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).
Static charge build-up on the glass of an Elliott ammeter, causing erroneous needle deflections.
| Identifier | ExFiles\Box 168\5\ img104 | |
| Date | 2nd May 1927 | |
| To Wd.{Mr Wood/Mr Whitehead} from EFC. X4622 EFC L/T2.5.27. ELLIOTT AMMETER. X.4622. It has been noticed that the Elliott ammeter is somewhat subject to the known effect in electrical instruments of a deflection of the needle brought about by a static charge on the front face of the glass which is excited by gently friction on that surface, and the production of this charge is enhanced by the fact that the glass becomes warm and dry when the chassis has been running for a period. Should one inadvertently brush one's hand across the instrument face, an error in the instrument may be set up which may lead to incorrect deductions concerning the charging rate, etc. It is a fact that this disturbance is always at once eliminated by breathing on the glass, but this fact may not be known to the observer. This effect is not of any importance in the Weston instrument, for one reason apparently that the glass is further from the dial. As stated, however, it has been noticed to be fairly considerable in the Elliott instrument. We should be pleased if you would write to Messrs. Elliott Bros. and ask them if they are aware of this effect and if they have any suggestions to make as regards its elimination, such, for instance, as the use of slightly conductive, instead of highly insulated glass. Owing to the errors in judging the charging system, to which the effect may lead, it is desirable to eliminate it if it can conveniently be done. EFC. | ||