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MSO5000 Power Analyzer โ€” Technical Overview

Project Title: Real-Time Power Analyzer using Rigol MSO5000
Author: Aether Research Institute (ariDev1)
Date: 2025-08-31 Repository: GitHub/MSO5000_liveview

Purpose

This project turns a Rigol MSO5000 into a real-time power analyzer for high-resolution measurements of power, energy, and phase relationships, using open software and SCPI-based waveform extraction. It aims to approach (and in some cases exceed) commercial meter functionality while remaining transparent and auditable.

โš™ System Overview

  • ๐Ÿ–ฅ๏ธ Python GUI (Tkinter + matplotlib)
  • ๐Ÿ”Œ Live waveform acquisition via SCPI (VISA)
  • ๐Ÿงฎ Real-time computation of:
  • Active Power (P)
  • Apparent Power (S)
  • Reactive Power at the fundamental (Qโ‚) with correct sign (inductive +, capacitive โˆ’)
  • Power Factor (PF = P/S) and fundamental angle ฯ†โ‚
  • ๐Ÿ“ˆ Live PQ plotting with quadrant display
  • ๐Ÿงช Calibration via expected power or correction factor

Methodology

1) Waveform Extraction

Voltage and current are acquired from the oscilloscope via SCPI, rescaled, and converted to NumPy arrays for analysis, e.g.:

:WAV:SOUR CHANx
:WAV:MODE NORM
:WAV:DATA?

Acquisition settings (sample rate, record length, channel scales/units, probe factors) are preserved for traceability.

Given sampled waveforms \( v[n] \) and \( i[n] \) (with proper scaling to volts and amps):

  • Vrms
    \( V_\mathrm{rms}=\sqrt{\tfrac1N\sum_n v[n]^2} \)
  • Irms
    \( I_\mathrm{rms}=\sqrt{\tfrac1N\sum_n i[n]^2} \)
  • Active power (time-domain average of instantaneous power)
    \( P=\tfrac1N\sum_n v[n]\cdot i[n] \)
  • Apparent power
    \( S=V_\mathrm{rms}\,I_\mathrm{rms} \)
  • Reactive power (fundamental) โ€” IEEE 1459 compliant
    Estimate the fundamental frequency \(f_0\) in the window, form RMS phasors \(U_1, I_1\) at \(f_0\) (orthogonal projection), then \( S_1=U_1\,I_1^*,\quad P_1=\Re\{S_1\},\quad Q_1=\Im\{S_1\} \) with sign convention: \(Q_1>0\) inductive (current lags), \(Q_1<0\) capacitive (current leads).
  • Power Factor (total, signed)
    \( \mathrm{PF}=\frac{P}{S}\quad(\text{sign}(PF)=\text{sign}(P)) \)

Important correction: the earlier \(Q=\sqrt{S^2-P^2}\) is not used (it is signless and invalid under distortion). We now report \(Q_1\) from fundamental phasors with correct sign.

3) Phase / Angle

For reporting the phase relation, the tool uses the fundamental phasor angle
\( \varphi_1=\arg(U_1 I_1^*)=\arctan2(Q_1, P_1) \) Cross-correlation can be employed internally for rough delay alignment or diagnostics, but the authoritative phase for PF/Q is the fundamental angle \(\varphi_1\). This is robust for distorted waveforms and consistent with the Qโ‚ definition.

๐Ÿ“Š Visualization Features

  • Real-time PQ vector plot using \(P\) and \(Q_1\) with quadrant classification
  • Live PF and ฯ†โ‚ display
  • Time-based energy integration:
  • Real energy (Wh) from \(P\)
  • Apparent energy (VAh) from \(S\)
  • Reactive energy (varh) from \(Q_1\)

Screenshot

Calibration Options

Method Description
Correction Factor Manual scalar applied to current path (for probe/clamp calibration).
Auto Calibration Enter an expected power; the tool computes a correction factor.
Unit Detection The scopeโ€™s CHANx:UNIT? is queried to determine if a channel is in V or A, preventing double scaling.

These options mirror the original design while ensuring scaling is traceable.

Data Logging

  • CSV logs (e.g., under /oszi_csv/) capture timestamped results: P, Qโ‚, S, PF, Vrms, Irms, ฯ†โ‚, fโ‚€ and energy counters (Wh/VAh/varh).
  • Session summary plots saved as PNG alongside logs for audit.

Error Handling and Stability

  • Blocks conflicting actions (e.g., power analysis vs. long-term logging simultaneously)
  • Detects non-finite results and skips invalid reads
  • Tracks DC-offset settings; handles scope disconnections gracefully

What You Gain

  • Open, transparent power analyzer with raw-data traceability
  • Reproducible results and configurable probing/scaling
  • Sign-correct \(Q_1\) and robust PF/angle in distorted conditions
  • Practical accuracy without vendor lock-in

Screenshot

License

Open-source; use at your own risk. Accuracy depends on oscilloscope bandwidth, probe/clamp/shunt calibration, and SCPI reliability.