TX to Ae


Inductance calc.


Rosa's mutual inductance correction for the round-wire solenoid.
David W Knight. April 2010.

Rosa_km.pdf (version 1.03)
+ Open document spreadsheet: Rosa_km.ods .

Rosa's mutual inductance correction, used for obtaining round-wire solenoid inductance from the corresponding current-sheet 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 one-line formula that is accurate to within ±0.000 000 013.

Cited documents available:

Investigation of Rosa's round-wire 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 Cross-Section. F W Grover, JBS Vol 3. 1929. BS RP90.