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 performance and calibration of an A.T. Speedometer.
| Identifier | ExFiles\Box 70\3\ scan0381 | |
| Date | 5th March 1928 | |
| To EP.{G. Eric Platford - Chief Quality Engineer} from EFC. c. BY CWB. c. JLE.{J. Lee Evans - Chassis Test Manager} By/Mtn. c. Roy{Sir Henry Royce}/Ms. X8783 sp.{Mr Spinney} EFC/T5.3.28. A.T. SPEEDOMETER. X 4308 Your reference EP{G. Eric Platford - Chief Quality Engineer}5/H.2.3.28. Will you kindly note that the A.T. speedometer is considered an electrical instrument so that this instrument comes under this Dept. We are assured by the O.O. that all the instruments received for some months now, that would be since about July last, have had their temperature error considerably reduced, as requested by us some considerable time ago. It would appear that the speedometer referred to in your note must be one of old stock. If you care to send this along we will tell you exactly how correct it is, both at normal and high temperatures. It is not correct to say that this is a phenomenon which is not very clearly understood, because we understand it completely. Previous to the modification, the instrument suffered a good deal, in fact far too much, from temperature variation. Now they have been brought within a reasonable limit. We asked for the instrument to read nearly correct at the highest temperature (about 25ºC) to which it is possible for it to get in position on the dash. That means that when cold the instrument will read a few percent high, but the difference now is nothing like as great as it was originally. This agrees with your remark of how you consider the instrument should be arranged. To make quite certain, Mr. Mills is obtaining for me a definite assurance that all the instruments now delivered are arranged as stated. We have obtained a Phantom A.T. speedometer from a recent delivery for test so as to know exactly what the performance is. The exact details given by us are that the instrument shall read correctly at 25ºC and have a variation which does not exceed 4% between 15ºC and 30ºC. Such a performance was realised on an experimental instrument which we had specially altered for test. It appears that under extreme conditions of atmospheric temperature, the temperature of the instrument may reach 30ºC. EFC. on the dash. If you think we should arrange for the reading to be correct at that temperature and therefore nearly always to read high, will you please say. | ||