" GRASS SI LAGE I Q 3 2000 I500 O O: 2 2 I000 E g 500 I- (D 0 FIGURE I/ I I TRANSDUCER D- 3) I I I 5 I0 I5 20 25 30 PRESSURE P.S.I. I8. CALIBRATION CURVES WITH DIFFERENT DEPTH 0F SILAGE IN CONTACT WITH TRANSDUCER 3o 3000 INCHES PER 2500 I 0 g 2000 I500 O O: 9 2 I000 E g 500 I— U) 0 FIGURE I I I I I '4 I HYDRAULIC PRESSURE CALIBRATION N0 SILACE I " GRASS S I LAC E 2" C RASS SI LACE 4" CRASS SI LACE I8. I I TRANSDUCER D-3) I I I 5 I0 I5 20 25 30 PRESSURE P.S.I. CALIBRATION CURVES WITH DIFFERENT DEPTH OF SILAGE IN CONTACT WITH TRANSDUCER 31 I I I I 4 - HYDRAULIC PRESSURE CALIBRATION 2500 ._. I" CORN SILACE 9—. 4" CORN SILACE / .__. IO“ CORN SILACE f INCH 2000 V / / INCHES PER \\ \ \\ / /, / E 3‘: I- 500L / / I m , J (TRANSDUCER 0-5) 0 I I 0 5 I0 I5 20 25 50 PRESSURE P S. I. FIGURE I9. CALIBRATION CURVES WITH DIFFERENT DEPTH OF SILAGE IN CONTACT WITH TRANSDUCER 32 20.50.10.443 1:; 55.200 Z. mmwdim It; mw>m30 29.559440 on 0N ON 0 mmswwwma m _ q fl 9 I IO 0 N I KI 'I'S'd Om wwdfm mmdmw MID EBDSSBBd OBBDSVBW muonomZdik ON 0. mmzmmwmn. USDQKOZ... It? Dwmdmzoo demraSo .ON mmDGE wmamwwma m _ _ mw<..=m 2100 38 DSSEUd OBBDSVBW 'I'Sa APPLICATION OF PRESSURE TRANSDUCERS T0 MEASURING SILAGE PRESSURES Thirty-one transducers of the type described in the previous chapters were built for the measurement of silo pressures during the Summer in 1959. Owing to the limit in the harvesting time of corn silage, those pressure trans- ducers were installed in the silo right after they were calibrated against the known hydraulic pressure. The excellent calibration curves were obtained and reproduced in successive calibrating runs. Those pressure transducers were installed in the wall at 0', 2.5', 5', and 10' in four projections, with one at 20' and one at 30' above the bottom of the silo. The silo was 30' x 60' in size and located at BIh‘H Farm, in Mulliken, Michigan. Transducers were embedded in the corrugated concrete staves with their diaphragm sur- faces flush with the inside face of the staves. The new staves were installed in place of old staves. As there was 2.5 feet corn silage left in the silo, the silage was dug out to install the transducer at 0' elevation and refilled again after the transducer was installed. Another 13 trans- ducers were installed on the top surface of the corn silage in the silo along two diameters perpendicular to each other and 5' apart. All the leads were brought out of the silo into a shelter and connected to the Ibung's Strain Indicator. 33 27 TEMPERATURE 93— I04°P 75°F 62—68°F A v A .4 fi" t ‘ 300 I 0 Z a: DJ Q (0 LL] 52000 Z O 0: 9 2 2 I000 < (r I- (I) O 0 5 FIGURE I6. IOI5 20253035302520|5 PRESSURE P S.I. TEMPERATURE EFFECT I050 28 COMPRESSED AIR SUPPLY LINE PRESSURE CACE (HYDRAULIC PRESS e 4' ‘l‘. REGULATOR VALVE . ,STEEL RELEASE L_ .3 PLATE VALVE I} PLYWOOD __ CIRCULAR CABLE TO STRAIN AIR " 341:3: MR PLATE INDICATOR PRES r-t;._\-j..j=. PRES INNER TUBE % [SLFLTT 0F 4x8" \ TIRE PRESSURE TRNIISDUCER‘ SILAGE SILAGE FIGURE I7. CALIBRATION APPARATUS FOR PRESSURE TRANSDUCERS .WITH SILAGE IN CONTACT WITH THE DIAPHRAGM 29 transducers under the circular plate held firmly in place by the hydraulic press. Silage was placed in all the open spaces, before the circular plate was put on. Different depths of corn and grass silage between the diaphragm and the tube was tested. A known pressure was applied to the tube from the compressed air supply line, and the strain was measured. The results were shown in Figure 18 and 19. ““3 It was found that the slope of the curve was greater than that of the hydraulic pressure calibration, for silage of one inch depth was placed between the diaphragm and the pressure source. When the depth of the silage was increased, I the strain output decreased. This was due to the fluffy condition of the silage, which continued to condense without much pressure transmitted to the diaphragm of the transducer at first. It was found that the output of the pressure transducer with corn or grass silage of one inch depth in contact with the diaphragm was higher than that without them. The comparison of the calibration curves obtained ferm the hydraulic pressure calibration and the calibration with silage in contact with the diaphragm was shown in Figure 20. INCHES PER 3000 2500 I I .__. HYDRAULIC PRESSURE CALIBRATION .__. NO SILAGE .__. I " GRASS S I LAG E ._— 2" GRASS SILAGE .._.. 