Local Battery

In Fig. 125 two stations are shown connected by a grounded line wire. The transmitter of each station is included in a low-resistance primary circuit including a battery and the primary winding of an induction coil, the relation between the primary circuits and the line circuits being established by the inductive action between the primary and the secondary windings of induction coils, the secondary in each case being in the line circuits with the receivers. IMG:384091999325875926_fig125_t.gif.png:Illustration_ Fig. 125. Local-Battery Stations with Grounded Circuit Fig. 125. Local-Battery Stations with Grounded Circuit View full size illustration. Fig. 126 shows exactly the same arrangement but with a metallic circuit rather than a grounded circuit. The student should become accustomed to the replacing of one of the line wires of a metallic circuit by the earth, and to the method, employed in Figs. 125 and 126, of indicating a grounded circuit as distinguished from a metallic circuit. IMG:384091999325875926_fig126_t.gif.png:Illustration_ Fig. 126. Local-Battery Stations with Metallic Circuit Fig. 126. Local-Battery Stations with Metallic Circuit View full size illustration. In Fig. 127 is shown a slight modification of the circuit shown in Fig. 126, which consists of connecting one end of the primary winding to one end of the secondary winding of the induction coil, thus linking together the primary circuit and the line circuit, a portion of each of these circuits being common to a short piece of the local wiring. There is no difference whatever in the action of the circuits shown in Figs. 126 and 127, the latter being shown merely for the purpose of bringing out this fact. It is very common, particularly in local-battery circuits, to connect one end of the primary and the secondary windings, as by doing so it is often po ible to save a contact point in the hook switch and also to simplify the wiring. IMG:384091999325875926_fig127_t.gif.png:Illustration_ Fig. 127. Local-Battery Stations with Metallic Circuit Fig. 127. Local-Battery Stations with Metallic Circuit View full size illustration. The advantages to be gained by employing a local battery at each subscriber's station a ociated with the transmitter in the primary circuit of an induction coil are attended by certain disadvantages from a commercial standpoint. The primary battery is not an economical way to generate electric energy. In all its commercial forms it involves the consumption of zinc and zinc is an expensive fuel. The actual amount of current in watts required by a telephone is small, however, and this disadvantage due to the inexpensive method of generating current would not in itself be of great importance. A more serious objection to the use of local batteries at subscribers' stations appears when the subject is considered from the standpoint of maintenance. Batteries, whether of the so-called "dry" or "wet" type, gradually deteriorate, even when not used, and in cases where the telephone is used many times a day the deterioration is comparatively rapid. This makes nece ary the occasional renewals of the batteries with the attendant expense for new batteries or new material, and of labor and transportation in visiting the station. The labor item becomes more serious when the stations are scattered in a sparsely settled community, in which case the visiting of the stations, even for the performance of a task that would require but a few minutes' time, may consume some hours on the part of the employes in getting there and back.