Measuring current without breaking the circuit is the whole point of a clamp-style sensor, but "clamp it around the conductor" describes three genuinely different sensing technologies, each with different physical limits on what it can measure. Picking the wrong one doesn't just mean reduced accuracy — for DC current measurement specifically, the wrong sensor type simply won't read anything at all.
Three Sensing Mechanisms
Conventional current transformer (CT). A closed iron core wound with a secondary coil surrounds the conductor; changing magnetic field from AC current induces a proportional current in the secondary winding. This is the oldest and generally most accurate AC current sensing method, but it fundamentally only works with alternating current — a steady DC current produces no changing flux, so a conventional CT reads zero regardless of how much DC current is flowing.
Hall effect sensor. A small Hall element sits in a narrow air gap within an otherwise similar iron core. The Hall element directly senses magnetic flux density rather than relying on induced current, which means it can measure DC current as well as AC. This DC capability is the main reason to choose Hall effect over a conventional CT, at the cost of generally being somewhat more expensive.
Rogowski coil. A flexible coil with no iron core at all. Because there's no magnetic core to saturate, a Rogowski coil handles very high currents linearly, and its flexible form factor lets it wrap around irregularly shaped conductors. The trade-off: its raw output is proportional to the rate of change of current, requiring an integrator circuit to produce a usable reading — and it cannot measure steady DC current at all, only AC and current transients.
Comparing the Three
| Factor | Conventional CT | Hall Effect | Rogowski Coil |
|---|---|---|---|
| Measures DC | No | Yes | No |
| Measures AC | Yes | Yes | Yes |
| Core type | Closed/split iron core | Iron core with air gap | No iron core (flexible) |
| Saturation risk at high current | Yes | Yes (lower than CT) | No |
| Form factor | Rigid clamp | Rigid clamp | Flexible, wraps around irregular shapes |
| Requires integrator | No | No | Yes |
| Best suited for | General AC current measurement, metering | Mixed AC/DC applications, motor drives, battery systems | High-current, irregular conductors, transient/pulse measurement |
Choosing for the Application
If DC current measurement is required at all — battery systems, DC motor drives, solar/EV charging circuits — only a Hall effect sensor will actually read it. This is a hard physical limitation, not a specification to shop around.
For straightforward AC current measurement at line frequency, a conventional CT remains the most cost-effective and typically most accurate option.
For high current, awkward conductor geometry, or tight panel spaces, a flexible Rogowski coil solves the installation problem a rigid CT or Hall sensor can't.
For transient or pulsed current measurement — welding current, switching transients, short-circuit testing — a Rogowski coil's fast response makes it the preferred choice.
A Note on Output Signal Compatibility
Confirm the sensor's output signal matches what the connected meter expects. Conventional CTs commonly output a standard ratio current directly compatible with many meters; Hall effect sensors typically output a proportional voltage or current signal; Rogowski coils output a low-level voltage that requires an integrator before it represents actual current.