HMS AB-7002 Dual Redundancy Configuration



Dear HMS Support Team,

We are doing a PLC system replacement and our requirement is to integrate and establish new communication to the existing Modbus-Plus network. We tested using simplex network (working as intended) but on redundant configuration, we are facing some issues.

Below network architecture refers to our design and implementation using AB-7002. When we connect both the gateways to the BM85, both DCS (master) modules (Active and standby) goes to error/switchover state. Both gateways are polling the data properly from the (slave) redundant communication card of the PLC. We believe that the gateways shall be properly configured for redundancy to distinguish network queries from the master and/or standby modules.

Kindly provide configuration settings and/or advise if AB-7002 can meet this dual redundancy requirement.


Kind Regards,


Hello @Zedd,

I am not fimilar with redundant systems using modbus plus and would not be able to provide you specific configuration settings.

From what I have been able to look up on the Communicator Modbus plus module there are not specific settings for redundancy. They are each going to act as individual modbus plus modules. If redundancy is possiable it will need to be set on the modbus plus master side. Do they each have unique node ID’s?

Does the system work with just one device connected?


Dear @deryck_hms ,

Thanks and appreciate the reply. In simplex mode (one gateway connected either in Modbus plus trunk A or B), it is working and values are transmitted to the DCS (master) correctly. Issue if we connect both on the existing redundant trunk network.

We also had initiated the same issue to HMS technical support team and understood that they will escalate to HMS HQ for further testing and analysis as we are intending to utilize these gateways on upcoming customer migrations / projects as well.

Hoping we will have some positive workarounds/solutions from them.

We will update this thread as per their feedback / issue resolution. Thanks.



Thanks for the update. Let me know if there is anything else I can assist with, It sounds like you are in good hands working with your local support team.