During the frequent trials of steam launches and other fast-moving machinery at the New York Navy Yard, continual trouble was experienced with mechanical counters, and the electrical counter, an illustration of which accompanies this, was devised to replace the former.
It consists essentially of an electrical escapement in combination with a stop-timepiece. By turning the lever on the left, the time movement is started and stopped at exactly the same instant as the escapement, and thus we have simultaneously the time and number of revolutions. The other two projections shown are to bring the hands of the watch and counter respectively to zero.
The counter has proved very useful in many ways, particularly in getting the slip of launch screws over a measured course. It could be arranged aboard ship to take in succession the revolutions of the main and auxiliary engines by leading a wire from each to a switch at the instrument, which could be placed in the most convenient place. At the highest speed tried on a lathe, 1500 revolutions per minute, the counter proved to be accurate, not losing a revolution in over 10,000, as measured by a mechanical hand-counter attached before the lathe started and read after it had been stopped. It is probable that one can be made to work to several thousands of revolutions per minute; the present one was made from parts taken from a scrap-heap, and its success is largely due to the mechanical skill of Mr. J. S. Gordon of the New York Navy Yard.
The success of the counter demonstrated the feasibility of a revolution indicator which the writer has long had in view, and which has since been designed in all of its details but not yet constructed. The accompanying diagram shows the arrangement and general appearance of the revolution and direction indicator, and the essential principles are given in the following description :—
On each shaft of the main engines, and on as many auxiliary engines as desired, one or more contacts are made at each revolution, each of which sends a current to any register that is open to the circuit. On the shafts of the main engines is a simple form of commutator, F, by means of which the direction' of motion of the shaft is also shown on the register. All of the shaft circuits are led to a clock, in connection with which is a device for changing from one series of circuits to a second one, and vice versa, at regular intervals of time. From the clock, circuits are led to as many registers as are desired, the number that can be put up being practically unlimited; four are here shown, one of which, that in the engine-room, having also circuits from the auxiliary machinery.
The method of working is as follows:—When a reading is desired, it is first observed if the direction-hand, marked G, is indicating; if it is, it will be necessary to wait an interval of time, the maximum of which is ten seconds, until it returns to the zero mark. When it is at the zero mark the button A is pushed in, and after another interval, the maximum of which is ten seconds, the revolution-hand begins to move and stops at the figure corresponding to the number of revolutions being made per minute, and remains there until B is pushed in, when it returns to zero ready for another indication. It is thus seen that before a reading can be taken, an interval of time between thirty and ten seconds is required; it is not necessary, however, to Stand by the register, as, after the button A is pushed in, the hand will remain at the point at which it stops until returned to zero by B.
On the register for the bridge the direction-hand is made large and a lever C added, by means of which it may alone be kept in the circuit and indicate continuously as long as desired. To the engine room register are connected in addition, by means of a switch, circuits from the various auxiliary engines, so that their revolutions may be taken singly or in succession when desired.
The ideal revolution indicator is, of course, one that will show at a glance at any time the number of revolutions the engine is making, but of all of these that the writer knows of or has imagined, none seems to be practicable or sufficiently accurate. On the other hand, the apparatus here described is positive in action and accurate, and, from the simplicity of its parts, little liable to get out of order.