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).
Technical leaflet describing the design and method of using the K.B.B. Vibrometer.
| Identifier | ExFiles\Box 138\2\ scan0136 | |
| Date | 1st April 1938 guessed | |
| PAGE 1 KELVIN BOTTOMLEY & BAIRD LTD. GLASGOW & LONDON DESIGN OF THE K.B.B. VIBROMETER. The design is based on the tuned vibrating reed principle. In making observations the reed is tuned to respond to the particular vibration under examination, and great sensitivity is thus obtained. Means are provided for turning the instrument about both its vertical and horizontal axes till the maximum amplitude is found, the angles being indicated on scales provided. The instrument is constructed of small weight in order that, when attached to the machine under observation, it will not sensibly affect the vibration existing, or introduce lag. Its weight is 2 lbs., and its construction provides great rigidity. Fig. 2 shows the complete instrument opened out ready for use. The vibrating reed R, slightly loaded at the free end is clamped at its lower end in the jaws B formed at the foot of the upright pillar C. The movable spring clamp D slides friction tight on the pillar and carries a marker operating over a reed length scale E let into the pillar. The pillar C can be set so that the plane of vibration of the reed is in any angular position (which position is indicated on the turret angle scales engraved on the blocks) and the pillar clamped in any position. The spanner-shaped carrier arm A is adapted for securing the Vibrometer to the machine under test—for example under one of the bearing nuts. By means of the sliding bush H which carries D the free length of reed is varied and the reading on the scale E when the reed is thus tuned (when referred to the calibration curve supplied for the particular reed in use) allows of the frequency being read off. An amplitude scale F is provided at the upper end of the pillar C for the purpose of indicating relative intensity of vibration when the reed has been tuned by moving the bush carrying the spring clamp D.{John DeLooze - Company Secretary} Reeds of different thickness and loading may be used for different speeds, and with each Vibrometer three reeds are supplied covering speeds of 300 to 5000 r.p.m., with their calibration curves, the forms of which are indicated in Fig. 3. The instrument is supplied in a small leather case, Fig. 1 showing the Vibrometer arranged for packing in the carrying case. PAGE 2 KELVIN BOTTOMLEY & BAIRD LTD. GLASGOW & LONDON METHOD OF USING THE VIBROMETER. (1) Remove instrument from its leather case and open out as in Fig. 2. (2) Select suitable reed, insert the unloaded end through the spring clamp D and into jaws B right to the bottom, securing with clamp screw G.{Mr Griffiths - Chief Accountant / Mr Gnapp} (3) Place spanner-end A under the bearing nut of machine under test, arm of A being at right angles to shaft of machine. (4) Set pillar C until scale F is parallel to arm of A, the flat of the reed R being parallel to the shaft, and the instrument (and reed) vertical. (5) Move H until reed has its maximum vibrating length, i.e., bush H is in lowest position. (6) Slide bush H slowly upward thus shortening the free length of the reed R.{Sir Henry Royce} (7) Continue as (6) till reed has maximum amplitude (speed of machine being constant). A reading may now be taken noting the number of the reed, vibrating length of same and amplitude of swing of free end (on scale F). The scale F is provided with a false zero mark, the distance between this and the zero of the scale is equal to the length of the loading weight fixed to the end of the reed. If therefore F is adjusted while the reed is in motion until the end of the “apparent” line made by the vibrating weight coincides with the false zero mark, a direct reading of amplitude of the end of reed is obtained. (8) As in many cases the maximum vibration is not in the horizontal plane, the pillar C should now be canted over in the vertical plane at right angles to the shaft, and any increase or decrease of amplitude of R noted. With turbine machines which are only out of “static” balance the vibration will be in a plane at right angles to the shaft, and the maximum will usually be found (the Vibrometer being fixed under the bearing nut on either side of the bearing) when the top of the instrument is leaning outwards from the shaft at an angle of 10° or 15° to the vertical. The angles can be read approximately on the turret scale. (9) By turning the Vibrometer about its horizontal plane and noting the position of maximum vibration by the turret scale and mark on end of support A, the direction of maximum resultant vibration not in a plane at right angles to the shaft is indicated. The direction or line of vibration when the instrument is set and tuned for the maximum will be parallel to the edge of scale F.{Mr Friese} (10) In cases of bad vibration it is not difficult after the instrument has been correctly tuned to decide as to the angle or inclination in which it shows maximum vibration, but where the vibration is small some care and experience with the instrument is necessary. | ||