Dynamometer

“ If P represent the average value of the component of a force in the direction of the displacement, s, of its point of application, the product Ps measures the work done during the displacement. When the force acts on a body free to turn about a fixed axis only, it is convenient to express the work done by the transformed product Tθ, where T is the average turning moment or torque acting to produce the displacement θ radians. The apparatus used to measure P or T is the dynamometer. ”

“ Fig. 1.
In the ordinary strap dynamometer a flexible band, sometimes carrying segments of wood blocks, is hung over a pulley rotated by the motor, the power of which is to be measured. If the pulley turns with left-handed rotation, the friction would carry the strap toward the left, unless the weight, Q, were greater than P. If the belt does not slip in either direction when the pulley rotates under it, then Q-P exactly measures the friction on the surface of the pulley; and V being the surface velocity of the pulley (Q-P) V, is exactly the work consumed by the dynamometer. ”

“ All questions relating to the total quantity of transient currents, as measured by the impulse given to the magnet of the galvonometer, may be solved in this way without the necessity of a complete solution of the equations. The heating effect of the current, and the impulse it gives to the suspended coil of Weber's dynamometer, depend on the square of the current at every instant during the short time it lasts. Hence we must obtain the solution of the equations, and from the solution we may find the effects both on the galvanometer and dynamometer ”

“ Transmission Dynamometers.—The essential part of many transmission dynamometers is a spring whose deformation indirectly measures the magnitude of the force transmitted through it. For many kinds of spring the change of form is practically proportional to the force, but the relation should always be determined experimentally. ”

“ Between every engine and its train there should be interposed a dynamometer, that is, a powerful spring to measure the force exerted by the engine.
It may, perhaps, be objected that this would require a certain amount of movement between the engine and its train. A very small quantity would be sufficient, say half an inch, or less. The forces in action are so very large, that even a still smaller amount of motion than this might be sufficiently magnified. Its indications should be marked by self-acting machinery governing points impinging upon the paper on which the velocity is marked. ”

“ They measure (1) the gas consumed by the engine, (2) the horse-power given to the dynamo machine, (3) the current in the circuit in webers, and (4) the resistance of the circuit. Thus exact calculations can now be made as to the horse power expended in any part of the circuit, and the light given out in any given period by an electric lamp. The dynamometers used in these measurements were described, but at present, in some cases, the description given is for various reasons incomplete, so that we shall take a future opportunity of writing of these instruments. ”

“ His greatest invention was the dynamometer used for ascertaining the power for driving machinery. It was first used in the York mills in 1837, and was considered preferable to any known apparatus for determining the power actually used in driving machinery. ”

“ One day, when we were nearing the Straits of Bab el Mandeb, partly in order to relieve the tedium of the voyage, and partly in order to obtain statistics of comparative strength, I produced my Collin’s dynamometer. This is an oval piece of polished steel, small enough to be held flat in the hand and compressed in a greater or less degree, according to the amount of force expended, the pressure being registered by means of cogged wheels acting on an index which in its turn moves a second index on a dial-plate. ”

“ The size and cost of dynamometers rapidly increase with the maximum currents which they are designed to carry, and when more than 500 amperes are to be measured, the use of other instruments and methods is recommended. ”

“ This experiment gives the theory of the dynamo. Instead of passing only one wire through the field of force of a magnet, we have hundreds bound lengthwise on a revolving drum called an armature. Instead of one magnetic pole in a dynamo we have two, or [Pg 96] four, or twenty according to the work the machine is designed for—always in pairs, a North pole next to a South pole, so that the lines of force may flow out of one and into another, instead of escaping in the surrounding air. ”

“ The increased amount of energy that will be required to keep the dynamo moving at a certain rate of speed when the load is on—in other words, when the circuit is closed—will depend upon the amount of current that is going out from the dynamo to perform work at other points. As the amount of current used outside for the various purposes is constantly changing, it follows that the load on the dynamo is constantly changing also. As the load changes, the speed will change, unless the amount of water that is flowing into the turbine is changed in a like proportion ”

“ Probably the modern dynamo is the most efficient, the most accurately measurable, the least wasteful of its power, and the most manageable, of any power-machine so far constructed by man for daily use.
The motor.--This is the twin of the dynamo. In all essentials the two are of the same construction. A difference in the arrangement of the terminals of the wire coils or the wrappings of armature and field magnet, makes of the one a dynamo and of the other a motor. Nevertheless, they are separate studies in electrical science. ”

“ It was found that one of these dynamos would run as a motor if a current were sent through the coils of the armature and the field-magnet; in fact, the current from one dynamo may be made to run another similar machine as a motor. Thus the dynamo is said to be reversible. If the armature is turned by a steam-engine or some other power, a current is produced. If a current is sent through the coils, the armature turns and does work. If the machine is used to supply an electric current, it is a dynamo. ”

“ There are two types of dynamo, one generating a direct and the other an alternating current. (By alternating we mean first a positive and then a negative current impulse.) We cannot enter into a technical description of the dynamo in a popular treatise such as this.
The dynamo has evolved from the germ discovered by Faraday, till to-day it is a machine, the construction of which requires the highest class of engineering skill. When in action it seems like a great living presence, scattering its energy in every direction in a way that is at once a marvel and a blessing to mankind. ”

