Patent GB-483836-A (GB)
Title: Improvements in fire prevention devices for cinematograph projection apparatus
IPC: G03B21/18
Filed: 1936-11-04
Abstract: 483,836. Kinematograph apparatus. SEBASTIANI, P. Nov. 4, 1936, No. 30050. Convention date, Nov. 11, 1935. [Class 97 (i)] A fire-prevention device for kinematograph projection employs a current interrupter mounted above the film gate and intermittently actuated by the film, and is characterized in that the interrupted current charges a condenser which discharges during the interruptions, the current impulses thus produced acting on a relay which controls a circuit serving for actuating the fire protective flap. Fig. 2 is a cross section of the interrupter used. Rollers r, r<1>, mounted on a common spindle, are frictionally driven by the margins of the film. A collar s on the same spindle has two V-shaped notches b<4>. The sleeve t, loose on the spindle, has two teeth which are pressed into the notches by the spring b<5>. The sleeve t carries a contact ring v on a layer of insulating material u. At each intermittent movement of the film and of the rollers r, r<1> the teeth on the sleeve t tend to rise out of the notches b<4> owing to the inertia of the sleeve. Consequently the sleeve t and contact ring are forced to the right until the latter engages two contacts b<2>, b<3> connected to the points b, b<1>. Fig. 1 shows the interrupter in position on the projector and also the associated apparatus. A steady E.M.F. is applied to the points a, a<1> and each time contact is made between the points b, b<1> the condenser m is charged. Part of the charging current passes through each of the limbs k<1>, k<2> of a differential relay k, the armature k of which carries a mercury switch k<3> normally held in the " off " position by a spring. In series with the respective limbs of the relay are a choke l with a parallel variable resistance n<1>, and a resistance n<2>. When contact between b. b<1> is broken the condenser is discharged through the same circuits and through the resistance n<3>. As the speed of the projector increases, a greater fraction of the charging and discharging currents passes through the limb k<2> of the relay on account of the increasing reactance of the choke l. At a certain projector speed the attraction from this limb of the relay is sufficient to operate the mercury switch k<3>. This is used to switch on the power to the motor, and operate a fire-protective flap. Auxiliary means are used to run the projector up to the critical speed. Contact in the switch k<3> operates the relay o. To obtain a powerful response this is connected directly to a, a<1> the resistance n<4>, connected to i, i<1>, only coming into circuit when the relay has moved. The relay closes the contacts f, f<1> to supply the motor M, and e, e<1>, to operate the electromagnetic device F to lift the protective flap A. Contacts g, g<1>, h, h<1> close the circuits of the sound lamp and of a relay in the auditorium lighting circuits. The projector may be run up to the critical speed by hand, or bv depressing the button z. The contacts d, d<1> in an alternative motor circuit are thus closed and held closed by the motor current flowing in the coil x, attracting an armature w and holding the lever w<1> in the notch y<1> of the rod y. When the contacts f, f<1> are closed this device is returned to its original position by the spring y<2>. To stop the projector the button z is pulled out, thus closing the contacts c, c<1>, short circuiting the limb k<2> of the relay, releasing the armature, and opening the switch k<3>.