Patent GB-548228-A (GB)
Title: Apparatus for indicating electric currents
IPC: H01K3/30
Filed: 1941-03-31
Abstract: 548,228. Indicating-apparatus. DOWLING, J. J., and SOLUS TEORANTA. March 31, 1941, No. 4309. Convention date, July 2, 1940. [Class 106 (iv)] [Also in Group XXXVI] The values of two currents and their ratio are simultaneously indicated by optical means on a screen or the like. Fig. 1 shows an arrangement for testing the luminous efficiency of electric lamp bulbs. A source of constant D.C. voltage such as a battery A supplies the lamp B under test in series with a small resistance D, across which is connected a mirror galvanometer Q in series with a resistance E. The lamp B is placed in an integrative sphere S so that the output of a photo-electric cell F is proportional to the mean spherical candle power. This output is applied to a second mirror galvanometer R. A spot of light is focused on the mirror of the galvanometer Q by means of a cylindrical lens so that a vertical straight line is formed on a screen. A spot of light is similarly focused on the mirror of the galvanometer R and from there is reflected on to two inclined mirrors in turn so that a horizontal straight line is formed on the screen. The deflection of the galvonometer Q, and hence the position on the screen of the vertical line, is proportional to the current taken by the lamp, and hence to the watts, since the voltage is constant. The position of the horizontal line indicates the lumens emitted by the lamp, the point of intersection of the lines giving the luminous efficiency. An area in which this point must lie for standard limits of efficiency may be marked out on the screen. Fig. 2 shows a modification for testing by alternating current. The primary windings O, O1 of two matched transformers are connected in parallel across an A.C. source A<SP>1</SP>, each primary having a resistance P, P<SP>1</SP> in series, these resistances being equal. The primary winding of a third transformer Z is connected in series with a variable resistance T between the junction points U, Y of the transformers O, O<SP>1</SP> and resistances P, P<SP>1</SP>. The secondary winding of the transformer Z is connected through a rectifier W to the mirror galvanometer Q. The secondary winding of the transformer O is left open and the secondary winding of the transformer O<SP>1</SP> is provided with tappings V<SP>1</SP>, V2, V3 so that lamps to be tested can be plugged into appropriate voltages. A second variable resistance T<SP>1</SP>, ganged with the resistance T, is connected in series with the photo-electric cell F and mirror galvanometer R. To prevent injury to the galvanometers by an overload, an overload relay such as a gas relay valve may be included in the circuit of the transformer Z and operate relays to cut out the two galvanometers and switch on a warning signal. The gas relay valve may have its own transformer. The screen may be graduated vertically in lumens and horizontally in watts, or the value of any two currents can be simultaneously indicated as well as their ratio. The indications may be photographically recorded. The invention is applicable to the plotting of any curves the co-ordinates of which can be represented by two electric currents, such as the characteristic curves of radio valves, magnetic hysteresis curves for simultaneously indicating the velocity and temperature of a circulating fluid, or for recording on a screen at a central station the bearings of a ship from two observation posts on shore. The Specification as open to inspection under Sect. 91 comprises also another arrangement shown in Fig. 9 (Cancelled). The beam of light from a point source X2 falling on the mirror galvanometer R is reflected as a spot of light on to a cylindrical mirror N the radius of curvature of which is equal to its distance from the galvanometer mirror. The spot of light is then reflected towards a point axially above the galvanometer R. Two mirrors L, M are arranged so as to make the spot of light move in a vertical plane and the beam to move at right angles to its original direction, swinging about the point g, which is the position of the image of the mirror of the galvanometer R formed by the cylindrical mirror N and the plane mirrors L, M. The mirror of the galvanometer Q is placed at this position g. The vertical movement of the spot of light on the screen K, due to the deflection of the galvanometer R, corresponds to the lumens and the horizontal movement due to the deflection of the galvanometer Q, corresponds to the watts. The position of the spot on the screen gives their ratio. In a modification, the mirrors L, M are placed between the galvanometer R and the mirror N, which is then placed with its axis horizontal, and the beam is reflected by the mirror N to the mirror of the galvanometer Q. This subject-matter does not appear in the Specification as accepted.