How can onboard and external filters be combined in industrial servo systems?

In servo systems, onboard and external filters need to work together to form a distributed filtering architecture. Etymotic's matching strategy: Onboard filters target high-frequency noise and local transients, such as by connecting a 100nF C0G capacitor in parallel at the DC bus capacitor, and using a PBZ1608A-102Z0T ferrite bead (1kΩ) and ESD protection in the IGBT drive power supply. External filters (usually installed at the rack entrance) handle low-frequency conducted interference and interference from the power grid, including a CMZ7060A-701T common-mode inductor and two capacitors.

A key matching point is impedance matching: the onboard filter presents high impedance, and the external filter presents low impedance to avoid resonance. Typically, a certain distance (e.g., 20cm) of cable is reserved between the external filter output and the servo drive input; this distributed inductance can form an additional filtering stage with the onboard capacitor. Actual measurements show that this matching scheme provides 5-10dB more attenuation margin than a single filter, which is particularly beneficial for meeting the stringent CISPR 11 Class B limits. When configuring the external filter, ensure that it is properly grounded.