THD Sweep Measurement

Wiki: THD Sweep Measurement System

This software allows for continuous measurement of Total Harmonic Distortion (THD) during a frequency sweep (sweep sine) with an OROS system.

🚀 Installation & Launch

Using the Executable (Recommended)

1. Go to the Template:Code folder.
2. Launch Template:Code.

Note: The executable is standalone and contains all dependencies.

Using Python Sources

1. Ensure you have Python 3.8+ (32-bit preferred for NVGate compatibility).
2. Launch the script via Template:Code or via command line: Template:Code.

🛠 Required NVGate Configuration

For the software to function correctly, your NVGate project must be configured as follows:

1. FFT Analyzer:
   • Window 1 (Window1): Must display the response channel (Microphone).
   • Window 2 (Window2): Must display the reference channel (Sweep Sine).
2. Markers:
   • The software will automatically create and manage a Max marker in Window2 and a Harmonic marker in Window1.
3. Simulated DC Inputs:
   • Enable simulated DC inputs in the Front-end.
   • DC1 will receive the THD value in %.
   • DC2 will receive the THD value in dB.

📊 Metrological Details

Calculation Formula

The software calculates THD relative to the fundamental ($THD_f$) according to the IEC 61000-4-7 standard:

$THD_{\%}={\frac {\sqrt {\sum _{n=2}^{10}H_{n}^{2}}}{H_{1}}}\times 100$

• H1: Amplitude of the fundamental.
• H2 to H10: Amplitude of harmonics (the software tracks the first 9 harmonics by default).

Precision and Latency

• Maximum Asynchronous Mode: There is no artificial delay between measurement cycles.
• Latency: A total cycle time (Frequency Read -> Calculation -> DC Write) of < 150ms is recommended.
• Recommended Sweep Speed: 4 octaves/min. This ensures a good balance between measurement speed and tracking accuracy.
• FFT Windowing: Use a Hanning window for the best frequency resolution during a sweep sine.

💻 Development and Compilation

Project Structure

File	Role
thd_gui.py	Graphical user interface (Tkinter)
thd_sweep_measurement.py	Core calculation and NVGate communication
Toolkit NVdrive/	pynvdrive library to control NVGate

Recompiling the Executable

<syntaxhighlight lang="bash"> pyinstaller --onefile --windowed --name "THD_Sweep_Measurement" --add-data "Toolkit NVdrive;Toolkit NVdrive" thd_gui.py </syntaxhighlight>

❓ Troubleshooting

• "Error 4 bytes": Network buffer error handled automatically by a 20ms pause. Check local network load if it persists.
• THD at 0% or --: Ensure the signal is present in Window1 and the Max marker in Window2 detects a valid frequency (> 0 Hz).
• NVGate not connected: Verify that NVGate is running and the "NVDrive" option is enabled in settings.