Hello,
I have a Micrologix 1400 controlling 3 Benshaw VFD's via Modbus.
This setup has been work fine for years. until one day, the 3rd VFD blewup! literally, the door blew off the enclosure.
The 3rd VFD was then replaced, but now we are having Modbus communication problem, the PLC can't communicate to any of the drives anymore, the PLC message instruction times out with error. After doing some testing I found that by removing VFD#2 from the Modbus loop, it allowed VFD#1 and VFD#3 to communicate, However if I start up VFD #1 I instantly lose Modbus communication??
I tried running VFD 2 locally, even though Modbus is disconnected and communication is still good.
I can't run VFD 3, since the pump is not in water
So I'm suspecting electromagnetic interference (EMI).
but why?
-All Modbus cables are shielded and grounded from the PLC panel.
Also note, we have a hart gateway/modem called HRT-710 for the flow meters and this device communicates just fine on Modbus, regardless. even with VFD#2 connected to the Modbus loop which seemed to caused no communication to all 3 VFD's.
If anyone has any clue or ideas please share them, I'm not sure what to look at anymore, can an oscilloscope tell me anything?
Thanks everyone !!
I have a Micrologix 1400 controlling 3 Benshaw VFD's via Modbus.
This setup has been work fine for years. until one day, the 3rd VFD blewup! literally, the door blew off the enclosure.
The 3rd VFD was then replaced, but now we are having Modbus communication problem, the PLC can't communicate to any of the drives anymore, the PLC message instruction times out with error. After doing some testing I found that by removing VFD#2 from the Modbus loop, it allowed VFD#1 and VFD#3 to communicate, However if I start up VFD #1 I instantly lose Modbus communication??
I tried running VFD 2 locally, even though Modbus is disconnected and communication is still good.
I can't run VFD 3, since the pump is not in water
So I'm suspecting electromagnetic interference (EMI).
but why?
-All Modbus cables are shielded and grounded from the PLC panel.
Also note, we have a hart gateway/modem called HRT-710 for the flow meters and this device communicates just fine on Modbus, regardless. even with VFD#2 connected to the Modbus loop which seemed to caused no communication to all 3 VFD's.
If anyone has any clue or ideas please share them, I'm not sure what to look at anymore, can an oscilloscope tell me anything?
Thanks everyone !!