Konel — A substitute for platinum
2
Pi to ν! PI To reduce the probable error in the measurement of one commodity only, is obviously of negligible benefit. It is evident also that the probable errors in the measurement of the various commodities logically should be the same. Commodities purchased by weight are weighed on a scale with a probable error of perhaps 0.5 per cent, as the scales ordinarily are used; commodities purchased by volume are measured or metered to within perhaps 0.5 per cent also. It would seem, then, that unless electric power is by far the largest commodity pur- chased, it will be impractical to meter it to an accuracy better than that attained in the measurement of other commodities supplied. ob a? a. A 7 / y R -B. Pi 2 + P 2 2 Pi 2 + P2 2 2n 1 per cent for the individual = 0.22 per cent for the total. If Pi = P 2 = 0.5 per cent and = 5 0 (a more usual case) the probable error will be 0.5 per cent for the individual but only 0.07 per cent for the total. This aggregate error of 0.07 per cent is within the limits of precision accuracy; still 0.5 per cent represents a reasonable accuracy which may be expected in most cases. From the foregoing it may be seen that the resultant probable error decreases in the same proportion as do the errors Pi and P 2 . If the probable individual error and the probable total error in meter registration are plotted against Pi, assuming P 2 to remain constant at 1 per cent, curves A, Fig. 3 are obtained. If Pi = P 2 , curves result as Pi and P 2 vary together. The curves A show that if P 2 = 1 per cent, it does little good to reduce Pi below 1 per cent, since reducing it to zero reduces the total error to only 0.71 per cent. As a final conclusion it appears a well established fact that no certain advantage is to be expected from more accurate metering apparatus than now is available. That accuracy better than 0.5 per cent in a meter or current transformer is of no commercial advantage has been amply demonstrated. Furthermore, this conclusion is supported by the fact that current trans- former errors cannot be measured with present com- mercial testing apparatus with much better accuracy than 0.1 per cent in ratio and 5 min. in phase angle. Consequently, attempts to meet accuracies of better than 0.5 per cent generally result in arguments which never are settled satisfactorily. I PER CENT PROBABLE ERROR IN TRANSFORMER Fig. 3. Probable error in registration for different current-transformer and watthour-meter errors — probable error in current transformer Pi = probable error in watthour meter element . 2 constant at 1 per cent B. P 2 = Pi Konel— A Substitute For Platinum To return to the expressions for probable error in meter registration, and to consider numerical examples: ρ 2 j ρ 2 Individual probable error = * — Total probable error = * | — λ 2 If Pi = P 2 = 1 per cent and = 2 0 , (a small number) the probable errors are A MAN set out to find a cheap substitute for platinum. He was so successful that for almost a year his results were not taken seriously. Oxide-coated filament for radio tubes was known as early as 1904; platinum as a core appeared to be the best material for life, strength, and emission of electrons. From Research Narratives, May 15, 1931, published by the Engineering Foundation, 29 W. 39th Street, New York, . Y . Based on information supplied by Erwin Foster Lowry, Ph. D., research physicist, Westinghouse research laboratory, East Pittsburgh, Pennsylvania. AUGUST 1931 659
Transcript of Konel — A substitute for platinum
Pi t o ν! P I
η To reduce t h e probable error in t h e m e a s u r e m e n t of one commodi ty only, is obviously of negligible benefit . It is ev ident also t h a t t he p robable errors in t h e measurement of t h e var ious commodi t ies logically should be t h e same.
Commodi t ies purchased b y weight a re weighed on a scale wi th a p robable error of pe rhaps 0 . 5 per cent , a s the scales ordinar i ly a re used; commodi t ies pu rchased by vo lume are measured or metered to wi th in p e r h a p s 0.5 per cent also. I t would seem, then , t h a t unless electric power is b y far t h e largest c o m m o d i t y pu r chased, i t will be impract ical t o me te r i t t o an accuracy bet ter t h a n t h a t a t t a ined in t h e measu remen t of o the r commodities supplied.
o b
a ? a.
A
7 λ /
y
R - B .
Pi2 + P 2
2
Pi 2 + P22
2n
1 pe r cen t for t h e individual
= 0 . 2 2 per cen t for t h e t o t a l .
If Pi = P 2 = 0 . 5 pe r cen t a n d η = 5 0 (a more usua l case) t h e p robab le error will b e 0 . 5 pe r cent for t h e ind iv idual b u t only 0 . 0 7 pe r cent for t h e t o t a l . Th i s aggrega te error of 0 . 0 7 pe r cen t is wi th in t h e l imits of precision accuracy ; still 0 . 5 per cen t represents a reasonable accuracy which m a y be expected in mos t cases.
