the development of the time bridge astronomical photometer · the following block diagram (see fig....
TRANSCRIPT
The development of the timebridge astronomical photometer
Item Type text; Thesis-Reproduction (electronic)
Authors Kesselman, Martin Samuel, 1923-
Publisher The University of Arizona.
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THE DEVELOPMENT OF THE TIME BttlDGE
ASTKONOMICAL PHOTOMETER
by
M artin S.’ Keggelnan
A T hesis
su b m itted to th e f a c u l ty o f the
D epartm ent o f Physics
in p a r t i a l f u l f i l lm e n t o f th e
req u irem en ts f o r th e degree of
MASTER OF SCIENCE
in the G raduate C o lleg e , U n iv e rs ity of A rizona
1950
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TABLE OF CONTENTS
I . In tro d u c tio n :
1. S ta tem en t o f problem2 . P h o to e le c t r ic method in
s t e l l a r photom etry3 . H ie ;tim e b rid g e as a s t e l l a r
photom eter
I I . Theory and o p e ra tio n o f the tim e b r id g e photom eter- c r
page
1 . The b r id g e c i r c u i t analogy ' ^2 . The req u irem en ts f o r a tim e b r id g e 3* B r ie f e x p la n a tio n o f th e v a rio u s
c i r c u i t s4 . B lock diagram : 9
Power Supply . ‘ " ■ ■ "
: ! • V oltage r e g u la t io n 132• V oltage r e g u la t io n curve 163 . S t a b i l i t y m : 17
IV . Development o f th e in p u t c i r c u i t
1 . Hie m onostab le m u l t iv ib r a to r 1@2 . E xperim en ta l d e lay g a te 203 . C o n d itio n s f o r s ta b le o p e ra t io n 214 . Hie in p u t d e lay g a te 235 . O p era tio n s and waveforms 246 . D e te ra in a t io n o f k 2®
. 7 . S e n s i t iv i ty curves’ - 338 . P h an ta s tro n d e lay c i r c u i t 359 . O p era tio n and waveshape 37
V. C onclusion ' t = - , 43
V I. B ib lio g rap h y
219766' 6 6
r-4 01 10
to b- r-
INTRODUCTION
The o r ig in a l id e a f o r th e tim e b rid g e photom eter wae
th a t o f D r. R. E. Corby o f th e D epartm ent o f Physios a t th e
U n iv e rs ity o f A rizona, th e o r ig in a l work h av in g been done
by W.H. P arker in 1948• The work was co n tin u ed and f u r th e r
improvements e f f e c te d by S • Becker in 1949.~ The p re s e n t
problem was u n d ertak en in an e f f o r t to s t i l l f u r th e r improve
and r e a l i z e th e f u l l c a p a b i l i t i e s o f th e in s tru m e n t. One o f
th e c i r c u i t s , developed by Mr. B ecker, em ploying th e tim e
b r id g e p r in c ip le showed g r e a t prom ise a t low l i g h t l e v e l s .
I t was th e re fo re d ec id ed t h a t a d d i t io n a l r e s e a r c h sh ou ld be
c a r r ie d b u t to ad a p t th i s p r in c ip le o f th e bridge to s t e l l a r
pho tom etry . In th e o r i g i n a l in s tru m e n t, d i f f i c u l t y was
en co u n tered in co u p lin g th e o u tp u t o f th e p h o to m u lt ip i ie r
tu b e to th e r e s t o f th e tim e b r id g e . To accom plish th i s
co u p lin g D.C. a m p lif ie r s were u se d , and s e r io u s problem s in
s t a b i l i t y were in tro d u c e d . !Bie l im i t in g f a c t o r in th e p re
v ious equipm ent was s t a b i l i t y . T h ere fo re th e p re s e n t program
1 . "Development o f an E le c tro n ic P ho tom eter", W.H. P a rk e r , T hesis p rep ared in D ept, o f P h y sio s , U niv . o f A rizona 1948. U niv. L ib . G a ll #E9791.
2 . "P ho tom etric M ethods", S . B ecker, T h esis p rep a red in Physics D epartm ent, U niv. o f A riz o n a ., 1949, t r i v .
‘LibraT*;' I'r ,■ ' ■ i :
2
had a (tw ofold p u r p o s e : . to .d e v e lo p a new in p u t c i r c u i t In
o rd e r t h a t r th e coup ling from . th e p h o to m u lt ip l ie r tube may
be accom plished by a more d i r e c t m ethod; and to in c re a s e th e
o v e r a l l s t a b i l i t y o f th e e q u lp n e n t.
S in ce , th e tim e b r id g e is , to_ be used f o r s t e l l a r photo
m e try , a; survey o f th e problem s in v o lv ed and tech n iq u es used
w i l l be c o n s id e re d . Photom etry , had i t s o r ig in in , 1915 when
E ls t e r and G e lte l developed th e f i r s t u s e f u l p h o to tu b e .
S ince t h a t th n e : th e gas p h o to m u lt ip l ie r and f i n a l l y th e
m u ltie le m e n t p h o to m u lt ip l ie r have been dev e lo p ed . I t la
t h i s l a s t m entioned tube which was used in th e tim e b r id g e .
The m easurem ent. o f s t e l l a r l i g h t i n t e n s i t i e s i s in h e re n tly
d i f f i c u l t s in c e th e l i g i t energy in v o lv ed i s o f th e o rd e r o f
5X101.% w a t t s . This i s th e amount o f l i g h t t h a t i s c o l
le c te d by eye from a s t a r t h a t i s j u s t v i s i b l e , and, a s t r o
nom ically sp eak in g , a b r ig h t s t a r . ^
The p h o to e le c t r ic m ethods u sed in astronom y a re th e
fo llo w in g : : : ̂ ^ ^ ...
(a) vThe..".output c u r r e n t o f a p h o to m u lt ip l ie r tube i s
a p p lie d d i r e c t l y to a s e n s i t iv e g a lv an o m eter. T h is . i s an -ex
trem ely s e n s i t iv e m ethod, W t d i f f i c u l t to ..do s in c e i t . i s
n ecessa ry to r e f r i g e r a t e th e p h o to m u lt ip l ie r tube i f very4 ............
sm a ll l i g h t I n t e n s i t i e s a re to be d e te rm in ed .
3 . " P h o to e le c t r ic Phenomena*, Hughes & D uBridge, p . 3 5 .
4 . " E le c t r o n ic s ' in Astronomy", G.E. K ro h ,.E le c tro n ic s v o l . 2 n o . 8 Aug. 1948 p . 101.
3
I r h :.n Llj-: i.: • ' ' \ - «■: ; : '(b) D.C. a m p lif ie r s a re used to am plify th e sm a ll
c u r re n ts in v o lv e d , and a continuous re a d in g i s p o ss ib le*
Hie s e n s i t i v i t y o f th is method i s l im ite d by s t a b i l i t y f a c
to r s •
(cj A.C• a m p lifiers are used when the l i $ i t s tr ik in g
th e p h o to c e ll i s m ech an ica lly in te r r u p te d . The o u tp u t ou r-y:. ■ :. A o;. T.f - '-v: '■ c •:u;- , :r e n t o f the p h o to m u ltip lie r i s p u ls a t in g and e x i s t in g A.C.
a m p lif ie r tech n iq u es a r e u se d . G re a te r s t a b i l i t y and s e n s ! -: " -fi , • • V : J “ ” . •. r': - ' /'e' ' r >-* " * ‘ 1 ' V- r- . ; „ *-• . *• • ' • . . - * . *•
t i v l t y 1# 'pb# mlble" w ith ' till#''"'type Inmtikimeht then li: posmible
w ith D.C. a m p l i f ie r s • To d a te th i s in s tru m e n t is th e b e s t*
o f a l l th o se tech n iq u es which r e q u ir e a c o n s ta n t read ing*t * 1 ! V' '"V 1 " i ; ; - f. P, ' ■ ^ 'j ‘ * i •> i <" ̂' T t - ' f*. "* " 3 ; - * - - ;; -. '•*. ‘ - * ' =
(d) A ccum ulation M ethod: The o u tp u t c u r re n t o f the
m u l t i p l i e r tube ' i s u sed to ch a rg e’ a condenser vh io h is th en
d isch a rg ed th ro u g h a g a lv an o m ete r. Though more in c o n v en ie n t
then th e c o n s ta n t re a d in g ty p e in s tru m e n ts , i t i s co n s id e red
a s u p e r io r m ethod.
