



Rosa_km.pdf (version
1.03) + Open document spreadsheet: Rosa_km.ods . Abstract: Rosa's mutual inductance correction, used for obtaining roundwire solenoid inductance from the corresponding currentsheet inductance, is difficult to calculate and is traditionally given in tabular form. This article describes accurate approximation formulae which have been fitted to the tabulated data and to a recent exact calculation given by Robert Weaver (see below). A formula given in 2006, before the new calculations became available, is found to fulfil its original accuracy claims but is improved by further parameter adjustment. A truncated series formula given by Grover in 1929 is accurate for large N, but inaccurate for small N. Extending the series in a manner that forces the formula to produce zero when N=1 provides a oneline formula that is accurate to within ±0.000 000 013. Cited documents available: Investigation of Rosa's roundwire mutual inductance correction for the solenoid inductor. by Robert S. Weaver (electronbunker.ca), July 2008 (PDF). Formulas and Tables for the Calculation of Mutual and Self Induction. E B Rosa & F W Grover, 3rd edition 1916, with 1948 corrections. BS Sci.169. (15MB PDF). Comparison of Formulas for the Calculation of Inductance of Coils and Spirals Wound with Wire of Large CrossSection. F W Grover, JBS Vol 3. 1929. BS RP90. 