F r o m t h e foregoing i t m a y be seen t h a t t h e r e su l t an t p robab le error decreases in t h e same propor t ion as do t h e errors Pi a n d P 2. If t h e p robable individual error a n d t h e p robab le to t a l er ror in me t e r regis t ra t ion a re p lo t t ed aga ins t Pi, a ssuming P 2 t o r emain cons t an t a t 1 pe r cent , curves A , Fig. 3 a re obta ined . If Pi = P 2, curves Β resul t as Pi a n d P 2 v a r y toge ther . T h e curves A show t h a t if P 2 = 1 pe r cent , i t does l i t t le good t o reduce Pi below 1 pe r cent , since reducing i t t o zero reduces t h e to ta l er ror t o only 0 . 7 1 per cent .
As a final conclusion i t appea r s a well establ ished fact t h a t no cer ta in a d v a n t a g e is t o be expected from more accu ra t e me te r ing a p p a r a t u s t h a n now is avai lable . T h a t accuracy b e t t e r t h a n 0 . 5 pe r cent in a m e t e r or cu r r en t t rans former is of no commercial a d v a n t a g e has been a m p l y demons t r a t ed . F u r t h e r m o r e , th i s conclusion is suppor ted b y t h e fact t h a t cu r ren t t r ans former errors canno t be measured wi th presen t commercia l t es t ing a p p a r a t u s wi th m u c h b e t t e r accuracy t h a n 0 . 1 pe r cen t in ra t io a n d 5 min . in phase angle. Consequent ly , a t t e m p t s t o mee t accuracies of b e t t e r t h a n 0 . 5 pe r cent general ly resul t in a r g u m e n t s which never a re set t led satisfactori ly.
I PER C E N T P R O B A B L E ERROR IN T R A N S F O R M E R
Fig. 3. Probable error in registration for different current-transformer and watthour-meter errors
Ρ ι — p r o b a b l e error in current t rans former Pi = p r o b a b l e error in w a t t h o u r m e t e r e l e m e n t Α. Ρ2 c o n s t a n t a t 1 per c e n t B . P2 = Pi
Konel— A Substitute For Platinum
To r e t u r n to t h e expressions for p robab le er ror in meter regis t ra t ion, and t o consider numerica l examples :
ρ 2 j ρ 2 Individual p robable error = * —
Tota l p robab le error = * | — λ 2 η
If Pi = P 2 = 1 per cent and η = 2 0 , (a small number )
the probable errors a re
A M A N set ou t t o find a cheap subs t i t u t e
for p l a t i n u m . H e was so successful t h a t for a lmos t a yea r his resul t s were n o t t a k e n seriously.
Oxide-coated filament for r ad io t ubes was k n o w n as ear ly as 1 9 0 4 ; p l a t i n u m as a core appeared t o be t h e bes t mate r ia l for life, s t reng th , a n d emission of electrons.
F r o m Research Narratives, M a y 15, 1 9 3 1 , p u b l i s h e d b y t h e E n g i n e e r i n g F o u n d a t i o n , 2 9 W . 3 9 t h Stree t , N e w Y o r k , Ν . Y . B a s e d o n i n f o r m a t i o n s u p p l i e d b y E r w i n F o s t e r L o w r y , P h . D . , r e s e a r c h p h y s i c i s t , W e s t i n g h o u s e re search l a b o r a t o r y , E a s t P i t t s b u r g h , P e n n s y l v a n i a .
A U G U S T 1 9 3 1 6 5 9
In 1925, five years after radio broadcas t ing had aroused publ ic imaginat ion, tubes were being m a d e in ever-increasing quant i t ies with p l a t i num or p l a t i n u m -ir id ium core filament. P l a t i n u m people were overjoyed, b u t no t makers of tubes . Mate r ia l for filaments was costing $186 an ounce.
Dr . E . F . Lowry, research physicist of t h e Wes t ing-house research labora tory , unde r took a search for a cheaper subs t i tu te . I ron, nickel, n ichrome, t ungs t en , var ious ferrous alloys a l ready were pronounced w o r t h less. All had a poisonous effect on emission or h a d proved mechanical ly weak. B u t nickel looked good t o Lowry in spi te of i t s r epu ted mechanical frai l ty.
T h e first filament of pu re nickel gave surpr is ing resul ts . Emission appeared t o be as good as w i th p l a t i num cores; no more t rouble arose from mechanica l failures. Scientists, t u b e manufac turers , even colleagues, hes i ta ted to believe t h a t t h e first a t t e m p t h a d succeeded when h i the r to undisputed a u t h o r i t y had p ronounced nickel no be t t e r t h a n o ther meta l s . Agains t c la ims t h a t nickel filaments should have a life of only 80 hr. , L o w r y produced tubes on life tes ts for 1,500 hr . a n d still b u r n ing. B u t none of his nickel filaments were m a n u factured commercial ly.
