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).
Investigation into the contact resistance of tungsten points in an electrical circuit.
| Identifier | ExFiles\Box 35\5\ scan 144 | |
| Date | 20th October 1920 | |
| To R.{Sir Henry Royce} from EPC. c. CJ. c. E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} c. EWT. for Oy. X.2894 EFC3/T20.10.20. X.2894 - TUNGSTEN POINTS. --CONTACT RESISTANCE. Tungsten points appear to introduce some considerable resistance at the points of contact. We noticed this first in the fact that the operating current of the battery ignition on the bench was somewhat less with Tungsten than with platinum points under otherwise identical conditions. In order to investigate this point more fully we took two rods of Tungsten about 4 mm. dia. and first of all passed, from a single cell, a current of 10 amperes through one of these rods by means of copper wires twisted round its ends, including in the circuit a variable resistance for adjustment. Afterwards the connections were twisted one round each of the two rods so that in each case the circuit was identical except that the contacts between the two rods completed the circuit. One end of each rod was ground flat but the other end left unground. When contact was squarely made between the ground faces, we found that only 9 amperes flowed. When the un-faced ends or the sides of the rod were placed in contact, or the ground faces tilted relatively, but still in contact, the full 10 amperes flowed. Afterwards the ground faces of the rods were discoloured by causing inductive sparking to take place between these faces making use of the field circuit of a dynamo and a 12 volt battery.. It was found that the positive rod | ||