what ispicture of smps
Hi,
Opto isolator will help if the noise you are seeing is due to ground coupling. You can use 6N137 type opto and you should use it at the TTL level before RS485, at the output of the Micro. You should then use an isolated power supply to power the 485 ICs and isolated section of the opto. You can derive this power supply from another winding of the mains transformer.
But from your description, it appears to be due to some power disturbance from Mains supply when your AC drive is being controlled, do you have any source of high switching current from SCR/ Capacitor/ Motor etc. that causes severe mains disturbance? You have mentioned that your 485 based controller is only one foot away.
How is your mains ground connected to the total system which includes your Micro Controller, AC Drive system etc.? Is the safety earth connected on the ARM kit side as well as on the AC drive side, if so there is the risk of a prt of the ground return current from AC drive flowing through the signal ground of ARM. If ARM and its logic is getting power from a 2pin type AC plug, this problem will not come. The heavy switching ground current, if any, should be prevented from entering ARM side. That is, connection to safety earth should be made only at the drive side and not at the ARM side.
Is there any chance of arcing in contacors, relays etc in the AC drive side?, if so, you may need ARM to be shielded. One thing you can readily try is to keep ARM a few meters away and connect to drive controls using a longer RS485 twisted pair wire. Also in this case, use a different power socket to connect mains power to ARM circuit to avoid sharing the same power board used for the drives.
Regards,
Laktronics