RS-485 "how to ensure network is solid before network is running


Thread Starter

rob williams

need to know of a method to check out a rs485 network prior to powering up the system/network. Possibly what else to check other than continuity...and what equipment or suggeations of what equipment can be used inexpensively.


Throught our cement plant we have rs485 network,we will check the following

1)continuity test
2)Earth continuity check
3)Earth should be connected only at one end of the controller,we connected at PLC end
4)Earth lekage to be checked at other end
5)If isolator are used then two earth should be seperated and ground at one end only
6) if leakage is more at another end ,you have to reroute the cable,where possible induction might occur
7)Surge protection device should be connected
8)if you are using modbus,then you can check the slave responce through modscan
9)if it is profibus then pc based software is available to check the slave responce
10)after that you can connect to the system
for further queries you can contact me in my e-mail address

Reza Hasseli

Beside checking 300 ohm cable resistance, I believe that if your system is expensive, it may be useful to make a 8051 based master and slave circuits which are able to communicate with each other on the RS-485 bus and check your bus with them first. So if your bus is dangerous, nothing expensive will be lost.
Hope this help you
This is something you're not going to know about until you do it, unless you have access to test equipment. You could hang an oscilloscope on the transmission lines and look for noise, or just run the system in a safe mode (with nothing dangerous activated).

If whoever installed it paid attention to the specifications and good installation procedures, and didn't cut any corners by using cheapo materials, you should be good to roll.

Otherwise, Good Luck!