GB507231A - Apparatus for determining the density of photographic film - Google Patents

Abstract

507,231. Capacitance measurements. LEIJONHUFVUD, A. S. Sept. 8, 1937, No. 24505. Void. Convention date, Sept. 8, 1936. [Class 37] [Also in Group XX] An apparatus for determining the density of photographic film, plates, and the like has an electric oscillation circuit including a condenser between the plates of which is introduced the photographic film, and a tuning device determining the change in the capacity of the condenser. The sender circuits include a thermionic valve 1 with anode 2, grid 3 and filament cathode 4, the plate circuit containing a tuning coil 8 and the primary coil 9 of a coupling transformer. The sender is controlled to give constant frequency. The secondary coil 10 is connected to the receiver R which comprises a thermionic valve 11 with electrodes 12, 13, 14, a testing condenser: 17 through which the film is passed and tuning condensers 19, 20. Indicator means connected between the coil 10 and the supply may comprise a telephone receiver, a glow discharge lamp or the like. The testing condenser consists of two metal plates of small area, suitable guiding means being provided for the film. Oscillations of high frequency are preferably used. In operation a blank film is first tested, the condenser 20 maintained at zero position and the condenser 19 adjusted to compensate for the change in the capacity of the condenser 17. The blank film is removed and the photographic film inserted, the condenser 20 being adjusted to bring the circuits into resonance. The adjustment of the condenser 20 is a measure of the density of the metal grains in the film. Alternatively, the tuning condensers may he connected in the sender circuit.