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).
Temperature-related accuracy variations in A.T. Speedometers.
| Identifier | WestWitteringFiles\S\March1928-May1928\ Scan037 | |
| Date | 15th March 1928 | |
| To R.{Sir Henry Royce} from EFC. c. BJ. E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} CWB. c. By.{R.W. Bailey - Chief Engineer} Wor.{Arthur Wormald - General Works Manager} A.T. SPEEDOMETERS. X4306 You will recollect that recently, at our request, the makers of these instruments incorporated a modification in the shape of an inductor cylinder of material of lower temperature resistance coefficient, whereby the change of reading with temperature was very much reduced. Also that the instruments were made to read correctly at some higher temperature than atmospheric. During the last week we have carefully tested two instruments taken from recent production in order to find out exactly the temperature at which they read correct, and the extent of the variation of reading with temperature. The variation of reading follows an exact straight line law with temperature, as would be expected on principle, and the extent of the fall of reading from 18°C to 30°C is almost exactly 5.0%. The former of the two instruments tested read correctly at very slightly over 26.0°C, and the latter read correctly at almost exactly 27.0°C. It is considered that these instruments should be made to read correctly at the highest temperature which the instrument reaches on the dash, (it has been determined to be about 30°C) in the most extreme conditions) and that the % increase of reading in dropping to 18°C should not exceed 4%. We are taking the matter up with the makers to see if such further improvement is possible. EFC. | ||