| | | What is a Rogowski coil? Rogowski coils have been used for the detection and measurement of electric currents for decades. They are based on a simple principle: an "air-cored" coil is placed around the conductor in a toroidal fashion and the magnetic field produced by the current induces a voltage in the coil. The voltage output is proportional to the rate of change of current. This voltage is integrated, thus producing an output proportional to the current. By using precision winding techniques, especially developed for the purpose, the coils are manufactured so that their output is not influenced by the position of the conductor within the toroid, and to reject interference from external magnetic fields caused, for example, from nearby conductors. Basically, a Rogowski coil current measuring system consists of a combination of a coil and conditioning electronics (see drawing below) They can be used in similar circumstances to current transformers but for many applications they have considerable advantages: • wide dynamic range. The same coil can be used to measure currents from milliamps to hundred of kiloamps, it is enough to change the RC value in the integrator • high linearity. According to the manufacturing (size, inductance value, ...) the maximum measurable frequency can range up to hundreds of kHz and in some special models also MHz • very useful with large size or awkward shaped conductors or in places with limited access. Thanks to the structure without hard core, the coil can be easily manufactured according to the application or to the available space • unlike traditional current transducers, there is no danger from open-circuited secondaries • they cannot be damaged by large overloads • they are non-intrusive. They draw no power from the main circuit carrying the current to be measured • they are also light weighted and in some applications are light enough to be suspended on the conductor being measured The transducer does not measure direct currents but, unlike a current transformer, it can carry out accurate measurements of AC component even if there is a large superimposed DC component, since there is no iron core causing saturation. This feature is particularly useful for measuring ripple currents for example in battery charging systems. | | Specifications Transducer Internal diameter: Locking: Colour: Weight: Material: Connection Cable Type: Length: Material: Electrical Characteristics Output level (RMS) (1): Output permissible load: Coil resistance: Accuracy (2): | | |
| | | approx 40 to 100 mm black from 30 to 80 g thermoplastic rubber UL94-V0 2 x 0.15 mm + shield approx. 3 meter thermoplastic rubber UL94-V0 150 or 180 mV / 1 kA @ 50 Hz (other values on request) > 15 kohm for best accuracy from 20 to 25 ohm ± 2% without calibration, better than ±1% with calibration resistor approx 8 Hz to 100 kHz 600Vrms max installation category CAT III pollution degree 2 4000VRMS / 1min from -10 oC to +80 oC 95% max. without condensation EN61010-1, TC44 SC ISO 10656 | | |
| | | (1) The Rogowski coil output is proportional to the rate of change of current. The calculation formula is: Ampere RMS x Hertz x K x 10-6, where K depends on manufacturing. The K value is 3 for 150mV model and 3.6 for 180mV model. (2) All accuracies are specified at 23°C (± 2°C) with conductor carrying the current centered in the coil. (3) The low limit is approximate and it is determined by noise effect on very low signals. | | |