AXL SE RS485 and Modbus RTU Polling
Hi all,
I'm setting up a Modbus RTU network being the Plcnext the Master.
I'm using the Modbus RTU library from the Plcnext store, it works "fine" i only have one important problem.
For the moment i'm doing some test and i only have 3 devices connected to the network, i can read and write to all of them, the problem is the speed of the data exchange.
The devices i have connected right now are 2 Power Meters, from which i read several data, and 1 AFD, from which i read and i write.
If i only enable coms with the poll enabled on the AFD, it works fine, but as soon i enable the coms with the 2 powermeters, the data doesn't get as fast as it should.
I have the polling enabled in all the 3 devices with 1s time, but if i change the speed setpoint of the AFD, sometimes it gets instantly, and sometimes it takes like 4-10s to get to the AFD.
I can see the Rx and Tx leds of the AXL SE RS485 blink every few seconds, when it should be blinking at least every second as the polling is set at 1s.
I tried to disable polling and make the request by hand but if any other device of the network has polling activated i have the same problem.
There's not so much data on the requests to make this go so slow, so i don't understand the problem, maybe the polling doesn't work as i'm expecting it to work?
Network speed rate is 19200, i can't raise it up because one of the devices doesn't allow faster config, but should be enough for this small application.
If i only needed to read from field devices it wouldn't matter that big delay time on the data transfer, but i need to control the speed of that AFD faster because it needs to change quite often in order to the system to work propperly.
Any hint?
Thanks
I'm setting up a Modbus RTU network being the Plcnext the Master.
I'm using the Modbus RTU library from the Plcnext store, it works "fine" i only have one important problem.
For the moment i'm doing some test and i only have 3 devices connected to the network, i can read and write to all of them, the problem is the speed of the data exchange.
The devices i have connected right now are 2 Power Meters, from which i read several data, and 1 AFD, from which i read and i write.
If i only enable coms with the poll enabled on the AFD, it works fine, but as soon i enable the coms with the 2 powermeters, the data doesn't get as fast as it should.
I have the polling enabled in all the 3 devices with 1s time, but if i change the speed setpoint of the AFD, sometimes it gets instantly, and sometimes it takes like 4-10s to get to the AFD.
I can see the Rx and Tx leds of the AXL SE RS485 blink every few seconds, when it should be blinking at least every second as the polling is set at 1s.
I tried to disable polling and make the request by hand but if any other device of the network has polling activated i have the same problem.
There's not so much data on the requests to make this go so slow, so i don't understand the problem, maybe the polling doesn't work as i'm expecting it to work?
Network speed rate is 19200, i can't raise it up because one of the devices doesn't allow faster config, but should be enough for this small application.
If i only needed to read from field devices it wouldn't matter that big delay time on the data transfer, but i need to control the speed of that AFD faster because it needs to change quite often in order to the system to work propperly.
Any hint?
Thanks
This discussion has been closed.
Comments
Take a look at the interval of ESM task, and it's priority, where you place your modbus processing FBs.
I found the problem, shame on me, i left activated one FC with slaveid = 0, so the master was timing out all the time.
Once i removed that everything started working in a continous way, not as fast as i would like to, but without interruptions.