485 communication issue, please experts help me, thanks so much! ! !
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First question: The PLC is a Siemens 300; when the 485 connector is connected, both the CPU and the I/O cards lose power. The DCS is from Zhejiang University Control Systems. When this 485 connector is used with another PLC, everything works normally. Why is this the case?Second question: The data from the refrigeration unit is transmitted to the DCS via 485 communication. There are no alarms on the PLC side, but some alarms appear on the DCS screen, although in reality there are no actual alarms. These apparent alarms are related to digital signals, while there are no alarms related to the data itself.
Third question: The PLC of the air compression unit transmits data to the DCS via 485 communication, but the data received differs significantly from what is displayed on the DCS. Please help resolve this issue. I would appreciate it if you could provide videos for learning about DCS as well as some software. Thank you
First, it’s probably a problem with your PLC485 connector. I’m not sure what it means by ‘no power’ – does it mean the circuit breaker has tripped?
Thank you for the reply. It works fine when the connector is plugged into another PLC; when there’s no power, all the lights on the CPU and cards go out
First question: It seems like this issue might be related to master-slave configuration, but I’m not entirely sure. Second question: It seems that as long as it’s confirmed that the data has been converted and that the 0 and 1 states are correct, there shouldn’t be any major issues. As for the digital alarm you mentioned, I think there are two possible scenarios. First, the switch on-site indeed changes, possibly due to external interference; such changes are brief and not easy to detect, with no actual issues with the communication. Secondly, there is no change in the signals at the site at all; only the status of the communication points changes. It is necessary to check whether it is one specific point or all of the communication digital switches, and to determine whether there are any external interference issues with the fiber optic communication cables. It is recommended to conduct a trend analysis on this set of digital data. Third issue: It’s likely a problem with data conversion; it’s necessary to check whether the data requires corresponding range conversion. In some cases, the difference is 10 times or 100 times, and range conversion is required in such situations. This is usually indicated in the communication parameter table provided by the PLC manufacturer