Fortress Technologies An E1T Timepiece, Руководство пользователя

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5.3 - BEAM STABILITY
The basic type of circuit used to supply
voltages to the tube is shown in Fig. 5.7. The
anode resistor, R
a2
normally has a value of
1M Ω . The straight line in Fig. 5.6 is the load line
for this value of resistor. If the beam is initially
at the position a of Fig. 5.6 (indicating the digit
zero) and the potential of the deflector
electrode x' is increased relatively slowly (so
slowly that the effect of the stray capacitance,
C, shown in Fig. 5.7 is negligible), the beam will
tend to be deflected towards the electrode x'.
As the beam moves, however, it can be seen
from the anode characteristic of Fig. 5.6 that it
begins to pass out of the slot in g
4
and less of it
strikes the anode. The resulting reduction in
anode current leads to a reduction in the voltage dropped across the resistor R
a
, and hence to an
increase in the common potential of the anode
and of the deflector electrode x". The slope of
the E1T characteristic is very steep at the points
where it is crossed by the load line shown and
therefore this increase in the potential of x" is
almost equal to the initial increase in the
potential of x' which caused it. As both
deflector electrodes are increased in potential
by almost equal amounts, the amount by which
the beam is deflected is virtually unchanged.
Similarly if the beam is at a and x' becomes
slowly more negative, the anode current is
increased (see Fig. 5.6) and this in turn causes a
reduction in the potential of x". Thus the
position a in Fig. 5.6 is a very stable one. The
intersections of the load line with the rising
parts of the E1T characteristic are the ten stable
beam positions which are required for storing the information about the state of the count. The
anode a
2
and the x" deflector plate are connected in a feedback system. The slope of the E1T
characteristic is very much greater than the slope of the 1 MS/ load line at the operating point
and this results in the feedback factor - and hence the stability of the operating point - being very
high. The positions a, c, e, g, i, etc. in Fig. 5.6 are all very stable.
If the beam is at any moment at b or d, any slight increase in the potential of x' will cause the
beam to be deflected towards this electrode and it can be seen from Fig. 5.6 that the anode
current will then increase as more of the beam passes through the slot in g
4
. The potential of the
anode and of x" therefore decreases causing the beam to swing farther away from the x"
electrode. Eventually the beam will come to rest at one of the stable points c or e. Similarly if the
beam is momentarily at b or d and the potential of x' is decreased slightly, the beam will move so
that the voltage of x" becomes higher until a stable operating point is reached. The positions b, d,
f, etc. are therefore unstable and the beam does not stay in a position represented by one of
these points for more than a minute fraction of a second.
Page 115 Version 1.0 Copyright Grahame Marsh/Nick Stock 2019
Fig 5.7 - The Basic Circuit for the E1T
Fig 5.6 - The E1T Anode Characteristic for Vx' = 156V