I'm planning a system that has two sub systems that need to communicate with the PLC via RS485. The baud rates are 9600 and 19200 bps.
The cables are static (i.e. not moving) and placed inside of a electric cabin.
In the cabin area there are a few more electric appliances, such as PLCs and stepper motors. Those are placed in other electric cabins or behind metal separation. The cabin is not tangent to the motors or PLCs but in a few meters distance from the motors, with a metal separation and the cabin between them.
At first, I thought about using CAT5e FTP cables due to low cost and because I have read that this application is possible. Unfortunately, my lack of understanding if that is considered a 'harsh environment' and if the Foiled Twisted Pair will be good enough for running the applications properly.
- Do you think using the CAT5e cables (with a proper termination resistors) will do a good job or should I consider other cable?
- If one of my sub-systems is working with EIA-RS485, will that shifting away from the standard can cause issues?
Thank you.
Best Answer
For RS485, CAT5 should be just as good as any other shielded twisted pair cable. The impedance should be within tolerance for RS485. What matters most is how you connect the common ground between devices, and how you connect the cable shield, and where you connect the terminators, but that does not depend on if the cable is CAT5 or something else.
The RS485 is defined by TIA/EIA so it means the same TIA RS485 standard.