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).
Testing of an A.T. Speedometer, specifically its accuracy variations with temperature changes.
| Identifier | ExFiles\Box 50\4\ Scan176 | |
| Date | 15th March 1928 | |
| V4308 To BY, from EFC. {E. Fowler Clarke - Electrical Engineer} C.c. EP. {G. Eric Platford - Chief Quality Engineer} CWB. Cc. BY {R.W. Bailey - Chief Engineer} /MCH. (Strikethrough) EFC {E. Fowler Clarke - Electrical Engineer} 1/T15.3.28. A.T. SPEEDOMETER. Herewith we attach copy of the figures to which we are working in judging the correctness of the A.T. speedometers which we test. These figures are approved and agreed to by those concerned, as corresponding to exact measurements on the road of the revs. per mile at which the speedometer drive revolves, when average tyres are used. Now referring back to our EFC {E. Fowler Clarke - Electrical Engineer} 1/T7.3.28, it will be seen that the instrument which was reported therein reads correctly at a temperature very slightly above 26.0°C, which, as in the case of the second instrument, reported in our EFC {E. Fowler Clarke - Electrical Engineer} 1/T5.3.28, is very nearly as we desire. Now referring to EP {G. Eric Platford - Chief Quality Engineer} 13/H14.3.28, we note that EP. {G. Eric Platford - Chief Quality Engineer} considers that the variation of reading between 18°C and 30°C should be within 4%, whereas it will be seen that both instruments we have tested have shown a variation of 5% between these temperatures. Accordingly we will approach the makers as to whether they can reduce the variation by this additional amount. We will send them a curve of the actual performance of instrument A.929 N.730 15/52, which we have tested. We also note that EP. {G. Eric Platford - Chief Quality Engineer} suggests that having got this variation within 4% we should specify th a correct reading at the temperature of 30°C, i.e. 86°F, it having already been proved that the temperature of the instrument board may at times reach this figure. We will take steps with the makers for this also to be the case. EP. {G. Eric Platford - Chief Quality Engineer} will note that from the tests we have made, the instruments which are at present being received will be correct at about 26.0 to 27.0°C, and as already referred to have a variation of 5% between 18.0 and 30.0°C. For the time being this is fairly satisfactory, but we will, as stated, approach the makers with a view to still further improvement. EFC. {E. Fowler Clarke - Electrical Engineer} | ||