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).
Analysis of different record types, time marking methods, and equipment construction.
| Identifier | ExFiles\Box 138\2\ scan0170 | |
| Date | 13th September 1938 guessed | |
| - 4 - (c) THE NATURE OF THE RECORDS. We must express complete satisfaction with the records provided by the celluloid system, the trace being of fine and constant width. The records were viewed by means of the Portable Viewer, wherein they are projected to a screen with a magnification of 10 X, from which accurate readings can be taken by using a separate movable celluloid scale. This viewer can also be used for obtaining photographic enlargements on plates or bromide paper. We are of the opinion that when the vibration under investigation is sufficiently steady to warrant it, the enlarged record would be satisfactory for Fourier analysis by a graphical or the "envelope" method. At the same time the permanent nature of the records is a point well worth stressing. A number of enlargements of typical vibrograph records are appended. It is pointed out that in order to take advantage of the optical properties of the Cambridge records it is necessary to employ parallel light for the illumination, and that in consequence the normal types of photographic enlarger (which as commonly arranged have provision for slightly diffused light), are not suitable for this work. The records which are appended have been made with the artifice filling the records with graphite from a soft pencil, and then printed in the usual manner. It is only fair to state that the records thus produced are considerably inferior to those obtained with transmitted parallel light, and it appears that the action of filling in the trace tends to destroy the outline. Consequently it is recommended that the correct viewing equipment be employed with these records. The records on the Askania instrument is made on a paper tape at the rate of 1.5" per second, each roll of tape being sufficient for a duration of over one minute. The paper tape consists of a red backing treated with a greasy substance on the working side, which is removed by the recording pointer. This record must, because of its opacity, be viewed by reflected light and on account of the colour and poor contrast is difficult to enlarge photographically. However under linear magnifications as low as 5 times the poor definition and discontinuity of the trace become apparent and would in any case limit the usefulness of further enlargement. Such a record is by no means easy to use and store without damage. (d) TIME MARKING. The timing waveforms on the diagrams are revealed as perfectly satisfactory, and the additional complication of a separate seconds clock and battery must be regarded as the legitimate price for the enhanced refinement. It should be pointed out that the Askania instrument could be adapted to the use of an external timing device if one was available. In connection with the need for the 1/10th second pulses we should perhaps point out that in many of our spheres of investigation conditions are not completely steady, but exhibit a long period fluctuating so that it is desirable to take readings over a space of several seconds in order to obtain some idea of the average conditions prevailing. (e) GENERAL FINISH AND CONSTRUCTION. The general construction and finish appear to be all that can be required in an instrument of this kind, and the complete apparatus is regarded as representative of a more refined technique than the Askania instrument. | ||