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SolidRio

QJ71MB91 - 232 value freezes

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Hello everyone.

I have the system:

RS232 Master (QJ71MB91) <-> AC3-M 232-485 (Owen) <-> Four Slave RS485 (Micom P116 Terminals).

Modbus RTU protocol. The length of the 485th line is 20m. Speed 19200. Station numbers and parameters are correct. PLC reads the value of current, and doesnt write anything. The system has been in operation since January 2017, until that moment there were no problems.

Recently, problems have begun. With an unpredictable frequency, the values of current freezes (it can work properly for 3 days or a week or can freeze 10 times every day). System bits of the QJ71MB91 (BFM 3104) at this moment of freeze indicate the loss of communication with all 4 stations. It freezes all the time for a different period. From 30 secs to 27 hours. We cannot reboot the module / station, because object in operation (continuous production). The indication of currents does not directly affect the operation of the object, but problem must be solved. There were many versions, but one very important remark is that at the moment of values freeze there is an indication on the module, as well as the SD and RD LEDs, therefore, the module receives something, but the information is incorrect. If you pull out the cable, there will be no RD indication, because no response from stations. Therefore, the cable is most likely good. One version that one of the terminals sends garbage to the network and puts it down. This version also fits the fact that one of the terminals was changed in 2019 and the firmware was changed on another, but from what moment the problem arose is not clear (the cells have not been used since 2019 and were put into operation back only now). There is also a suspicion that communication with all 4 terminals is lost - the problem with converter - AC3-M.

Since this is a continuous production, you will not try much on the go, but the plan is to disconnect one station at a time and look at the behavior of the network, but if it does not help, we will change the AC3-M at a planned stop.

I am writing with a view to, maybe someone share their experience with a similar problem.

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