Patent GB-759441-A (GB)
Title: Method and apparatus for photographically recording traces formed on the screen of a cathode ray tube
IPC: G01R13/20
Filed: 1954-10-12
Abstract: 759,441. Photographing cathode-ray tube screens. TECHNICON CARDIOGRAPH CORPORATION. Oct. 12, 1954 [Nov. 20, 1953], No. 29344/54. Class 98 (1). Apparatus for photographically recording a series of figure traces successively formed on the screen of a cathode-ray tube by the application of signal voltages to both the horizontal and vertical deflecting elements of the tube is characterized in that provision is made to apply a sweep voltage to one of the elements during the formation of each trace whereby the trace is moved over the screen during its formation to clear the screen for formation of the next trace. The photographic film may be moved in synchronism with the movements of the traces. The apparatus shown is used for comparing voltages derived from different parts of a person's body, which voltages vary during each cycle of the action of the heart, the voltage variation differing to some extent from one cycle to the next. One voltage is developed across electrodes connected to the left arm and left leg of the subject, and are applied at LA, LL to an amplifier 15, the output of which is further amplified by an amplifier 16 and applied to the Y-plates 12 of a cathode-ray tube 10. A second voltage is developed across electrodes connected to the left arm and right arm of the subject, and applied at LA, RA to an amplifier 17. The output of amplifier 17 is applied through resistors 19, 21 to an amplifier 18 connected to the X-plates of the tube 10. A trace 20 will be formed on the tube screen, indicating the resultant of the two voltages and an image of the trace is formed by a lens 22 on a photographic film 24, which is fed from a roll 38 over a guide roller 42, across the image-receiving area to a feed roller 36, and is held in frictional contact with roller 36 by a spring- loaded roller 48. Finally the film is fed into an open-ended chamber 46 where it forms a roll under guidance of a leaf spring 54. The feed roller is driven by a variable-speed motor 26 through reduction gear 28. A potentiometer 56 is connected across a battery 63, and has a slider 58 fast with the shaft of the feed roller 36..The variable voltage from the slider 58 is applied to the input of amplifier 18, the resistors 19, 21 serving to isolate the amplifier 17 from the potentiometer. Thus a sweep voltage is superimposed on the signal voltage applied to the X-plates to move the trace as a whole across the screen of the cathode-ray tube. The speed of movement may be adjusted, as by means of a variable resistance in series with the potentiometer 56, until the speed of the image of the trace formed on the film is the same as the speed of the film. The speed of motor 26, or the ratio of the gear 28, may be adjusted so that the traces are recorded in synchronism with the heart beats. A time scale may be provided by means of a generator 73, which applies timed brightening pulses to the grid 71 of tube 10. If the pulses are of saw-tooth wave-form, the bright spots indicate the direction of movement of the spot along the trace. In a modification, the sweep voltage is derived from a conventional voltage generator, part of the output of which is applied to a frequency multiplier, amplified, and used to drive a synchronous motor driving the film feed roller.