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).
Calibration and temperature error of a speedometer.
| Identifier | ExFiles\Box 50\4\ Scan169 | |
| Date | 1st March 1928 | |
| X4308 B.156. To Hs {Lord Ernest Hives - Chair} /AJL. from EFC. {E. Fowler Clarke - Electrical Engineer} EFC {E. Fowler Clarke - Electrical Engineer} 5/T1.3.28. SPEED METER B.156. 765. 16/52. This instrument is fitted with the latest alteration to overcome the temperature error. We have tested the instrument and at a temperature of 17.4°C its reading at 600 r.p.m. is 55.7 m.p.h. N.B. A more convenient speed than 700 r.p.m. at which to give the reading of these instruments is 600 r.p.m. because this is the speed (approx.) at which our driving spindle rotates; your figures of 60 m.p.h. at 700 r,p.m., and 66 m.p.h. at 700 r.p.m. become 51.4 and 56.6 m.p.h. respectively. You will therefore see that we are .9 m.p.h. down on your top figure and /4.3 m.p.h. up on the correct indication at normal temperature. It might be possible for us to put in a little more magnetism to make it read the small amount higher, viz. 56.6 m.p.h., but we are not undertaking this until we have received your confirmation. But in view of its present nearness to that figure, we should require only a further small amount. Will you please let us know. Your figure of 60 m.p.h. at 700 r.p.m. does not appear to be in exact agreement with other figures we have received from two other independent sources, which give the correct figure for 16/52 axle as 52.5 at 600 r.p.m. EFC. {E. Fowler Clarke - Electrical Engineer} | ||