when a certain PLC is running for more than apprx 3/4 hours , the communications dies away pretty quickly all of a sudden, even tho its working perfectly up to then is this some kind of loss of synchronisation or what? is the fact that there is a couple of PLC's on this network interefering
and how would one go about solving it?

Marie

 

It's possible that a slave takes a very long time to respond . So the master receives the response of the slow slave after the request of the next slave (in the polling).

Try to locate the adress of the slave in resquet when the communication is lost.

How many devices have you on this network?
What device is the master (plc, pc)?
How many different devices have you on this network (plc, PC, regulator, remote/IO,...)?

Vincent ([email protected])

 

Be carreful with cables's ground : connect them your cable have a shield ?

 

If you are running master on NT, try modbus protocol analyzer at www.imperioustech.com.