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).
Continuation of a review and comparison of the Cambridge vibrograph instrument, covering its construction and use.
| Identifier | ExFiles\Box 138\2\ scan0168 | |
| Date | 13th September 1938 guessed | |
| - 2 - GENERAL CONSTRUCTION OF THE CAMBRIDGE INSTRUMENT. (contd). (a) This drive is provided with a variable speed clockwork motor which allows of a maximum film velocity of some 2 cms/second. In the standard vibrograph, which was the pattern demonstrated, the recording medium is carried upon a drum such that the length of record available is some 16 cms., it then being necessary to remove the drum and place a new strip in position. There is also a continuous-reading pattern of instrument available at increased cost, in which 600 cms. of the medium can be accommodated, the drive in this instance being by 12 volt electric motor, and satisfactory for records of 4-6 minutes duration. (b) NOTE ON THE CAMBRIDGE SYSTEM OF MECHANICAL RECORDING. This system of recording is claimed as a special feature of all Cambridge mechanical recording instruments. The stylus used is spherical-ended (R=0.03 mm) so that the loading on the record is sufficient to produce plastic deformation in materials of low elastic limit such as celluloid etc., no material actually being removed as would be the case in scratching. The diagram so produced consists of a smooth and well-defined line with desirable optical characteristics, which when viewed by transmitted parallel light permits of considerable degrees of enlargement. In practice a microscope with graticule eye-piece or an arrangement for direct optical projection may be employed, and the makers claim that enlargements of upwards of 100 diameter are possible without loss of definition. We ourselves have viewed records wherein the linear magnification of the record was 10 times, corresponding to increasing the original vibration amplitude 70 times. (c) PROVISION FOR TIME-MARKING ON RECORDS. An independent clockwork driven contact-maker is utilized to actuate the time-marker. This, which is arranged as a separate unit, provides 1/10 second timing marks with every tenth mark suppressed; and is actuated by a 2-4 volt battery, the mean current being very small. The contact-maker and the battery are connected to the Vibrograph by a 4-way cable. 3. THE CAMBRIDGE INSTRUMENT IN USE. We propose to review the various features of the Cambridge instrument and to compare them with those of the Askania vibrograph where possible, as Derby and Hucknall now have experience in the use of this instrument. (a) SIZE AND WEIGHT ..... CONVENIENCE IN USE. Cambridge: Weight 8 lbs. Askania: Weight 4 lbs. Fig 1A 17 X 6 X 5 inches. Fig 1B 9 X 6 X 3 inches. As will be seen from the accompanying photograph, the Cambridge Vibrograph consists of the instrument body proper with the stylus projecting some ½" from the lower face, the overall length being increased by some 6" on account of the handle. It appears that the instrument was originally designed for use on flat surfaces in structural and marine work where access for the larger instrument is relatively easy. The spring loading of the recording mechanism has been arranged so that when the full weight of the instrument is applied to the stylus, the recording pointer is brought to the centre of the record. Consequently it is most simple to use the instrument on a horizontal surface, but when in use on a vertical plane it is difficult to apply the requisite | ||