Convinced t h a t he was working in t h e r igh t direct ion he t r ied 20 per cent cobal t ; t h e crystal l ine s t ruc tu re was unsat isfactory and could n o t b e d rawn . T h e case looked hopeless when he t h o u g h t of t h e qual i t ies of cobal t - ferrot i tanium (a compound of iron and t i t a n i u m ) wire used in exper iments several years previously . T h e first filament of nickel, cobalt , and fe r ro t i tan ium, in p ropor t ion of 80, 20, and 10, gave resul ts b e t t e r t h a n ever before. H u n d r e d s of exper iments h a v e since been m a d e , b u t t h e alloy used t o d a y is essential ly t h e s ame as t h a t produced b y Lowry ' s first a t t e m p t .
H e n a m e d t h e new meta l "kone l , " and in December 1926 persuaded t h e West inghouse L a m p C o m p a n y t o m a k e 50 commercial tubes wi th i t as filament core. A b o u t t h e same t ime, t h e manufac tu re r s discovered t h a t Lowry was r ight also a b o u t nickel a n d s t a r t ed t o use t h a t for filaments. Wi th in a yea r every m a n u facturer ceased t h e use of p l a t i num in rad io tubes , a n d none has used i t since. P la t inum- i r id ium cost $1,600 pe r lb . ; konel costs a few dollars.
Use of konel n o t only appreciably increased t u b e life (operat ing 175 deg. colder t h a n p l a t i num filament), b u t also showed definitely t h a t t h e filament core h a d a m a r k e d influence on emission. A new theo ry of elect ron emission from oxide filaments has been formula ted ; on th i s work t h e discoverer is now engaged.
Konel is ha rde r t o forge t h a n high-speed steel a n d is ve ry tough a t high t empera tu res , when m o s t me ta l s lose the i r s t rength . I t is extremely res i s tan t t o m o s t acids, does no t spu t te r , does no t scale like iron u n d e r hea t , a n d has a high electrical resis tance. These unusua l character is t ics give promise of m a n y uses outs ide radio tubes . I t is an electric furnace p r o d u c t of ex t reme pur i ty .
Mutual Impedance
of Grounded Wires
A formula is given for the mutual impedance between two insulated wires of negligible diameter lying on the surface of the earth and grounded at their end-points.
By R. M. FOSTER A m e r i c a n T e l . & M e m b e r Α . I . Ε . E . T e l - C o - N e w Y o r k
W Ε A S S U M E t h e e a r t h t o be flat, semi-infinite in extent , of un i t permeabi l i ty , of negligible dielectric cons tan t , a n d of uniform conduc t iv i ty λ, using c. g. s. e lec t romagnet ic un i t s . T h e air is also assumed to b e of u n i t pe rmeabi l i ty a n d of negligible dielectric cons t an t . All d i sp lacement cu r ren t s a re t h u s neglected b o t h in t h e ea r t h a n d in t h e air . Th i s is t h e a s sumpt ion which is ordinar i ly m a d e as a first approx imat ion a t power frequencies for t h e shor te r t ransmiss ion lines.
T h e m u t u a l impedance be tween circui ts consist ing of insu la ted wires of negligible d i ame te r lying on t h e surface of t h e ea r th a n d grounded a t the i r end-poin ts is t h e n found to b e
Z l 2 = 2V\ S f j dSds ( ~7~ )
cos € ] + -3 [1- (1 + yr)e-^] \dSds(l)
T h e in tegra t ions a re ex tended over t h e two wires S and s, the i r e lements d S a n d d s be ing separa ted b y t h e dist a n c e r a n d m a k i n g t h e angle e w i th each o ther . In th i s formula γ = ( ί 4 τ λ ω ) κ is t h e p ropaga t ion c o n s t a n t in t h e ea r t h for p lane waves which v a r y wi th t h e t i m e as eiœt, where ω = 2 π t imes t h e frequency a n d i = ( - 1)K.
Th i s m u t u a l impedance formula (1) m a y be wr i t t en in t h e equ iva len t form
Z l 2 = f f i · dSds ( ~ )
cos e f 2 1 ι + i œ ~ V J T T ^ t i - a + T ^ L J jdSds (2)
T h e complex factor
2
F r o m " M u t u a l I m p e d a n c e o f G r o u n d e d W i r e s L y i n g o n t h e Surface of t h e E a r t h , " Bell System Technical Journal, J u l y 1 9 3 1 .
660 ELECTRICAL E N G I N E E R I N G
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