At industrial communication sites, engineers are most concerned about transient overvoltage and overcurrent that can occur in the communication network due to surges. These surges may cause the bus communication network to send incorrect signals or even lead to system failure. To prevent such accidents, it's crucial to implement proper protection measures during the early design phase. This article will walk you through effective strategies for surge protection in industrial communication systems.
First, let's understand what a surge is. In industrial environments, surges can be caused by lightning strikes, switching of heavy inductive loads, or other electrical disturbances. These surges can result in transient overvoltages that affect data buses and potentially damage components, leading to signal errors and significant losses. As a result, surge protection—especially against lightning and overvoltage—is an essential consideration in bus design.
There are two main types of surge protection: common-mode and differential-mode. Common-mode surges, often caused by lightning or high-current switching, appear between the line and ground. On the other hand, differential-mode surges typically arise from nearby high-voltage lines with poor insulation relative to data cables. Although differential-mode surges generally have lower voltage and current levels, they can persist longer in the communication network. Optocouplers and magnetically coupled devices are rated for common-mode withstand voltage, but they are not designed to handle differential-mode surges. If the differential-mode voltage exceeds the circuit’s tolerance, it can damage the front end without affecting the back end.
Next, let's look at conventional surge protection methods. One approach is isolation using optocouplers or magnetic couplers, which separate input and output signals. If the surge voltage remains below the device’s nominal rating, these isolators won’t be damaged, even if the surge persists for a long time. However, this method only protects against common-mode surges, not differential-mode ones.
Another method is the "evasion" approach, where the equipment's ground is connected to a single point, allowing surge energy to be safely dissipated. Additional protective devices like TVS diodes, varistors, and gas discharge tubes (GDTs) are used to clamp the surge voltage and divert harmful currents before they reach the data ports. When combined, isolation and evasion methods offer more comprehensive protection, as the evasion devices can suppress both common-mode and differential-mode surges, while the isolation devices protect the host equipment.
For example, in CAN interface protection, optocouplers or magnetic couplers are often used alongside transceivers. Integrated transceiver modules simplify the design and improve environmental adaptability. While common-mode protection is widely implemented, this article focuses on enhancing differential-mode protection. GDTs, TVS diodes, and common-mode inductors are commonly used in such applications.
A more efficient solution is the use of specialized surge suppression modules. Zhiyuan Electronics, for instance, has developed the SP00S12, a compact module that combines potting and isolation technology to meet IEC61000-4-5 ±4kV standards. It provides reliable protection against lightning, surges, and overvoltages in various communication systems, including CAN and RS-485.
Testing is also crucial to ensure that surge protectors meet the required standards. The IEC61000-4-5 standard outlines the immunity requirements for equipment exposed to surges. During testing, different surge voltages are applied, and the response at the signal input and output is measured. For example, when a 4kV surge is applied to the SP00S12, the output voltage is reduced to around 17.1V, demonstrating its effectiveness.
In conclusion, choosing the right surge protection strategy depends on the application, environment, and performance requirements. Whether using traditional discrete components or advanced integrated modules, the goal is to ensure reliable and safe communication in industrial settings.
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