LS G7MU with ATV31

desuhardi

Member
Join Date
Oct 2005
Location
Indonesia
Posts
46
Hello,

I'm using modbus rs485 with LS/LG PLC G7MU to control several inverters ATV31 Schneider. I can start, stop, send speed ref, receive feedback etc, one by one.
The problem is I can't start all inverters in the same time, together. If I send start signal on the same time for all inverters, communication become error. Then I put some delay, after send start to inverter-1, delay 10sec, then start inverter-2...............
The condition is same to receive feedback signal from inverter, must one by one.
Each inverter has its own ID.
Please help if any information, how to start all inverters together on same time.

Thank you
 
Hello,

Unfortunately Modbus is a serial communication and it's transmissions need to be sequential. You need to manage your READ/WRITE commands within your controller.
I am not familiar with the LS/LG PLC G7MU and not sure what sort of message buffering function it uses, but in principle you will need to condition your commands and allow for transmission times/response times within your code...

Normally I use some sort of sequence pointer address driven by a free running clock pulse. You can then adjust the clock pulse to achieve optimum (and reliable) communications...

The more drives (and the more commands to and from those drives), you add the longer your message times will take to execute, and you could end taking several seconds to poll all drives connected...

Hope this helps.

Rob
 
Last edited:
Hi Kidblue,

Thanks for information.
So with serial modbus, I can't send signal to different slave in exactly same time... :confused:

Regards
 
Doesn't modbus have a broadcast function? I have never had the need to use it, but this may be something that could be used.
Obviously, you would still have to read each device individually though.
 
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