GB448904A - Improvements in and relating to photo-electric photometers - Google Patents

Abstract

448,904. Photometric apparatus. HOLOPHANE, Ltd., and ENGLISH, S., Holophane House, Elverton Street, Vincent Square, London, andEVERETT, EDGCUMBE, & CO., Ltd., and EDGCUMBE, K., Colindale Works, The Hyde, Hendon, London. Feb. 27, 1935, No. 6270. [Class 97 (i)] A photo-electric photometer for measuring the intensities of illuminants of different colours, such as an incandescent electric lamp and a vapour discharge lamp, is provided with a manually operable resistance control for applying colour correction factors to the galvanometer readings in order to compensate for the difference between the colour sensitivity curve of the photo-electric cell and that of the eye, so that the galvanometer reads directly in light intensity units or known multiples thereof when the control is set to the appropriate position for the colour of the light to be measured. The apparatus shown consists of two similar photo-electric cells M, N connected to a galvanometer G which is provided with shunt resistances R1, R2 connected to studs C, D over which a contact arm T is adapted to move. When the arm is in contact with stud C, the galvanometer is shunted by the resistance R2, and when on the stud D, the shunt resistance is R1+R2. When the' arm T is on a further stud E, no shunt is applied to the galvanometer. Further studs A, B are provided, the stud A enabling the galvanometer to be short-circuited for transport and'the stud B providing an " off position for the arm T. A second arm T1 rotates with the arm T over studs A1 ... E1, and is adapted. to insert resistances R3, R4 in series with the galvanometer, these resistances being of such magnitude as to maintain constant the total resistance of the galvanometer circuit between the points Q, R. There is also provided an arm V movable over studs F, H, K, L to vary the scale of the readings. In position F the cells M, N are connected in parallel to the points Q, R and the galvanometer reading divided by ten represents foot-candles. In position H only the cell N is connected to the points Q, R and the galvanometer circuit is shunted by a resistance R5 of such magnitude. that the galvanometer reads foot-candles directly. The shunt resistances R6, R7 connected to the studs K, L provide for further modifications in the scale of the galvanometer readings.