| 摘要 |
A signal selection system, including a plurality of detection circuits having inputs receiving respective direct voltage signals and outputs connected to a scan bus. Each detector circuit includes an operational amplifier having a non-inverting input receiving one of the direct voltage signals, an inverting input connected to the scan bus, and an output connected via a diode to the scan bus, so that the scan bus is maintained at essentially the highest or lowest signal of the signals being scanned, depending on the orientation of the detector circuit diodes. The system includes a plurality of indicators, associated respectively with the detector circuit diodes, for indicating whenever the associated diode is forward-biased, and an alarm circuit connected to the scan bus for indicating whenever the scan bus voltage exceeds a maximum value if the signal being detected is the highest signal, or whenever the scan bus voltage is less than a minimum value if the signal being detected is the lowest signal. The operational amplifier outputs are connected through respective resistors to a first constant reference voltage, and the scan bus is connected through a load resistor to a second constant reference voltage, the resistors and reference voltages being selected so that, in the absence of an operational amplifier output signal, the associated diode will be forward-biased to allow sufficient current to flow through the load resistor to maintain the scan bus voltage at a value which causes the alarm circuit to indicate.
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