RS 485 question

Hi,

I have a PLC, which is daisy linked to 9 Pepperl Fuchs IQT-F116-R4M-V1 RFID readers at different points of the system. The PLC is housed in an enclosure which contains 6 VFDs. The PLC is powered by one SMPS, whereas the RFID units are powered by another SMPS. Care has been taken to keep the PLC & RFID wiring away from the VFDs.

Communication has been established,using a 4 core shielded cable. 2 cores for the 24 VDC and the other 2 for RS485. This cable doesnt have twisted pairs

When the system isnt running, (when the VFDs are not running), the communication works, but as soon as any of the VFD is run, the communication collapses.

Planning to change the comm cable to a CAT5 and use the twisted pairs for communication, while using the existing cable for 24 VDC. Pl let me know if this will help, or otherwise what could be a better alternative

Thanks

Ron

You also need to have the properly shielded cables from VFD to your motors so the high frequency doesn't land on your control wiring.

The CAT5 will defitely help, but make sure you use one of the twisted pairs for your 485 communication (i.e. brown/brown-white), so if you have to make an RJ45 connection, keep that in mind.

Hi everybody,
please let me know about the rs485 communication.

Here's some info on it :
https://en.wikipedia.org/wiki/RS-485

You have a broad request - there is a lot to know about it.

Thanks friends. Will be trying it out with the CAT5 tommorow.

The CAT5 will defitely help, but make sure you use one of the twisted pairs for your 485 communication (i.e. brown/brown-white), so if you have to make an RJ45 connection, keep that in mind.
__________________
This statement is false.

I like this

Ron

You should always use twisted pairs for RS485 communications
And shielded twisted pairs is even better just be sure to bond only one end of the shields to a good ground point preferably at the PLC end.

The last time I checked standard Cat5 cable in not shielded it wouldn't help you if the VFD is generating noise and giving you the problem.
Gary