| 摘要 |
1,142,536. Light intensity measurement. P. GOSSEN& CO. G.m.b.H. Oct. 16, 1967 [June 6, 1967], No. 46973/67. Heading G1A. [Also in Division G2] A light intensity measuring device in which adjustment of a light attenuation device varies the amount of light falling on a photo-sensitive element, has two indicator lamps one of which flashes on and off at a rate dependent on the size of the displacement of the light attenuation device from its correct setting. In the exposure meter shown a photo-resistor 1 forms a potential divider with a resistor 3 or a resistor 4 according to the setting of a range switch 6. In operation a diaphragm 19 is adjusted varying the amount of light falling on the photo-resistor 1 until the correct setting is reached. At this correct setting both of a pair of transistor 7 and 7' of oppositely conductive types will conduct causing both of a pair of lamps 16 and 16' to glow continuously. If for example the diaphragm initially is set allow too much light to fall on the photo-resistor, the resistance of the latter is low and the transistor 7' is near cut-off. A capacitor 10' charges slowly until a unijunction transistor 12' breaks down rapidly discharging the capacitor. This charging and discharging continues in repetitive manner. A transistor 14' conductive during the charging periods causes a lamp 16' to glow during these periods. As the diaphragm is adjusted towards it correct setting the transistor 7' is more conductive and the lamp 16' flashes more frequently. At the correct setting the resistance of the transistor 7' is so low that the unijunction transistor 12' cannot be switched to conduction and the lamp 16' burns continuously. If the diaphragm is set to pass too little light the lamp 16' glows continuously and the lamp 16 flashes in a manner similar to the above. Resistors 18 and 18' are provided to limit the lowest flashing frequency. A modification employing two photoresistors one for each half of the circuit are provided. They are selected alternately by a switch and diodes 8 and 8' are not required. |
