How to attenuate noise in the PMS measurement circuit of an electrical force measurement switch?

The PMS measurement circuit (voltage/current sampling) is susceptible to power switching noise, common-mode interference, and spatial radiation coupling, leading to fluctuations or distortions in the sampled values, directly affecting measurement accuracy. The core challenge lies in extracting weak power frequency signals while filtering out high-frequency noise. EMC design requires multi-stage filtering and isolation protection. A PBZ2012E060Z0T ferrite bead (6Ω@100MHz) is connected in series on the secondary side of the transformer or before the sampling resistor to attenuate differential-mode noise above MHz.

An ESD5V0D3B electrostatic discharge protection diode (Vrwm=5V, Cj<50pF) is connected in parallel to ground on the sampling line to provide an electrostatic discharge path and clamp overvoltage. For high-precision ADCs, the reference source and analog power supply must use π-type filtering, for example, using a CMZ2012A-900T common-mode inductor (90μH) with 10μF/0.1μF decoupling capacitors. During wiring, the sampling lines should use twisted-pair or shielded cables, with the shield connected to a clean analog ground at a single point. This solution can reduce the background noise of the measurement circuit by 20dB, ensuring that the measurement error is still less than 0.5% within the EN 55032 Class B conducted emission limits.