Equivalence of Measurements on Soft Magnetic Materials in the U.K. and Measurements for Operational Conditions
Measurements on soft magnetic materials were made to determine the measurement capabilities available to the partners of a government-funded collaborative research project, with 16 partners from industry and academia. One of the objectives of this project was the development of advanced magnetic materials for novel electrical machines for use in harsh environments such as gas turbines. To establish the measurement confidence necessary to deliver this project objective, an equivalence study was undertaken. A reference core of soft magnetic material that has been measured over a period of many years at the National Physical Laboratory (NPL) was distributed and the dc and ac properties were measured. The measurement systems of the three laboratories are independent and this ensured that no correlations that could skew the results existed. In the analyses, the measurements at NPL were used as the baseline. With the core capabilities established, it was possible to develop the new measurements required to deliver the overall project objectives. At NPL, a standard permeameter method was modified for the measurement of strips. This was incorporated into a stress machine to measure the dc properties of the soft magnetic materials used by the partners, at stress levels of up to 700 MPa. The results for seven materials are presented and the changes in the properties with applied stress compared to establish which materials exhibit favorable properties.
Final Report of CCEM Key Comparison CCEM.M-K1: Magnetic flux density by means of transfer standard coil
The delegates of the CCEM discussion meeting on international comparisons in magnetism recommended in May 2000 in Sydney that a worldwide intercomparison of magnetic flux density by means of a transfer standard coil should be proposed in addition to and in accordance with the EUROMET project No?446. A field coil of the Garret type was prepared and provided as transfer standard by PTB acting again as pilot laboratory. The single layer coil produces a field with a flux density of about 2?mT if it carries the maximum permitted current of 1?A. This standard was circulated in 2001 and 2002 to nine other national metrology institutes worldwide. The standard coil has also be used to compare the ac field calibration set-ups of the various laboratories. In order to provide a frequency response different to that of the standard used for the EUROMET comparison, the current distribution network at both flanges of the standard coil had been modified with the result that the frequency dependence of the coil constant shows a minimum at f?=?4?kHz. Each participant was asked to apply the measuring methods and to use the equipment as available for his daily work to tranfer the unit of magnetic dc and ac flux density. So, quite different methods have been applied within the intercomparison. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the Mutual Recognition Arrangement (MRA).
Coercivity measurements on high permeability nickel-iron alloys using a modified NPL vibrating coil magnetometer
A method for the rapid measurement of low coercive force materials (e.g. high permeability nickel–iron alloys) has been developed by modifying the NPL vibrating coil magnetometer to improve its sensitivity and by providing a magnetic shield to reduce the effects of the ambient magnetic field. A comparison of the results has been made with those obtained by the traditional ring method.