| 摘要 |
1482567 Machinery safety devices XENEX CORP 28 Oct 1974 [29 Oct 1973] 46547/74 Heading F2J [Also in Division G1] A presence detection system comprising a plurality of sets of a light source and phototransistor 20a and 22a, 20b and 22b,..., each defining a channel, each photodetector receiving light from its source unless its channel is obstructed, multiplexers 26 and 28 with clock 30 connected to their channel address inputs 62 and 64 for sequentially and synchronously connecting the light sources to pulse generator 32 and the photodetector to detection means 34 respectively, means 34 including missing pulse detector 40. Each photodetector has a biasing system (Fig. 4a, not shown) which controls the electrical output for a given light pulse, a feedback amplifier 48 adapted to produce an output such that its input is equal to a predetermined level and switching field effect transistor 50 for disconnecting amplifier 48 from the bias means only when the source is energized, whereby the photodetector is compensated for changes in ambient conditions. Detector 40 detects if a pulse is missing and causes relay 44 to be de-energized, thereby to stop a machine. Self-checking means includes masterchecker 51, with inputs from pulse generator 32 and multiplexers 52 and 54 and includes plural selected test points some in missing pulse detector 40 and includes a binary comparator in missing pulse detector 56, so that if pulses from any of the test points are low, the output of detector 56 remains low and relay 44 is de-energized. The circuits are shown and described in detail. |
