Cyclopedia of Telephony and Telegraphy, Vol. 1 / A General Reference Work on Telephony, etc. etc. - American School of Correspondence

TABLE IX

Condenser Data

Capacity	Shape	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	1

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.

Fig. 124. Condenser Symbols
[View full size illustration.]

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.