Bench power supply
Output voltage
- Current limit
- —
- Mode check
- CV expected
Virtual engineering lab
RL Time-Constant Measurement
Measure current build-up in a series RL circuit and compare the sampled 63.2% crossing with the analytic time constant τ = L/R.
Electrical Engineering / InstrumentationintroductoryValidated educational model
0% complete0 / 0 requirements
Complete the procedure, collect the required measurements, pass the engineering validation, and answer every graded concept question correctly.
What you should establish
- Predict an RL time constant from inductance and series resistance.
- Relate resistor voltage to circuit current for oscilloscope measurement.
- Verify that the bench-supply current limit exceeds the steady-state RL current.
- Compare measured and analytic time constants.
Work through the experiment
Collect evidence from the model
- Analytic time constantRL time constant calculated from L/R.Pending
- Scope-measured time constantInterpolated 63.2% crossing from the sampled current waveform.Pending
- Final currentIdeal steady-state current VS/R.Pending
- Initial inductor voltageIdeal inductor voltage immediately after the source step.Pending
- DMM resistance checkIndependent resistance reading before energizing the circuit.Pending
- Current-limit marginBench-supply current limit minus steady-state current.Pending
Verify the result, not just the workflow
- RL time-constant checkCompares the sampled 63.2% current crossing with τ = L/R.Pending
Only a passed engineering check satisfies guided completion. Warnings and failures remain visible even if the procedure checklist is complete.
Answer the graded multiple-choice questions
Choose one answer for each question. Each selection is graded immediately and saved locally. Guided Lab completion requires every concept question to be correct.
Concept score: 0 / 3 correct
Integrated virtual bench
Ideal instrumentsRL transient bench
Resistance check
COM + VΩ · circuit unpowered
Confirm the modeled series resistance before applying the source.
Oscilloscope
—Transient response
Adjust experiment parameters to preview the ideal response, then run the experiment for validation.
Series R–L network
- Analytic τ
- —
- 63.2% measurement
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- Current-limit margin
- —
Measurements
Instrument readings
- Analytic time constant
- — RL time constant calculated from L/R.
- Scope-measured time constant
- — Interpolated 63.2% crossing from the sampled current waveform.
- Final current
- — Ideal steady-state current VS/R.
- Initial inductor voltage
- — Ideal inductor voltage immediately after the source step.
- DMM resistance check
- — Independent resistance reading before energizing the circuit.
- Current-limit margin
- — Bench-supply current limit minus steady-state current.
Result visualization
Transient measurement check
Compare the analytic first-order time constant with the oscilloscope-style 63.2% crossing and verify the source current-limit margin.
- Analytic τ
- —
- Measured τ
- —
- Final current
- —
- Current-limit margin
- —
Independent check: I(τ) = 0.6321(VS/R) and τ = L/R.
Theory
Equations and model
First-order inductor current rise
An ideal inductor initially opposes a sudden current change. In a series RL circuit the current rises exponentially toward VS/R.
τ = L/RI(t) = (VS/R)(1 − e^(−tR/L))I(τ) = 0.6321 VS/ROscilloscope current measurement
A scope measures voltage, so the lab uses the voltage across the known series resistor as a current-sense signal.
VR(t) = I(t)RI(t) = VR(t)/RValidation
Independent checks
RL time-constant checkNot run
Compares the sampled 63.2% current crossing with τ = L/R.
- Expected
- —
- Simulated
- —
- Error
- —
- Tolerance
- 0.25%
Run the experiment to perform this check.
Engineering interpretation
Run the experiment to generate an engineering interpretation.
Assumptions and limitations
Assumptions
- Ideal resistor and inductor.
- Ideal DC step source provided the current limit is not reached.
- Inductor winding resistance is represented only by the explicit series resistor.
- No magnetic saturation, parasitic capacitance, or source/wiring inductance.
Limitations
- Current-limited RL response is detected and rejected instead of being solved in Phase 1.6.
- Core loss, saturation, winding resistance, noise, and measurement non-idealities arrive in later work.
Local experiment export
Phase 1.9Save your measurements and setup
Exports are generated in your browser. No account or server upload is required.
- Settings JSON
- Current parameter values for reproducibility and later project handoff.
- Measurements CSV
- Completed instrument readings with labels, units, and descriptions.
- Plot PNG
- The current canvas-based scope, transient, sweep, or statistics visualization when available.
- Summary
- Markdown report with objectives, setup, measurements, validation, interpretation, assumptions, and graded guided concept-check results.
Ready to export the current local experiment state.
What this experiment should establish
- Predict an RL time constant from inductance and series resistance.
- Relate resistor voltage to circuit current for oscilloscope measurement.
- Verify that the bench-supply current limit exceeds the steady-state RL current.
- Compare measured and analytic time constants.
Questions to answer from the experiment
- Why is the ideal inductor current still zero at the instant immediately after the voltage step?
- What happens to the RL time constant if series resistance doubles?
- Why is voltage across the series resistor a useful way to observe current with an oscilloscope?