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36 · INST1P-~FNTATIC!T~ AND ~EAS'~NT IN TTI:5 FIELD 07 DIELECTRICS . . ~ ~. P. H.~Dike. [Beds & Northrup Company ' Philadel~;a, Pa. ~ . . In tI-ie. preparation of this report, it has beers d..f:~cll t to Segregate in the literature the co~poner~t,s Which fall r:~.thi.n;the scope of instrumentation and measurement. With no precedent as a guide, since the committee has -`lot . attempted ~p other. years to divide tine subject along the seams lines, it has been necessary; to choose the material rather arbitr~.ril~r. T`e have therefore looked first for new ins assentation', arid second for new ar,~ications of previous].',, -'' existing instruments and methods of measl~emert. Papers Which report data on measl~re~.ents of properties of d~el.ectrlcs' but filch do nct.emphas~'ze methods' are not discussed ' ~ . . .. . . . , .... . The field to be covered has thus been restrlcted9 perhaps too nar,ro~ly9 as ev~de.^ngsd,,by, able 'brevity of thus reportO ~ Fischer1 describes a simplified instr''~:ept for the measurement of the dielectric constant~~.of liquids,.'-. It uses a'6~$,eie,.ctr¢-n-ra~J ':ube'as ~,omb~ned' crystal controlled oscillation (.freq~enc:' about 305 megac~,?cles)''and ¢.sci..~2`on indicator and a 25Z6GT vo3.tage-cloub~ing rectifier. By the use of ? con';en~iona1 capacitance substitution method., d.~.elect~ic~const!ants frOrn ~ to 7 ma, be measured de' rectly with a sensitlvi'~y of 0.03 K unit. Dielectric ccns~ants thrown. 1 to 80 or more are measured with a sensitivity of -about O.2 ~ unit by a method in enrich the substance being measured is placed Within the call of three resonant circuits Resonance is attained high air as a dielectric, then bitt the liquid In question. This latter method is empi~ri-cal and ~ Taxation curve must be prepared) Measurements by either method may be completed in a very fed minutes. IS71-CL raping simple methods should increase the anal ytica]. usefulness c r this physical-. constant. ,. . ~. . . . Dielectric constants and d.ipo:Le moments there measured by Kaspu~in~ using lD cm wares. The power was supplied by a ribbon-f~.a~i~en-~ magnetrons with a lecher system of silvered copper Direst An aperiodic indicator consisting of a copper Wire loop, a crystal detector and a galvanometer was used. The second Drude method position of resonance corals be fixed With an accuracy of 0005 mm. Det;er~.i~nation of dipole momer~tsgpc, Were made With carefully purified substances, lay brie me~tod of polar solutions measuring the d:celectr7c constants of the pure co~npcnents and of solutions of various concentrations from 5 to 7~ mo1 per cents Solutions of acetic acid, ether] acetates etc. ire pure carbon ted;~achioride, benzene and carrion disu~`fi~e Were used, a:~d the values of dipole moments Were found to be ire fair agreement ~i.T'th theory. Another appl~.ca~on of radio-frequenc.~3r toy the study of the dielectric properties of solutions has heed made in the laboratories of Brown lini.versit,y3. A study eras made of systems with large dielectric losses At readily accessible rad~o-frequencies .
