Patent GB-653101-A (GB)
Title: Improvements in and relating to variable frequency generator
IPC: A61N1/32
Filed: 1948-06-25
Abstract: 653,101. Photo-electric production of alternating current. BRITISH THOMSON-HOUSTON CO., Ltd. June 25, 1948, No. 17182. Convention date, June 26, 1947. [Class 40 (iii)] [Also in Groups VI and XL (c)] An electromedical set comprises means for obtaining substantially sinusoidal current of a frequency adjustable smoothly between 2 and 100 c.p.s. and either modulated at a frequency adjustable between 2 and 120 cycles per minute or unmodulated from a pair of photo-cells acted on by rotary shutters of adjustable speed. Alternatively, direct current may be applied to the patient. Both kinds of current are applied through meters having several ranges and are adjustable in intensity. A safety device is incorporated whereby the apparatus can only be started into operation when the patient circuit is adjusted for zero intensity. Generating photo-electric impulses. A shutter disc 16, Fig. 1, with a number of apertures 20, is driven between a lamp 15 and photo-cells 12, 12<SP>1</SP>, so that they are illuminated alternately, by an eddy-current disc motor the current coil of which is supplied from an adjustable potential divider to vary the speed. The disc may also be acted on by a D.C. excited drag magnet fed from a potential divider 46, Fig. 5, to give a lower speed range. The impulses generated in this way are modulated by an eccentricallymounted disc 27 driven by a similar eddycurrent motor with a permanent drag magnet. The disc of this motor is provided with a hole which normally is without effect but which when the motor is rotating very slowly brings it to rest with the hole registering with the poles of the driving magnet. In this position, the disc is clear of the apertures on the disc 16. Amplifying photo-electric impulses. Each photo-cell is coupled by a cathode follower valve 65 (65<SP>1</SP>) with an output circuit involving a pair of valves 66, 68 (66<SP>1</SP>, 681), the current path through the patient involving for one half-cycle the valves 66, 68 in series, the grid of 68 being connected to a tapping on the cathode resistor of 66, and for the other the valves 66<SP>1</SP>, 68<SP>1</SP>, which are similarly connected. Switching, adjusting and supervising. The main switch 38 connects the mains to a rectifier set providing two sources of D.C. for the amplifier and a third for the drag magnet 26. The patient-plug is connected via a reversing switch 83 and the appropriate coil of either a three-range A.C. meter 77<SP>1</SP> or a two-range D.C. meter 77 which is connected up by a relay 78, 78<SP>1</SP> when D.C. or slow A.C. treatment is being given, to a circuit which is connected to the output of the patient potential divider 87 by a relay 86<SP>1</SP> which operates and locks up (provided that the potential divider is at its zero setting) when the apparatus is switched on. The potential divider is connected at will either to the high-tension supply or to the output of the amplifier. The current-coils of the motors are fed by transformers, the primaries of which are excited from speed-adjusting potential dividers 59, 59<SP>1</SP>, or calibrating rheostats 58, 58<SP>1</SP>. A further adjustable source is provided for the lamp. When it is desired to stop the motor driving the modulating disc, the switch 61 is operated to provide a much reduced current and the motor then stops in a definite position with the shutter disc clear of the photo-cells.