Patent ID: 8400930

Claim:
A communication quality diagnostic unit for diagnosing quality of communication for transmitting and receiving frames at predetermined interval time, said unit comprising: a frame-interval time detector for monitoring interval time between the frames, a frame-interval abnormality determiner for detecting the number of occurrence when a first threshold value representing at least one interval time is exceeded by the frame-interval time and making determination as the case of diagnostic abnormality when a second threshold value is exceeded by the number of occurrence as detected, and a diagnostic abnormality notifier for notifying a host unit of the diagnostic abnormality as an alarm, wherein the frame-interval time detector monitors transmit/receive frames on a field-bus used in a communication environment where a plurality of field equipment units connected to the field-bus used in a process control system for exchanging input/output of processes communicate with one unit of a controller, wherein the frame interval is a period having non-existence of frame.