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).
The operation of a standard pattern recording accelerometer and showing typical records produced by the device.
| Identifier | ExFiles\Box 138\2\ scan0182 | |
| Date | 1st June 1926 guessed | |
| TYPICAL RECORDS. Fig. 9. B A A B Reproduction (actual size) of a record obtained on the ram of a shaping machine with quick return motion. The "ripples" are due to imperfectly formed teeth in the driving gears. Fig. 10. The portion A—A of Fig. 9, as viewed through the microscope (Fig. 8). Fig. 11. The portion B—B of Fig. 9, photographically enlarged. 6 RECORDING ACCELEROMETERS. Standard Pattern. THE standard pattern Accelerometer illustrated in Fig. 1 can be used for recording either horizontal or vertical accelerations, depending upon the position in which it is placed relative to the direction of the movement being investigated. Fig. 2 shows the case opened to give access to the mechanism, while a plan of the instrument, as placed for recording vertical accelerations, is shown diagrammatically in Fig. 3. The mass M is supported by two flat steel strips, H and H1, and is connected by means of an additional steel strip N to a member O moving on knife-edges K and K1. This member carries a flat strip of aluminium L, the extremity of which is free to move between the poles of a magnet P. Fixed to the aluminium strip L is the stylus Q. Any movement, therefore, of the mass moves the stylus across the celluloid film A which is caused to pass round the roller T by means of clock-work mechanism not shown in the diagram. The speed of travel of the film may be varied from approximately 3 to 20 mm. per second. The eddy currents set up by the movement of the aluminium strip between the poles of the magnet critically damp the movement. With the standard spring, the natural period of the whole system is approximately 0·025 second. With this period the sensitivity is approximately one millimetre on the actual record for an acceleration equal to "g," i.e., 32·2 ft. per sec. per sec. (981 cm. per sec. per sec.); the record can be measured to an accuracy of one hundredth of this value. Other sensitivities can be quickly obtained by substituting suitable control springs, the period being correspondingly altered. The pressure of the stylus on the film may be varied by means of the screw C. An electromagnetic marking mechanism, not shown in the diagram, is fitted so that a time scale, generally tenths of a second, can be marked on the film by means of an additional stylus operating on the back of the film. It is thus possible for the stylus making the record of accelerations to pass over the whole of its range without fouling the time-marking stylus. Alternatively, the second stylus may be arranged to give records of the instantaneous positions of the moving object, or other datum marks. The complete mechanism is enclosed with-in a compact case, fitted with two hinged lids (see Fig. 2). On the front of the case are carried the various switches for controlling the mechanism, together with the terminals for connection to the time-marker and to the 12-volt battery for the damping electromagnet. The clockwork mechanism is started or stopped by rotating the knob D, but it can also be started independently by depressing the push button G when it is only desired to run a short length of film for calibrating purposes. The records may be easily calibrated by running the film with the instrument set first on its long base and then on its short base, or vice versa, pressing the button G for a second in each position. This operation gives a definite "step" in the record, the height of which represents the acceleration "g" due to gravity. The speed of the film is adjusted by means of the regulator lever E.{Mr Elliott - Chief Engineer} Three toes are provided upon each of two adjacent sides of the base, enabling the instrument to be placed on either its long base, for recording vertical accelerations, or its short base, for recording horizontal accelerations. Fig. 2. 9 x 5 x 8 inches. Fig. 3. 3 | ||