Signal transmitter and signal quality monitoring device

A signal quality monitoring device for monitoring quality of a signal received by a transmitter and, when the signal is of low quality, selectively issuing one of a plurality of alarms with different grades in accordance with a grade of low quality of the signal, comprising:

• a plurality of producing/canceling sections, associated with the plurality of alarms with different grades respectively, each for successively discriminating whether the current signal is in the corresponding grade of low quality and, when the current signal has stayed in the corresponding grade of low quality for a producing time period, producing continuous output of an alarm of the corresponding grade while, when the result of the discriminating becomes negative and the current signal has stayed off the corresponding grade of low quality for a canceling time period, canceling the continuous output of the alarm of the corresponding grade;
• an alarm holding section for, when a grade of low quality of the current signal shifts from one to another of said plural alarms with different grades and said corresponding one of said plural alarm producing/canceling sections has canceled the continuous output of the corresponding one of the plural alarms of the plural grades as a consequence of expiration of the corresponding canceling time period, if the corresponding another of said plural alarm producing/canceling sections except said corresponding one alarm producing/canceling section discriminates that the current signal is in the corresponding another grade, holding the continuous output of the one alarm regardless of the cancellation by said corresponding one alarm producing/canceling section, until said another alarm producing/canceling section produces the continuous output of the corresponding another alarm as a consequence of expiration of the corresponding producing time period.

A signal transmitter communicably connected to a ring network, comprising:

• a receiving signal selector for selecting one from two signals, which are identical in contents and which are received by said signal transmitter from two directions of the ring network, based on signal quality information of at least one of the two signals;
• a signal quality monitoring section, provided for the at least one signal, for monitoring quality of the at least one signal and, when at least one signal is of low quality, selectively issuing one of two alarms with different grades, as the signal quality information, in accordance with a grade of low quality of the at least one signal, said signal quality monitoring section comprising:
• a first-grade alarm producing/canceling section for successively discriminating whether the at least one signal is in a first grade of low quality and, when the at least one signal has stayed in the first grade of low quality for a first producing time period, producing continuous output of a first-grade alarm while, when the result of the discriminating becomes negative and the at least one signal has stayed off the first grade of low quality for a first canceling time period, canceling the continuous output of the first-grade alarm;
• a second-grade alarm producing/canceling section for successively discriminating whether the at least one signal is in a second grade of low quality and, when the at least one signal has stayed in the second grade of low quality for a second producing time period, producing continuous output of a second-grade alarm while, when the result of the discriminating becomes negative and the at least one signal has stayed off the second grade of low quality for a second canceling time period, canceling the continuous output of the second-grade alarm;
• and
• an alarm holding section for, when a grade of low quality of the at least one signal shifts from one to the other of the first and the second grades and the corresponding one of said first-grade alarm producing/canceling section and said second-grade alarm producing/canceling section has canceled the continuous output of the corresponding alarm as a consequence of expiration of the corresponding canceling time period, if the other of said first-grade alarm producing/canceling section and said second-grade alarm producing/canceling section discriminates that the at least one signal is in the other grade of low quality, holding the continuous output of the one alarm regardless of the cancellation by said one alarm producing/canceling section, until the other alarm producing/canceling section produces the continuous output of the corresponding other alarm as a consequence of expiration of the corresponding producing time period.

A signal transmitter communicably connected to a ring network, comprising:

• a receiving signal selector for selecting one from two signals, which are identical in contents and which are received by said signal transmitter from two directions of the ring network, based on signal quality information of at least one of the two signals;
• a signal quality monitoring section, provided for the at least one signal, for monitoring quality of the at least one signal and, when the at least one signal is of low quality, selectively issuing one of a plurality of alarms with a plurality of different grades respectively, as the at least one signal quality information, in accordance with a grade of low quality of the at least one signal, said signal quality monitoring section comprising:
• a plurality of producing/canceling sections, associated with the plurality of alarms with different grades respectively, each for successively discriminating whether the at least one signal is in the corresponding grade of low quality and, when the at least one signal has stayed in the corresponding grade of low quality for a producing time period, producing continuous output of an alarm of the corresponding grade while, when the result of the discriminating becomes negative and the at least one signal has stayed off the corresponding grade of low quality for a canceling time period, canceling the continuous output of the alarm of the corresponding grade;
• an alarm holding section for, when a grade of low quality of the at least one signal shifts from one to another of the plural alarms with different grades and the corresponding one of said plural alarm producing/canceling sections has canceled the continuous output of the corresponding one of the plural alarms of the plural grades as a consequence of expiration of the corresponding canceling time period, if the corresponding another of said plural alarm producing/canceling sections except said corresponding one alarm producing/canceling section discriminates that the at least one signal is in the corresponding another grade, holding the continuous output of the one alarm regardless of the cancellation by said corresponding one alarm producing/canceling section, until said another alarm producing/canceling section produces the continuous output of the corresponding another alarm as a consequence of expiration of the corresponding producing time period.