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FEBRUARY 1941

.:

SUPPLY APPARATUS WITH STABILIZED VOLTAGE

a dry battery of 120 volts is used. The maximum, . current is 100 mA. ', A mains voltage variation of 5 per cent cauaes an'output voltage variation of less than 0.004 percent of the value chosen. The c.hange in the out-put voltage under the influence of the load isshown in ,fig. lOa for two different ~utput voltages.The slope' of this characteristic gives the internalresistance. For currents' greater than 30 mA this'is found to be a maxlllU:.n of 0.5 ohm at an adjust-ment on 150 volts, and 1ohm maximum at an ad-justment on 300 'volts. For' C1:lrren~ssmaller tha~30,mA the internal resistance may amount to fourtimes these values.

In fig. lOb it is shown for' two different valuesof the output voltage how the' internal impedance'of the apparatus depends' upon' the ,frequency.It may be seen that it is smaller than 1.6 ohms for

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all frequencies. The fact that at 100'kc/s the im-pedance still amounts to more than 1 ohm may beascribed to ,the series resistance of the electrolyticcondensers. At still higher frequencies the imped-ance is smaller due to the fact that in parallel withthe electrolytic condensers a paper condenseris intro-duced whose series resistance is many times smaller., The dimensions of the whole apparatus, whichis co!_posed of a'@;:tëXOl!age àp~and, the~y org~€?described" are 20X43X31 cm.The w,eight is abou\ ~9kg. In this weight iS,includedthat of the batter!~2.5 kg) which will hardly everneed to be renewe,d ~ the course of one,year. Fig. 11shows the exterior of,\he appáratus; for the sakeof comparison an accum~ator battery is also shownwhich 'gives about' the san;lC power at the samevoltage. Weight and volum),of the battery are about'three times as great.· '\. " .,' "',''"

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THE CONTROL OF CONTACT,PRESSURES

by W. WERNER

For the satisfactory functioning of 'switches,,contact jsprings, etc. it is necessary that the contactpressure should lie between certain 'limits: at toolow a pressure the transition resistance becomestoo great and the contact' spots may become toohot, at too high a pressure a too rapid wearing offmay occur upon repeated closing .of the' contact .., For each case the permissible limits of the contact,pressure can best be det~rmined experÎIn:~ni~lly.·For example, for' a certain type of mains switches.which are used in radio receiving sets, it' Was found"

that the contact pressure must liè between 60 ,aIld Fig: 1. 'Principle of the .arrangement for testing contact ..,120 g. ,pr'èssurt;s;c the switch-to be tested; a and.è auxiliarv conta~~s:. In the mass production of these switches the ,'1., ' /,' ." • ' "

question arose, as to how it is possible to find out farther, at a: certain, extension of the spring kl,rapidly and simply whether. the individual product ,; its forèe will be large énó~gh ii) overcome the' pullsatisfies the requirement given above., For ,t},le ~f k2' so that' the. contact a is then opened. If on the,determination of pressures o( sp~ings s~veral, contrary 1£2 is' much. weaker tha~' kl, then uponmethods are known: In the ,case in", question, , pulling;" contact a will first he opened' and 'onlyhowever, a particularly simple solution could be afterwards contact e. If· 1£1' is, sufficiently stiff,found which was specially adapted td the' methods contact ij will even. first be closed hefore e is opened.of mass production, by making use Ófthe ~wii:ching . The auxiliary contacts a and. b, are so adjustedaction of the contact to be tested itself. Thè prin- that a' is .öpened when thè 'contact pressure, :qt~ç,ciple of the method is represented Ï:Jl. figs. 1 and 2. is just decreased byûû g by the pulling doWït;;ä'ndIn fig. le is the switch to, be tested (diagrainmatic], " so that b is, closed whenthl:s, deérëase amourits toa and b are two adjustable auxiliary contacts. In 120 g. Thus if the, contact pressure of the switchthe initial state a and c are closed, and b op~n. in question' lie's within the desired, limits, uponWhen the lower contact strip of e is pulled down, pulling down, a will first open,' then' e ,a~d, finally

