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).
Article from 'ENGINEERING' magazine describing the Collins Micro-Indicator for high-speed engines.
| Identifier | ExFiles\Box 33\5\ Scan046 | |
| Date | 9th June 1922 | |
| Reprinted from “ENGINEERING,” June 9, 1922. THE COLLINS MICRO-INDICATOR FOR HIGH-SPEED ENGINES. Constructed by THE CAMBRIDGE AND PAUL INSTRUMENT COMPANY, LIMITED, 45, GROSVENOR PLACE, LONDON, S.W. 1. Fig. 1. Fig. 2. Fig. 3. Fig. 4. (7294.A) 745B The micro-indicator constructed by the Cambridge and Paul Instrument Company, which we illustrate in Figs. 1 to 3, above, was one of the striking novelties of the Royal Society Soiree of this year, and was mentioned in our notice of these exhibits, on page 630 ante. We need not dwell upon the utility of an instrument which, within half a minute, almost automatically, will produce 10 successive permanent records of the performance of a highspeed engine on a card which is ready either for immediate inspection and measurement in a very simple microscope, used after the manner of a pocket telescope, or for photographic enlargement. Indicator diagrams taken at rapid intervals not uncommonly draw the attention of the designer or manufacturer of an engine to unsuspected or obscure defects, in a manner which enables him to determine the cause of the poor performance, and the convenience of the micro-indicator will be particularly appreciated on motor cars and on flying machines when track tests or trial flights are being conducted, and where there is neither space nor time for elaborate instruments and methods of testing. The records are mechanical, not optical or photographic, and the operator need not leave his seat to take them. The micro-indicator has been designed by Mr. W. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Collins, director of the Cambridge and Paul Instrument Co., Ltd. The indicator consists of a cylinder A and a piston B (Figs. 1 and 2), both made of a hard non-corrodible metal. The rising piston forces upward the flat spring C to which the style D is attached; the style scratches a record on a slightly curved disc or card of celluloid E which is provided with 10 notches; the diameter of the disc is about 1 in. This disc is carried by a frame attached to the front sector of a small vertical post; a back sector on the same post is rocked to and fro’ by a connection to the piston of engine; the post also supports the helical spring which takes up any back lash. The style D scratches a small indicator diagram on the surface of the card. This action takes place when the Bowden wire is operated, causing the pawl F to press against one of the 10 notches of the disc; the disc turns about its horizontal axis by one-tenth of its circumference, each time the Bowden wire is moved, so that 10 consecutive diagrams are drawn near the circumference of the card. Contact between the style and the disc is, however, only possible when the automatic electric switch of the indicator energises the iron-clad electromagnet G which will be seen in the back of the card, and which draws the parts into contact by means of a small chain which extends from the armature to a pin close to the style. This switch, another ingenious piece of apparatus, is not shown in our illustrations; only the two switch terminals to which the switch wires are attached being visible on the left-hand side. The switch is actuated by a belt from the engine, and its object is to permit of taking a single cycle only, and thus to avoid confusion when the diagram is rapidly changing its forms due to variation of load, ignition, carburetion, &c. The switch circuit is ordinarily open, i.e., the style does not touch the disc until the key of the switch is pressed. Without this device the consecutive records might overlap and be spoiled, because the style contact might be maintained for more than a complete cycle of the engine under test. The whole instrument, which is mounted on the top of the engine cylinder, weighs only about a pound. The moving parts are light and they move through small distances; there is little inertia, an entire absence of linkages and uncompensated joints, and there is, therefore, small liability to wear. With a piston area of 1/2 sq. in. the natural period of the recording system is about 1/1100 of a second. The actual indicator diagrams obtained measure about 3 mm. in length by 2.5 mm. in height. The raised edges of the scratch render the records very distinct in spite of their small size. Examined in the microscope we mentioned, with a scale or a graticule in the field of view, the diagrams are quite convenient for area measurements. The microscope is merely a tube prolonged to form a simple frame; the disc is placed in a slot in the frame, and the tube is then turned so that the light from a window or lamp falls through the celluloid disc from behind; there is no special substage nor illuminator. Dimensions may be read correctly within 0.01 mm. Some photographic enlargements of the diagrams are reproduced in our Fig. 3; enlargements of 20 diameters will usually be sufficient. Fig. 4 (which is not reproduced from ENGINEERING) shows a direct photographic enlargement of a single diagram obtained with the micro-indicator. When viewed through the microscope mentioned above the diagram appears about half this size. | ||