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).
Potential fault with a client's ammeter related to it being earthed to the chassis frame.
| Identifier | ExFiles\Box 46\3\ Scan009 | |
| Date | 23th November 1923 | |
| W/S. {Derby Works / Sales} X4-117 To Cx {Major Len W. Cox - Advertising Manager} /DH. {D. Henderson - Showroom} from EFC. {E. Fowler Clarke - Electrical Engineer} EFCB/T23.11.23. RE CAPTAIN SLADE. Answering your Cx {Major Len W. Cox - Advertising Manager} /DH {D. Henderson - Showroom} 15/LR. {Mr Ellor} 22.11.23, asking for information regarding a client's ammeter which gave out, the reason for which was reported by the makers to be an overload, we can give you some light on this matter if it so happens that on this particular car the case of the ammeter is earthed to the chassis frame. On most cars we believe that the ammeter case, being inserted in a wooden instrument board, is not earthed, but there was a feature on the early ammeters, by which if the case of the ammeter were earthed, then in adjusting the zero of an instrument with a screwdriver by means of the little adjusting screw at the bottom of the glass face, one might inadvertently make a circuit between the screw and the case of the instrument and cause damage to be done to the instrument on account of the full potential being applied, not merely to the ammeter terminals, but directly to the more delicate operating coil of the instrument itself. This is a matter that has been taken up with Messrs. Weston, and on the ammeters now being received the feature has been eliminated. We always considered this a fault of the instrument and told Messrs. Weston so, but they did not at first agree that it was a fault, contending that the instrument case should always be insulated. If the instrument case is earthed on client's chassis, this will be an explanation which will simultaneously comply with both Ek's and the makers' statements. If not the case, then we shall have to look further, but for the moment perhaps this is unnecessary. x 12 volts EFC. {E. Fowler Clarke - Electrical Engineer} | ||