Current Shunts, Clamps, And Current Probes
Definition: a current result produced by a transducer whose range, ratio, bandwidth, phase, insertion effect, offset, saturation, common-mode capability and calibration match the waveform and measurement point.
Choose The Measurement Point
| Location | What it answers |
|---|---|
| supply positive or complete return | amplifier input current and supply-side power |
| one amplifier output conductor | load current for that output path |
| load-bank branch | branch current sharing and hotspot risk |
| battery or alternator branch | source contribution, not automatically amplifier-only current |
Verify that parallel grounds, capacitors, multiple power runs, chassis paths, or other loads do not bypass the sensor.
Sensor Families
- Kelvin shunt: high accuracy and bandwidth when resistance, temperature, insertion loss and common mode are controlled.
- AC/DC Hall or hybrid probe: convenient isolation and waveform capture with range, offset, phase and saturation limits.
- Current transformer: AC only; cannot report DC and low-frequency behavior below its specified range.
- Clamp meter: useful for declared DC or AC ranges, but often too slow or bandwidth-limited for synchronized audio waveform power.
Shunt Design
Vshunt = I × Rshunt
Ploss = I² × RshuntChoose enough voltage for resolution without changing the circuit under test. Use separate Kelvin sense points at the resistive element, record hot resistance and temperature coefficient, and guard the shunt against fault current and touch.
Probe Setup
- Choose range and bandwidth from DC offset, RMS current, peak current and switching content.
- Zero and degauss as required.
- Center and orient the conductor as the probe specifies.
- Verify scaling and polarity.
- Deskew against the voltage channel before calculating instantaneous power.
- Check for overload, saturation and drift after the run.
Common Failure
A supply-side DC clamp reading multiplied by a separately updating output-voltage meter is not amplifier output power. It mixes input and output quantities, unrelated time windows, and usually different bandwidths.