Tektronix 434, Инструкция по эксплуатации

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o f applied voltages, th e screen (target) operates in the co n ­
ve n tio n a l m o d e , s im ila r to a c o n v e n tio n a l cathode ray tu b e .
Circuit Description—434
The storage screens co n ta in a special coated surface
w h ic h c o n tin u e s to e m it lig h t w hen bom barded b y the
flo o d gun electrons, provided the surface has been w ritte n
b y the w ritin g gun beam and s h ifte d to the stored state.
The tw o targets are e le c tric a lly isolated fro m each o th e r,
w h ic h allow s sim ultaneous presentations o f stored in fo rm a ­
tio n on one h a lf and non-store (co n v e n tio n a l) in fo rm a tio n
on th e o th e r h a lf o f th e view ing area.
Fig. 3-17 illu stra te s th e basic c o n s tru c tio n o f th e 43 4
storage tu b e . The flo o d guns are low -energy e le c tro n guns
w h ic h d ire c t a large area flo w , or cones, o f electrons to w a rd
th e e n tire screen. T h e c o liim a tio n electrodes shape th e
flo o d spray fo r u n ifo rm coverage o f th e storage targets. The
opera tin g level o f th e tu b e is the p o te n tia l d iffe re n c e
betw een the ta rg e t backplates and th e flo o d gun cathodes.
The c o liim a tio n electrodes have no e ffe c t on th e b o m ­
barding energy o f th e flo o d gun electrons.
In th e store m ode re a d y -to -w rite state, th e in s u la to r sur­
face o f th e ta rg e t tends to charge d o w n to a p o te n tia l lo w e r
th a n the b a ckp late p o te n tia l, and to w a rd the p o te n tia l o f
th e flo o d gun ca th o d e . T h is is due to flo o d gun c u rre n t
fro m th e in s u la to r surface. T he p o te n tia l to w h ich th e
ta rg e t charges is called its rest p o te n tia l. T h is p o te n tia l is
such th a t th e flo o d gun e le ctro n landing energy is n o t
enough to illu m in a te th e p h o s p h o r in th e ta rg e t. T he target
is n o w ready to w rite . See Fig. 3-18.
In th e w ritin g process, th e target is scanned by the
w ritin g gun electrons. These high energy electrons increase
the ta rg e t secondary emission over the area th e y scan, so
th a t th e ra tio o f secondary c u rre n t to p rim a ry c u rre n t
becomes greater th a n one. (T h is is shown in Fig. 3-18 as the
firs t crossover p o in t.) W hen th is ra tio exceeds one, th a t p a rt
o f the b o m barded surface sh ifts to a new stable state.
W ritin g has been accom plished and th is segm ent o f the
ta rg e t is n o w stored.
In th e w ritte n state, the p o te n tia l d iffe re n c e betw een the
flo o d gun cathode and ta rg e t becomes greater and th e flo o d
gun electrons n o w have a landing energy th a t is s u ffic ie n t to
p ro v id e a visual d isp la y. T h is visual d is p la y w ill c o n tin u e as
long as th e flo o d gun beam covers the target.
A t high sweep rates, th e w ritin g beam c u rre n t is n o t
adequate to b rin g the p o rtio n o f th e ta rg e t scanned above
th e crossover p o in t; th e re fo re , th e flo o d gun e le ctro n s w hen
landing on th e bom b a rde d area w ill rem ove the charge
developed b y the w ritin g gun e lectrons, and the target w ill
discharge to its in itia l re a d y -to -w rite state w ith o u t being
3 -2 6
F ig . 3 -1 7 . P ic to r ia l d ia g ra m o f sto ra g e tu b e C R T .