Having co n s id ered th e v a r io u s methods and t h e i r r e l a
t iv e m e r i t s , i t would seem d e s i r a b le to in d ic a te What ch a r
a c t e r i s t i c s th e tim e b r id g e has which would make i t d e s i r a b le
from th e a s tro n o m ic a l s ta n d p o in t . The tim e b rid g e g iv es a
con tinuous re a d in g vh ioh makes i t a co n v en ien t in s tru m e n t.
F urtherm ore i t i s o f th e accum ulation type w hich, as in d ic a te d
p re v io u s ly , i s d e s i r a b le . S ince the astronom er is u s u a l ly
5 . Sm ith , J . , The L im itin g M agnitude O bservab le w ith aP h o to e le c tr ic S t e l l a r Photom eter, A s tro p h y s io a l Jo u rn a l 176:296, (1932).
4
Ntin te r e s te d in th e average v a lu es o f i n t e n s i t i e s r a th e r than
th e in s ta n ta n e o u s v a lu es (which a re g iven by a l l methods
ex cep t th e accum ulation m ethod) the tim e b r id g e i s u n u su a lly
d e s i r a b le . The o p e ra t io n i s as fo llo w s . The p e r io d o f o p e r
a t io n i s 1 /60th o f a second . W ith no 11^ t f a l l i n g on th e
p h o to m u ltip lie r tu b e , a p u lse i s g en e ra ted which i s seme
f r a c t io n o f th e p e rio d o f o p e ra t io n . I t i s added to a nega-
t iv e p u lse a c ro ss th e tim e b rid g e and a zero o u tp u t r e s u l t s •
However, when l i g h t i s f a l l i n g on th e pho to tu b e th e condenser’ V.;-; V". 7'b.charges up a d d i t io n a l ly d u rin g th e same f r a c t io n o f th e p e r -
•• > •• • ' ; " > * ' • • - ' t • ' • •• — , ...- - ■' ' - - » - • «■ •» "• • - * ' L-:. i." «. «• .. • . • -- 1 "
io d to cause a w ider p u ls e . Now th e tim e b r id g e has an■' - V. •, C-p -y- V V f l ■ I."--': ; : . .o u tp u t w hich i s a p o s i t iv e p u lse r e p r e s e n t in g th e energy
t h a t f e l l on th e p h o to tube d u rin g th a t f r a c t io n o f th e p e r io d <r." :: - : v. " pr Iv-V;'. - p ■- vh:; - v r;:.-
This p u lse i s in te g r a te d and i t g iv es a m e te r re a d in g . % eV- ;:m e te r re a d in g r e p re s e n ts th e in te g r a te d v a lu e o f th e l i g h t
in te n s i f y
\' v
V
l on'
i ; %
I" / c;. y ■■ * - '• ’ « : •.
v - r '
b o i '
v:- : ■;:
Cb - . r . :
5
I I
.
THEOKY AND OPEttATIOH OF THE
TH E BHIDOE PHOTOMETER
The tim e b rid g e may be d e f in e d ae an in s tru m e n t whieh
i s capab le o f i n t e r p r e t in g v o lta g e changes as changes in
tim e . Though tim e may be in no way connected w ith th e
in fo rm a tio n which th e d ev ice r e c e iv e s , th e in fo rm a tio n re n -\
dered i s p ro p o r t io n a l to th e in p u t , b u t th e p aram ete r i s
now tim e . C onsider th e o rd in a ry b r id g e c i r c u i t ( in f i g .
2 -1 ) in which th e r e s i s t o r s R3 arid S4 have been a d ju s te d to
g iv e no rea d in g on th e g a lv an o m eter. I f th e sw itc h ac ro ss
K3 were to be. c lo se d , D would r i s e very r a p id ly to seme
h ig h e r p o te n t i a l and th e m e te r would read c o rre sp o n d in g ly .
The sw itch a t R3 i s now opened, C r i s e s in p o t e n t i a l , and
th e e q u ilib r iu m c o n d itio n i s r e s to r e d . The rea d in g depended
on th e d i f f e r e n c e in th e tim e in t e r v a l between th e o ccu rren ce
of th e v o lta g e changes. The b r id g e i s th e r e fo r e s e n s i t iv e
to ev en ts which o ccu r a t d i f f e r e n t t im e s . I f b o th sw itch es
were to be o p e ra ted s im u lta n eo u s ly then th e m e te r would f a i l
to in d ic a te . I f one o f th e sw itch es o p e ra te s a f t e r th e o th e r
then a re a d in g r e s u l t s . I t i s s i g n i f i c a n t to n o te th a t th e
sw itches m ust be in a p a r t i c u l a r p o s i t io n b e fo re a re a d in g
w i l l r e s u l t . I t i s th e re fo r e n e c e ssa ry to s e t th e system
a f t e r each s e r ie s o f e v e n ts . I f th e sw itch es a re re p la c e d
A -h
C 1//
by s u i t a b le ooRtroX c i r c u i t s i t i s p o s s ib le to b u ild a tim e
b r id g e . By analogy to the above, i f a f ix e d p o s i t iv e p u lse
i s g en e ra ted and a p p lie d to A/ arid a h e g a tiv e p u lse i s s im u l-
ta n eo u s ly g en e ra ted and a p p lie d to B, th e b r id g e rem ains ;
b a lan ced . : I f th e - p o s i t iv e p u lse a p p lie d to A i s now allow ed *
to vary in w id th so as to exceed the n e g a tiv e p u ls e ^ e n th e
d i f fe re n c e w i l l be in d ic a te d . The tim e b r id g e then m ust have
a means of g e n e ra tin g s i» u I ta r ie d u e ly two p u lse s o f o p p o s ite
p o l a r i t y . There mus t a ls o be p ro v is io n f o r th e v a r ia t io n o f
one p u lse w ith some in p u t s ig n a l . % e d i f f e r e n c e between
th e two p u lse s m ust be d e te m in e d and th i s "d iffdrarice used
to o p e ra te seme c o n v e n ien t in d ic a to r such aS a m il l ia m e te r .
The fo llo w in g b lo ck diagram (See F ig . 2^2) "wi1! ! i l l u s t r a t e '
th e r e la t io n s h ip o f each c i r c u i t w ith r e fe re n c e to th e -o th e r s .
S in ce i t i s Im p o rtan t t h a t th e l i g h t from a s t a r be used to
vary th e o u tp u t o f th e p o s i t iv e g a te , a pho to tube i s in d i
c a te d . The b lock diagram i s p e r f e c t ly g e n e ra l , and i t i s in
th e ad a p tio n o f the g e n e ra l p r in c ip le to a p a r t i c u l a r fu n c tio n
th a t th e method o f v a r ia t io n need be c o n s id e re d .
The fo llo w in g w i l l e x p la in th e o p e ra tio n o f th e v a rio u s
c i r c u i t s . The e x p la n a tio n w i l l n e c e s s a r i ly be b r i e f s in c e
many o f th e se c i r c u i t s were used by Mr. Becker in h is o r ig
in a l work bn t h i s in s tru m e n t. R efe ren ce w i l l be made to th e
& "P ho tom etric M ethods", S . B ecker. U. o f A. T hesis 1949. x. '
8
sch em a tic , f i g . 2 -3 . .
The t r ig g e r g e n e ra to rs d e s ig n a te d as T ^ , TgA>T^g, and
Tgg in th e schem atic a re b ia se d beyond c u t - o f f , to th e
ex ten t, t h a t only upper t i p o f th e v ary in g s in u s o id a l in p u t
w i l l cause conduction to tak e p la c e . The o u tp u t o f th e f i r s t
tube i s n e g a tiv e , and i t i s coupled th rough th e c a p a c ito r
to th e cathode r e s i s t o r o f th e fo llo w in g s ta g e , which i s
a ls o beyond c u to f f . D i f f e r e n t i a t io n ta k es p la ce and p o s i
t iv e p u lse s on ly a re a c c e p te d . The e f f e c t then i s to p ro
duce a n e g a tiv e p u lse which may be used to key th e rem ain ing
c i r c u i t s . The p u lse developed i s 150v in m agnitude and 600
m icroseconds wide a t the b a se .
The t r i g g e r p u lse i s fed to th e v a r ia b le p u lse g en era
t o r , Ty to T ig . The o p e ra t io n o f th i s g a te w i l l be co n s id e red
in d e t a i l in C hap ter I I I .
