| 摘要 |
<p>A photocell (42) is placed beneath an object at each location, so that if the object is removed the illumination of the corresponding photocell will increase, and hence its electrical conductance, thus providing an indication of removal. The photocells at several locations are connected in a parallel circuit with each other, and a voltage supply source is connected to the parallel circuit through a common currept- sensing resistance (82,132) so that if an object is removed from any location a voltage drop is detected across the common current-sensing resistance. Each branch circuit at each location is provided with its own current-sensing series resistor (46), and a separate conductor is run from each such series resistor to a central control. Indicators (66) corresponding to each location are provided so that upon removal of the object from any location, the corresponding indicator will thereby be activated.</p> |
