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 explaining the comparative basis for two dynamo output performance curves.
| Identifier | ExFiles\Box 62\3\ scan0156 | |
| Date | 30th January 1931 | |
| Mr. Burton, Messrs. Rolls-Royce of America Inc. 30th January, 1931. -2- Curve I represents the output as the machines are at present and curve III represents the output after modification, these curves being on strictly comparative basis in respect of the facts that they are both taken (a) With the dynamo carcase at the same indicated temperature of 80°C. (b) With the operating dynamo terminal voltage at the constant value of 14.0 and (c) In both cases with the machine set to a similar temperature rise (by adjustment of the control brush) when working on peak output. You will appreciate the fact that it is necessary to state the case thus explicitly because an observation of output, except under explicitly stated conditions is of little value for comparative purposes and in fact, a casual observation of output by the ammeter on the car (on the assumption that the ammeter is correct) would, owing to temperature and operating voltage being different from those under which the curves were taken, in most cases considerably differ from the outputs as shown by the present curves. Yours faithfully, FOR ROLLS-ROYCE LIMITED. | ||