The f ix e d n e g a tiv e g a te , d e s ig n a te d as tu b es 3 , 4 , 5
and 6 in th e sch em a tic , in th e q u ie s c e n t s t a t e , has tubes
5 and 6 conducting h e a v i ly . Bie n e g a tiv e p u lse i s a p p lie d
to Tc which in tu rn coup les a la rg e n e g a tiv e p u lse to tu b e 5 : . , ! : i
6 . The n e g a tiv e v o lta g e coup led tiurough th e condenser tu rn s ' / ' ....... - " ; % :6 o f f and th e a c tio n i s m a in ta in e d , s in c e th e drop in c u r re n t
due to 6 , th rough i t s common cathode r e s i s t o r , allow s 4 to
conduc t, thus h o ld in g th e p o te n t i a l a c ro s s th e cathode r e
s i s t o r in 5 down. This a c t io n co n tin u es u n t i l such tim e as
the charge on th e condenser can be n e u t r a l iz e d th rough th e
h ig h r e s is te n c e in th e g r id c i r c u i t o f tube 6 . As soon as
P kof
Q e n e r + 4
Fig 2 2 B / ock D i a g r a m
10
th e g r id r i s e s s u f f i c i e n t l y , tube 6 conducts and th e g a te
r e v e r t s to th e i n i t i a l c o n d i t io n s • a p ro v is io n was made in
t h i s g a te to vary i t s w id th by means o f a v a r ia b le condenser
in th e g r id c i r c u i t o f T6. The m atch ing o f th e two p u lse s
i s now accom plished in th e f ix e d g a te by i t s m anual v a r ia
t i o n . This has th e advan tage o f h o t d i s tu r b in g th e o p e ra
t in g p o in t o f th e v a r ia b le g a te as was done p re v io u s ly . The
b e s t o p e ra t in g p o in t f o r th e v a r ia b le g a te may be chosen
f o r maximum s e n s i t i v i t y , and i t rem ains f ix e d .
The o u tp u t o f th e two g a te s a re how added th rough th e
u se o f th e .b r id g e . By re fe re n c e to f i g . 8 - 1, i t can be seen
th a t co rresponds to 5QK r e s i s t o r in th e p la te c i r c u i t o f
Tio and th e r e s i s ta n c e th rough th e power su p p ly . Rg c o r re s
ponds to th e 1 0 0 K ,re s is to r in th e cathode c i r c u i t o f Tg, and
Rg and R4 co rrespond to th e 1 Megohm and th e 50K r e s i s t o r
r e s p e c t iv e ly . The s e le c t io n o f th e v a lu e s o f Rg and R4
depend on th e r e l a t i v e am p litu d es o f th e r e s p e c t iv e p u ls e s .
The n e g a tiv e p u lse has an am p litu d e o f 185 v o l ts and th e
p o i.i t iv e p u lse i s 200 v o I ts in am p litu d e . The o u tp u t o f th e
b rid g e i s a p o s i t iv e p u lse when l i g h t i s a c t in g on th e photo
c e l l . This p o s i t iv e p u lse i s coupled to th e p u lse a m p lif ie r
and th e r e fo r e i t i s n ecessa ry to b ia s th e a m p lif ie r so th a t
i t i s c u t o f f , to in s u re th e a m p lif ie r w i l l on ly accep t p o s i
t iv e p u ls e s . I f th e a m p lif ie r can accep t e i t h e r p o s i t iv e o r
n e g a tiv e p u lse s , i t i s d i f f i c u l t to s e t th e o p e ra t in g p o in t w ith
11
7 •no s ig n a l In p u t . A f te r p a ss in g th rough th e second a m p lif ie r
a p o s i t iv e puls© i s a p p lie d to th e g r i d >o f th e 616
The a m p lif ie r s have se rv ed a n o th e r p u rp o se , namely th a t o f
nc lean in g " up th e p u ls e .
The o u tp u t tube accep ts th e p o s i t iv e going p u lse s and
an in te g r a t io n i s perform ed in th e p la te c i r c u i t . That i s
to s a y , i f th e tube i s co n s id e red as a r e s i s t o r w ith a v a ry
in g v o lta g e a p p lie d a c ro s s th e r e s i s t o r and co n d en ser, which
a re in s e r i e s , and i f th e o u tp u t i s ta k en ac ro ss th e conden-8
s e r , t h a t o u tp u t i s the in te g r a te d in p u t . B a s ic a lly th e
s i t u a t i o n i s as fo llo w s : i f
e ( t ) * 1kp4 q/C and q/C « i R p ( l )
th en i t can be shown th a t
Q u a l i ta t iv e ly a l l th e c i r c u i t s have been co n s id e red
excep t t h a t o f th e p h o to m u lt ip l ie r tu b e . Any o f th e m u l t i
p l i e r tu b es may be used as th e 1P21 o r th e 1P22 depending on
th e w avelengths and s e n s i t i v i t i e s d e s i r e d . E i th e r a b a t te r y
shou ld be used o r a w e ll r e g u la te d power su p p ly . The h ig h
v o lta g e power su p p ly used w ith th i s in s tru m e n t i s sch em a ti
c a l ly re p re s e n te d in th e schem atic f o r th e e n t i r e su p p ly .
7 . "P ho tom etric M ethods, S . B ecker", U n iv e r s i ty o f A rizonaT h e s is , (1949). •
8 . " E le c tro n ic C irc u its and Tubes", C ru f t E le c tro n ic s S t a f f , p . 147, McGraw-Hill Book Company, In c . (1 9 4 7 ).
12
The o u tp u t o f th e p h o to m u ltip lie r was ta k en ac ro ss one o f
th e r e s i s t o r s In th e s e n s i t i v i t y c o n tro l w hich a re In s e r ie s
w ith dynode n in e .
13
I I I
POWER SUPPLY
As s ta te d in th e in t r o d u c t io n , th e prime purpose o f
t h i s work was to d ev e lo p a new in p u t c i r c u i t and to in c re a s e
o v e r a l l s t a b i l i t y * I t was reco g n ized e a r ly in th e problem
th a t th e d e te rm in in g f a c to r in s t a b i l i t y would be a w e ll
r e g u la te d power su p p ly . The f i r s t c o n s id e ra tio n in d ec id in g
what type o f supply to u se would be d ic ta te d by th e ty p e o f
lo a d . In th i s case th e load i s c o n t in u a l ly v a ry in g s in c e
p u lsed c i r c u i t s a re in v o lv e d . The c o n s id e ra tio n th en i s to
c o n s tru c t a supply which i s in d ep en d en t o f th e v a ry in g lo a d .
I f such a supp ly i s c o n s tru c te d , th en th e r e w i l l be no i n t e r
a c tio n o f one c i r c u i t on th e o th e r , and s ta b le o p e ra t io n
r e s u l t s • The v o lta g e r e g u la t io n th a t i s d e s ire d may be
accom plished in a number o f w ays. To e l im in a te l in e v o lta g e
changes, th e l in e v o lta g e was passed th ro u g h a s o la t r a n s
fo rm er w hich, i f i t i s loaded to i t s r a te d c a p a c i ty , w i l l
h o ld th e v o lta g e s te a d y , though th e re may be f lu c tu a t io n s o f
as much as te n v o l t s . This i s t r u e o f slow v a r ia t io n s in
v o lta g e , ttap id v a r ia t io n s s t i l l may come th rough and be fe d
in to th e power su p p ly . Die power supply t h a t was f i n a l l y
decided upon made u se o f v o lta g e r e g u la to r gas tu b e s . The
o th e r cho ice was to u se s e r ie s r e g u la to r tu b e s , which a re
S c h e n n 3 ^ - v c D a m o j th e ITnne ^ n c ig ^ P v»o4*om e4ei
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fiq. 3 - 2 Voltagre R c q u la4-toia Curv e
r e g u la r vacuum tu b e s • The schem atic in d ic a te s how th e
r e g u la t io n was to be a c h iev e d . The o u tp u t o f th e f i l t e r
(and th i s a p p lie s to bo th th e p o s i t iv e 300 v o l t supply and
th e n e g a tiv e su p p ly ) were fe d ac ro ss th re e v o lta g e r e g u la to r
tubes in s e r i e s , and th e v o lta g e dropped . This would I s o la t e
f u r th e r th e in p u t f lu c tu a t io n s from th e rem ainder o f th e
c i r c u i t . From th i s p o in t th e v o lta g e was fe d in to two sep a
r a t e c i r c u i t s f o r th e two 500 v o l t su p p lie s t h a t were needed .
G reat c a re was tak en to decouple th e two power su p p lie s
th rough th e use o f KG f i l t e r s . The c h a r a c t e r i s t i c s o f th e
power su p p lie s i s In d ic a te d by f ig u re 3- 2 . The v o lta g e reg u
l a t io n was good o v er a range: o f ap p ro x im ate ly 20 m illia m p s .
