Lesson 4: Data acquisition

Introduction: Electric drive systems are multi-physics devices that require capturing data across different domains for evaluating performance. This lesson will guide you through the intricacies of data acquisition in these systems.

Understanding Data Acquisition:

  • Signals to Consider:
    • Directly from the Unit Under Test (UUT).
    • From testing environment’s devices.
    • These signals help in evaluating results or tracing back problems.
  • Commonly Measured Quantities:
    • Voltage, current, torque, force, acceleration, acoustic noise.
    • Speed, position, temperature, flow rate, pressure.
    • Digital messages on the communication bus (e.g., CAN).

Figure Many types of signals from different sources are present during a measurement and must be measured simultaneously

Challenges in Data Acquisition:

  1. Collecting Concurrent Signals:
    • The sheer number and variety of signals make simultaneous collection challenging.
    • Signals can be analog low voltage or already digitalized by the sensor, requiring varied interfaces on the acquisition device.
    • Often, recording is distributed across different modules or measuring cards.
  2. Time Synchronization:
    • Ensuring signals share the same time-base is crucial for obtaining meaningful data.
    • Without this, it’s tough to form a consecutive chain of events for analysis.
    • Each signal or set of signals comes with a timestamp synchronized to a master device.

Achieving Precision in Data Acquisition:

  • Accuracy: The system’s accuracy should be 10x better than the smallest deviation to be evaluated.
    • Example: If the maximum allowed torque deviation is 2 [Nm], the system should resolve the signal in 0.2 [Nm] levels.
  • Sampling Frequency:
    • The Nyquist-Shannon theorem dictates that the sampling frequency should be at least double the frequency of the measured signal: π‘“π‘ π‘Žπ‘šπ‘π‘™π‘–π‘›π‘”>2β‹…π‘“π‘ π‘–π‘”π‘›π‘Žπ‘™
    • In practical terms, often a frequency 10 times higher is used for sampling.
    • If sampling frequency is less than double the signal’s frequency, aliasing occurs.
  • Avoiding Aliasing:
    • Measured signals go through a low-pass filter before digital sampling.
    • This filter cuts off high frequency parts to prevent aliasing.

Conclusion: Data acquisition in electric drive systems is intricate. Understanding the challenges and the science behind accurate data capture is vital to obtain meaningful results and insights from tests.


  1. Why is time synchronization crucial in data acquisition?
  2. Explain the relationship between the sampling frequency and the signal’s frequency as per the Nyquist-Shannon theorem.
  3. What’s the purpose of using a low-pass filter before digital sampling?
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