How can a poor grounding of an I/O module cause malfunctions?

Poor grounding of I/O modules can cause malfunctions through various mechanisms. High-impedance grounding prevents effective discharge of common-mode noise, resulting in significant common-mode voltage fluctuations on the signal ground. When these fluctuations exceed the common-mode input range of the receiver chip, they can lead to misinterpretation of digital signals or distortion of analog signals. Ground loops can induce power frequency magnetic fields or radio frequency interference, generating additional noise current in the signal loop, which is superimposed on the useful signal. Ground potential differences can directly cause inconsistencies in reference levels between remotely connected devices, resulting in communication errors.

Transient currents such as EFTs or surges can generate large voltage drops when flowing through poor grounding paths, and this voltage can couple to sensitive circuits through parasitic capacitance. In addition, poor grounding reduces shielding effectiveness, making the module more susceptible to radiated interference. Solutions include checking and ensuring all grounding connections are secure and have low impedance; using star or planar grounding to reduce ground impedance; adding common-mode chokes or isolators to sensitive interfaces; and using differential transmission for long cables.