Choosing the Right Sampling Frequency and Density for Sheath Current Acquisition

[Shinar-of-Clark]

​1. Background
​We are currently developing a Sheath Current Acquisition (SCA) unit. The primary goal is to monitor high-voltage cable metal sheaths for various damage conditions, such as insulation aging and grounding anomalies.
​2. Proposed Sampling Tiers
​For a 50Hz power environment, I have categorized the acquisition into three tiers for your consideration:
​Tier 1: Basic
​Parameters: 64 points/cycle (Sampling Rate: 1.28 kHz)
​Features: Ultra-low power consumption. Focuses only on RMS trends without complex analysis.
​Tier 2: Standard
​Parameters: 128 points/cycle (Sampling Rate: 6.4 kHz)
​Features: Balances accuracy and MCU overhead. Capable of basic FFT harmonic analysis.
​Tier 3: High-Fidelity
​Parameters: 256 points/cycle (Sampling Rate: 12.8 kHz)
​Features: High waveform reconstruction accuracy. Ideal for transient capture and precision diagnostics.
​3. My Recommendation & Concerns
​My current recommendation is to use 256 points per cycle at 50Hz.
​Rationale:
​Data Depth: 256 points provides sufficient headroom for subsequent DSP filtering and fault diagnosis.
​Memory Efficiency: 256 is a power of 2 (2^8), which ensures maximum efficiency for FFT operations and DMA buffer management on STM32 chips.
​Performance Challenges: However, I am concerned that higher sampling frequencies may struggle to meet real-time processing requirements on the STM32, especially when balancing network communication and other concurrent tasks.
​If you have any suggestions regarding the number of sampling points or any other technical feedback, please feel free to share. Let's discuss!