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βœ… MSO5000 Live Monitor β€” Power Analysis Setup (Low-Side Shunt + Two Standard Probes)

Use two standard passive probes that ship with the MSO5000 and a R010 (10 mΞ©) low-side shunt.
This setup works for DC and AC (50/60 Hz or other fundamentals) with highest practical safety when the shunt is truly low-side (near ground).

🧰 Hardware

  • Shunt: 10 mΞ© (R010), mounted in the return path (between load return and supply negative).
    Prefer Kelvin (4-wire) connections at the shunt pads for sensing.
  • Probes: the two standard Rigol passive probes (switchable 1Γ—/10Γ—).
  • Scope: RIGOL MSO5000 (earth-referenced BNC shell).

⚠️ Bench scopes tie the probe ground clip to protective earth (PE).
Low-side shunt means the most negative node is near ground potential β†’ safe to clip grounds there. Never clip probe grounds to two different potentials.

πŸ”Œ Wiring (low-side)

Screenshot

  • CH4 measures the shunt drop (mV). Tip on the load side of the shunt, ground on Supply(βˆ’).
  • CH3 measures voltage vs Supply(βˆ’) (DC bus or AC line vs neutral/return).

Tip: Keep shunt sense leads short/twisted. If available, solder thin sense wires directly at the shunt pads.

Channel pairing for minimal skew

  • Use the same ADC pair: CH3 (voltage) + CH4 (shunt) share one pair on MSO5000 β†’ best phase alignment.

CH3 β€” Voltage

  • Unit: VOLT
  • Probe switch: 10Γ— (mandatory for high voltage; 1Γ— is limited to a few volts)
  • 20 MHz BW Limit: βœ… (cleaner PF/phase)
  • Vertical scale: match your bus/grid voltage (e.g., 100–200 V/div for ~160 V DC with 10Γ—)

CH4 β€” Shunt (current via V/R)

  • Unit: VOLT
  • Probe switch: 1Γ— (maximize mV sensitivity)
  • 20 MHz BW Limit: βœ…
  • Vertical scale: mV/div (start around 5–20 mV/div)
  • Invert: off initially (we’ll verify polarity in β€œSanity Checks”)

Acquisition

  • Sample rate: high enough to capture your spectrum (β‰₯10Γ— highest relevant freq)
  • Record length: cover β‰₯ 5–10 periods of the fundamental (for stable Ο†/Q)
  • Coupling: DC on both channels

βš™οΈ Live Monitor β€” Power Analysis Settings

Field Set To Notes
Voltage Ch 3 Uses CH3 waveform (volts)
Current Ch 4 Uses CH4 shunt drop (volts)
Current Probe Type Shunt βœ… Enables Vβ†’I = V/R
Probe Value 0.01 (for 10 mΞ©) In ohms
Correction Factor 1.0 Use for calibration only
DC Offset For DC: enable and zero CH4 at no-load if needed. For AC: usually off.
25M [v]/[i] Off for mains/DC unless you need wideband
➀ ⚑ Measure Click to start

What the software does:
- Computes P = ⟨v·i⟩ directly in time domain (valid for any waveform).
- Converts CH4 to current via I = Vshunt / 0.01 Ξ©.
- For AC, extracts the fundamental phasors to get Q₁ with correct sign (+ inductive, βˆ’ capacitive) and φ₁.

πŸ§ͺ Sanity Checks (5 quick steps)

1) No-load zero (optional, DC): Power supply on, load disconnected.
- CH4 should read ~0 mV (small offset is okay). If needed, use DC Offset zero in the app.

2) Resistive load test: Connect a purely resistive load (lamp/resistor).
- Expect PF β‰ˆ 1, Q β‰ˆ 0 (AC), P β‰ˆ UΓ—I (both DC & AC).

3) Polarity: With normal power into the load, P should be positive.
- If P is negative, toggle Invert (CH4) in the scope or the app’s β€œInvert current” option.

4) Magnitude sanity:
- At 5 A, shunt drop β‰ˆ 50 mV. If you see ~5 mV (Γ—10 error) or ~500 mV (Γ—10 too big), check probe 1Γ—/10Γ— and scope Probe menu.

5) Noise: Enable 20 MHz BW limit on both channels. Use 1Γ— on CH4 for better mV resolution.

🎯 Precision Tips

  • Kelvin sense: If your shunt carrier has separate sense pads, use them. Avoid sensing across long copper pours.
  • Grounding: One single ground reference at Supply(βˆ’). Don’t make a second ground connection elsewhere.
  • ADC pair: Prefer CH3+CH4 (or CH1+CH2) to minimize inter-channel delay.
  • Phase trim (rare): If you still see a fixed Ο† offset with a purely resistive load, note it and apply a tiny correction factor or offset in software.
  • Bandwidth: For fast pulsed loads, raise sample rate and record length; keep BW limit on unless you need the HF content.

πŸ›‘ Safety

  • Never clip a probe ground to a live/hot node. Bench scope grounds are earth-bonded.
  • Verify the supply is floating or that bonding Supply(βˆ’) β†’ PE is acceptable for your setup.
  • High-energy DC (e.g., 160 V) requires appropriate probe voltage ratings (use 10Γ— on CH3).
  • Keep leads short; secure the shunt mechanically (it runs hot at high current).

🏁 Quick Reference Table

Signal CH Scope Unit Probe switch BW Limit App Probe Type App Probe Value
Voltage vs Supply(βˆ’) 3 VOLT 10Γ— On β€” β€”
Shunt drop (V across R) 4 VOLT 1Γ— On Shunt 0.01 Ξ©

πŸ“Œ Troubleshooting

Symptom What to check
P negative on a normal load Flip CH4 Invert (scope) / reverse clamp orientation if you used one
Current too small/large by Γ—10 CH4 probe switch (1Γ— vs 10Γ—) and scope Probe menu; Probe Value = 0.01 Ξ©
PF jitter / noisy Q Enable BW limit; increase record length; improve shunt wiring (Kelvin)
Disagreement vs external meter (AC) Confirm line frequency lock (window covers β‰₯5–10 periods); ensure shunt value is exact (measure it)

Formula reminder

  • Current from shunt: \( I(t) = \dfrac{V_{\text{shunt}}(t)}{0.01\,\Omega} \)
  • Instantaneous power: \( p(t) = v(t)\,i(t) \), P = average of \(p(t)\)
  • AC fundamental (for Q₁): \( Q_1 = \Im\{U_1\,I_1^*\} \) (positive = inductive, negative = capacitive)