How to select the filter for the measurement circuit of an electrical force measurement switch (PMS)?

The selection of filters for PMS measurement circuits requires a balance between noise suppression and signal integrity. Improper selection can lead to signal distortion or ineffective filtering. Selection depends on the signal type (voltage/current), frequency bandwidth (typically DC-2kHz), and noise spectrum (primarily switching frequency harmonics, such as 20kHz-1MHz). For current sampling (shunt or CT output), due to its small signal amplitude and low impedance, a low-DCR, high-saturation-current ferrite bead, such as PBZ2012E060Z0T (6Ω@100MHz, DCR<0.05Ω), should be selected, with a 100pF-1nF C0G/NP0 capacitor connected in parallel to form a low-pass filter.

For voltage sampling (resistive voltage divider network), a 100pF capacitor can be connected in parallel across the voltage divider resistor for filtering, and a 100Ω resistor and a 10nF capacitor can be connected in series before the ADC to form a first-order RC filter. To address common-mode interference, a CMZ2012A-900T low-value common-mode inductor (90μH) is connected between the differential sampling line pairs. All filtering components must be high-precision, low-temperature-drift models (e.g., ±1%, C0G) to avoid introducing additional measurement errors. With proper selection, the filter network can attenuate noise >10kHz by more than 40dB, while the phase delay of the power frequency signal is less than 0.1°, meeting the 0.5S-level metering accuracy requirement.