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).
Test report on the temperature effect and accuracy of an A.T. Speedometer.
| Identifier | ExFiles\Box 50\4\ Scan174 | |
| Date | 7th March 1928 | |
| Y4308 To EY. from EFC. {E. Fowler Clarke - Electrical Engineer} c. EP. {G. Eric Platford - Chief Quality Engineer} CWB. c. EY/Mtn. EFC {E. Fowler Clarke - Electrical Engineer} 1/T7.3.28. A.T. SPEEDOMETER. B.140. N.488. 14/52. This instrument has been taken from recent production to check its accuracy and see exactly the temperature effect. Driven at an exact speed of 600 r.p.m. its K.P.H. readings at various temperatures were as follows :- Temperature. K.P.H. Corresponding M.P.H. 17.8°C (atmospheric) 75.2 46.7 26.0°C. 72.6 45.1 30.3°C. 71.5 44.4 We do not know at the moment the number of revolutions per mile at which this instrument will be driven, but the middle figure above of 45.1 m.p.h. at 26.0°C, at which temperature figure we should like the instrument to be correct, corresponds to 36000 / 45.1 = 798 revs. per mile. Further it will be seen that the percentage change in the reading from 17.8°C to 30.3°C reckoned on the middle figure is 100 x 2.3 / 45.1 = 5.1% which is slightly higher than we wish for. We are returning the present instrument to Ey/Mtn. and we think it might be worth while doing another instrument taken from production in a similar way. EY. has arranged to give us a table showing the m.p.h. of the car for our standard speed of 600 r.p.m. of the speedometer for each combination of axle ratio and type of tyre used. We can then express the error of an instrument directly or say at which temperature it is reading correctly. EFC. {E. Fowler Clarke - Electrical Engineer} Returned to production after test | ||