US1913449A - Electric oscillator - Google Patents

Description

June 13, 1933. M. KOBAYASHI ELECTRIC OSCILLATOR Filed Feb. 24, 1930 RZMWEUSU T/ME ATTOP/Vf) Patented June 13, 1933 UNITED STATES PATENT OFFICE MASATSUGU KOBAYASHI, OF AZA HIKAWA, TOYOTAMA, TOKYO, JAPAN, ASSIGNOB TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORA- TION OF NEW YORK ELECTRIC OSCILLATOR Application filed February 24, 1930, Serial This invention relates to electric oscillators, and particularly to a modification of the structure of a well-known type of vacuum tube oscillator to enable-it to generate a wave of a particular form.

It is an object of the invention to generate a saw-tooth wave by means which is sim-- pler, less expensive, and inherently more stable as to frequency and wave form, than prior alternative means.

The invention is especially adaptable for use with a cathode ray oscillograph device or the like to insure that the cathode ray traces a path as in accordance w th conventional representation rather than in the form of Lissajous figures. The invention 15, therefore, especially adaptable for use in the socalled sweep circuit for cathode ray osc1llographs. It is accordingly a further object of the invention to mprove operatingcharacteristics of systems ofthe above character and especially to provide sweep circuit means for cathode ray oscillographs which excel in simplicity, economy, both as to original plant and operation, and in frequency and wave form stability.

The novelty of the invention resides 1n the use of a modified form of vacuum tube oscillator for obtaining a saw-tooth wave as adapted, for example, for use in a sweep circuit for a cathode ray oscillograph as by being applied to a certain pair of reflector plates therein. Hitherto reliance has been had on devices which did not include vacuum tubes as Wave generating means, but

which used neon tubes or the like, functioning merely as circuit interrupters. Familiar instances of these prior means are disclosed in Knoop Patent 1,613,954, January 11, 1927, and Kipping Patent 1,592,274, August 13, 1926.

In these prior means a condenser 1s perlodically charged and discharged by means of an interrupter constituted by a neon tube or the like, the charge or discharge being made linear by causing the current to flow through a saturated vacuum tube or other current limiting device. The present invention in a general way may be considered as an adaptation of these prior means for use with a ticular the saw-tooth wave form of the out- No. 430,531, and in Japan March 5, 1929.

vacuum tube interrupting means. The vacuum tube used is of the conventional three-eleinent type having coupling coils in the input and output circuits. A portion of the output circuit is branched, one branch being constituted by a capacity and the other by the usual space current source and a high resistance. 1n the operation of the device the condenser is charged by the space battery through the resistance, the tube being adjusted so that during the charge practically no current flows in the plate-filament path. However, when this current: does begin to flow, on account of the inductive coupling between the output and input circuits it tends to very rapidly accelerate, discharging the condenser very rapidly. As a result, there is a cyclical, slow and fairly uniform charge and a constant and very rapid discharge, the wave, therefore, being of the saw-tooth yp 0 her features and characteristics of the invention will appear from the following detailed description taken in connection with the accompanying drawing in which,

Fig. 1 illustrates a preferred form of the oscillator circuit of the invention;

Fig. 2 is a circuit representation, not illustrative of the circuit of the invention as a whole but which is useful in the explanation of the operation of said circuit; and

Fig. 3 illustrates in general the saw-tooth wave form of the output current or potential of the oscillator of the invention and in parput current.

In the circuit of Fig. 1 reference character '1 represents a, transformer whose primary and secondary windings are inserted respectively in the plate circuit and the grid circuit of a conventional three-element vacuum tube VT having a space current source S. The ratio of transformation of the transformer T is large and the high voltage side is connected in the grid circuit. Reference character C represents a condenser and R a high series resistance. If a suitable direction is given to the mutual inductance of the transformer T in this circuit, the plate current of the Vacuum tube pulsates and the wave form of the current flowing through resistance vR, becomes like that illustrated in Fig. 3, which may be described by the term saw-tooth. Hence, a voltage having a saw-tooth wave form may be obtained from the terminals of the resistance. Theifrequency of pulsation may be varied to suit the urpose of use by a proper choice of trans ormer, condenser and resistance. The reason that a pulsating electric current of a saw-tooth wave form may be generated with the circuit arrangement of Fig. 1 may be briefly explained as follows:

With reference to the circuit of F g. 2, 1llus- 'trating in part the circuit of the invention which is illustrated in more detail in Fig. 1, and considering a case in WlllCll the prlmary and the secondary windings of the transformer are inserted respectively in the plate circuit and the grid circuit of the vacuum tube, it may be seen that for the alternating values of the plate and grid voltages and of the plate current the equation holds, where R is the internal resistance of the plate-filament circuit of the vacuum tube 2' the plate current, 6 the terminal voltage of the coil connected in the plate circuit, e, the terminal voltage of the coil connected in the grid circuit and the ratio of ampllficatlon factor.

If L denotes the inductance of the coil connected in the plate circuit, 1' its resistance and M the mutual inductance between the primary and secondary coils and if the grid current is neglected because it is small, 6,, and a may be expressedas follows If these values of 6 and e are substituted in Equation (1) d If this differential equation is solved, the equation is obtained, where 2', is the value of current corresponding to t=o, that is, '5 =45 e t 0 L :i: pM Since, if the value of R+r L :12 pM evident that i lncreases slowly at first and then very rapidly as time passes. Theoretically the value of the current increases very rapidly to infinity according to the last equation, but actually it is limited due to the current saturation, etc. of the vacuum tube. Having in mind the relations above pointed out, the operation of the circuit of Fig. 1 may be explained as follows:

The voltage of the space current source S charges condenser 0 through high resistance Rgand raises the terminal voltage of this condenser, this voltage also being the plate voltage of vacuum tube VT. If the transformer constants are of such values as to render the value of R+r LiuM negative, the plate current is small at first,

butincreases very rapidly with time. But since R is a high resistance, the plate current cannot be supplied only by the current through R so that a part of the load is supplied from the condenser C. The terminal voltage of the condenser then drops and the plate current diminishes to a small value as before whereupon the charging of the condenser is restarted by the current through R the other pair of terminal plates, and if the frequency of the oscillator system for generating currents of saw-tooth Wave form is properly regulated, the unknown Wave form may be pictured in conventional form on the fluorescent screen of the oscillograph.

Again, since the saw-tooth form of waves implies the presence of many higher harmonic waves, it is possible to take out a desired higher harmonic wave and obtain a correspondin relatively high frequency current.

at is claimed is: i

1. An oscillation generator comprising a space discharge device having an input and an output circuit, a source of space current for said device in said output circuit, a condenser in generally parallel relation with said output circuit, a resistance in series with said source, said resistance and source being in parallel with said condenser, means coupling said input and output circuits at a point in said output circuit in common to the portions thereof traced through said condenser and said source, and an energy transfer circuit connected to the terminals of said resistance.

2. A saw-tooth wave generator comprising in combination a space discharge device including a cathode, an anode and a control electrode, a space current source for the anodecathode circuit of said device, a condenser in generally parallel relation with said source, a resistance in series with said source and in generally parallel relation with said condenser,a coupling coil connected between the anode and said source and condenser, and a control electrode-cathode circuit including a coil in coupled relation with said anode coupling coil, the normal adjustment of the device being such that substantially no current flows in the anode-cathode circuit until a super-threshold value of the potential across said condenser is reached, and an energy transfer circuit connected to the terminals of said resistance.

In witness whereof, I hereunto subscribe my name this 29th day of January, 1930.

MASATSUGU KOBAYASHI.

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