Which item is a common source of signal noise?

Which item is a common source of signal noise?

• A. VFDs
• B. Ground shields properly
• C. Shielded cables
• D. Short cable runs

Answer: (A)

VFDs are a common source of signal noise because they switch motor power at high speeds using PWM, which creates fast transients and high-frequency EMI. Those switching transients can couple into nearby analog and digital signal lines, disturbing 4–20 mA loops and HART communications. Ground shields properly, shielded cables, and short cable runs all help reduce this noise by lowering coupling and the loop area, rather than producing it. So the item most likely to generate interference among the options is the VFD.

VFDs are a common source of signal noise because they switch motor power at high speeds using PWM, which creates fast transients and high-frequency EMI. Those switching transients can couple into nearby analog and digital signal lines, disturbing 4–20 mA loops and HART communications. Ground shields properly, shielded cables, and short cable runs all help reduce this noise by lowering coupling and the loop area, rather than producing it. So the item most likely to generate interference among the options is the VFD.