|Rogowski Coils: Operating Limits|
|The graph below illustrates the enormous range of currents and frequencies that can be measured using Rogowski coils.The limits shown are given as a guide only and it is sometimes possible to design a special system for operating outside the limits.|
The direct output from the coil depends on the rate of change of current. For sufficiently high currents and frequencies the output can be large enough to cause a voltage breakdown. Coils with a low mutual inductance are best for high currents and frequencies.
Every coil has a self-resonant frequency caused by its self-inductance and inter-turn capacitance. The resonance also depencs on other factors such as cable capacitance. The resonance can be controlled by suitable damping circuitry, but generally it is not practicable to use a coil above its resonant frequency. The limits are shown by the vertical broken lines. See separate page for special High Frequency Coils.
At low currents and low frequencies the direct output from the coil is very low and the usefulness of the current transducer is limited by noise effects. Rigid coils which have a large mutual inductance are best for very low current measurements. The low current limit can be extended by using multiple primary turns round the coil or in the case of a flexible coil by wrapping the coil several times round the conductor. Electronic methods of signal recovery such as filters or phase-sensitive detectors are also useful.
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