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~here is a conflict betweeti: the elasticity of thesprings kl and k2 (to which:,the ~ónÛlCt pressur~s .of e and a, respectively are proportional]. If 1£1is much weaker than 1£2 then, upon pulling, at acertain moment the ~O~!~ct',e ~ill 'open; if,pu~ed

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62 PHILIPS TECHNICAL REVIEW Vol. 6, No. 2

b will be closed (order: a open, c open, b closed).Three relays A, Band C are operated by the threecontacts a, band c, and are connected in the manner

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shown in fig. 2. On the basis of this figure oneascertains that with each of the three switchingorders mentioned the final result is that one of thethree lamps -,Oor + burns, by which means thequalification of the contact pressure being testedis obtained as "too weak", "good" or "too strong".By bending the contact springs a deviation can thenimmediately be improved.

Fig. 3 is a photograph of the apparatus as con-structed. The switch to be tested is slid into theholder M, and the upper contact strip is then placedabove the pressure finger projecting from theapparatus. Upon pressing the holder down in themanner described one of the three lamps L islighted.

Fig. 2. Connections of the apparatus. The contacts are allshown in the initial state; current hereby flows through therelays A and C but not through B. Upon flow of currentthrough a relay the corresponding switch rod (dash-dot line)is raised. Thus for example if a is opened relay A opens, withthe result that the switches Al and A2 are opened, Ao closed.Upon opening c relay C opens, the switches Cl' C3 and C4

are thus closed, and C2 and Cs opened. Upon closing b relay Bcloses and the switches B; and B2 are closed. If the switchingorder is: c open, a open, b closed, C then opens, A howeverremains closed (because Cl is now closed and a thereforeshunted), B closes; of the three lamps L only the one marked-burns. With the switching order: a open, c open, b closed,A and C open, B closes; only lamp 0 burns. With the order:a open, b dosed, c open, A opens, B closes, C remains closed(because Bl is now closed and c is shunted), and lamp +burns. Fig. 3. Photograph of the apparatus. M holder, L lamps.

.ABSTRACTS: OF RECENT ,SCIENTIFIC PUBLJCATIONS OF THEN.V. PHILIPS" GLOElLAMPENFABRIEKEN

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FEBRUARY 1941

1509: J. D. Fast: The preparation of metals bypowder metallurgy and decomposition me-tallurgy' (Öst. Chem. Z. 43, 27·33 'and48·54, Febr. and Mar. 1940). (Öriginal inGerman).

Following a consideration 'of the relationshipbetween powder metallurgy and ceramic processesand of several f~rerunners of powder metallurgy, thç·different sucóessive treatments used in the prep·'aration of hard cemented carbides' are dealt with'and the influence of gases on the sintering processis discussed. Hypotheses are hereby developedabout the coming into effect of the forces of cohesionû:I>on compression and, a~óu~ t~e part ,wlîi~h theoxide films always present on.the 'graing of thè metalpowders play in' this process. Furthermore the me-chanisin of 'the shrinkage' phenomena 'occurringUp6,ll sintering jis "studied aria, the"p~enoniena ofrecrystallisation and' coalescence' o~~ürring' at' th~same time. As an example óf the' applicátion'iofpowder , metallurg)r~·.jh.e·, preparatien .~of ductile· ~~ngste~ ;i8'd~.sc!iJ:)~d,as. "yep. a~;:the :p~el;~~atio~ oftp:e.so·éall~d: "hard ceme~ted:cär1)ides':' and seyeral

~,otÎîer-·applib~tio~~.'. ".," :'" ;:' -.:" , . " ',I '

.. Decomposition" metallurgy i~. of partienlar impor-ta~ce. in the p~eparatio:U in' a' ductile form of the~etals ~ith a high: melting point in the tita~i~mgroup. A description is given of the method used:In conclusion the preparation of pure, nickel andiron by the method of decomposition metallurgyis' discussed. .