I t was in th i s range th a t th e equipm ent was o p e ra te d . Of
c o n s id e ra b le s ig n i f ic a n c e was th e m anner in which th e o th e r
p o s i t iv e supp ly m a in ta in e d a s te ad y v o lta g e re g a rd le s s o f
th e v ary in g lo a d . S in ce th e s u p p lie s a r e i d e n t i c a l only one
curve was ta k e n . This th en gave us good rea so n to b e l ie v e
t h a t th e power s u p p lie s would do th e work ex p e c te d . S ince
t h i s curve r e p re s e n ts a slow change, which th e vo I t age reg u
l a t o r tu b es could fo llo w , some o th e r means o f d e te rm in in g
what would happen i f a v a ry in g load were p laced on th e supp ly
was n e c e s s a ry . W ith th e load c u r r e n t s e t a t v a r io u s v a lu e s ,
th e o u tp u t o f an audio o s c i l l a t o r was fe d in to th e supp ly a t
v a rio u s p o in ts to de term ine i f th e s ig n a l would be coupled
to th e o th e r su p p ly . No s ig n a l could be observed on th e
sco p e , r e g a rd le s s o f th e above, when in a c tu a l o p e ra t io n
f ' i 3 - 3
l OOU -A. /COOVL*
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th e re was s t i l l some s a a l l v a r ia t io n in v o lta g e between th e
power su p p lie s , and co u p lin g was observed between th e o irQ u its
which may, o r may n o t , he due to the power s u p p l i e s . The
h ig h v o lta g e supp ly used fo r, p h o to m u lt ip l ie r i s o f conven
t i o n a l d es ig n (see F ig . 3-5)# The p a r t i c u l a r c i r c u i t i s
u sed in o th e r pho tom etric equipm ent f o r th e same p u rp o se .
From th e s ta n d p o in t 'o f s t a b l e o p e ra t io n i t a lso m ust be w e ll
r e g u la te d . S ince i t i s u sed s a t i s f a c t o r i l y in o th e r eq u ip
m ent, no f u r th e r t e s t s w ere made on i t . F o r th e b e s t- •
stability, a h ig h v o lta g e b a t te r y shou ld be u se d . * ‘
The o v e r - a l l s t a b i l i t y o f th e f i n a l l y designed c i r c u i t
l e f t much to be d e s i r e d . The power s u p p lie s f a i l e d to de-
l iv e r a smo o th o u tp u t , thus add ing to th e in s t a b i l l t y , and
th e re was co u p lin g between th e g a te s a t What w o u ld :c o rre s
pond to low l i g h t i n t e n s i t i e s . D eeeup ling sh o u ld have been
ach ieved th rough th e p ro p e r arrangem ent o f th e p h y s ic a l
components on th e c h a s s i s , c a r e f u l w ir in g and a good power
su p p ly . A ll th e se had presum ably been ta k e n in to c o n s id e ra
t i o n . To a tte m p t to de te rm ine where th e co u p lin g was coming
from , b a t t e r i e s were u sed in p la c e o f th e power s u p p l ie s .
Each c i r c u i t was i s o l a te d in d e p e n d e n tly . The f i la m e n t sup
p l i e s were d u p lic a te d so th a t no p h y s ic a l o r e l e c t r i c a l
co n n ec tio n s rem ained . All tubes were checked by rep la cem en t.
None o f th e se th in g s gave any c lu e as to where th e co u p lin g
was coming. The co u p lin g was p e c u l ia r in t h a t i t was i n t e r
m i t t e n t . There were tim es when th e co u p lin g was a b se n t and
17
th e equipm ent worked f in e a t th e low l i g h t l e v e l s . There
d id seem to be some co n n ectio n between th e o u tp u t c i r c u i t
and th e co u p lin g , s in c e i t i s p o s s ib le to remove th e o u tp u t
tu b e , re p la c e i t ; and th e co u p lin g w i l l f a i l to appear f o r
a v d iile . This i s a very p e rp le x in g problem and no adequate
s o lu t io n has been fo u n d . % e s o lu t io n may l i e in a more
c a r e fu l p lacem ent o f p a r ts and com ponents, b u t t h i s was in
a d v isa b le to do a t t h a t tim e .
There rem ains th e problem o f e x p la in in g where i n s t a b i l
i t y is l ik e ly to o ccu r due to v o lta g e f lu c tu a t io n s . F lu c
tu a t io n s o f v o lta g e in any c i r c u i t which i s .concerned w ith
th e g e n e ra tio n o f th e p u lse s w i l l cause i n s t a b i l i t y . F lu c
tu a t io n s in any o f the a m p lif ie r s which g iv e r i s e to v a r ia
t io n s in am p litudes w i l l n o t a f f e c t th e o u tp u t . S ince i t
was shown in s e c t io n 2 t h a t th e o u tp u t i s th e in te g ra te d
in p u t to th e f i n a l s ta g e , th e o u tp u t w i l l vary on ly i f th e
w id th o f th e p u lse v a r ie s , p ro v id in g t h a t th e p rev io u s
a m p lif ie r s a re o p e ra t in g a t s a tu r a t i o n . Under th o se co n d i
t io n s sm a ll f lu c tu a t io n s in v o lta g e w i l l n o t a f f e c t th e
am p litude o f th e in p u t to th e o u tp u t s ta g e , t te fe r in g to
th e g e n e ra l sc h em a tic , i t i s n ecessa ry t h a t th e fo llo w in g
tubes be p rov ided w ith s t a b i l e v o l ta g e s « Tubes 3 , 4 , 5 ,
and 6 , f o r th e f ix e d g a te g e n e ra to r , and tu b e s 7 , 8 , 9 , 11,
and 12. Tube 10 i s only an i s o l a t i o n s ta g e and does n o t
e n te r in to th e d e te rm in a tio n o f th e p u lse w id th . F u r th e r
m ore, th e v o lta g e sou rces shou ld be e n t i r e ly in d ep en d en t.
18
In connec tion w ith th e v a r io u s ex p e rim en ta l c i r c u i t s t r i e d ,
f u r th e r in fo rm a tio n co n cern in g th e s t a b i l i z a t i o n o f th e
p u lse s w i l l be given*
i v
DEVELOBfiENT OF THE IHPUT CIHGUIT
As in d ic a te d in th e in tro d u c to ry m a te r i a l , i t became
ap p a re n t t h a t th e in p u t c i r c u i t o r ig in a l ly in u se w ith th i s
in s tru m e n t was u n s a t i s f a c to r y , s in c e i t in v o lv ed th e u se o f-
D.C• a m p l i f ie r s . In th e fo llo w in g m a te r ia l an e x p la n a tio n
o f th e v a r io u s c i r c u i t s t r i e d w i l l be g iv en .an d , where pos
s i b l e , some a n a ly s is o f th e c i r c u i t s w i l l be a tte m p te d . The
c i r c u i t s u sed could be c la s s e d as m u l t iv ib r a to r s on p h an ta s-
t r o n s . The m u l t iv ib r a to r type w i l l be t r e a t e d f i r s t .
The f i r s t c i r c u i t which was developed could very p ro p e r ly
be c a l le d a m onostab le m u l t iv ib r a to r o f th e type in f i g . 3- 2 ,
3 -3 . In b o th cases th e c o n t r o l l in g tim e c o n s ta n ts a re in a
g r id c i r c u i t . In th e d e s ig n o f such c i r c u i t s i t i s n ecessa ry
to d e te rm in e how th e tim e o f de lay v a r ie s w ith th e v a rio u s
c i r c u i t p a ram e te rs , and w hat f a c to r s g iv e r i s e to good wave
fo rm s. Having a knowledge o f th e s e f a c to r s i t i s p o s s ib le
to then d e te rm in e what m ust be done to g e t s t a b le o p e ra t io n .
S ince th e tim e th a t tu b e VI rem ains c u t o f f (see f i g . 3-2)
depends o n •th e v a r ia t io n o f th e g r id v o Ita g e w ith tim e, th e
fo llo w in g eq u a tio n s may be w r i t te n : Where v i s In s ta n ta n e o u s
v o lta g e on th e g r id o f VI, Vi r e p re s e n ts th e i n i t i a l v o lta g e
on th e g r i d ; v0 i s th e v o lta g e ac ro ss th e co n d en ser; Vg
' - V - r
V,.
3~2 T ypic&l Mevto s ta klc Mult*»iribr*A Vote.
