How to protect the EMC of the inverter encoder interface

Protecting the encoder interface of the frequency converter from EMC is crucial for ensuring the accuracy and reliability of motor speed/position control. Encoder signals are typically differential signals, such as A/A-, B/B-, Z/Z-, and may have high frequencies. Protective measures include: using shielded twisted-pair cables to connect the encoder and ensuring the shield is securely grounded at the frequency converter end. Implement common-mode filtering before the encoder signal enters the interface chip, for example, using a common-mode choke such as the CMZ2012 series. TVS diode arrays can be connected in parallel on each pair of differential signal lines to suppress ESD and transient overvoltage. The interface chip should be a differential receiver with a high common-mode rejection ratio.

Provide isolated power to the encoder to prevent interference through power coupling. On the PCB layout, the encoder interface circuit should be kept away from power sections, and signal lines should be strictly routed as differential pairs, with control impedance and length matching. For long-line transmissions, terminating resistors may need to be considered. Verify the protection effectiveness by testing the waveform quality of the encoder signal during frequency converter operation. In situations with extremely severe interference, consider using a parallel interface with a resolver or absolute encoder and strengthening isolation. Eintech provides common-mode filtering and transient protection devices for encoder interfaces to help improve interface robustness.