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).
Tests for magnetic interference between speedometer and rev counter instruments on a Bentley.
| Identifier | ExFiles\Box 59\2\ Scan328 | |
| Date | 12th January 1934 | |
| 86081 E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Wst. c. to Wor.{Arthur Wormald - General Works Manager} c. to Sg.{Arthur F. Sidgreaves - MD} c. to By.{R.W. Bailey - Chief Engineer} c. to EV.{Ivan Evernden - coachwork} Hs{Lord Ernest Hives - Chair}/Wst.10/MA.12.1.34. SPEEDOMETER AND REV COUNTER MAGNETIC INTERFERENCE ON BENTLEY. The request of a Bentley customer for all his instruments, including the speedometer and rev counter to be mounted together on a wooden instrument board has resulted in tests being carried out to determine the magnetic effect of the speed instruments on the other two electrical instruments e.g. the electric petrol gauge meter and the ammeter. Both the speedometer and rev counter are instruments which incorporate revolving permanent magnets and these magnets owing to the unavoidable leakage magnetic flux produce rotating magnetic fields beyond the instruments. If the ammeter and petrol gauge meter, both of which incorporate a magnetic system, are placed within the effective radii of these rotating magnetic fields the indicating needles flicker due to the iron inductor in these instruments being magnetically affected. Tests have been carried out to ascertain the minimum distance the instruments referred to could be placed relative to each other and also whether it would be possible to magnetically screen the instruments against all interference. The minimum distance permissible between the instrument centres was found to be 6 1/2 inches with a plain wooden instrument board. Upon attempting to magnetically screen the instruments when placed close together as required we found that unless the instruments had an iron dial plate and were completely surrounded with a sheet iron cylinder, it was impossible to eliminate the effect. | ||