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).
The testing of an A.T. eddy-current speedometer regarding changes in reading due to temperature and time.
| Identifier | WestWitteringFiles\Q\2-July1927-September1927\ 50 | |
| Date | 19th August 1927 | |
| To R.{Sir Henry Royce} from EFC. ORIGINAL. EFC2/T19.8.27. c. BJ. BY.{R.W. Bailey - Chief Engineer} A.T. SPEEDOMETER. X4308 Referring to your R2/M8.8.27, last two paragraphs concerning possible change of reading in the A.T. eddy-current type speedometer, we had already made a number of tests with these instruments to prove the change of reading with temperature as a result of which the matter was taken up with the makers. They agreed that there was some change with temperature, and submitted improved instruments containing inductor cylinders of different material and specific resistance. We definitely confirmed their contention that the change with temperature was considerably reduced and, in fact, brought down to an amount which could not be considered unreasonable in service, the instrument reading a shade only high when cold, and a very small amount low when at the highest temperature likely to be realised. In regard to change of reading with time (at the same temperature), we have now also taken up this aspect of the matter with the A.T. Speedometer people, and they have assured us most emphatically that the ageing of the permanent magnets is such that no change takes place. They substantiate this by a statement that they have taken special care to test speed indications of instruments which have been out for a number of years and been returned for adjustment to the mileage recorder, etc. Knowing that it is possible for magnets of this shape to be aged in such a manner as to be permanent, we are satisfied with their assurance in regard to their particular instruments. EFC | ||