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).
Notes on the use of the Strobophonometer for detecting detonation.
| Identifier | ExFiles\Box 165\4\ img167 | |
| Date | 1st September 1932 | |
| x4691. To Hs.{Lord Ernest Hives - Chair} from Hs{Lord Ernest Hives - Chair}/Ud. Hs{Lord Ernest Hives - Chair}/Ud.4/ADB.9.32. NOTES ON THE USE OF THE STROBOPHONOMETER FOR DETECTING DETONATION. Principle of the instrument is to obtain a measure of the "loudness" of sounds. A standard microphone receives the sound and the electrical vibrations are passed to a valve amplifier. The output from the amplifier is measured on a milliammeter and the scale deflection of this is proportional to the loudness of the sound. Controls are provided for sensitivity and damping. The method of using the instrument to investigate detonation in an engine cylinder is as follows :- The microphone is mounted in an indiarubber pad which is strapped on to the cylinder jacket (in case of water cooled engines) in the region of the head. A selector switch or commutator is fitted to either the camshaft or the crankshaft and enables the microphone to be connected with the amplifier for any desired angular period at any crankangle. For detonation work it is usual to listen over a period of 100° of C.A. starting 10° to 15° before T.D.C. The damping and sensitivity controls are adjusted to give the desired scale deflection and sensitivity. The scale reading is then a measure of the sound emanating from the cylinder jacket and produced by the vibration of the cylinder jacket walls. Any change in the engine running conditions which produces a change in the vibrations in the water jacket will change the strobophonometer reading - an increase in noise being indicated by increase in the reading. By moving the selector switch it is possible to obtain a measure of the intensity of the noise throughout the cycle. Using the instrument (suitably damped) without the selector switch in circuit gives a measure of the general noise level throughout the cycle. | ||