The contents of this article have been partiallydiscussed in Philips teclin, Rev. 4, 309, 1939 (The

. ' . preparatien of metals in a compact form by pressingand sintering) and 3, 345, 1938 (Zirconium and itscompounds with a high melting point). ,

· ~510: K. F. Niessen: Calculation of the elec-trical field strength produced at a givenpoint by a half-wave aerial over a flatearth as a function 'of the total . energy'supplied to the aerial I (Physica 7, 586·602,July 1940). (Original in German).

On the basis of an example it is .explained how'the vertical electric .field at a point above a flat~arth can be calculated when the field is inducedby ~an aerial of' a half wave length,' whose lowerextremity lies above the earth's surface. It is foundpossible to express this field with the help of thetotal energy supplied to the aerial, part of- which

ted (the effective part) and the rest absorbed

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by the earth [non-effective part). The problemis first solved for the radiation. of a pure dipolewhich in the further treatment is laid at the middleof the aerial. The reflection formula, which is oftenused as an approximation in such problems, might':here le,ad to quite incorrect results.

1511: J. L. Sn 0 e k: On -theeffective length of asmall Barkhausen discontinuity (Physica7, 609·624, July 1940).

The. irreversible part of the magnetization isgiven by the product of magnitude and number ofthe so-called Barkhausen discontinuities. 'At verylow' field strengths most ferromagnctic .substancesfollow Ra ylei gh t.s law in. close approximation,according to which law the irreversible part of themagnetization with a small hysteresis loop increaseswith the square of the maximum field strength,This law furnishes a conditióJ! which "xriiistbe satis-, •• ,' no 'fied by the laws which govê'fn the 'mag1iiude and·,

- ~ ~. .number of the Bar lcha us eft; discontinv,ities. Verylittle is yet known about th~se laws; it 'ls"however,established that with decreaging field 'sf.rengtp. theBarkhausen discontinuitiés 'beéome ;~ery small.'.The path o,f the lines. of forë:,:!of such.~~{very small ''.'discontinuity can be calcu!~ted in, f,ljlvance, be-.

, ginning' with several plausible' assü!llptions.' Inthis way an "effective length" of the discontinu~tyis found, and on the basis of this it is possible to'choose the most favourable experimental val',lesfor the detection of these very small discontinuities.The calculation shows that the effective length is . :equal to the product of the reversible pernieabi~ ......and the thickness of the wire. f'. . /1512: M. .J. O. Strutt and K. S. Knol: Determi-

nations of the magnetic permeahility fr"OÎn ,~,

resistance measurements on iron wires of " ............,~,.,

varying structure at frequencies of theorder of magnitude of 108• ele., in con-nection with the magnitude of the elemen-tary zones of Wei s s (Physica 7, 63S·654,July 1940). (Original in German): <'",

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The permeability of iron wires at very high fre- .quencies can with certain assumptions be deter-mined from the ratio between A.C. and D.C. 'resistance. With the apparatus developed by the .authors the A.C. resistance of several, carefullyprepared wires is measured up to frequencies of3 X lOB cis. At room temperature the permea-bility remains nearly constant up to these frequen-cies. Upon a lowering of the temperature to -183°C,

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PHILIPS TECHNICAL REVIEW Vol. 6, No. 2'

which for these measurements is equivalent to anincrease of the frequency to about 109 cjs.; adecrease in the permeability takes place. The curves'obtained give an indication that the permeabilityat higher frequencies possibly again assumes aconstant value. The hypothesis that this behaviourmay he ascribed to a very thin non-magnetic film'on the surface of the iron wires is not confirmedby experiments with electrolytically depositedfilms of more than 10-4 ç:m thickness. A satisfactoryinterpretation is, however, possible in a manner in-, dicated by R. Beeker. This interpretation can befurther worked out with a simple model proposedby G. Heller; in particular, with' this model theorder of magnitude of the elementary: zones ofW e is s can be determined for the different wires.The results 'Obtained are compared with those ofother investigators. In. conclusion' several unex-plained problems are discussed and indicationsgiven for possible further experiments."