4" GRASS SILAGE I I I ' I 0 g 2000 I500 O a: 2 5 I000 E g 500 I- (D 0 FIGURE T I // (TRANSDUCER [P-3) I I I 5 IO PRESSURE I5 20 25 30 PSI I8. CALIBRATION CURVES WITH DIFFERENT DEPTH 0F SILAGE IN CONTACT WITH TRANSDUCER 31 I I I I - HYDRAULIC PRESSURE CALIBRATION/ \‘u 2500 ._ I" CORN SILAGE 4“ CORN SILAGE I0" CORN SILAGE V I 2000 / INCH \ \ \\;\ INCHES PER \ / /. MICRO \\ \ /, / E / / 4 E sooI / // , (n . J (TRANSDUCER D-3) 0 I I 0 5 IO I5 20 25 30 PRESSURE P S. I. FIGURE I9. CALIBRATION CURVES WITH DIFFERENT DEPTH CF SILAGE IN CONTACT WITH TRANSDUCER ZO_._.m30 ZO.._.> OIZm .OO x .0m “.0 .343 NI... ZO omemdms. mmmammmmn— JdeONEOI .MN ._ .w m memmme JQFZONEOI _ I,_._._ _ __ '1333 mmDoE 39V'IIS N800 :IO .LH9I3H 37 0 IO I- UJ UJ U. 20 DJ L9 4 3 30 (I) LL 0 E 40 O. LU O 50 60 0 FIGURE 24. 5 I0 I5 20 PRESSURE RSJ. SUMMARY OF HORIZONTAL PRESSURE MEASURED ON THE WALL OF 30'X SO' SILO WITH CORN SILAGE SUMMARY AND CONCLUSION In view of the non-homogeneous and non-uniform property of silage stored in silos, multiple point measurement of pressure is desired. In addition to this, high sensitivity and facilities for remote control is required. The pressure transducer made of SR-h A-18 strain gages was built and checked. cages were cemented to the back of a thin stainless steel diaphragm rigidly clamped on a brass body. The transducer was calibrated against known hydraulic pressure up to 36 psi; its stability observed with and with- out loading; calibrated against known pressure under differ- ent temperatures; calibrated against known pressure with silage in contact with the transducer diaphragm. Thirty-one transducers were made and installed in the wall and on the bottom of a 30' x 60' silo. The characteristics of transducers were summarized as follows: 1. The curves obtained from the hydraulic pressure calibration were excellent. It was reproduced with high accuracy in successive runs. 2. The output of the transducer was insensitive to a change in temperature. 3. The output measured with silage in direct contact with the transducer diaphragm was found correct 38 Tag tare-Fm. " "' “a.“ So. I 39 below 5 psi and 9 per cent higher at 10 psi than that measured from the hydraulic pressure calibration. Stability without loading was observed for six transducers over a period of two months. Four of them had a change less than 90 micro inches per inch in two months. The other two tended to creep. One transducer remained unloaded for 180 31 days and the strain readings observed continuously. A The maximum variation in zero pressure readings was found to be 360 micro inches per inch over 180 days Islam-- I . I and was considered too hign. The stability of a transducer under constant pressures of 10 and 20 psi was satisfactory. Change in readings tended to approach a constant decrease in output of 150 micro inches per inch. Measuring strains at a constant pressure as high as 30 psi was found unsatisfactory. RECOMMENDATIONS FOR.PURTEER STUDIES Diaphragm gages should be studied to replace the paper based gages. Bakelite type gages as well as bakelite type cement should be investigated in building the transducers. Stability of the transducers should be reviewed more thoroughly by using different glues in cementing the gages. The complete moisture-proofing should be investigated. Other remote controlled pressure measurement devices should be reviewed. 40 [lar- .. , . {RI-3 . 10. 11. 12. REFERENCES Beyer, F. R. and Lebow, M. J. (1952 Long-time strain measurements in reinforced concre . Soc. of Exp. SUP. Ana. pr00o v01. XI, NO. 2. 1u1-152. Cooper, A. M. (1956) Investigation of and instrumenta- tion for measuring pressure distribution in soil. . Thesis for de ree of Ph. D., Michigan State Uhiv., I East Lansing unpublished). Gergau, H. (1959) Measurements of grain silos. Swedish Geotech. Inst., Sweden, Proc. No. 17. “7-71. Gurney, W. W. (1936) Recommendation practice for the construction of concrete farm silo. Jour. Am. Conc. I Inst. VOl. 18, NO. 2. IL McCalment, J. R. (1946) Pressure and other factors affecting silo construction. New Jersey Agr. Expt. Sta. Me 7310 3-260 (1948 Silos: Types and construction. Farmers' 551. No. 1&20. UQS.D.A. Otis, C. K. and Pomary, J. H. (13%?) Density: A tool Perkins, A. E. (1953) Silage densities and losses as found fin laboratory silo. Ohio Agr. Expt. Sta. Res. Cir. 1 . Perry C. C. and Lissner H. R. (1955) The Strain Gage Primer. McGraweHill 330k CO. 45-65, 19832357"‘ Timoshenko S. (1959) Theory of Plates and Shells. "CONN-'Hill 300k CO, e e H-EO _- U. S. Waterway Experimental Station Technical Memorandum No. 210-1. Soil pressure investigation (interior report). vanden Berg, G. E. (1956) Measurement and analysis of soil pressure distribution under tractor and implement traffic in an artificial field. Thesis for degree of M. 3., Michigan State univ., East Lansing (unpublished). #1 I I I l I III III I 175 3068 3 IIIIIIIIIIII