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Redundant modbus

11/4/2007 8:30 AM	Rate (0)
Rasool S.Alizadeh Advanced Member Joined: 9/27/2007 Last visit: 3/10/2025 Posts: 37 Rating: (0)	I want to use redundant modbus in s7 with 2*cp 341 or other serial interface please tell me how can i do that rasool486@yahoo.com

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11/5/2007 6:21 AM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 1/16/2026 Posts: 12481 Rating: (2722)	Hello Rasool; Modbus standard topology only accepts one master on the network at one time. I have used relays to switch from a "defective" master to a stand-by unit in some applications, but there is no standard design. You will have to design, implement and test this yourself; for example,what determines one master unit is defective? Will you use a PLC digital output to cause the relay to switch beteen one master and the other? How will alarmingbe processed in the case of a loss of one master? How to connect the relay to connect only one master at a time to the bus? On another project we were lucky (rich?) enough to use valves and instruments that had 2 separate Modbus slave interfaces each, so we simply ran them on 2 separate networks, each with its master. Each master updated the PLC with its own data, from a separate bus, on a separate cable run. Expensive, but reliable and easy o maintain. Hope this helps, Daniel Chartier

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