^8^^* tpcr-i nn en "t a I Dc / A y Q Dr Xnput
21
r e p r e s e n ts th e p o te n t i a l a t w hich th e g r id a llo w s th e te b e
to conduct, and Vf i s th e $x>tentlml to wfaloh th e condenser
would charge i f p e rm itte d to do s o .
.... V = Vf-vc , .. _ . ■ : . : . : • . .
Vo = (V f+ V i) < l-« x p (- t/ttC )) ( 3 )
from which i t may be shown t h a t th e tim e o f d e lay T i s ’
T = HO in |(yr -hV1. ) / ( V g+ V fj} . (4)
The manner in which T v a r ie s may be seen i f th e d e r iv a t iv e
o f th e above ex p re ss io n i s w r i t t e n .
dT=d(RC) : ln [(Vf + V i)/(V f 4- Vg )J
+ KC dV-t) - (dVg+ dVf)]t Vf +• Vi) (Vg + Vf) J
F o r good s t a b i l i z a t i o n then i t i s n e c e ssa ry to have RC/Vf -h Vi)
and KG/(Vg4- V f} b o th s m a ll . This i s accom plished by making
th e denom inators la r g e ; t h a t i s to say th e waveform am pli
tude shou ld be l a r g e • G en era lly th i s means t h a t la rg e load
r e s i s to r s \m u s t be u se d . To u se h ig h load r e s i s ta n c e s i s to
ou t down on th e c u r r e n t th rough th e tu b es and g iv e o p e ra t io n
a t a low er g® ( th e m u tu a l co n d u c tan ce ), which m ust be h ig h
i f a f a s t waveform i s to be d e r iv e d . F or f a s t waveforms2> - :: - • • . ' 9 -■ : ■ ' ' ^ ' • :
0® 'c l c 2 m ust be la r g e , where i s th e m u tu a l conductance
and C^* i s th e lumped in te r s le o t r o d e c a p a c ita n c e from th e
g r id of tube one to ground. The same i s t r u e o f Cg*. Seme
compromise i s n ecessa ry f o r good s t a b i l i t y and good waveform.
W ith t h i s as background m a te r ia l , i t i s now p o s s ib le to ex
p la in th e o p e ra t io n o f th e c i r c u i t in f i g . 3 -3 . d(KC) can
9^ “Waveforms" , B. Chance, M .I.T . R a d ia tio n L a b o ra to r ie s S e r ie s Vol. 19 :179 , M cGraw-Hill Book Company, In c . New York (1949).
m
be made eq u a l to zero by cho ice o f oompomenta, s in e e tem
p e ra tu re e f f e c t a re re s p o n s ib le f o r change. - . : r
In th e q u ie sc e n t c o n d itio n VI i s co n d u c tin g and V2 la
c u t o f f . A n e g a tiv e t r i g g e r p u lse Is fe d to th e g r id o f VI.
The p la te p o te n t i a l o f VI r i s e s , and t h i s r i s e in p o te n t i a l
i s a p p l ie d a c ro s s th e condenser C to th e g r id o f V2 , - cau sin g
th e tube to conduct, and i t s p la te p o te n t i a l d ro p s . This
d rop in p o te n t ia l a c ro s s th e d iv id e r S2, M4, R3 i s s u f f i c i e n t
to h o ld VI c u to f f u n t i l such tim e th a t th e g r id o f V2 can
charge th rough th e 9001. The p o te n t i a l a t th e g r id w i l l drop
to its* c u t o f f p o in t , and th e cy c le can be re p e a te d . I t is
n ecessa ry t h a t th e g r id o f V2 be b ia se d s u f f i c i e n t l y n e g a tiv e .
so th a t th e p o s i t iv e go ing wave from Vl w i l l n o t cause i t to
draw g r id c u r r e n t . The c i r c u i t o p e ra te d f o r r e l a t i v e l y s h o r t
p u ls e s , b u t a t no tim e d id i t o f f e r s ta b le o p e ra t io n . S ince-v. A. ' : ' ■ ■ . : - . ' ■ " ' ■ : . - .. ■ ........
our prev ious a n a ly s is showed th a t E- shou ld be f ix e d f o r
s ta b le o p e ra t io n , i t can be seen th a t th i s p a r t i c u la r c i r c u i t
c o n tro ls th e tim e in te r v a l in two ways: one through v ary ing•• ̂ , : ' - : - ' : V ‘ • . - : . .th e charge c u r re n t to th e condenser; and th e o th e r i s the
v a r ia t io n o f th e g r id p o te n t i a l . The l a t t e r was ex trem ely
u n d e s ira b le . From th is c i r c u i t i t became ap p a re n t t h a t th e
v a r ia t io n o f tim e m ust be independent o f th e g r id c i r c u i t s
o f any o f th e tubes and depend only on th e ch a rg in g r a t e
th rough the 9001. The maximum delay th a t th i s c i r c u i t gave
was, 60£ o f th e p e rio d v tiich f o r th i s equipm ent i s l /6 0 of a
second . A d iode was p laced frcm th e g r id o f V2 to -50v to
23
a id in g e t t in g th e ch a rg e , b u t i t d id n o t a l t e r th e s t a b i l
i t y o f th e c i r c u i t , and th e c i r c u i t was d is c a rd e d in fa v o r
o f a n o th e r .
S ince th e m u l t iv ib r a to r type c i r c u i t f a i l e d to g ive
th e s t a b i l i t y d e s i r e d , an e n t i r e l y new ty p e o f c i r c u i t
was d es ig n ed — th e p h a n ta s tro n . S ince th i s d i f f e r s m arkedly
from th e m u l t iv ib r a to r , th e d is c u s s io n o f i t w i l l be de
la y ed , and the c i r c u i t f i n a l l y u sed w i l l be c o n s id e re d ,
s in c e i t , in some r e s p e c ts , resem bles th e m onostab le m u l t i
v ib r a to r . ;
THE INPUT DELAY GATE:
The f i n a l c i r c u i t f o r th e in p u t i s shown in f i g . 3-4f
The c i r c u i t v a lu es u sed w i l l be found in th e g e n e ra l sch e
m a tic d iagram . To e x p la in th e o p e ra t io n o f th e g a te , r e f e r
ence w i l l be made to f i g . 3-2 and f i g . 3-3 , th e e q u iv a le n t
c i r c u i t . From com parison o f th e e q u iv a le n t c i r c u i t to th e
c i r c u i t o f th e m onostab le m u l t iv ib r a to r , f i g . 3 -4 , i t can
be shown th a t th e two a re a lm ost i d e n t i c a l . In th e case of
th e m onostab le m u l t iv ib r a to r th e tim e c o n s ta n t r e s i s t o r K ■ ; | . :•
i s r e tu rn e d to a p o s i t iv e p o t e n t i a l , and VI i s o u t o f th e
c i r c u i t in th e o p e ra tin g c o n d i t io n . In th e c i r c u i t developed. : • ■ v i : ;.
th e tim e c o n s ta n t r e s i s t o r i s th e p la te r e s i s ta n c e o f th e
9001, o r T4, and i t i s re tu rn e d to a n e g a tiv e p o t e n t i a l .
T h e re fo re , our p rev io u s d is c u s s io n o f m u l t iv ib r a to r s shou ld
he a p p l ic a b le to th i s p a r t i c u l a r c i r c u i t . ’
t V
- 3 0 0 V
D ‘z.i a y-Z\> pU~f Q * r c "
25
'B ieq ii le a c e n t eond itloB a a re as fo llo w s : T1 ia eon- ,
d u c tin g h e a v i ly 5 T2 i s . o u t o f f ? f5 i s co n d u c tin g h e a v ily o r
as h e a v ily as T4 w i l l a llow i t to oenduot. A. n e g a tiv e in
i t i a t i n g p u lse is a p p lie d to th e g r id o f T1 whloh causes A
to r i s e in p o t e n t i a l , s in c e th e tu b e was co n d u c tin g h e a v i ly .
The r i s e in A, coupled th rough th e con d en ser, causes B to
r i s e a l s o . B i s norm ally a t some n e g a tiv e p o t e n t i a l , and
th e r i s e , due to th e i n i t i a t i n g p u lse m ust be o f s u f f i c i e n t
m agnitude to cause T3 to ou t o f f . S in ce T3 o p e ra te s a t .
n e a r ly zero b ia s , a r i s e , o f 20 v o l ts w i l l g iv e th e d e s ire d ,
r e s u l t . I f T3 i s co n d u c tin g h e a v i ly , C i s a t some n e g a tiv e
p o te n t i a l , ; s in c e th e ca thode i s a t some n e g a tiv e p o t e n t i a l .
