How to optimize conducted transmission for Human-Machine Interface (HMI) delivery?

Optimizing HMI conducted emissions to pass testing focuses on the filtering design of power and signal ports. Conducted emissions are typically tested in the 150kHz-30MHz frequency band. Optimization measures include: First, checking and optimizing the EMI filter at the power input. Ensure the common-mode inductor, such as the CMZ7060A series, has sufficient inductance and high impedance at interference frequencies; check the capacitance and mounting location of the X and Y capacitors; the filter must be tightly mounted at the power input, with its ground terminal connected to the chassis with low impedance. Second, check the noise suppression of the internal switching power supply, increasing differential and common-mode filtering at the input and output terminals, using additional ferrite beads and capacitors.

For conducted emissions generated through signal cables, common-mode filtering needs to be added at the signal ports, such as using common-mode chokes or filter connectors. Check that the shielding of all external cables is properly grounded at the device input. On the internal PCB design, ensure adequate power supply decoupling for digital circuits to prevent noise from coupling to the input/output ports through the power supply's internal resistance. During pre-testing, use a LISN and spectrum analyzer to measure the conducted noise spectrum in detail, adjusting filter parameters or increasing the number of stages for frequencies exceeding the standard. Etymotics' range of filters, beads, and capacitors offers a wide selection for optimized conducted emissions, and stable compliance can be achieved through iterative design and testing.