GB506544A - Electro-therapeutic apparatus - Google Patents

Abstract

506,544. Supply systems for consumption apparatus. ASSOCIATED P.A. EQUIPMENTS, Ltd., and DENNY, B. Dec. 7, 1937, No. 33875. [Class 38 (iv)] Periodic variation of the intensity of pulsating electric potentials supplied to electrotherapeutic apparatus is obtained by means of a resistance capacity timing circuit controlling a thermionic valve in the supply circuit. The secondary of an input transformer 6, the primary of which is supplied with alternating or intermittent current, and the primary of an output transformer 5, the secondary of which supplies the electro-therapeutic apparatus, are connected in series with a source of direct current A-B between the anode and cathode of a threeelectrode thermionic valve 4. The intensity of the pulsating electric potential available at the secondary terminals of transformer 5 is controlled by a biassing circuit which controls the potential applied to the grid of valve 4. The cathode and control grid of valve 4 are respectively connected to the movable contacts of potentiometers 8 and 7, provided for adjustment. Potentiometer 8 is connected directly across a source of direct current EF while potentiometer 7 is in series with a resistance 10 and a change-over switch 9 across the same source. Operation of the switch 9 changes the potential applied to the grid of valve 4. Auto. matic operation of this switch to produce a periodic variation of the intensity of the pulsating potential output is effected by a time-base circuit in which a change-over switch 13, mechanically coupled to switch 9, is operated periodically by electromagnet 14. The winding of this electromagnet is energized from the terminals of a condenser 18 charged from a direct current source C-D via switch 13 and resistance 15. The cycle of operations in this circuit is the charging of condenser 18 to the potential at which electromagnet 14 changes over switch 13 whereupon condenser 18 discharges through resistance 15, switch 13 returns, and charging starts again. A potentiometer 16 is provided to vary the charging and discharging time periods and a resistance 17 is connected across the direct current source. Condensers 11 and 12 are included in the biassing circuit to modify the rate of change of potential on the valve grid, and in a modification, Fig. 2 (not shown), these condensers are associated with potentiometers for adjustment. In this modification, the source of direct current for the anodecathode circuit is obtained from the alternating or intermittent current source by the use of centre - tapped transformers and diode thermionic rectifiers, while in a further modification, Fig. 3 (not shown), these diodes are replaced by Argon-filled thermionic relays having grid electrodes, the potentials of which can be varied by potentiometer to alter the output waveform. In this latter modification, the biassing and time-base circuits are combined in one circuit.