This n e g a tiv e p o te n t i a l i s s u f f i c i e n t , to cause T2. to rem ain
a t o u t o f f . When th e ca th o d e , o r B, r i s e s in p o te n t i a l T3
i s c u t o f f and C r i s e s to i t s p la te supp ly p o te n t ia l* 0
goes very p o s i t iv e , and th i s a c t io n w i l l a llo w T2 to conduct
h e a v i ly . S in ce T1 and T2 have a common cathode r e s i s t o r th e
heavy conduction o f IS th rough th e common r e s i s t o r w i l l keep
T1 c u t o f f u n t i l such tim e as T3 i s a b le to draw c u r r e n t .
This c o n d itio n w i l l e x i s t a g a in when th e tim in g condenser
has charged th rough T4 f o r a s u f f i c i e n t p e r io d o f tim e to
cause th e p o te n t ia l ac ro ss T4 to drop to th e c r i t i c a l p o in t
o r c u to f f p o in t o f T3 . At such tim e, T3 s t a r t s to conduct;
th e p o te n t i a l a t o f a l l s ? th e conduction th rough th e common
ca thode r e s i s t o r d e c re a s e s , and T1 s t a r t s to conduct a g a in .
This w i l l cause A to f a l l in p o t e n t i a l . % le drop in
26
p o te n t ia l i s coupled th rough th e eondenser to B, and th e
e n t i r e p rocedure i s re p e a te d u n t i l th e q u ie s c e n t o p e ra tin g
c o n d itio n i s re a c h e d . A p e r io d o f tim e i s n e c e s s a ry , a f t e r
the v a rio u s tubes have reach ed th e i r q u ie s c e n t s t a t e , f o r
th e condenser to re a c h i t s i n i t i a l o p e ra t in g p o in t , s in c e
i t m ust charge th rough H i, th e p la te r e s i s ta n c e o f T3, and :
i t s load r e s i s t a n c e . T3 i s capab le o f co n d u c tin g h e a v i ly ,
and th e charge i s tak en from th e n e g a tiv e s id e o f th e con
d en ser r a p id ly * Some d i f f i c u l t y i s en co u n te red in charg in g
th e condenser th ro u g h R l. The c i r c u i t u sed was f o r a r e l a
t iv e ly s h o r t d e la y ; and th e d io d e was connected to ground
and was e f f e c t iv e ly o u t o f th e c i r c u i t . However, i f lo n g e r
p u ls e s .a r e to be worked w ith , th en th e d iode p la te shou ld
be connected to 300 v o l t s . This a id s in e l im in a tin g s c a l in g —
th e i n a b i l i t y o f th e c i r c u i t to reach th e c o r r e o t o p e ra tin g
p o in t b e fo re th e a r r i v a l o f th e n e x t i n i t i a t i n g p u ls e . This
d is c u s s io n in d ic a te s q u a l i t a t iv e l y th e o p e ra t io n o f th e g a te .
Seme o f i t s c h a r a c te r i s t i c s and p ro p e r t ie s w i l l be co n s id e red
n e x t .
Hie v a r io u s c h a r a c t e r i s t i c waveforms a re in d ic a te d in
f i g . 3-4 and f i g . 3 -5 . S in ce th e waveform a t G i s th e con
t r o l l i n g f a c t o r in changing th e o p e ra tio n from th e q u ie s c e n t
to th e o p e ra t in g c o n d itio n , i t can be ex p ec ted t h a t th e wave
form s d e r iv e d f ran th is g a te w i l l be very s te e p . Such i s
th e c a se . The le ad in g edges tend to fo llo w th e i n i t i a t i n g
p u lse which has gone s lo p e , b u t th e t r a i l i n g edges a re a lm ost
Wave Form at
A
I— T HI*-------------- - P
Zoo v
__________ ir
F iq .
C
C har a c 'c W a u c s of tkc I n p u t G a t e
2-0 vi
•Vave Form a t D
F ie . 1
- iOOvr
Wave Form a t E
- 5 C h a r a c t e r i s t i c Waveforms o f m e Input C i r c u i t
2 1
e n t i r e ly w ith o u t s lo p e —a t l e a s t as seen on th e o s o i l l o -
soope. The m atch ing o f th e t r a i l i n g edges o f th e two g a te s
shou ld be very a c c u r a te . I f th e second g a te has th e same
c h a r a c t e r i s t i c s lo p e , then th e n o n l in e a r i ty due to d i f f e r
ences in t r a i l i n g edge s lo p e would be g r e a t ly m inim ized*
The waveforms r e p re s e n t d e lay tim es o f 60% o f a p e r io d ,
where th e p e r io d .is l / 6 0 th o f a seco n d . T his p a r t i c u l a r
g a te was found to be very s e n s i t iv e to p la te v o lta g e changes.
O p era tin g a t th e above f ig u r e , a change o f f iv e v o lts in
th e supply v o lta g e caused th e g a te to s c a l e . F ilam en t v o l t
age changes produced .20% v a r ia t io n s in p u lse w id th , when
changed 10%. This se rv e s to p o in t o u t th e n e c e s s i ty o f
e x c e l le n t v o lta g e r e g u la t io n . The only change In r e s i s ta n c e ,
which produced a v a r ia t io n in p u lse w id th , was a v a r ia t io n
in n l f i g . 3 -4 . This m ig h t be u sed as a means o f v a ry in g
th e p u lse w id th o f a f ix e d g a te , i f two s im i la r g a te s were
to be u se d .
DETEKMIMAHON OF k :
From th e e q u iv a le n t c i r c u i t o f th i s ( f i g . 3- 6 ) p a r t i
c u la r g a te , i t can be shown th a t th e i n i t i a l p o t e n t i a l a c ro ss
th e condenser in the q u ie sc e n t c o n d itio n is
Vi = (KP14-K2 ) 300 , Rp4 (ISO) - —n K pl-t- K2 + t t i ttp4 -t- Kp3 + tt4
Vf = 300Vg = 170 _
From eq u a tio n 4 th e c o n s ta n t in
T = kKC
Flgo 3-b The E q u i v a l e n t C i r c u i t o r t h e I n p u t Gate i n t h e Q u i e s c e n t C o n d i t i o n
Is e q u iv a le n t to
k * In (Vf + V i)/V c + V f)
e v a lu a t in g th e above e x p re s s io n we g e t .
k = ^ 4 ( 6 )
Prom th e s e n s i t i v i t y cu rv e , a d e te rm in a tio n o f th e a c tu a l
c o n s ta n t may be d e r iv e d . S in ce th e s e n s i t i v i t y curve g iv es
change in p u lse w id th w ith change in g r id v o lta g e i t may be
reduced to a c tu a l change in p u lse w id th by add ing a c o n s ta n t
term to th e o rd in a te and a b s c is s a . The s lo p e would rem ain
th e seme. From th e s lo p e o f th e s e n s i t i v i t y curve
k = . 1 4 ................' ’ ' .......... ..... 7 - ’ ' '
% e p la te r e s i s t a n c e which we have assumed c o n s ta n t changes,
as in d ic a te d by th e s e n s i t i v i t y cu rv e . T h e re fo re , th e above
i s p robably th e m ost r e l i a b l e o f th e two v a lu e s . The d i s
crepancy between th e two v alues su g g es ts t h a t th e s e n s i t i v i t y
o f th e g a te i s n o t b e in g f u l ly u t i l i z e d .
S E N S I T I V I E T t :. :: V - V . ' ' : J , *' r -
The c p e s tio n o f s e n s i t i v i t y o f th e g a te has been men
t io n e d . Two s e n s i t i v i t y curves have been ta k e n : one f o r
th e low v a lu e s o f in p u t g r id v o ltag e? and th e o th e r f o r h ig h
v a lu e , to d e te rm in e how much g r id v o lta g e change ban be a c
commodated by th e g a te w ith o u t s e a l in g . F ran th e curves s o -
p lo t t e d i t i s seen t h a t , f o r a f iv e in illia m p o u tp u t, i t i s
n ec e ssa ry to have an in p u t o f 16 m i l l i v o l t s • S in ce from
p rev io u s c o n s id e ra tio n s i t was shown t h a t
T = KC ARp
and■ . b .
