Coil (electronics)

“ The simplest is to let the current, or part of it, flow through a coil which is pivoted between the N and S poles of a strong permanent magnet. A spring keeps the coil in its zero position and if the current makes the coil turn it must do so against this spring. The stronger the current in the coil the greater the interaction of the loops of the coil and those of the iron atoms and hence the further the coil will turn. A pointer attached to the coil indicates how far; and the number of volts or amperes is read off from the calibrated scale. ”

“ In actual practice, when the wire is run through the paraffin bath not more than 50 per cent of the calculated wire will occupy the space. And the thickness of the paper rings must also be added when figuring the total length of the coil. In the iron-clad transformers or induction coils of highest efficiency used in the alternating current electric light system, the rule for determining the windings of the coils is based on the ratio of the turns of wire in the primary to the turns in the secondary, the electromotive force in the primary, and the lines of force cut by the windings. ”

“ The movable coil has attached to it an index needle moving over a scale, and a fixed coil of high-resistance wire is included in series with the movable coil between the terminals of the instrument. When a difference of potential is made between the terminals, a current passes through the movable coil, which then tends to place itself with its plane more at right angles to the lines of force of the field. ”

“ Fig. 167. 483. Induction Coils in Telephone Work. As the resistance of telephone lines is large, a current with a fairly high E. M. F. is desired. While the current from one or two cells is sufficient to work the transmitter, it is not strong enough to force its way over a long line. To get around this difficulty an induction coil is used to transform the battery current, that flows through the transmitter and primary coil, into a current with a high E. M. F. that can go into the main line and force its way to a distant receiver. ”

“ A good way of describing the value of an induction coil for wireless telegraph purposes is to state the length of oscillatory spark which can be produced between balls one centimetre in diameter connected to the secondary terminals, when these balls are short-circuited by a condenser having a capacity, say, of one-hundredth of a microfarad, and also one-tenth of a microfarad.
If a hammer or motor interrupter is employed with the coil, then a primary condenser must be connected across the points between which the primary circuit is broken. ”

“ Binding-Post. Fig. 27. A coiled spring serves very well as a connector. One end should be fastened to the apparatus, as shown, by clamping it under a screw-head. The other end of the coil should be pulled out a little, away from the other turns, so that you can stretch the spring in order to put the bare ends of wires between the turns. Any number of wires placed between these turns will be pinched and electrically connected. The coil should be about 1⁄2 in. long and less than 1⁄2 in. in diameter. You can make a coil by tightly wrapping stiff iron wire around a pencil. ”

“ When the space is filled up to the level of the paper disks and the paraffin is hard, loosen the set screw, and removing the outside disk, the coil can be slipped off, or a slight warming will loosen it. Any number of these coils can be made, and there are the advantages in this mode of construction that a bad coil will not spoil the whole secondary, and that the wire can be obtained in comparatively small quantities. ”

“ A coil much used for electric baths has a primary winding only, regulated by the sliding in and out of the iron core, which necessitates the use of an independent vibrator, or else by varying the current strength with a rheostat. The general directions given before will answer in the present case, the only data necessary being the size of wire, which should be about six to ten layers of No. 20 B & S. The coil with movable secondaries here comes into service. Strong currents are needed for bath work, and any variety of winding can be used with this make of coil. ”

“ There are a number of inductance coils and these are arranged so that they can be connected in or cut out and combinations are thus formed which give a high efficiency and yet allow them to be compactly mounted. The inductance coils of the aerial wire system and those of the secondary coil circuit are practically alike. For wave lengths up to 2,200 meters bank litz-wound coils are used and these are wound up in 2, 4 and 6 banks in order to give the proper degree of coupling and inductance values. ”

“ Fig. 2,412.—Westinghouse air cooled choke coil, for voltages of from 2,200 to 110,000. In construction, the coils are made of aluminum rod wound into a helix of about 15 inches in diameter and having 20 turns. The helix is supported on two insulators. For mechanical reasons it is necessary to have the aluminum rod of sufficient size to secure rigidity, consequently every coil has a capacity of 200 amperes and may be used on any circuit up to that capacity. ”

“ The coil is built on a tube of glued paper, and contains about 15 ft. of No. 16 gauge wire. The terminals consist of the brass bolts taken from discarded dry cells. A steel sewing needle serves as a shaft, and a piece of wire for the pointer. The various joints are made with soft solder, and suitable stops are provided to keep the armature from shifting laterally. In calibrating, a blank scale should be glued in position and as many 55-watt lamps as possible arranged so that they can be placed in the circuit, one at a time. On a 110-volt line, each lamp added will mark a half-ampere point. ”

“ As in the simple electromagnet, the proportions of diameter and length of the primary coil and core will determine its rapidity of action. A short fat coil and core will act much quicker than a long thin one. But on a short fat coil the outside turns would be too far removed from the intensest part of the primary field. A good proportion of core length is given in the following table:
The primary coil P consists of two or not more than three layers of insulated copper wire of large diameter, being required to carry a heavy current in a 2-inch spark coil, probably from 8 to 10 amperes. ”

“ It is, of course, absolutely necessary to employ in such a coil wires provided with the best insulation. Good coils may be produced by employing wires covered with several layers of cotton, boiling the coil a long time in pure wax, and cooling under moderate pressure. The advantage of such a coil is that it can be easily handled, but it cannot probably give as satisfactory results as a coil immersed in pure oil. ”

