Indicating Wattmeter

—An electrical instrument for measuring power developed in a circuit, and designed to show instantaneous values of power, or the rate at which energy is consumed in a circuit. Indicator. 1. Any form of annunciator. 2. An instrument by which the working steam records its working pre ure, from which the power of the engine may be calculated. It consists of a small cylinder communicating by a cock with the cylinder of the engine, and fitted with a piston, to which a pencil is attached. The roller upon which a card is fastened, is oscillated forward and backward by a cord attached to the piston rod of the engine. As the pencil rises by the steam pre ure, and is brought back by a graduated spring when that pre ure is reduced by expansion and condensation,a figure representing the pre ure at each point in the stroke of the engine; is traced upon. the card. | Indicator Card. The card of a steam engine indicator which shows the pre ure curves automatically traced, whereby the indicated horse power of the engine may be determined. The diagram is shaped like a foot; its length represents the stroke, and its height the steam pre ure in pounds. The average pre ure, cylinder area, and piston speed are the elements for calculating the horse power. Indicator Diagram. Tn steam engineering, a diagram of work traced by the pencil of the indicator upon an indicator card. From it are deduced both the behavior and the mean effective pre ure of the steam in the cylinder and thence the indicated horse power. To obtain the mean effective pre ure, the area of the card is divided transversely by equidistant ordinates, ten or more as most convenient, perpendicular to the atmospheric line. Now, with a scale corresponding to the spring with which the diagram was taken, measure the re ure in the center of each of these divisions he measurement being taken between the steam expansion and exhaust lines The average of all the measurements will give the mean effective pre ure,