From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter regarding drawings for a tachometer that operates on a frequency measurement principle rather than voltage.
| Identifier | ExFiles\Box 165\4\ img216 | |
| Date | 17th July 1933 | |
| COPY. 11, Cranbrook Road, Redland, Bristol, 6. 17.7.33. Lieut. Colonel L.F.R. Fell, Rolls-Royce, Ltd., 14, Conduit Street, W.1. Dear Sir, Ref. F3/JL.15733. I thank you for your letter as above and in reply am forwarding the drawings which will possibly assist your equipment engineers to appreciate the advantages of my tachometer. In this respect I am not quite certain that the pamphlet sufficiently emphasises the difference between the above and all existing commercial tachometers working off A.C. or D.C. generators, that is to say that my instrument operates on the frequency - measurement and not voltage - measurement principle. This signifies that not only can a simpler, cheaper and more reliable speed indicator be employed on the dashboard, but that the scale-readings of the former are not affected by changes in the permanent magnet strength of the generator. This trouble is all the more serious with ordinary electrical tachometers since the error due to the above cause develops insidiously. With reference to the pamphlets and drawings, I should be greatly obliged if you would arrange to have them returned when you have finished with them, as the number of copies that I possess is unfortunately limited. If also you should desire to have some reference to my technical qualifications, Professor W. Morgan, B.Sc. of the Faculty of Engineering, Bristol University, would, I understood, be very pleased to furnish same. Thanking you for your interest, Yours faithfully, (Signed) W.G. BIRD. (M.A., A.F.R.Ae.S.,A.Inst.P.) | ||