| 摘要 |
Pulsed infra-red rays from source 26 pass by way of collimating lens 28 and aperture mask 30 to diverging lens 22 from which they pass to partially-reflective window 18 whereat the rays are reflected as a beam onto parabolic mirror 16 which creates a substantially parallel curtain of rays across the space 14 to be monitored to impinge upon prismatic reflector 24. The beam reflected back from reflector 24 is in turn, reflected back by mirror 16 to the window 18 through which at least part of the beam passes to pass by way of an image lens 34 to detector 36 comprising, for instance, an array of photo-sensitive diodes. Should there be an interruption of the curtain in the space 14, for instance as indicated at 40, there is a corresponding interruption at the detector 36 which sends an appropriate signal to reactive equipment (not shown) such as an alarm, fault display, or machine shut- off mechanism. The mirror 16 is not essential, the beam reflected by the window 18 impinging directly on the prismatic reflector 24, (Fig. 2, not shown). <IMAGE> |