T = TARn- '
77P •Kp . (7) ;. i- ;r:
I t m ust be s p e c i f ie d t h a t th e m easurem ents were made w ith a
p u lse w id th o f 60% o f a p e r io d . The cu rves r e v e a l an l a -
p o r ta n t f a c t as to th e low v a lu es o f g r id v o l ta g e . There
i s a n o n l in e a r i ty a t low v a lu es which makes th e p re s e n t
in s tru m e n t u n r e l i a b le . As was m entioned p re v io u s ly , in con
s id e r in g th e power s u p p lie s in t h e i r r e la t io n s h ip to s t a b i l i t y ,
th e re appeared to be i n t e r a c t i o n between th e g a te s . The
curves in d ic a te t h a t i t ta k e s two m i l l i v o l t s to b reak th e
g a tes lo o s e , t t ia t i s to say th a t when th e p u lse o f th e v a r
ia b le g a te approaches th e f ix e d g a te , i t a u to m a tic a lly chan
ges i t s p u lse w id th in d ep en d en tly o f th e g r id v o lta g e , so
t h a t th e two become th e same w id th w ith co rresp o n d in g lo s s
o f o u tp u t. H erein l i e s one reaso n f o r th e poor s e n s i t i v i t y.V- *' r " - *
f o r t h i s in s tru m e n t. I f th e r e were no lo o k in g in , perhaps
th e curve would take th e s lo p e which i t appears to s t a r t
fo llo w in g a t th e tim e i t b reaks away from th e o th e r g a te .
The f ix e d g a te appears to in f lu e n c e th e v a r ia b le g a te th ro u g h
o u t i t s o p e ra t io n . On th a t b a s is i t m ig h t be rea so n ab le
t h a t , w ith no co u p lin g between g a te s , th e p re s e n t a r ra n g e
m ent could be th re e tim es as s e n s i t iv e as i t i s . The o th e r
*
re a so n i s t h a t 9001 i s o p e ra t in g a long th e curved p o r tio n
o f th e o h a r a c te r ie t i e p la te c u r r e n t , p la te v o lta g e cu rv e ,
th e r e f o r e , th e p la te r e s i s ta n c e can change very l i t t l e .
The u se o f a pentode w ith no lo ad r e s i s t o r in i t s p la te c i r
c u i t would p la c e th e o p e ra tio n in a more d e s i r a b le reg ion*
th e feed b ack back r e s i s t o r K4 ( f i g . 3 -6 ) could be p laced in
th e sc re en c i r c u i t* In t h i s same reg io n th e re i s an o th e r
c o n t r ib u t in g f a c to r to th i s n o n lin e a r i ty * S in ce th e p u lse s
do n o t have i n f i n i t e s lo p e s , th e o u tp u t o f th e b r id g e i s a
t r i a n g u l a r wave r a th e r th an a square w ave. Were i t n o t f o r
th e co u p lin g e f f e o t t h i s would show up r a th e r m ark ed ly , s in c e
th e f ix e d p u lse g e n e ra to r has a g r e a te r e lo p e th e n th e V arl*
a b l e . g a te • , .<: • • - -̂ - ;■ ■. 1. -.•« . ... ...
F ran th e d is c u s s io n o f th e in p u t d e lay g a te , i t can be
seen th a t a s im p le scheme has been a r r iv e d a t in -coupling
from th e p h o to m u lt ip l ie r to th e d e la y g a te , w herein th e
co u p lin g tube ( th e 9001) forms th e r e s i s ta n c e f o r a KC tim
in g netw ork . I t was f o r t h a t purpose t h a t t h i s work was
u n d e rta k e n . Rie s ig n a l developed by; th e p h o to tu b e i s p la c e d
on th e g ird o f th e 9001, betw een g r id and -300 v o I ts * The
v a r ia t io n s o f p la te v o lta g e w i l l n o t i n t e r f e r e w ith th e
a c t io n o f th e s ig n a l . :
PHANTASTRON DELAY GATE:
A fte r th e f i r s t a ttem p ts to develop a s ta b le m u l t iv i
b r a to r c i r c u i t f a i l e d , i t was dec ided t h a t an e n t i r e ly
m
d i f f e r e n t ty p e o f c i r c u i t sh o u ld be developed which had/
u n u su a lly f in e s t a b i l i t y — th e p h a n ta s tro n . F o r a change o f
- 10% in p la te v o lta g e the o u tp u t p u lse v a r ie d t . 1%, and
f o r a change in f i la m e n t v o lta g e 'o f 1‘ 10% th e change in p u lse
w id th is . ag a in * . 1%, b u t in th e ;o p p o s i te d i r e c t io n to th e10 ' ; "
p rev io u s change. T h e re fo re ,1- u n re g u la te d power s u p p lie s: r- . . . :m igh t be ad v an tag eo u s. However, w ith good r e g u la t io n even
b e t t e r s t a b i l i t y shou ld be fo rthcom ing* Two;methods o f
v a ry in g th e p u lse w id th ,w ere p o s s ib le : one by v a ry in g a
c o n tro l v o l ta g e , and th e o th e r by v a ry in g th e RC tim e o f
th e feedback c i r c u i t . . E i th e r method produces a l in e a r: . . ! , .
v a r ia t io n in p u lse w id th . The c i r c u i t employed i s in d ic a te d
in f i g . 3 -7 . This p a r t i c u l a r c i r c u i t g en e ra ted b o th a nega
t iv e and p o s i t iv e sq u a re wave, and w*a capab le o f g iv in g
d elay s o f 90% o f th e p e r io d • This long d e la y depends g r e a t ly
on the tu b e u sed , and i t? was found t h a t only a SAC7 p e r
m it te d g e r» ra t io n o f such a wide p u ls e . The d i f f e r e n c e
l i e s in th e sm a ll in te r e le c t r o d e c a p a c ita n c e o f th i s p a r
t i c u l a r tu b e . In th i s r e s p e c t t h i s c i r c u i t gave th e m ost: i ;
s ta b le o p e ra tio n f o r la rg e d e lay p e rio d s o f any o f th e: : - •
c i r c u i t s t e s t e d . ;
The d e lay tim e i s a l i n e a r fu n c tio n o f th e p la te v o l t
age and th e kC tim e o f th e feedback netw ork (see f i g . 3 -8 ) .
T = KgCg(V-V0 ) /E bb
10 . C lose; :IUN. and Lebenbaum, M .I . , D esign o f P h an ta s tro n Time Delay C i r c u i t s , b’l e o t r o h l o s : ' 19 :100 . (1948).
/, Replaced/ ^ t-3cov
■ O O I
r o n D e l a y CfQ i e I n p u t C / r c m t
38
where V and V0 r e p r e s e n t th e s e t t i n g o f th e d iode T3, w hitii
in tu rn determ ine* th e v a lu e o f p la te v o lta g e on T8 . For
a g iven s e t t i n g o f p la te v o lta g e , Rg could he v a r ie d to g iv e
v a r ia b le d e lay t im e s . Both method* were t r i e d and n e i th e r
proved s u c c e s s fu l . The f i r s t a ttem p t was to u se a very
la rg e tim e c o n s ta n t , and vary th e p la te v o lta g e by means o f
th e o u tp u t o f th e co u p lin g tu b e from the p h o to m u lt ip l ie r
tube (as shown in f i g . 3 -8 ) . S in ce th e v a r ia t io n in tim e
i s p ro p o r t io n a l to th e change in v o l ta g e , th e s e n s i t i v i t y
was no t s u f f i c i e n t . F u rth e rm o re , i t was in v io la t io n o f th e .
tim e b r id g e p r in c ip l e , s in c e t h i s m ig h t be co n s id e red a ty p e
o f D.C. A m p lif ic a tio n . From f i g . 3 -8 , th e v a rio u s wave forms
a re shown. I f th e 9001 were p laced in the g r id c i r c u i t , in
p lace o f Kg, th e problem o f Im p ressin g a s ig n a l on th e 9001
g r id would n o t be too g r e a t , s in c e th e g r id o f T2 rem ains
p r a c t i c a l ly c o n s ta n t d u r in g th e d e lay tim e . T his was done,
bu t whenever th e s ig n a l v o lta g e was im pressed th e g a te ceased
o p e ra t io n . The g r id a p p a re n tly could n o t be loaded in any
way and s t i l l o p e r a te . The f i r s t m ethod, t h a t o f u s in g a
v o lta g e change, wasn’ t s u f f i c i e n t l y s e n s i t i v e , and th e second
method was in o p e ra t iv e . The p h a n ta s tro n could no t be used as
an in p u t c i r c u i t f o r th e tim e b r id g e . At th e su g g e s tio n of
D r. Corby, th e m u l t iv ib r a to r type g a te was d ev e lo p ed .
l i . GI5ae "- R .R i: apd Lebenbam, Deelgn o f , PhantmatronTime DelarTrCihcuits . fflefttrohloi'; ; 19:100. (1 9 4 8 ).