“ In general, most of the experiments usually performed with a static machine can be performed with an induction coil when operated with very rapidly alternating currents. The effects produced, however, are much more striking, being of incomparably [Pg 164] greater power. When a small length of ordinary cotton covered wire, Fig. 107, is attached to one terminal of the coil, the streams issuing from all points of the wire may be so intense as to produce a considerable light effect. ”

“ Current Regulator for Induction Coils. Fig. 80. If your coil gives too much of a shock with one cell of App. 3 or 4, you can pull the carbon and zinc partly out of the solution to weaken the shock, or you can use a water regulator. T is an ordinary tin tomato can nearly filled with water, L is a lamp chimney. One wire, A, is fastened to T directly, or by a spring binding-post. The other wire, B, is fastened to a piece of copper, C, which may be raised or lowered inside of L. D is a piece of pasteboard with a small hole in its center. ”

“ For most purposes an induction coil is required which is capable of giving in the secondary circuit intermittent currents of very high electromotive force, and to attain this result the secondary circuit must as a rule consist of a very large number of turns of wire. Induction coils are employed for physiological purposes and also in connexion with telephones, but their great use at the present time is in connexion with the production of high frequency electric currents, for Röntgen ray work and wireless telegraphy. ”

“ The preferred plan of connections is illustrated in Fig. 127. The manner of operating renders it easy to obtain by means of a small and inexpensive apparatus enormous differences of potential which have been usually obtained by means of large and expensive coils. For this it is only necessary to take an ordinary small coil, adjust to it a condenser and discharging circuit, forming the primary of an auxiliary small coil, and convert upward. As the inductive effect of the primary currents is excessively great, the second coil need have comparatively but very few turns. ”

“ The current supply available will determine the type of the instruments, and whether an induction coil or a transformer is used. Unless current mains for light and power are already installed, it must be generated by an engine and dynamo, or recourse had to batteries. Induction coils may be operated on either direct or alternating current. Dry cells are most commonly employed to furnish the current for small induction coils, but a storage or some form of renewable primary cell, such as the Fuller and Edison, is necessary if the coil is a large one. ”

“ The lighting load is entirely connected to one single phase circuit, and the motors are started and operated from this circuit with the assistance of the teazer wire. The long coil indicates the main winding of the armature, which is similar in its arrangement and size to the ordinary armature winding of a single phase alternator. The short coil which connects at one end to the middle point of the coil above mentioned, and at the other to a third collector ring is called the "teazer" coil. Its use is to generate a pressure in quadrature with that of the main coil. ”

“ Close against the wall, within a few feet of where the sick man's bed had been, was an enormous focus tube, the platinum electrode turned so as to direct the rays through the wall. The machine was clamped in a holder, and stood on a square deal table, upon which also stood the most enormous induction coil I had ever seen. This was supplied from the main through wires coming from the electric light supplied to the house. This induction coil gave a spark of at least twenty-four inches. ”

“ If the coil is properly made, no effect on a magnet placed outside it can be discovered, whether the current is kept constant or made to vary in strength; but if a conducting wire C be made to embrace the ring any number of times, an electromotive force will act on that wire whenever the current in the coil is made to vary ”

“ Thus one coil may be in
parallel with the other, and the action on the plunger will then depend
on the relative currents passing through the coils.
Coil, Choking.
A coil of high self-induction, used to resist the intensity of or
"choke" alternating currents. Any coil of insulated wire wound around
upon a laminated or divided iron core forms a choking coil. The iron
coil is usually so shaped as to afford a closed magnetic circuit.
A converter or transformer acts as a choking coil as long as its
secondary is left open. ”

“ Fig. 152.—A Telephone Induction Coil. An induction coil consists of two fiber or hard-wood heads, about one inch square and one-quarter of an inch thick, mounted on the ends of an iron core composed of a bundle of small iron wires about two and one-half inches long. The core should be about five-sixteenths of an inch in diameter.
The core is covered with a layer of paper and then wound with three layers of No. 22 B. & S. single-cotton-covered wire. These three layers of wire form the primary. The primary is covered with a layer of paper and then the secondary is wound on. ”

“ The intensely disruptive power of the long spark is readily shown by its power to perforate substances, but great care must be taken that the secondary wires of a coil are led away from the body of the coil. A good plan is to hang two silk cords or stout threads from the ceiling, to which the secondary wires may be attached and kept in sight when experimenting at any distance from the coil. ”

“ The movable coils consisted of the same lengths of copper wire, in which there were taken one, two, or more loops, the resistance of each of these pieces being the same, so as to maintain that of the complete circuit constant. The coils were placed over the upper end of the magnet, and carried down until they rested upon the stop, the needle of the galvanometer brought to the zero of the scale, and then the coil pulled off the magnet with a quick motion. ”

“ At sea the wire would run to one or more metal plates on the bottom of the vessel, where the earth connection would be made with the water. The high-resistance secondary circuit of an induction coil is located in circuit between the condensing surface and the ground. The primary circuit of the induction coil includes a battery and a device for transmitting signals, which may be a revolving circuit-breaker operated continually by a motor of any suitable kind, either electrical or mechanical, and a key normally short-circuiting the circuit-breaker or secondary coil. ”

“ Constructing a Coil.—Such a coil is shown in section in Fig. 89, in which the core A is a hard rubber or fiber tube, with disk ends B of the same material. The primary wire C is large in cross section, and carefully insulated. The opposite ends are brought out through the disk heads, and run to the generator, that is, the battery or dynamo. The fine wire D, which constitutes the secondary winding, is also of insulated wire, wrapped over the primary, and its ends are connected up with the sparking mechanism, as will be more fully explained hereinafter. ”