How to avoid ground loop interference in the power measurement switch (PMS)?

When PMS devices are interconnected with multiple devices or connected to sensors, ground loops can form due to potential differences at the grounding points. These loops introduce common-mode currents into the signal circuit, which can reach tens of milliamps in severe cases, leading to measurement drift or communication errors. The key to avoiding ground loops is to cut off the circulating current path or eliminate the potential difference.

First, an isolation scheme should be adopted at the communication interface (such as RS485), using a transceiver module with isolated power supply or a magnetic coupling isolator ADuM1201 to achieve electrical isolation between the signal ground and the chassis ground/power ground. Second, for analog sampling lines, differential transmission should be used in conjunction with an instrumentation amplifier, whose high common-mode rejection ratio (CMRR>100dB) can effectively suppress ground noise. The cable shielding should adopt a single-point grounding principle, typically connecting to the chassis ground at the PMS device end and leaving the other end floating. If the system must have multiple grounding points, a PBZ1608A-102Z0T ferrite bead (1000Ω@100MHz) should be connected in series in the shielding layer to suppress high-frequency circulating currents.

Simultaneously, ensure that all equipment is reliably connected via equipotential bonding conductors, keeping the ground potential difference within 100mV. These measures can reduce measurement errors caused by ground loop interference to less than 0.1%, meeting the IEC 61000-4-8 power frequency magnetic field immunity requirements.