A b r i e f e x p la n a tio n o f th e o p e ra t io n o f th e p h an taa tro n
w i l l be g iv e n # ite fe ren o e w i l l be made to f i g . 3- 8 . T3 i s
s e t a t seme a r b i t r a r y p o te n t i a l , and th i s means th a t the ■
p la te v o lta g e cannot r i s e alxiVe th i s v a lu e . In th e q u ie s -^ .
ce n t c o n d itio n th e sc re e n g r id o f T3 i s s u f f i c i e n t l y nega
t iv e to s to p th e c u r re n t which would norm ally p ass to th e
p l a t e . The b ia s on th e tu b e i s o f th e o rd e r o f one o r two
v o l ts s in c e T1 i s connected to a p o s i t iv e v o l ta g e . The tube
would have zero b ia s i f T1 were n o t p r e s e n t , due to th e
la rg e value o f Kg. The sc re e n g r id then ta k es a l l th e space
c u r r e n t th a t would norm ally p ass to th e p l a t e . A n e g a tiv e
t r i g g e r i s a p p l ie d to th e g r id o f T2 th rough T l. The p o ten
t i a l o f th e g r id drops and th e p o te n t i a l o f th e ca thode drops
s in c e i t i s unbypassed by a condenser to m a in ta in i t a t a
cons t a n t p o t e n t i a l . This i s th e e q u iv a le n t o f r a i s i n g th e
su p p re sso r in p o te n t i a l and some p la te c u r re n t w i l l f lo w .
The sc re en g r id th en r i s e s in p o t e n t i a l . The sudden flow o f
p la te c u r r e n t th ro u g h RL, which i s a la rg e r e s i s t o r , causes
a sudden drop in p la te v o l ta g e . T his sudden change i s ap
p l ie d th rough th e condenser Cg to th e g r id o f T2 which cannot
charge r a p id ly th ro u g h Rg. T h e re fo re , t h i s n e g a tiv e v o lta g e
rem ains on th e g r id and causes th e tu b e to co n tin u e to draw
p la te c u r r e n t . Cg s t a r t s to charge th rough Kg a n d .th e g r id
v o lta g e r i s e s . This w i l l cause more p la te c u r r e n t to flo w ,
and a g r e a te r drop i s a p p lie d to th e g r id o f T2 which w i l l
ten d to e q u a liz e th e change in v o lta g e due to th e d isc h a rg e
?,1.0766
- - c
W a v e Form a t
F i g . 3-t i P h a n t a a t r o n D e la y Gate and Waveforms
th rough Rg. Rie n e t e f f e c t th en i s f o r th e g r id to rem ain
c o n s ta n t in p o t e n t i a l . This c o n d itio n e x is ts u n t i l such' " . . .
tim e as th e p la te v o lta g e drops to some very low v a lu e and
th e c o n d it io n s , upon which th e l i n e a r o p e ra t io n o f t i l l s
c i r c u i t depend, a r e no lo n g e r f u l f i l l e d . There i s no lo n g e r
s u f f i c i e n t v a r ia t io n in p la te v o lta g e to o f f s e t th e r i s e in
g r id v o l ta g e , and th e g r id r i s e s u n t i l i t re ac h es th e po
t e n t i a l a t which T1 s t a r t s to co n d u c t. The ca thode fo llo w s
th e g r id p o s i t iv e , which i s th e same as p e rm it t in g th e sup
p re s s o r to go n e g a tiv e , and th e p la te c u r r e n t i s aga in cu t
o f f . The S creen p o te n t i a l d ro p s , and th e cy c le i s com pleted
when th e s t r a y c a p a c ita n c e s a re charged up a g a in . To d e t e r
mine j u s t w hat c o n d itio n s a re n ec e ssa ry f o r th e o p e ra tio n
o f th e p h a n ta s tro n , to g iv e l in e a r d e la y s , th e fo llo w in g
a n a ly s is may be m ade. W ith re fe re n c e to f i g . 3 -8 , th e t o t a l
p la te c u r r e n t t h a t flow s i s g iven by th e fo llo w in g e x p re s s io n
ip a iL + l c * V (8 )
where 1^ i s th e c u r r e n t t h a t p asses th rough th e load r e s i s
to r? i 0 i s th e ch a rg in g c u r r e n t o f Cg, and i a i s th e c u r re n t
n ecessa ry to charge th e s t r a y c a p a c ita n c e s . From th e tube
c h a r a c t e r i s t i c s
Ip = 8m(«g + » s g / ' t ig + (9)
where Cg, egg v ep , a re th e in s ta n ta n e o u s p o te n t ia l s o f th e
g r id , sc re e n g r id , and th e p la te r e s p e c t iv e ly . The q u a n t i
t i e s in th e denom inator a re th e a m p lif ic a t io n f a c to r s f o r
th e sc re en g r id and p l a t e . I f v 0 i s th e in s ta n ta n e o u s
v o lta g e a c ro ss th e condenser a t any tim e.
ip = 8m [ (% b -h i^ v c ) + G sg/^sg +% b-RLiL)/W p] ( 10 )
S o lv ing ; f o r 1% we g e t _
Bg |i%b -Va-̂ flU + W u 1o ' la1 +an Rl + fin R l/»p (11)
I f d / d t ( 1^) i s to be c o n s ta n t , then th e denom inator m ust be
a c o n s ta n t , and th e num erator e i t h e r a c o n s ta n t o r some
l in e a r fu n c t io n o f tim e . I f th e o p e ra t io n o f th e c i r c u i t
i s above th e "knee" o f th e c h a r a c t e r i s t i c * p - ip curve f o r
th e pen tode7 then th e tube c h a r a c t e r i s t i c s a re e s s e n t i a l l y
c o n s ta n t. In th e n u m era to r, i g i s g e n e ra lly sm a ll compared
to i Q, a t l e a s t i t i s in th e c i r c u i t t h a t has been c o n s id e re d ,
and th e on ly v a lu e s to be in v e s t ig a te d a re v0 and i 0 .
i 0 = (Ebb-egVRg ( 12)
S in ce th e change In g r id v o lta g e i s sm a ll, i 0 can be co n s id e red
a c o n s ta n t . I t i s now p o s s ib le to show t h a t vc i s a l i n e a r
fu n c tio n o f tim e , and so com plete the d is c u s s io n .
d( v0 ) / d t = io /C
which i s a c o n s ta n t from eq u a tio n 12 . From t h a t which has
been d e r iv e d , i t fo llo w s th a t so long as th e p la te v o lta g e
rem ains in th e l i n e a r re g io n o f th e c h a r a c t e r i s t i c p la te
v o l ta g e - p la te c u r r e n t c u rv e s , th e change in p u lse w id th w i l l
be a l in e a r fu n c tio n o f th e change in p la te v o lta g e , and th e
q u ie sc e n t c o n d itio n w i l l be r e s to r e d when th e re i s any de
p a r tu re from th i s c o n d itio n f o r l i n e a r i t y .
45
V
CO N ew s ION
The purpose o f t i l l s program has been p a r t i a l l y a t t a in e d .
A new in p u t c i r c u i t has been developed which i s r e l a t i v e l y
s im p le , s t a b l e , and which p e rm its d i r e c t co u p lin g to th e
p h o to m u lt ip l ie r t&hm* The p a r t i c u l a r g a te i s n o t as s e n s i
t i v e as p rev io u s in p u t e f f rc u l ts , b u t t i l l s can be r e a d i ly
c o r re c te d by th e u se o f a pen tode as th e lo ad on th e 9001.
This c o r r e c t io n has been d is c u s s e d in th e t e s t . T h e re fo re ,
th e f ig u re o f m e r i t , i f ex p ressed in te rn s o f g^- th e m u tua l
conductance, i s 300,000 m io ro eh o s, and does n o t r e p re s e n t
th e u l t im a te perform ance o f t h i s g a te .
B e tte r v o lta g e r e g u la t io n i s needed , and s e r i e s r e g u la
to r tubes shou ld be in c lu d ed w ith th e gas type r e g u la to r used
I t i s f u r th e r in d ic a te d t h a t s im i la r g a te s sh ou ld be u sed to
a id in e l im in a tin g th e n o n l in e a r i ty t h a t e x i s t s a t th e equiva
l e n t o f low l i g h t i n t e n s i t i e s .
The c i r c u i t s d ev e lo p ed , and th e in fo rm a tio n g a in ed ,
in d ic a te t h a t th i s in s tru m e n t i s w e ll s u i t e d f o r a s tro n o m ica l
work
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