Patent GB-435820-A (GB)
Title: Method of and apparatus for measuring and, if desired, for registering the energy ofrays
IPC: G01J3/32
Filed: 1934-03-29
Abstract: 435,820. Photometric apparatus. MEIER, K. H., 7, Bleicherweg, Zurich, Switzerland. March 29, 1934, No. 9921. [Class 97 (i)] [See also Group XL] The intensity of light or other radiation is measured, and, if desired, registered, by projecting the radiation on a dispersion device so as to form a spectrum the parts of which are projected in rapid succession on a radiation-sensitive device by which electric currents proportional to the incident radiation are produced. These currents are added and, if desired, registered, by means of a measuring instrument. As shown in Figs. 1 and 2, light from a scene &c. K, illuminated by lamps L, L1, is directed by lenses S, S1, S2, and a magnesite reflector M to a prism P1, and the spectrum emerging from the prism is passed through a lens S3 and falls on a rapidly rotated disc T, This disc has a number of slots T1 .. T7 at different distances from its centre so that each slot passes a different portion of the spectrum. The light traversing the slots passes through a slot H<1>1 in a fixed plate H1 and is focused by a cylindrical lens S4 on a photoelectric cell P connected through an amplifier V to a measuring instrument W. The dimensions of the slots T1 &c. may be so chosen as to accentuate the effect on the cell P of certain parts of the spectrum, or to compensate for the selective sensitivity of the cell to certain wave-lengths. The measuring instrument may be arranged as shown in Fig. 3 in which a condenser K, which is charged by closing contacts 1, 2, is arranged in parallel with the cell P and is connected to the grid 21 of a thermionic valve D, the anode of the valve being connected to the winding of an electromagnet 10. The rotary armature of the magnet carries an arm 4 adapted to close the contacts 1, 2, and also carries a loose ratchet wheel 5 co-operating with a pawl 7 on the armature and a pawl 15 on the magnet. When the condenser K is initially charged it produces negative potential on the grid 21 and there is consequently no current in the anode circuit. As the condenser discharges owing to the lowered resistance of the cell P caused by the incident radiation, the current builds up so that the armature is rotated carrying the arm 4 with it, the wheel 5 being held by the pawl 15. When the arm 4 has moved sufficiently it closes the contacts 1, 2 to recharge the condenser so that the anode current ceases. The armature is returned against a stop 8 by a spring f, the wheel 5 being turned during this rotation by the pawl 7. The total radiation falling on the cell P is measured by measuring the total rotation of the wheel 5. In another arrangement of measuring circuit the cathode of the cell is connected to a filament electrometer and the pulsations of the filament are converted by means of a thermionic valve and a transformer into an alternating current which operates an electromagnetic counter. In another arrangement a cell of the copper oxide &c. type, which does not require an applied E.M.F., is used instead of the cell of the kind shown. Fig. 6 shows an arrangement for measuring the radiation from a R÷utgen ray tube 100. The radiation is received by a rock salt &c. crystal 106 mounted on an oscillating table 105 on which is also mounted a metal ionization chamber 104 in which is stretched an insulated wire 117. The chamber and the wire 117 are connected to a thermionic valve amplifier in such a manner that a condenser connected to the grid of the valve is arranged in parallel with the chamber. For measuring the radiation absorbed by a body two photo-electric cells are used, one receiving the incident radiation and the other the radiation transmitted by the body. Each of these cells may be provided with a measuring circuit such as that shown in Fig. 3, the two measuring instruments being connected to a differential gear, or the cells may be arranged in a bridge circuit with a single measuring instrument by which the desired difference is indicated.