Fortress Technologies An E1T Timepiece, Руководство пользователя

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5.1.2 - Ribbon Shaped Electron Beams
In tubes such as the E1T in which the beam is deflected only in one plane, a ribbon shaped
electron beam of relatively large cross sectional area can be used (since the resolution in one
plane is unimportant), but in normal cathode ray tubes a very small circular beam must be used
to obtain good resolution in two dimensions. For a given charge density in the beam and a given
applied voltage, a larger current will flow in a ribbon shaped beam than in a small circular beam
owing to the larger cross sectional area of the former. A large current is desirable in the E1T so
that the stray electrode capacitances can be quickly charged. The ribbon shaped beam enables
the tube to operate from fairly small voltages. This favours high operating speeds because the
change in the electrode potentials (and hence the change in the charge of the stray
capacitances) is kept small. The use of a ribbon shaped beam also has the additional advantages
that the dimensions of the tube (and hence the inter-electrode capacitances) can be small and
that the alignment of the tube need be carried out accurately only in one dimension. In the E1T a
beam current of about 1 mA is used at an applied potential of about 300V.
5.2 - ANODE CHARACTERISTICS
The anode characteristics of the E1T must be
examined in order to ascertain why the ten
holes in g
4
enable the electron beam to exist in
ten stable states. If the horizontal slot in g
4
(shown in Fig. 5.4) were not present, the main
anode current I
a2
plotted against the deflector
voltage of plate x" (V
x''
) would be as shown in
Fig. 5.5 (a) provided that the potential of the
other deflector plate, V
x'''
were kept constant.
When the potential of x" is altered, the beam is
deflected and passes through a series of
maxima and minima as it passes across the
holes in g
4
. The anode current will be a
maximum when the beam is centred on one of
the holes in g
4
and will be zero when it is
entirely intercepted by g
4
. In normal operation
the main anode, a
2
, is connected directly to the
deflector plate x". The potentials of x" and of a
2
are therefore identical and Fig. 5.5(a) is the
dynamic anode current/anode voltage
characteristic for this method of connection
when the potential of x' is constant. The
presence of the horizontal slot in Fig. 5.4
changes the anode characteristic from that shown in Fig. 5.5(a) to that shown in Fig. 5.5(b). When
the beam is in a position to the left of the fifth vertical slot in Fig. 5.4, a constant current passes
through the horizontal slot and this current is super-imposed on any current which may pass
through one of the vertical slots. Hence the shape of the Fig. 5.5(b) characteristic. In practice the
characteristic is further modified by the fact that the slots in g
4
are not of constant width. The
actual E1T anode characteristic is shown in Fig. 5.6 for the case when the x' deflector electrode
has a potential of 156 V. It may be noted that when both of the deflector electrodes have the
same potential (V
x'
= V
x''
= V
a2
= 156V), the beam is not deflected and the tube indicates a
number in about the middle of the decade.
Page 114 Version 1.0 Copyright Grahame Marsh/Nick Stock 2019
Fig 5.5 - Theoretical Characteristics of the EIT, (a)
When g4 Has No Horizontal Slot and (b) When the
Horizontal Slot is Present in g4