1513: C. J. Bakker: Het periodiek systeem derelementen (The periodic system of theelements, explanation of the plate). (Ned.T. Natuurk. 7, 305-310, Aug. 1940) ..

Thè plate 'to be explained represents the periodicsystem of .the elements. In each of the oompart-

-ments of the chart is indicated: atomic number,atomic symbol, atomic weight according, to the

,international table, electron configuration of theneutral 'atom in the usual notation, as well as the 'isotope, relations graphically. Chemically analogouselett..ents àre indicated by striking colours. Althoughboth by its arrangement of data and by its make-upthe plateis already very instructive, inthe explana-tion a further critical discussion of the electron con-figuration, isotope and radioactive properties' maybe foun'd. The latter -are also indicated in the chart

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15J.4*: J:v:-an Niekerk'a~d Miss M. S. C. Bliek:.___ D~ methodiek der vitamine-D ijking _op .

'---.... kuikens (The methods of vitamin D stan-, :---:---dardization 'on chicks) (Landbouwk. T. 52,

349-353, May, June 1940). .

*,) An adequite number of .reprints for the purpose of dis-tribution is not available of those publications marked withan asterisk. Reprints of other publications may be obtained

, on applicationsto the Natuurkundig Laboratorium, N.V.Philips' Gloeilampenfabrieken, Eindhoven (Holland),

: Kastanjelaan.

This is a communication about à demonstratienin Wag~ningen during the 10th Netherlands Agri-culture Week. In the 'standardization on rats thediffer?nce hetween animalie and vegetable vitamin,D is not manifested. This can, however, be establ-:ished in breeding chicks whereby at the same timethe i~formation is obtained whether a product,containing vitamin D is suitable .for poultry feedand perhaps for cattle feeding also. With a simplycomposed ,feed, during the first 3 to 4 weeksof life, 'rickets occur which. can easily be observed

• in an X-ray photograph on the heel joints of the- chicks. Addition of vitamin D in different coneen-trations to the feed shows a relation between theextent of the rickets and the lack of vitamin D. Apreparatien consisting entirely of animalievitaminD gives the antirachitic effect to 'the same degreeas cod liverscil. The relation mentioned betweenthe antirachitic effect and the concentration ofanimalie vitaminD given is dete~mined in a stan-dardization curve. The. exposure technique in theX-ray examination is simple, large' groups of chickscan be examined in a few hours. '

1515: E. J. W. Ver we y and J. H. de Boer: Thepotential curve of the alkali halide mole- 'miles (Rèc. - Trav. chim. Pays Bas 59,633~649, July-Aug. 1940). '

,)~o what degree the electrostatic picture of theionié bond in vapours of the alkali halides is' correctin the neighbourhood of the minimum of the poten-tial curve ~s,investigated for three points, namely:1) the nuclear distances at absolute zero calculatedfrom atomic distances' determined with the helpof electron diffraction at 1200 °C.in the vapour a~dthe atomic _distances in the corresponding crystallattices, 2): the fundamental frequenci~s' ,of theatomic vibrations, calculated from the potentia~,curves compared with the values from, the spectra,and 3) the binding or molecular energies at absolute

\ , . .zero compared with thermal data. The expressionfor th~ energy U = -e2jr + bJrn with n=',Ü givesa correct picture. By taking 'into account the po-,'larizations the picture is .improved, and the molec-, ''ular : energies .can also hé calculated accuràtelywithin the errors of obs~rvatioiI. For all alkalihalidesn, = 12 is then found to he the best valu~:..The exponential repulsion according to Born andMayer is foundjncapable of being used. "

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