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).
Results of electrical experiments on an instrument's coils and armature.
| Identifier | ExFiles\Box 48\3\ Scan164 | |
| Date | 6th December 1920 | |
| Contd. -5- EFC {E. Fowler Clarke - Electrical Engineer} 1/T6.12.20. de-operate and this necessitates a reverse current in any case, so long as the law of traction is much more rapid than the spring law, as it is in the majority of cases. These considerations are borne out by actual experiments with this instrument. The following are the results obtained, the instrument being operated in every case in conjunction with a dynamo, and for the purposes of noting the reverse current in the series coil, also in conjunction with a battery. Instrument cold (18°C). On raising the dynamo voltage the armature lever was drawn home very definitely at a point corresponding to 12.4 volts, .190 ampere in the shunt coil showing a resistance of this coil of about 65.5 ohms. Immediately after the pull up of the armature, the shunt current fell to .115 ampere (battery still disconnected) thus showing now a total resistance of 107.5 ohms, i.e. an insertion of additional resistance of 42.0 ohms. Now allowing the voltage to drop it was found that the armature very definitely went back at 10.2 volts, .095 ampere (107.5 ohms), and after falling back the current increased to .155 ampere at the same voltage (65.5 ohms approx). The fact that the voltage was less to de-operate than to operate shows that if the battery had been connected there would have been a reverse series current. On switching the battery in and repeating the drop off, we found this to occur at 11.9 volts, .110 ampere and 2.6 reverse amperes in the series coil. | ||