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).
Test report on slate resistance and its effect on ignition spark gaps for a utility test.
| Identifier | ExFiles\Box 37\1\ scan 115 | |
| Date | 14th November 1921 | |
| X3199 EFC. AB35. X.3199 SLATE LEAK FOR UTILITY TEST. X.430. The slate resistance reported AB.2.6.21, has been arranged with mercury troughs at each end to secure improved contact. Used in this way, the resistance reads normally about 2 megohms, though it varies between twice and half this amount. The contact must still be imperfect, as on the battery ignition only a 2 mm. spark can be obtained, if the leak is placed across the gap, showing that the resistance is probably less than 1 megohm to H.T. currents, owing to the bridging of small spaces by discharges. If the leak is connected by the screw terminals, sparks from 7.0 mm. downward can be obtained at the gap, on the battery ignition. For use on magnetos it is found that the mercury contact is most suitable, Using a Bosch ZR.6 magneto with the safety gap blanked, the following maximum sparks were obtained. Speed (r.p.m.) Gap (MM) Plain With leak. Contact breaker. 160 7.0 5.0 Nearly fully retarded. 770 8.5 6.5 Fully advanced. It thus seems that, provided the resistance of the slate to H.T. current remains fairly constant (which it is more likely to do than is the resistance to L.T. current, depending on contact), the slate will | ||