“ It is well to remember that when dynamos are working, they are, or contain for the time being, very powerful magnets, therefore if we bend over them to examine them, Look out for your watches! our watches will get magnetised, which does not improve their qualities as time-keepers. Say that our dynamo is now going round at the required speed, which may be 500 or 600 revolutions per minute; the engine is not using much steam as yet, because very little work is being done. ”

“ Experiment has shown that when a dynamo is used to produce an electric current, which, in its turn, drives another dynamo serving as a motor, the double con version of energy may be performed with no very serious loss. In favourable cases, when the dynamo and motor are close together, the motor will yield more than 80 per cent, of the work which is spent in driving the dynamo. When they are far apart there is an additional loss, due to the resistance of the conductor which connects them, and a further loss due to its imperfect insulation. ”

“ Ans. When no current is being generated by the dynamo, little power is required to drive it, but when the external circuit is closed and current is forced through it against more or less resistance, work is being done, hence more power is required. In other words, there is an opposition to the mechanical force applied at the pulley which is proportional to the electric power delivered by the dynamo. An opposing reaction or reverse force then is set up in a dynamo when it does work.
Fig. 395.—Circuit with generator and motor. ”

“ We have seen how in the dynamo the armatures became the source of induced currents by being made to cut the fields of force of electro-magnets. Now, a dynamo can be made to work in an opposite way; that is, by making the magnetic fields of force rotate in front of the coils or armatures. In the motor, the field of force is mostly established by the current directly from the dynamo. ”

“ Day and night the mighty river here pulls away at its turbine harness; and man, having once adjusted that harness, may take his ease and enjoy the fruits of his ingenuity.
As we return now to the top of the building, we shall view the spinning dynamos with renewed interest, and a few facts regarding their output of energy may well claim our attention. In their principle of action, as we have seen, all dynamos are alike,—depending upon the mutual relations between the wire-wound armature and a magnetic field. ”

“ In this there is merely conversion of electrical energy at a high potential into electrical energy at a low potential, or vice versa, but in the dynamo the mechanical energy which must be applied to maintain the relative movement of magnetic field and conductor is absorbed, and reappears in an electrical form. A true transformation takes place, and the proportion which the rate of delivery of electrical energy bears to the power absorbed, or in other words the efficiency, is the more remarkable. ”

“ The dynamo is an instrument invented for the mechanical generation of electricity by taking advantage of the principle that electrical energy is produced by moving magnets near coils of wire, or coils of wire near magnets. A current is thus started by induction, and, once started, the mechanical power exerted in making the magnet or coils revolve is continually converted into electricity until the accumulated electrical energy becomes very powerful. The original energy comes of course from the coal burned in the steam-engine which makes the magnet or coils revolve. ”

“ NOTE.--The action of an equalizing bar in equalizing the load on compound dynamos run in parallel may be explained as follows: The compound winding of a dynamo raises the pressure in proportion to the current flowing through it, and if, in a system of parallel operated compound dynamos without the equalizing connection, the current given by one machine were slightly greater than the currents from the others, the pressure of that machine would increase. With this increase in pressure above the other machines, a still greater current would flow, and so raise the pressure further. ”

“ It must be understood, of course, that the amount of electricity generated in any dynamo is precisely measurable, and that by no possibility could the energy thus developed exceed the energy required to move the coils of wire. Were it otherwise the great law of the conservation of energy would be overthrown. In actual practice, of course, there is loss of energy in the transaction. The current of electricity that flows from the very best dynamo represents considerably less working power than is expended by the steam engine in forcibly revolving the armature. ”

“ The dynamo is a machine that converts mechanical into electrical energy, and the [Pg 68] great practical value of energy in this form is that it can be distributed through a conductor economically for many miles. We can transmit mechanical power by means of a rope or cable for a limited distance, but at tremendous loss through friction. We can transmit power through pipes by compressed air or steam, but there is a great loss, especially in the case of steam, by condensation from cold. ”

“ The Dynamo, Dynamo-Electric Machine or Generator, is a machine for converting mechanical energy into an electric current, through electromagnetic induction. The dynamo is a machine that will convert steam power, for example, into an electric current. Strictly speaking, a dynamo creates electrical pressure, or electromotive force, and not electricity, just as a force-pump creates water-pressure, and not water. They are generally run by steam or water power.
Fig. ”

“ The Thomson-Houston Dynamo. In considering the current generator the first thing to be decided upon is the definition of the term dynamo. The following is thought to be a correct definition,—A dynamo or dynamo electric machine is a machine which is used to convert energy in the form of mechanical motion into energy of electric currents, or vica-versa. Those used to generate currents of electricity are called dynamos, those used to generate mechanical motion are known as motors. ”

“ Now from our great alternating current dynamo we first fill the ball at the top of the oscillator with electricity, and then we make a motion that corresponds to squeezing it. What happens? Just what happens when you have two rubber balls connected with a tube. You squeeze one of them, and push the air, or water, into the other ball. In that way we push the electricity into the earth, but it comes back to us on the stationary waves, from the opposite side, and when it does we are ready to give it another mighty push with another tremendous squeeze from our dynamo. ”