How does the failure of I/O module isolation devices affect EMC?

Failure of isolation devices in I/O modules directly leads to the loss of their EMC protection capabilities and may trigger systemic failures. Optocoupler failure may manifest as LED aging causing a decrease in CTR, resulting in signal transmission errors; or insulation breakdown leading to a short circuit between the primary and secondary sides, causing the isolation barrier to fail, allowing high voltage or loud noise to directly enter the system side, causing damage or malfunction of subsequent circuits. Failure of digital isolators or isolation amplifiers can also lead to the loss of isolation function. Once isolation fails, the previously blocked ground loop will form, allowing common-mode interference to pass freely, drastically reducing system immunity and making it highly susceptible to failure in EFT and surge tests. Furthermore, the failed isolation device itself may become a noise source or a point of failure. Therefore, high-reliability isolation devices should be selected in the design, and their derating should be considered. In terms of circuit design, monitoring mechanisms can be added, such as monitoring the output of the isolation power supply for normal operation, or verifying the correctness of signal transmission through readback. For safety-critical applications, redundant isolation designs can be adopted. During regular maintenance, insulation resistance tests can be performed to detect potential deterioration in isolation performance in advance.