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).
Copy of a patent specification for improvements in indicating mechanisms using a wheatstone bridge.
| Identifier | ExFiles\Box 165\4\ img039 | |
| Date | 28th March 1928 | |
| COPY Patent Application Corresponding with United States Application No. 265452 filed March 28, 1928, Edward John Martin, Impt. in indicator. Copy of the specification as filed. B-3722. This invention relates to improvements in indicating mechanisms of the type in which sensitive resistance elements such as carbon piles are placed in one side of a wheatstone bridge and the bridging element is provided with a movable part interposed between the resistance elements and adapted to vary the resistance thereof. Variation in the resistance of the rheostats produces a difference in potential across the bridge causing a flow of current which may be employed to operate a suitable indicator, preferably an oscillograph. Our improvement consists in making the movable member of the bridge in the form of a relatively rigid element preferably in integral arm extending outwardly from the frame in which the rheostats are mounted. We have also adapted indicating mechanism of this type for use in measuring rapidly fluctuating pressure variations particularly the pressure variations occurring in the combustion chamber of an internal combustion engine. For this purpose we have connected the movable arm of the indicator with a rigid thrust member having a part projecting into the combustion chamber through a suitable opening therein. The opening is preferably sealed by means of a diaphragm connected to the thrust member and to the chamber. With the described apparatus variations in pressure in the combustion chamber produce movement of the thrust member which is transmitted to the relatively rigid element of the indicating mechanism and operates the latter. By using a rigid arm for the movable element of the indicating mechanism and operating the arm by means of a rigid thrust member directly exposed to the combustion chamber pressure we are enabled to use the diaphragm for sealing only and to relieve it of strains to which it would be subjected were it directly employed to actuate the indicating mechanism. By this means the life of the diaphragm is greatly lengthened. The invention involves other features of novelty which will be pointed out in the course of the following description. In the drawings: Figure 1 is an elevation of our indicator with parts in section and the cover removed, and showing the circuit with which it is used. Figure 2 is a view on line 2-2 of Figure 1. Figure 3 is a view on line 3-3 of Figure 1. -1- | ||