Patent GB-562817-A (GB)
Title: Improvements in or relating to wave-form analysing apparatus
IPC: A61B5/04
Filed: 1943-02-11
Abstract: 562,817. Wave-form analysers. WALTER, W. G. Feb. 11, 1943, Nos. 2282 and 11700. [Class 40 (iii)] [Also in Group XXXVI] Apparatus which auto matically performs con tinuous analyses of com plex semi-periodic wave forms, such as those associated with the poten tials obtainable from biological material, e.g. electro - encephalogram or heart action potentials, or of the oscillations of vibrating machinery, comprises a number of reeds responsive to different frequencies and provided with light shutters which in the position of rest screen associated vacuum photoelectric cells from a steady light source around which the photo-electric cells are grouped. The outputs of the cells are used to charge condensers in accordance with the energy of vibration of the associated reeds, the condensers being scanned by a rotating arm to control an oscillograph. In a modification, Fig. 7, barrierlayer selenium cells 71a, 71b ... 71x are variably screened from a light source by aluminium shutters 70a, 70b ... 70x carried by the reeds 3a, 3b ... 3x. Each cell is connected between the control grid and cathode of an associated multi-grid valve 72a, 72b ... 72x. The anodes of the valves are connected directly to the switches 15a, 15b ... 15x leading to the alternative banks of condensers 16a, 16b ... 16x and 17a, 17b ... 17x which are also connected to the banks of contacts 34a, 34b ... 34x and 38a, 38b ... 38x scanned by contact arms 31, 28. The charges acquired by the condensers in this arrangement are negative and have to be inverted before passing to the grid of the valve driving the oscillograph. A phase-inverting circuit for this purpose is shown in Fig. 8 and includes a transformer 82 having primary terminals 74a, 79a for connection to the terminals 74, 79, Fig. 7. The secondary winding is connected to the grid of the valve 46 through a rectifier 83 and is given a negative bias of 40 volts. When using this circuit a switch 80a, Fig. 7, is left open and the marking pulses are not derived from the contacts 35a, 35b, &c., but by means of a separate scanning arm 87 which is carried by the switch 27 and scans special marking contacts arranged in a separate bank. In an alternative circuit, Fig. 9, the cathode of the valve 46 is connected through a terminal, 79b to the terminal 79, Fig. 7, and the grid is connected through a terminal 85a to a tapping 85 on a resistance 78, Fig. 7, so as to be biassed negatively. The cathode is also connected through a potentiometer 89 to a terminal 74b<1> connected to the terminal 74, Fig. 7. The negative charges acquired by the condensers drive the cathode of the valve 46 negative with respect to its grid and cause the anode current to increase and operate the recording oscillograph 48. The marking pulses are derived from the contacts 35a, 35b, &c., but are transmitted through terminals 79, 79b to the cathode of the valve 46, which is driven momentarily more positive by 5 volts through connection to a tapping 81, which is 5 volts positive with respect to the tapping 75. The reeds, energizing solenoids, and photo-voltaic cells used in the circuit shown in Fig, 7 may be arranged as shown in Fig. 13. Six reeds are shown arranged in pairs 93x, 93i ; 93r, 93d ; 93n, 93c, corresponding to frequencies of 30, 9 ; 18, 4 ; 14, 3. The reeds extend radially outwards from a central ring 90 against which they are clamped by plates 91. Each pair of reeds passes through a single energizing coil and carries weights 92 on screw-threaded rods for tuning. The free ends of each pair of reeds are adjacent to the poles of a magnet 93, of which one is provided for each pair of reeds. At right angles to each reed is fixed a light aluminium shutter 94 which extends in front of a housing 95 provided for each reed, in which a photovoltaic cell is located. The housing 95 has a front aperture 96, Fig. 13B, to the rear of which is a U-shaped retainer 97 passing through pairs of holes in the upper and lower walls of the housing. This retainer limits' the forward movement of a transparent shield 98 against the pressure of a Z-shaped beryllium-copper spring 99 which bears against a terminal 100 and against a photo-voltaic cell 101 adjacent to the shield 98. A wire 102, brought out through the side wall of the housing, is connected to a strip contact on the front of the cell. In the middle of the supporting ring 90, Fig. 13, is a mercury-vapour enclosed fluorescent lamp 103. In the rest position the cells are screened by the shutters 94 from the lamp 103.