How can a poor grounding of the power measurement switch (PMS) cause measurement errors?

Poor PMS grounding introduces additional noise voltage and current, directly superimposed on weak measurement signals, leading to significant measurement errors. Common mechanisms include: excessively high grounding impedance degrades the high-frequency bypass effect of the filter capacitor (Y capacitor), converting common-mode noise into differential-mode noise that enters the sampling circuit; ground loops induce power frequency current in the sampling circuit, causing baseline drift; and unequal grounding potentials at multiple points cause reference voltage offset. For example, if there is a 100mΩ impedance between the ADC's AGND and sensor ground, and a 10mA common-mode noise current flows through it, a 1mV error voltage will be generated, equivalent to 3 LSBs for a 5V full-scale 16-bit ADC. Diagnostic methods include measuring the noise voltage between AGND and PE; if it exceeds 10mV at 50Hz or 50mV at high frequencies, grounding is poor. Remedial measures include: improving the single-point connection between AGND and PE (using a ferrite bead or inductor), strengthening the sensor shield grounding, using differential inputs in the sampling circuit, and improving CMRR. After optimization, the error introduced by grounding noise can be controlled within 0.05%FS.