Ring-shaped synchronous network system and time slave station

A ring-shaped synchronous network system

• to which a time master station and one or more time slave stations are connected so as to form a dual ring configuration via transmission paths and
• in which a synchronization correction cycle between the time master station and the time slave station is a natural number times a communication cycle with which the time master station and the time slave station periodically communicate with each other, wherein
• the time master station includes:
• a synchronization signal inputter that receives an input of a synchronization signal from an external device;
• a first synchronization frame transmitter that, when the synchronization signal is received, transmits a first synchronization frame, which is transmitted in a first direction along the transmission path, with the synchronization correction cycle;
• and
• a second synchronization frame transmitter that, when the synchronization signal is received, transmits a second synchronization frame, which is transmitted in a second direction opposite to the first direction along the transmission path, with the synchronization correction cycle,
• the time slave station includes:
• a first frame receiver that receives a frame from the transmission path in which the frame is transmitted in the first direction;
• a second frame receiver that receives a frame from the transmission path in which the frame is transmitted in the second direction;
• and
• a processor comprising:
• a slave clock counter that counts the communication cycles;
• and
• a synchronization error detector that detects a synchronization error between the time master station and the time slave station,
• the synchronization error detector includes:
• a first synchronization error detecting counter that counts the synchronization correction cycles of the transmission path in which a frame is transmitted in the first direction;
• a second synchronization error detecting counter that counts the synchronization correction cycles of the transmission path in which a frame is transmitted in the second direction;
• a first synchronization-enabled time period counter that counts a first synchronization frame reception-enabled time period which is a reception-enabled time period of the first synchronization frame when a count value of the first synchronization error detecting counter reaches a first set value;
• a second synchronization-enabled time period counter that, when a count value of the second synchronization error detecting counter reaches a second set value, counts a second synchronization frame reception-enabled time period that is a reception-enabled time period of the second synchronization frame;
• a first synchronization error determiner that determines whether the first synchronization frame is received during the first synchronization frame reception-enabled time period by the first frame receiver;
• and
• a second synchronization error determiner that determines whether the second synchronization frame is received during the second synchronization frame reception-enabled time period by the second frame receiver.