Patent GB-510216-A (GB)
Title: Improvements in or relating to indicating and/or recording arrangements employing cathode ray tubes
IPC: G01R13/28
Filed: 1938-05-12
Abstract: 510,216. Cathode-ray oscillographs. HOLZER. W., and SCHWARZ, G. May 12, 1938, No. 14210. Convention date, May 12, 1937. [Class 37] Two or more operations are recorded with the aid of a single cathode ray tube in combination with a selector, the brightness of the electron beam being controlled synchronously with the switching over of the selector, so as to avoid the luminous band between the curves due to switching over. In the apparatus shown in Fig. 2 a cathode ray tube K has its deflecting plates a connected to a selector M assembled together with a control generator to form a unit. The control generator for supplying a rectangular potential comprises two multi-electrode valves V1, V2 each having control grids 1, 2 so arranged that a potential impulse of rectangular form is produced. The grids 2 act as anodes of the control generator, the grids 1 serving as control grids. The stream of electrons passing through all the grids is modulated synchronously with the control frequency at the grids 1, 2. The other electrodes in each valve correspond to the electrodes of a tetrode and act as a selector. The grids 4 serve as control grids and are connected through resistances R2 to the measuring potentials. The rectangular potential is tapped from one of the anode resistances R1 of the control generator part of the valves V1, V2 and is fed through a biassing battery c to the brightness control electrode d of the tube K. Instead of a rectangular potential a sinusoidal control potential may be employed. In this case each of the potentials to be indicated is connected to a grid of a screen grid valve, the valves being in push-pull and forming a selector. The changes in potential across the anode resistances of each of the valves are each applied through a coupling condenser to a separate deflecting plate of the cathode ray tube. Each screen-grid valve alternately liberates a stream of electrons at the maximum value of the sinusoidal high-frequency control potential applied thereto and the measuring operation amplified thereby is connected to the deflecting plate of the cathode ray tube. The relative brightness of the two curves representing the potentials to be indicated is regulated by adjusting the potential of the control electrode d by means of the battery c and the tapping on the resistance R1 so as to alter the portion of the brightness-potential curve in use. The higher brightness valve is allocated to, the potential of higher frequency to be indicated. In a modified arrangement, Fig. 4, the selector M and control generator St are separate. In parallel with the anode resistances R1 of the control generator is the primary winding of a transformer T. The ends of the secondary winding are connected through a full-wave rectifier G to the anode A of the cathode ray tube K, the brightness control electrode I being connected to the centre point. Each time the rectangular potential jumps over, there is set up in the secondary winding of the transformer a current impulse which is converted, through the rectifier G, into a blocking potential on the electrode I. The rectangular potential may be fed as a control potential to the control electrode I by a tapping on one of the resistances R1, enabling a uniform adjustment of the brightness of the two curves to be made, with the elimination of the intermediate band. In an alternative arrangement one of the ends of the secondary winding of the transformer T is connected to the electrode I, whilst the other end is connected to the anode A through a rectifier. By this means every second line between the curves is eliminated. In another arrangement, Fig. 5, the secondary winding of the transformer T is connected to a deflecting coil Sp having a field which attracts or repels the electron beam and displaces it from the aperture in the anode A. The brightness control electrode I is connected to the resistance R1 through a biassing battery c. If the transformer T, Fig. 4, is connected as shown in dotted lines, a peak is obtained in the secondary winding each time the rectangular potential jumps over. The action of one of these peaks may be rendered ineffective by rectification in the cathode ray tube by means of a half-wave rectifier G<SP>1</SP>, or by suitably dimensioning the inductances and reactances as in the case of an induction coil, while the other peak may be used for extinguishing the beam jumping over. Both peaks may be utilized for suppressing the beam during the jumping over by employing the brightness control shown in Fig. 5. With this arrangement, the beam becomes luminous at the instant when neither valve carries current, thereby giving a common zero line for the two curves. Fig. 7 shows an arrangement for use with control potential of very high frequency. Two condensers C3 of small capacity are connected in series by resistances R3. At the instant when the potential jumps over the condensers are discharged and charged in the opposite direction, so that current only passes through the resistances R3 during the reversal of the charge and a potential is set up across these resistances only during this short period. These potentials are connected to the grids of two valves V5 of a push-pull amplifier. During each jumping over one of the valves is operative and a rectified current impulse is produced by the resistance R4, which is connected to the control electrode I.