The development of the time bridge astronomical photometer · The following block diagram (See Fig....
Transcript of The development of the time bridge astronomical photometer · The following block diagram (See Fig....
The development of the timebridge astronomical photometer
Item Type text; Thesis-Reproduction (electronic)
Authors Kesselman, Martin Samuel, 1923-
Publisher The University of Arizona.
Rights Copyright © is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.
Download date 21/04/2021 05:36:52
Link to Item http://hdl.handle.net/10150/553798
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
"X; Kl'
nr;?il0 ::so-; ; B Jtii":?*ijui.-!
n.t sv::1;: ,'.
3 .':'-' 'i d v v l r i u r '2 orl'vi v-.j n c : : n i r d ; ; ; :
r.c.: ? v;f7
-3 --'j ' i o ,
‘l-> •’.on.:-.
k< p r 5 1 i: •• '£ u q n iL%!
. o.'iv -iCrV: .?..?•■ fjn.tnpot
^ xk r k S #
*V.» xdin/rovJL;;U o-Jaab^O orfd n i
/
b / -i /■':■/ o:i s i uOif
, ; ; i :— !v ■■•♦-'■ v/ : novocrccrA • r-i' lOvODilLi''
m i f fy ? s oV /
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
<►i Zoo Zr
1 i Aftt,
1*-
tHc^- A v y w
Tie
i r.C-Ot
loo K
• l
IOOK
5 K
-* - / 6"o v
*-
i - f
/ 9 o o ir«
V 1 1 -
I
->*lSov
3 oo v-
-e •* 15o v
o Q irnci
^ — 3o o V- To Clrxassil
O— \5ov
O -T StiOV
(o za $q 5 0 6o 7o 8 o
/oat/ Curren t ( *1-4)
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*
/ooo A.-
vvwwISK
♦
V olbd^e few<v- m r m n ---------- —
to Vi- VVWVwvlb<
4 * (d - 4
TZShj>
5k look
zaoki
a io k
1 F 7
JLio K
2ZOK
125 k
i
i oe K
leo K
6 Vf?150
1 e» K r . /o - / » ok a '« d # r-o
w
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
BIBLIOGRAPHY
1 . ’’Development o f an E le c tro n ic P ho tom eter", W.H. P a rk e r , Ohegle p rep ared in th e D epartm ent o f P h y s ic s , U n iv e rs ity of A rizona, (1948) *
2 . ”Photometric Method”, 8 . Becker, T hesis prepared In th e Physics Department, U n iv ers ity o f A rizona, 0-949).
3 . " P h o to e le c tr ic Phenomena” , A.L, Hughes and L .E . D uBridge, M cGraw-Hill Book Company, I n c . , New Y ork, (1932), p . 35.
4 . Kron. G .E .: E le c tro n ic s In Astronomy. E le c t r o n ic s , 2 :1 0 1 ,(1 9 4 8 ) .
5 . Sm ith , J . , Hie L im itin g M agnitude O bservab le w ith a P h o to e le c tr ic S t e l l a r P hotom eter, A s tro p h y s ic a l J o u rn a l, 176:296, (1932).
6 . ’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 , M cGraw-Hill Book Company, I n c . , New York and London, (1947), p . 147.
7 . "Waveforms", B. Chance, M .I .T . R a d ia tio n L ab o ra to ry s e r i e s , M cGraw-Hill Book Company, I n c . , New Y o rk ,(1949), 19:179 .
8 . C lo se , K.N. and Lebenbaum, M . I . , D esign o f P h an ta s tro n Time Delay C irc u its , E le c t r o n ic s . ' 19:100, (1948).