RS-485 (formally known as TIA/EIA-485) networks provide the backbone for communications in applications ranging from industrial control systems to roadside traffic message boards. In environments where high voltages are present, electrical isolation from the communication bus to logic controllers is regularly employed for human safety and equipment protection.

Often overlooked are the benefits of isolation affecting system performance rather than simply protecting it from dangerous voltages. These benefits come in the form of uninterrupted, error-free communication in the presence of harsh ground perturbations and other system level noise that would otherwise render a non-isolated system inoperative.

This article discusses the performance benefits of using isolation in RS-485 networks, identifies characteristics of networks that could benefit from using isolation, and explains the trade-offs of various wiring configurations to maximize performance in an isolated system. It is presented in two parts, as pdf files (no registration required):

• Part 1: Ground and common mode voltage disturbances; transmitted but not received signals, click here.
• Part 2: Isolated communication works; additional wiring improvements; networks that need isolation; maximizing the benefits of isolation, click here.

About the authors
Jeff Marvin is the Burlington (MA) Design Center Manager for Linear Technology Corp. He joined Linear in 2006 to lead the design center. Jeff previously spent thirteen years at Motorola and Freescale Semiconductor in analog design and management. Jeff holds an MSEE from Arizona State University and a BSEECC from Rochester Institute of Technology.

Brian Jadus is a Senior Design Engineer with Linear Technology's Mixed Signal Products Group, working on interface products at Linear Technology Corporation. Brian holds BS and MS degrees in Electrical Engineering from the Rochester Institute of Technology.