The world of data communication is busy, even noisy. Industrial communication systems, such as balanced RS-485 / RS-422, often require transmission between multiple devices over long distances. While having many devices communicating with each other on the same twisted-pair cable is robust and cost-effective, it also introduces two major challenges:
Because of the long distances and the surrounding electrical devices/equipment, RS-485 / RS-422 networks are often exposed to electrical noises, remote lightning, and line surges, which can cause transient voltage to run across the serial communication system and the valuable equipment.
Because multiple devices (nodes) are connected, the ground potential at different nodes could be different, which can cause ground currents to flow through “the path of least resistance” via either the common earth ground or the ground wire.
Both voltage and current surges can cause serious damage to valuable, mission-critical equipment such as computers, PLCs, and industrial manufacturing and data processing equipment; these surges can even endanger human lives. Ground loop problems also exist on unbalanced signals that rely on the ground pin being zero volts, such as RS-232 and USB.
There are a few methods of voltage and current surge protection in the industry, and the most effective are Optical Isolators and Surge Protectors:
An optical isolator (or opto-isolator) is used to block high voltages and transients so that a surge in one part of the system will not disrupt or destroy other parts. Optical isolation uses an LED (Light Emitting Device) and a photosensitive transistor to transfer data across the isolation barrier – typically an air gap; in other words, data is transmitted using light instead of electrical signals, so there is no physical connections between the grounds and the data lines, thus removing the ground loop problems and effectively preventing electrical surges and spikes from destroying other parts of the system. Furthermore, because optical isolation uses light to transmit data across the isolation barrier, it also gains the advantage of immunity from electrical- and magnetic-field interference. This makes optical isolation an effective solution in industrial areas where strong electric or magnetic fields could be present.
The main function of a surge protector is to limit the voltage introduced to an electrical device by either blocking or shorting to ground any voltages above a safe threshold. Surge protectors are mainly used for protecting power and data lines against electrical surges and spikes, including those caused by lightning. However, it is important to note that solely relying on surge protectors could be insufficient or even do more damage than good, as in the cases of improperly installed or poorly selected surge protectors. In many applications, surge protectors are used in conjunction with optical isolators to provide much more effective protection.