THD Sweep Measurement

= 💠 THD Sweep Measurement Utility - User Guide

Welcome to the Total Harmonic Distortion (THD) Sweep Utility documentation. This tool is a high-performance bridge between OROS NVGate and real-time THD analysis, specifically optimized for sine sweep measurements.

🚀 Overview

The utility automates the tracking of a moving sine peak (sweep) to compute distortion THD in real-time.

💎 Key Features

• Real-Time Tracking: Follows the sweep peak across the frequency spectrum.
• High-Precision THD: Calculates THD using the fundamental + 9 harmonics.
• Live Data Feedback: Pushes results (%, dB, and Frequency) back into NVGate.
• Integrated Diagnostics: One-click verification of the entire measurement chain.

🛠️ NVGate Pre-Requisites

Before running the software, ensure your NVGate project is set up as follows:

1. Windows Setup:
   • Reference Window (Window2): FFT trace of the source signal (Generator output).
   • Response Window (Window1): FFT trace of the tested device (Microphone/Sensor).
2. Marker Setup:
   • Add a Max Marker in the Reference Window.
   • Add a Harmonic Marker in the Response Window.
3. DC Inputs:
   • Enable Simulated DC Inputs 1, 2, and 3 in the Frontend configuration.

⚙️ Configuration Reference (The "Brain" of the App)

The configuration panel maps the utility's logic to your specific NVGate project. Applying these settings correctly is critical for the tracking to work.

Field	Technical Role	Detailed Function
Window Ch4 (Sweep)	Reference Source	The utility looks in this window to find the peak frequency of the sweep. It uses the Max Marker to "identify" where the generator is at any given millisecond.
Window Ch1 (Resp)	Analysis Target	This is where the actual THD measurement happens. The tool reads the signal amplitude from this window to calculate distortion relative to the reference frequency.
Max Marker #	Frequency Tracker	This marker is the "eyes" of the application. It constantly reports the X-axis (frequency) position of the strongest signal in the Sweep window.
Harmonic Marker #	Harmonic Sampler	The utility physically repositions this marker to the frequency found by the Max Marker. Once moved, it reads the Fundamental (H1) and all Harmonics (H2-H10) to compute the THD.
Nb Harmonics	Calculation Depth	Defines how many harmonics are summed. Default is 9, meaning the tool analyzes up to the 10th order (Fundamental + 9 harmonics).
DC1 IDN (THD %)	Linear Output Bridge	The Instrument Description Name (IDN) is the internal address in NVGate. This setting pushes the calculated THD percentage directly into the first Simulated DC input.
DC2 IDN (THD dB)	Logarithmic Bridge	Similar to DC1, but pushes the THD value converted to decibels (dB), allowing you to log or display dB values directly inside NVGate.
DC3 IDN (Freq)	Frequency Bridge	Pushes the current tracked frequency (in Hz) to a DC input. This allows NVGate to plot THD versus Frequency in a Cross-Plot or Waterfall.

💡 Pro Tip: If you change these values, click "Apply Configuration" to update the logic immediately. If a window name is wrong, the Diagnostic will immediately turn RED.

🕹️ Operational Workflow

1️⃣ Connectivity Test

Click the 🔍 DIAGNOSTIC button first.

• It checks if NVGate is open.
• It verifies that the markers exist in the right windows.
• It tests writing to the DC inputs and reads them back to ensure accuracy.
• Result: If the log turns GREEN, you are ready to measure!

2️⃣ Measuring

Click ▶ START.

• The utility sends a Run command to NVGate.
• It stabilizes for 2 seconds (allowing the FFT to populate).
• It begins the loop: Track Peak → Move Harmonics → Calculate THD → Write to DC.

3️⃣ Monitoring

• Purple Card: Live THD in dB (Standard for audio).
• Yellow Card: Live THD in % (Linear scale).
• Teal/Blue Cards: Current tracked Frequency and Fundamental amplitude.

📊 Technical Specifications

Data Mapping

The utility automatically configures NVGate Simulated DC inputs with the following:

• DC 1 (THD %): Magnitude set to Percentage (0.0 to 100.0).
• DC 2 (THD dB): Magnitude set to Ratio (-200.0 to 0.0 dB).
• DC 3 (Frequency): Magnitude set to Frequency (0.0 to 40,000.0 Hz).

THD Formula

The tool uses the standard RMS summation:

THD = sqrt(H2² + H3² + ... + H10²) / H1

Where H1 is the Fundamental and H2-H10 are the Harmonics.

❓ Troubleshooting

• Log is RED?: Check if the Window names in NVGate match exactly (case sensitive) with the names in the Configuration panel.
• "Access Denied" Error: Ensure no other instance of the software is running in the background.
• Values not updating?: Ensure NVGate is in RUN mode and the traces are active.

--- Generated by OROS Gemini CLI - 2026

• 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.