adccommunitymod (AutomationDirect) asked a question.
Created Date: April 02,2009
Created By: clintonp
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I'll soon ship my first systems that include MODBUS? RTU interfaces. As I write the User's Manual, I'm wondering how much I should worry about grounding problems and ground loops. My first thought was to tell the installer to check between the MODBUS? RTU cable ground (assuming that there IS one!) and the ground terminal on the ZL-CMA15L comm port adapter, with AC and DC meters, to see if there's any potential difference BEFORE connecting the plant cabling to my machine. My fear is that they'll hook up the network and smoke the D0-DCM. My second thought was to forget about it and assume that ground is ground in modern installations. What do you think? Anybody ever had a problem? It would be tedious to write the procedure, and have to define how much is OK, et cetera. Paul in Wisconsin
Created Date: April 02,2009
Created by: Do-more PE
Are you using RS-232, RS-422, or RS-485?
RS-232 is the only one to really have to worry about since it is a ground referenced signal. It will either not work or smoke depending on the amount of difference.
The other two are differential signals.
It's still good to check for potential difference with a meter on both AC and DC settings. Anything over a few tenths of a volt could be bad. Over 0.5 volts and I wouldn't think about connecting. My two cents.
Created Date: April 02,2009
Created by: clintonp
Are you using RS-232, RS-422, or RS-485?
Yes.
The system is configured to support whichever physical line protocol is already in place.
If I were installing the machine, I would check for ground compatibility. These machines are customer-installed. I'm going to guess that a plant electrician that's hooking up a new slave to an existing network might have some knowledge of networking issues. It seems a bit risky, but the risks of trying to give a detailed document might be greater.
Thanks for your response!
Paul
Created Date: April 02,2009
Created by: clintonp
I'll soon ship my first systems that include MODBUS? RTU interfaces. As I write the User's Manual, I'm wondering how much I should worry about grounding problems and ground loops.
My first thought was to tell the installer to check between the MODBUS? RTU cable ground (assuming that there IS one!) and the ground terminal on the ZL-CMA15L comm port adapter, with AC and DC meters, to see if there's any potential difference BEFORE connecting the plant cabling to my machine. My fear is that they'll hook up the network and smoke the D0-DCM.
My second thought was to forget about it and assume that ground is ground in modern installations. What do you think? Anybody ever had a problem? It would be tedious to write the procedure, and have to define how much is OK, et cetera.
Paul in Wisconsin