04.08.08
A later method of condenser making which has not
A later method of condenser making which has not yet been thoroughly
proven in practice, but which bids fair to produce good results,
varies from the method just described in that a paper is used which in
itself is coated with a very thin conducting material. This conducting
material is of metallic nature and in reality forms a part of the
paper. To form a condenser of this the sheets are merely rolled
together and then boiled in paraffin and compressed as before.
Sizes. The condensers ordinarily used in telephone practice range in
capacity from about 1/4 microfarad to 2 microfarads. When larger
capacities than 2 microfarads are desired, they may be obtained by
connecting several of the smaller size condensers in multiple. Table
IX gives the capacity, shape, and dimensions of a variety of
condensers selected from those regularly on the market.
TABLE IX
Condenser Data
+————+—————+———————————+
| | | DIMENSIONS IN INCHES |
| CAPACITY | SHAPE |———-+———-+———–+
| | | Height | Width | Thickness |
+————+—————+———-+———-+———–+
| 2 m. f. | Rectangular | 9-1/6 | 4-3/4 | 11/16 |
| 1 m. f. | ” | 9-1/6 | 4-3/4 | 11/16 |
| 1 m. f. | ” | 4-3/4 | 2-3/32 | 13/16 |
| 1/2 m. f. | ” | 2-3/4 | 1-1/4 | 3/4 |
| 1 m. f. | ” | 4-13/16 | 2-1/32 | 25/32 |
| 1/2 m. f. | ” | 4-3/4 | 2-3/32 | 13/16 |
| 3/10 m. f. | ” | 4-3/4 | 2-3/32 | 13/16 |
| 1 m. f. | ” | 2-3/4 | 3 | l |
+————+—————+———-+———-+———–+
Conventional Symbols. The conventional symbols usually employed to
represent condensers in telephone diagrams are shown in Fig. 124.
These all convey the idea of the adjacent conducting plates separated
by insulating material.
[Illustration: Fig. 124. Condenser Symbols]
Functions. Obviously, when placed in a circuit a condenser offers a
complete barrier to the flow of direct current, since no conducting
path exists between its terminals, the dielectric offering a very high
insulation resistance. If, however, the condenser is connected across
the terminals of a source of alternating current, this current flows
first in one direction and then in the other, the electromotive force
in the circuit increasing from zero to a maximum in one direction, and
then decreasing back to zero and to a maximum in the other direction,
and so on. With a condenser connected so as to be subjected to such
alternating electromotive forces, as the electromotive force begins to
rise the electromotive force at the condenser terminals will also rise
and a current will, therefore, flow into the condenser. When the
electromotive force reaches its maximum, the condenser will have
received its full charge for that potential, and the current flow into
it will cease. When the electromotive force begins to fall, the
condenser can no longer retain its charge and a current will,
therefore, flow out of it. Apparently, therefore, there is a flow of
current through the condenser the same as if it were a conductor.
Means for Assorting Currents. In conclusion, it is obvious that the
telephone engineer has within his reach in the various coils–whether
non-inductive or inductive, or whether having one or several
windings–and in the condenser, a variety of tools by which he may
achieve a great many useful ends in his circuit work. Obviously, the
condenser affords a means for transmitting voice currents or
fluctuating currents, and for excluding steady currents. Likewise the
impedance coil affords a means for readily transmitting steady
currents but practically excluding voice currents or fluctuating
currents. By the use of these very simple devices it is possible to
sift out the voice currents from a circuit containing both steady and
fluctuating currents, or it is possible in the same manner to sift out
the steady currents and to leave the voice currents alone to traverse
the circuit.