37 The quantities of heat generated! as a result of energy a.~bscrptJion in a radio-frequency fields by several quaternary and ternary ammonium salts in solvents of low dielectric constant were investigated calorimetrica.~.ly. This was raccor£~- plished by placing the substance in a two-electrode cell to which is affixed a capillary thermometer tube. The rate of rise of the thermometric f'uid is measu:~, as the cell is energized by the source of rad`.~-f~:equexlcies. The frequencies used Were in the range from 1.83 to 28.18 Mc. The method is simple in pr~nciplc, aid gives an absolute measurement of dielectric losses of the cell and its contents In principle the method is not new, having been used by P-arms in 19029 and k`S,T her experimenters in the 30'so The instrumentation is, however new. Measurements of dielectric constants and dissipai;~.on factors in the frequency band 100-1000 ~negacycJes have been carried cut by folksy making use of v , v ~ both of which ~disk-shaped specimens a resonant cavity method. The susceptance Variation method which has been so successfully applied in the range 104 to 10 cries is made use of in tilis range (10 to 10 cycles). Two types of re-en.trant cylindrical cavities were used, in are usea. One is a fixed car with resonant frequencies ranging from 40Q to 60o megac;'rcl.es, depending upon the size ant! the dielectric constant of the specimen. The other Thorpe has a continously variable length and was designed for a frequency range of 300 to 1oCO megacycles. It 'nas the advantage of being adjustable to the desired frequency Within this range. Calibration was accomplished empirically by measurements oil materials whose d~- el~ctric characteristics are known at frequencies on both sides of the range from 10 to 109 cycles. In spite of the fact that the calibraticn is empirical, the method has advantages over more precise ones. Measurements may be made rapidly and the calculation of' results is extremely simple. Sensitivity is so high ti!~.t very small specimens can be used, making it possible to sample direction the material to be measured. A further important advantage lies in the si~,~lplici-;~y of the specimens this minimizes the d~fficu' lies of exact spe,~irren dimen`Yior~ing as rrel:L as the possible changes in specimen material properties resu:~ting from ~.achin~ng and ~ ~ ~ 1 ~ grlnctlng operatlons. A Scheming bridge suitable for a wide range of frequencies' described by Field and Easton:, is nor! commercially available. It has direct reading ranges in capacitance from 100~ f to 1 - f at 1 Ec9 1OOf4~ f to 1100, <~- f at 100 C' lOKC and lOOKC, ancL in dissipation factor from 0.00002 to 0.56. By a substitution method capacitance from C. f to 1000 ~ ~ ~ croon be measured With internal standard, and to ~ tc ~ Pith external standards. Dissipation factors can be measured up to 0.56 X F where C' Is the capacitance of the standard condenser and Cx that of the unknowns x The substitution method may be used up to ~ Mc protruded the unknown capacitance is less than 500 tthuf. The maximum input is ~ Satin corresponding to 50 volts at 60 C or 300 volts at ~ I(C. This bridge has the practical advantage over its predecessors of being direct reading in capacitance and dissipation factor at four discrete frequencies makings possible the rapid study of the frequency characteristics of a specimen. Tt may also be used at loner, higher, and intermediate frequencies, but Without the direct reading feature. The extension of range to the higher frequencies has been made possible by careful attention to the design of th.= input transformer. The bridge is useful in ~easure- ments of capacitance and dissipation factor of capacitors, the inter-comparison of standard capacitors and the measurement of dielectric constants and dissipation
