How does interference from external cables couple in HMI (Human Machine Delivery) systems?

External cables are the primary channel for HMI to interact with the external electromagnetic environment. Interference mainly enters or escapes through two modes: conducted coupling and radiated coupling. Conducted coupling refers to interference directly entering the device through the cable conductor. For example, noise from the power grid enters through the power line, or a space field induces a common-mode voltage on the signal line, which is then converted into a differential-mode voltage and affects the signal. Radiated coupling refers to the cable acting as an antenna, receiving electromagnetic interference from space or radiating internal noise from the device. The type and connection method of the cable directly affect the coupling efficiency.

Unshielded parallel cables are susceptible to electric and magnetic field coupling; unshielded twisted-pair cables have better suppression of magnetic field coupling; shielded cables can effectively suppress electric field and spatial radiated coupling, but the shielding layer must be properly grounded. Crosstalk can also occur when multiple cables are bundled together. Methods to reduce coupling include: using shielded cables as much as possible and lapping the shielding layer 360 degrees to the chassis at the device entrance; shortening cable length; avoiding routing cables near strong interference sources; adding filtering circuits at cable ports, such as common-mode chokes and TVS; and using differential transmission for sensitive signals. Understanding the interference coupling mechanism and using Audiotech's filtering, protection, and shielding components for targeted treatment is key to protecting HMIs from external cable interference.