| 摘要 |
<p>An error detection system is provided for a two-state fiber optic sensor (10) . An amplified photodetector signal is sampled by each of an ON-OFF threshold detector (24) , a disconnect threshold detector (26) and a slope detector (28). The ON-OFF threshold detector (24) monitors whether the detector signal is above or below an ON-OFF threshold value corresponding to the parameter being sensed and activates an appropriate sensor output. The disconnect threshold detector (26) monitors the constant low level detector signal corresponding to low level light received by the detector even when the threshold detector (24) is in the OFF state, and triggers an error signal should the detector signal fall below a disconnect threshold value. The slope detector (28) monitors the rate of change of the detector signal. Where the detector signal changes rapidly, such as during normal sensor switching, the slope detector (28) permits the detector signal to pass to a latch (30), which retains in memory the last detector signal which changed rapidly enough to trigger the slope detector (28) and produces an output corresponding to the ON-OFF status of the last detector signal in memory. A slowly changing detector signal will not trigger the slope detector (28). Where the ouputs of the ON-OFF threshold detector (24) and the latch (30) differ, a comparator (34) triggers an error signal.</p> |
