Temporal Offset
Mathematical models of sensor behavior show a time delay between the input signal and the resulting output. This transfer function phase lag is measured in degrees or radians and describes how far the output trails the input in a periodic system. It is a fundamental property of all physical measurement systems with thermal or mechanical mass.
Inertia
The mass of the sensing element prevents it from responding instantly to high-frequency changes. As the frequency of the input oscillation increases, the transfer function phase lag also increases. This happens because the energy cannot move through the system fast enough to keep pace with the signal.
The magnitude of the lag depends on the time constant of the sensor.
Automated Systems
Feedback loops rely on timely data to maintain stability in a process. If the transfer function phase lag is too large, the control algorithm may apply corrections based on outdated information. This can lead to oscillations or even total system failure.
Tuning a PID controller requires a precise understanding of this delay to compensate for the inherent slowness of the sensor.
Dynamic Errors
Inaccuracies occur when the phase of the measurement is shifted relative to the actual event. Calculating the transfer function phase lag allows engineers to reconstruct the original signal more accurately. This is particularly important in vibration analysis or rapid thermal cycling.
Verification involves comparing the sensor output to a high-speed reference during a known excitation. Digital compensation filters can sometimes reduce the effective lag in the signal chain.
