MODBUS RTU Help

[wdwune]

Hi All,

So, I am fairly new to PLC and am trying to learn as much as I can for my job. Currently, I am working on interfacing a PLC to a VFD to access its frequency, accel time and decel time using MODBUS RTU (RS485). It's actually my first time working on MODBUS but I've read (and watched some tutorials) about it.

The problem is, I'm still stuck with a "Host communication Error". I really don't know where to go from here since I think I've searched google for any supplementary files provided by the suppliers of the products and applied them but still no progress. *sighs*

In any case, the PLC I am using is IDEC's SmartAxis FT1A Touch while the VFD is LS-iG5A. Is there anyone here who have worked with these products? Or can anyone share his knowledge with connecting VFDs to PLCs regardless of the product models?

Your help is greatly appreciated. I am really desperate now since I am just learning this all by myself and have undergone no training whatsoever aside from college laboratories.

Thanks in advance!

Best Regards,
wdwune

 

[gclshortt]

http://www.idec.de/produkte/-broschueren/sps/FT1A-Pro-Lite-UsersManual_FT9Y-B1378-4.pdf

Make sure your cable is correct and you have the terminating resistor on the last slave.

The PLC is the master and may have to be addressed as such in the unit. Refer to the manual above.

https://www.inverterdrive.com/file/LS-Starvert-iG5A-Manual

The VFD must match the communication parameters in the master. Baud rate, Stop Bits, Parity, Data Bits, etc.

Hope this helps,

 

[jdbrandt]

Hi All,

So, I am fairly new to PLC and am trying to learn as much as I can for my job. Currently, I am working on interfacing a PLC to a VFD to access its frequency, accel time and decel time using MODBUS RTU (RS485). It's actually my first time working on MODBUS but I've read (and watched some tutorials) about it.

The problem is, I'm still stuck with a "Host communication Error". I really don't know where to go from here since I think I've searched google for any supplementary files provided by the suppliers of the products and applied them but still no progress. *sighs*

In any case, the PLC I am using is IDEC's SmartAxis FT1A Touch while the VFD is LS-iG5A. Is there anyone here who have worked with these products? Or can anyone share his knowledge with connecting VFDs to PLCs regardless of the product models?

Your help is greatly appreciated. I am really desperate now since I am just learning this all by myself and have undergone no training whatsoever aside from college laboratories.

Thanks in advance!

Best Regards,
wdwune

Since you don't know where the problem is, some data is called for.
I have used 232analyser, by CommFront, http://www.232analyzer.com/232default.htmin the past, for this. It will show the data flow in both directions, if you have the right hardware.
And, in the "OnceBittenTwiceShy" category, I always put some sort of potential-isolator device on the network. CommonMode problems are beyond difficult to troubleshoot, and the isolator simply makes them all go away.
Good Luck.

 

[BITS N BYTES]

This is a great resource with superb documentation and an excellent free ModBus analyser.

http://www.chipkin.com/products/software/modbus-software/cas-modbus-scanner/

 

[tragically1969]

This is one of the most invaluable bits of kit for RS485, use this and modpoll etc. to prove slave comms before starting with PLC programs etc.

http://uk.rs-online.com/web/p/products/6877834/