Cross-Physics Sensor Replacement in Industrial Control Circuits
Cross-physics sensor retrofits require matching phase delay, thermal drift coefficients, and input filter bounds before changing the transduction element.
Sample Rate Aliasing
Signal Distortion Phenomenon
Inaccurate digital representations of a physical process occur when a measurement system samples too slowly. If sample rate aliasing is present, high frequency components of the input signal appear as lower frequency fluctuations in the data. This error makes it impossible to reconstruct the original signal correctly.
Frequency Foldback
Noise or vibrations that exist above the Nyquist frequency are reflected back into the visible part of the spectrum. For example, a 60Hz hum sampled at 50Hz will appear as a 10Hz signal in the resulting data. This phantom signal can trigger control actions or lead to incorrect diagnosis of mechanical issues.
Digital Reconstruction
Accuracy of the data depends on having at least two samples for every cycle of the highest frequency present in the input. While this is the theoretical minimum, practical systems often sample five or ten times faster to ensure a high quality signal. Higher sampling rates allow for better digital filtering and more precise timing.
Nyquist Limit
Hardware filters are placed before the analog to digital converter to block any energy above the safe threshold. These anti-aliasing filters ensure that the converter only sees frequencies that it can accurately digitize. Proper filter design is essential for maintaining the integrity of the measurement in environments with high frequency noise.