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534 gine speed ahead and astern. said that while at first working satis- factorily except as affected by angu- lar variation, difficulties due to mov- ing contacts introduced irregularities into the circuit resistance which caus- ed errors in the reading of the meters. It is claimed that the reason the direct current machine and voltmeters were used was the impossibility of utilizing the magneto in its true form --an alternator without contacts--be- cause an alternating current voltmeter . reads but one way, regardless of the polarity of the circuit and that there- fore deflections to both sides of a central zero to show speeds ahead and astern, were impossible of attain- ment in the then existing state of the ert, History of the Hutchison Marine Tachometer. Several years ago, Miller engineer, turned his attention to pro- ducing a dependable tachometer be- cause of the very evident market for such a device. officers confirmed his opinion. The problem was attacked from an entire- ly new standpoint. As a result, the tachometer installed on one of the United States cruisers in June, 1908, continues in satisfactory service with- out any attention whatever other than occasional oiling. The secret of success appears to be in the abandonment of magnetos with revolving armatures and commutators, with consequent impossibility of keep- ing clean contacts, and the adoption of a special inductor type magneto, with stationary armature and poles, hence leading the current from the armature without contacts. The mag- neto is, furthermore, of. such design as insures absolute permanence of magnetism. The Generating Unit. Clamped around the propeller shaft is ,a split sprocket (Figs. 1 and 2). Rotation is imparted to the driven sprocket by Morse silent chain. The driven sprocket is not keyed to shaft, but is rotatably mounted thereon. Two | oppositely coiled flat spiral springs transmit the rotation to the flywheel and shaft, one end of each spring be- ing attached to the driven sprocket and the other end of each to the fly- wheel. Hence any irregularity of. ro- tation caused by variations in the angular velocity of the main shaft, is smoothed out by the springs, impart- ing to the flywheel and shaft a con- stant resultant speed. The springs It is Reese" Hutchison of New York, an electrical - Assurances from naval & TAE MarRINE REVIEW are protected against breakage from sudden reversal of the propeller shaft by a radial arm which engages a pin attached to flywheel when reversal takes place. On the inside of flywheel at the end opposite to that occupied by the flat springs gear teeth are cut. These engage two pinions which actuate magnetos. : One pinion is keyed to inductor shaft of one magneto, the other is 30 mounted that when the direction of rotation of the main shaft is "ahead" the inductor of the second magneto is exactly in the same rotative rela- tion to its armature and pole shoes as that of the first magneto. current from the second magneto is - therefore in absolute phase with that from the first. But when the main shaft is reversed in rotation, the sec- ond pinion rotates idly on the shaft of its magneto through 90 degrees HE INDUSTRIAL INSTRUMENT CO. BU eee 2 al ae Na Bic. 34. before beginning to rotate same. This causes the inductor of the second magneto to assume an exactly oppo- site relation to its armature and pole pieces to that obtaining at the instant in the first and hence the current from one is 180 degrees electrically out of phase with the other. There are therefore, two wires from each running to the indicators. At "ahead" these circuits are in phase and when the main shaft is reversed or astern one is 180 degrees out of phase with the other. The Indicators. The indicators, Figs. 3 and 4, are especially designed to withstand con- tinued vibration. They are waterproof and rust proof, and not affected by the rolling or pitching of the ship. Fig. 3 shows the engine room type, having large .scale and prominent pointer. It may 'be read from a dis- tance of 20 to 30 ft., and when placed in line of vision with the man at the _without The December, 1909 throttle, enables him to bring his en- gine to any desired speed, quickly and accurately. Ae ~ the pilot house Fig. 4. illustrates type of indicator. It has 'no. iron, steel or other compass. deflecting metal in its construction, and may be placed in proximity to the compass affecting it. The current used in this system is alternating and of exceedingly small quantity. There- fore, no compass trouble from this source is possible. In fact every pos- sible contingency seems to have been guarded against. - This. same indicator is used as a chart room and stateroom type as in the pilot house, excepting that an iron case is used instead of brass. By installing one of these indicators in the staterooms of the captain and chief engineer, both may 'be kept in close touch with the engine perform- ance at all times. Fig. 5 shows the bridge binnacle type, supporting, in the case of :a twin screw equipment, two indicators --one for each shaft, properly marked. The construction is of ibrass through- out and it can be placed alongside the compass binnacle with impunity. The scale is placed' at an angle so as to be easily read when standing. The entire fixture is waterproof, and of strong construction. Illumination of the scales is provided by an oil lamp or electric light attachment similar to the compass binnacle when desired. Each of these instruments has two coils--a moving coil, to which the pointer is attached; "and a fixed- or field coil. The moving coil is con- nected electrically to one of the mag- netos, the fixed coil sto the other. When the-two magnetos are in phase, the pointer is deflected to the right, indicating speed ahead. When - they are out of phase, the pointer is de- flected to the left, indicating speed astern. The more rapidly the shaft revolves in either direction, the high- er the voltage generated, and the greater the deflection of the pointer calibrated to- conform' thereto. It all appears extremely simple, in fact, it could scarcely be more go. Without any contacts, complications Or switches and no parts subject to damage other than from unusual physical abuse, it is claimed to be a perfectly dependable and steady tach- ometer which should commend itself to those interested. The makers, The .Industrial Instru- ment Co., Foxboro, Mass., say that each outfit is assembled and calibrat- ed before shipping for installation. The conditions under which it must