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CATHODE PARAMETER CONVERTERS
The intensive introduction of electronics into experimental and applied physics, computing technology, measuring, control, automatic, and telemechanical apparatus has led to the need to create automatic high-speed parameter converters for these devices according to prescribed mathematical laws. Rapid and reliable conversion of parameters can be successfully carried out1, 2, 3 by means of cathode commutators having shaped lamellae that are a geometric representation of the prescribed functional dependencies.
Fig. 1.
The use of electron-beam commutators for this purpose has made it possible to construct devices for converting parameters according to any prescribed functional dependence, much more simply and reliably than with the aid of other electronic devices.
A cathode converter with a flat beam4 consists (Fig. 1) of an electron gun 1, which produces a flat beam of electrons 2, an electrode
(blade) of a shaped form 3, a screen 4 located behind the blade, and deflecting plates 5, serving to swing the electron beam in a direction perpendicular to its plane. The shape of the blade is shown separately in Fig. 2. One of its edges, \(a\), is cut according to the form of a curve corresponding to a given functional dependence \(y=f(x)\), while the other three edges \(b\), \(c\), and \(d\) are straight, two of them forming the \(X\) and \(Y\) axes. Assuming the current density \(j\) to be constant over the cross section of the electron beam, one may accept (for a sufficiently small beam width) that the current \(I_l\) to the blade will be equal to
\[ I_l = hyj=\frac{f(x)I_p}{y_1}, \tag{1} \]
where \(I_p\) is the total beam current, and \(y_1\) is the extent of the beam cross section
Fig. 2.
Fig. 3.
in the plane of the blade in the direction of the \(Y\) axis. The current \(I_k\) to the screen or collector is correspondingly equal to
\[ I_k=\left(1-\frac{f(x)}{y_1}\right)I_p. \tag{2} \]
The deflection of the electron beam in the direction of the \(X\) axis is directly proportional to the voltage \(U\) applied to the deflecting plates:
\[ X=\beta U, \tag{3} \]
where \(\beta\) is a constant determined by the parameters of the commutator. Therefore expression (3) may be represented in the form
\[ I_l=\frac{I_p}{y_1} f(\beta U). \tag{4} \]
It follows from this that the current to the commutator blade—and, consequently, the voltage taken from the resistance connected to it—may be arbitrary preassigned functions of current or voltage.
At present, the method described is most often used to obtain prescribed functional dependences on time, i.e., to obtain pulses of a given form in various devices. For this purpose it is sufficient that \(U\) be an appropriate, for example linear, function of time.
Soltes\(^1\) described one of the instruments of this type, developed by him for obtaining signals of quadratic form with the aid of a mask with a parabolic cutout (Fig. 3).
The heated cathode 1 is arranged along the axis of the cylinder. Inside it is the heater 2. The planes of the deflecting electrodes 3
and 4 are perpendicular to the axis of the cylinder. Mask 5 and collector 6 are coaxial with cathode 1.
Figure 4 shows two possible forms of the mask with onefold and multiple parabolic contours. A mask with a multiple contour proved to be considerably more expedient, since with such a form its nonuniformities in the emitting ability of individual sections of the active surface of the cathode distort less the form of the prescribed functional dependence.
Fig. 4.
The operation of this converter is based on the following property: a flat beam is focused on the cylindrical surface of the mask, which is coaxial with the cathode. As the voltage on electrodes 3 and 4 of the deflecting system is changed, the electron beam swings along the mask in the direction of the cylinder axis, changing the electron current to the collector of the instrument. According to Soltes¹, the functional dependence, specified by the shape of the mask, of the anode current on the applied voltage was maintained with an accuracy of up to 2%.
A parabolic dependence of the electron current to the collector on the voltage applied to the electrodes of the deflecting system is also obtained when a beam of electrons of rectangular cross section is moved over a triangular mask (in the case of a uniform distribution of electrons over the transverse section of the beam).
To obtain a stepwise dependence of the anode current on voltage, the mask shown in Fig. 5 may be used.
Fig. 5.
Fig. 6.
Münster² described a cathode commutator for a parameter converter with a circular beam of electrons, in which the beam is moved along a contour corresponding to the prescribed functional dependence.
A schematic diagram of the commutator is shown in Fig. 6. It consists of an electron gun 1, two pairs (2 and 3) of electrodes of systems for electrostatic deflection of the electron beam, target 4, and collector 5.
The target is made of a material with a secondary-electron-emission coefficient greater than unity. A figured mask is deposited on its surface, constituting a layer of carbon powder whose secondary-electron-emission coefficient is less than unity. Owing to this, the beam of electrons incident on the mask gives a direct current in the lamella circuit; and the beam incident on the part of the target not covered by the mask gives a current in the opposite direction. Only the beam of electrons incident on the edge of the mask can give a current in the lamella circuit equal to zero. Negative feedback in the lamella circuit to electrodes 2 of vertical deflection of the electron beam gives a change in voltage forcing the electron beam to deflect in the vertical
direction (toward the edge of the mask) until the beam current at the target becomes equal to zero.
The electron beam deflected in the horizontal direction is thereby displaced along the contour of the mask, while the value of the voltage applied to the vertically deflecting electrodes 3 varies according to a law determined by the shape of the mask.
The voltage to be converted is applied to the electrodes 2 for horizontal deflection of the beam. The converted voltage is taken from the electrodes 3 for vertical deflection.
Of considerable practical interest are new systems of cathode parameter converters,^3 whose operation is based on changing the secondary-electron-emission coefficient as the angle of incidence of the primary electrons is varied. The basic circuit of a commutator of this type is shown in Fig. 7. Its operation reduces to the following. Deflection of the electron beam 1, produced by the electron gun 2, in the vertical direction leads to a change in the angle of incidence of the electrons on the surface of the target 3, as a result of which the secondary-electron current to the collector 4 changes. The nature of the relief of the target determines, in this way, the mathematical law of conversion of the voltage applied to the horizontal-deflection plates of the commutator.
Fig. 7.
L. G.
References Cited
- A. Soltes, Electronics 22, No. 8, 122 (1950).
- A. Münster, Radio Television News 44, No. 4, 8—A (1950).
- Smith, Proceedings of JRE 40, No. 6, 666 (1952).
- L. Goncharskii, Author’s Certificate 81495 of 4/III 1949, published in Bulletin of Inventions, No. 6 for 1950.