What is the difference between a low-pass filter and a notch filter; when would you use each in sensor conditioning?

• A. Low-pass removes low frequencies; notch removes a broad range of frequencies.
• B. Notch removes all high frequencies; low-pass removes a narrow, specific frequency.
• C. Low-pass removes high-frequency noise; notch suppresses a narrow frequency like mains interference; use LPF to smooth signals and notch to reject mains interference.
• D. Notch filters amplify mains frequencies to improve measurement.

Answer: (C)

Low-pass filters let through the low-frequency content and attenuate higher frequencies. This helps remove high-frequency noise and smooth a sensor signal, which is especially useful before digitizing the signal or when you only care about slow-changing phenomena.

A notch filter, or band-stop filter with a very narrow stopband, specifically attenuates a narrow range of frequencies around a chosen frequency (like mains interference at 50 or 60 Hz) while leaving most of the spectrum intact. This is useful when you know a persistent interference is present at a particular frequency and you want to reject that specific frequency without harming nearby signal components.

So, a low-pass filter is used to smooth and limit bandwidth by removing high-frequency noise, while a notch filter is used to suppress a particular interference frequency (mains hum) with minimal impact on the rest of the signal. The statement aligns with this: the low-pass removes high-frequency noise, the notch suppresses a narrow frequency like mains interference, and you apply a low-pass to smooth and a notch to reject mains interference.