38 factor of di electr~cs. Tt is possible to discriminate between lumped and d.istriL- uted capacitance in ~ gh-value~l resiStorS9 by losing the bridge to observe the variation in characteristics of the resistors over a frequer~c~.T range. Considerable at,tex~tion was give rat durirl~ 10,47 To }nebulous of measu.re;nerlt~o:f insulation resistance of various materials and part~cu~la~y of laminates. Not. milch of this information has been published but it has keen reported. on in technicc~3 meetings. A.S.rt'.M. Gc;mmittee 3-9 has been carryln-g on a study of the rate of COl1~ ditioning of laminated materials as indicated by i.r~s~Gation resistance measurements on specimens of various shapes, the resistance being measurers bean tapered pin electrodes. Res~t,~ from several ?abc~ratories are in good agreement arcs` shoal the With the tapered pin electrodes, and by inference With arty other electrode system which does riot employ a guard- circuit to intercept; currents ogres i:;he surface of the specimens the surface currents are so large as to swamp out., the ~rol,~ur,e curreni;sO As ~t is the latter that, incLicate the progress of conditioning in the interior of the specimen, no useful ,~nfor~n`~.tion on the effectiver~e:;s of the conditior~ing cro- cedure wa~ forthcomingO Further teats on specimens provided Titan guards shoaled that at the end of 40 days in an =tmospher.~ with a relative h'~ridit,~ of 90 percent and a temperature of 35°C9 a specimen of laminated material 3,/' thick was s:ti11 not in a state of equilibriums where vv.ilk tapered pin. el-ec~Jro6~`es a sinli.ia~ spec.~men would apparently have reached equilibrium in Entree days. ~aperec?` pin electrodes are; ,sho~n to be useful' on1-`,r for discrim:Lnating between materials on a casts of surf ace character) StiG S . hilt and his associates6 have shown that ~=ee-eJec+,roc4.e disc sr~ecir:~ens feral themselves to- convenient experin~ental d.eterm~nat;ion of suffice and volume resistances, particularly where long-~.~m~? humioit,y exposure is entailed. They used e:Lecf,rodes consisting of conducting silver paints <and have shorn experimentally that such paint films are porous and cto note appreciably modify the extent or rate of moisture absorption by the specimen material. . . . .. . Hamburger and Amey7 have studied both the thecrct,ica1 and Fr~ct;~.cal. con- siderations involved in the use of such three-electrc;de disc specimens. The re;~ul~;s indicate that, by gropers pror}ortioning the s~ecim.en and electrons d.i~nens~s, a single such arrangement DIGS accurate and ~ rect evaluation of both surface and volume resisti~rities i' or Sian ranges of ambient conditions acid natal propert,;esO The principle disadvant`~4ge is that the metI~od is not readily applicable to measure- ments of volume resistivit~r parallel to the .lan~inaticus of laminated plas tic sheet materials. Iiiany investigators nor! are using silver paint electrodes in insulation resistance studies. There appears to be little doubt as to the edv?~nt`~-ges of this te?CP~iqUC. Some reports have been received, hor<Tever7 regarding undesirable e].ec- trol~yti~ voltages arising from the presence of such paint f: :Ims. Certain paints seem to be far better then others in this respects A more c~et~`iJed Study of such phenomena appears in order prier to complete acceptance of silverer paint electrodes by the various standard~.~zing agencies.
39 )3Il3LIGGF.~;FIIY ~i'i~chlar, Robert B.' Anal. Chem. 19, pp 835-1s37 (1947' 2. 7~a~putin9 A. P., J. Ex~tl Theoret. Plays. 17~ pi 30-40 (~947) (in Russians 3. ~barbaugh,, Ae H. or. Schmetzer; ''e9 Eckstron', IT. CO and Kraus: ~. A., J. Chem. Plays. 15, pp 47-54 19.7) 40 WOrkSS C. N. ;, J. drop. Physics lab pp .6Q5~612 (1947) 5. Field, R. F. and.Eastor~, I. G., General Radio Experimenter AXLE, Ago 1l' p 6 (Aprix 1947) 6. Wilt. R. K., C'i~apmar~, J. J. and Raskin, B. L.9 Morlern P'as~'cs 24 NO. 8, pp ]..51., 152 (191~7) Hamburgers Fo Jr. and A.mey, T?, G.' Annual Report of 1947 Conference on Electrical Trs1~lation9 ricer. of F.Jng'~.neering and Inclust~ri`~.1 Resea.rcil, National Research Council p 16 (Publication of the complete paper is anticipated in 1948) NOl'E - Two artic].es on in.s~;r,.~nents p~bli..shed in J-947 were cited in 'she Digest of Literature on Dielectrics For 1946. TI~e~y meres . . . . . ''A Voltmeter Which E.xtendr; the Range cuff' I:easuremen~t Ten Times - From 50 to 500 me. Alfred A. Barher Laboratories. Radio 3i, 24 (1947 Jo "U H F Signal Generator for.General Laboratory TTse. Frequency Ra,..:ge 500 to- 1350 mcO Hewlett - Packard Co., EL~0o if? '.27.9 94 (Pete. )047~;?
