How to protect against fast pulses during EFT in industrial servos?

The servo system must withstand the EFT/Burst test of IEC 61000-4-4 standard (±2kV/±4kV on power lines, ±1kV/±2kV on signal lines). Etymotic's protection solution includes:

1) Power port protection: Use combined protection at the AC/DC input terminals: a gas discharge tube (e.g., 2R090L-8X6) as primary coarse protection, a varistor (e.g., 14D series) or TVS (e.g., SM8K series) as secondary clamping, and decoupling between the two using an inductor (PWR series) or resistor.

2) Signal/control port protection: Each signal line is connected in series with a ferrite bead (PBZ series) or resistor, and in parallel with a TVS (e.g., SMBJ series) to ground. For communication ports, use dedicated protection devices such as ESDSM712.

3) Optimized grounding: Provide a low-impedance, large-area discharge path for EFT current, avoiding high voltage differentials in internal circuits.

4) Software fault tolerance: Add delay confirmation for fault signals that are prone to false alarms after interference.

With multi-level protection and good grounding, servo devices can withstand EFT tests without permanent damage or loss of function.