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).
Letter to the Weston Electrical Instrument Co. Ltd. regarding a zero error fault in ammeters for Bentley Chassis.
| Identifier | ExFiles\Box 168\5\ img266 | |
| Date | 27th December 1933 | |
| 81162 Wa{Mr Wallis}/Wst.YMA. 27th, December, 1933. The Weston Electrical Instrument Co.Ltd., Kingston By-Pass, Surbiton, SURREY. Dear Sirs, Weston moving iron ammeters for R.R. and Bentley Chassis. We have been carrying out experimental tests in our electrical laboratory following a complaint we had received that the needle on the Weston Ammeters did not always return to zero. A number of tests were made by passing D.C. currents of various values through the instrument in both charge and discharge direction, and observing the position of the needle upon switching off. It was definitely proved that a hysteresis effect existed i.e. the needle always returned with a positive error on the side indicated by the current. The zero error upon switching off a current of 10 amperes was in some instances as much as 2 amperes. This zero error is considered to be serious as it often happens that a car will be brought to rest with headlamps and other accessories switched on which, with the existing ammeter, upon being switched off would show a spurious discharge of 2 amperes. To most discriminating drivers this would suggest a discharge on the electrical system and would consequently lead to much confusion and inconvenience. | ||