| 摘要 |
<p>A fault indicating unit for digital demultiplexer is used to produce an alarm signal each time the signal extracted is not significative. Fault conditions can occur when there is a loss of supply, loss of clock, loss of frame lock or other fault. It has only one quartz oscillator. The unit has a servo oscillator tuned to the mean frequency of a faulty clock and produces a restored clock signal. A counting circuit is connected to the time base circuit of the demultiplexer to produce a signal corresp. to normal operation.</p> |
