3 VFD-s on Modbus RTU

[dub]

I can't configure program for 3VFD-s on MODBUS  485 RTU protocol.  PLC comunicate only with first one. depending on what I call the first one.

I try with all three in the first place and everyone is doing this, which means that the parameters are correct in them.

I know the PLC can only communicate with one at a time but I do not know how to write it.

 

V1210 and 3 VFD-s -MODBUS RTU.vlp

[sgull]

Hi Dub

In net 8, 14 and 20 you are constantly writing to all 3 drives drive at the same time when MB0 is off.

I think you should put a delay on this and make a condition where you set a bit to communicate with the first drive and reset it after communication has finished.

Use this bit to prevent communication with the other drives until this is complete (same as what you did with MB5 in net 3)

Regards

Denis

 

[dub]

HI Denis

I tried what you suggested, at least I think I did, but without success.

 I know it all depends on the timing but I have no idea. I know that two vfds can work if I use NO and NC contact SB3

V1210 and 3 VFD-s -MODBUS RTU 1.1.vlp

[sgull]

Hi Dub

In rung 7 for example you are resetting MB7 once the action is complete.

A normally open of MB7 should be in the same net before the modbus command to prevent it from being continuously called.

Similiar to rung 10

Regards

Denis

 

[dub]

Thanks, i did it

Everything works, even  direction change  on all three VFD-s.