| 摘要 |
PROBLEM TO BE SOLVED: To provide a photodetector for a doorway, surely capable of detecting an object on the doorway by the presence of the shade of a beam of light to be generated in a space between a light projector and a receiver set up in door ends each. SOLUTION: This doorway photodetector has a light projector 1 generating a beam of light and projecting it, and a light receiver 2 being opposedly set up to the light projector 1 and receiving the light, and the projector 1 and receiver 2 opposedly set up to both side ends of a door or a side end and a fixed part of the door, through which detects an object on the doorway on the basis of light receiving and shading conditions of the light receiver 2. In the case where photoelectric operations are carried out in time of on-off operations of the door, a distance between the projector 1 and receiver 2 is largely varied, but the amplification factor of a factor variable amplifier to amplify a light receiving signal is controlled on the basis of a light receiving quantity of the light receiver by a central processing unit. Therefore, any possible saturation in a light receiving element of the light receiver 2 and in the factor variable amplifier is prevented from occurring, thereby any small object on the doorway at the time of closing the door can surely be detected. |
