04.08.08
Posted in Uncategorized at 5:21 pm by admin
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.
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04.07.08
Posted in Uncategorized at 2:51 am by admin
Electrostatic Capacity. It is the possession of electrostatic
capacity which enables the condenser, of which the Leyden jar is a
good example, to be useful in a telephone line. The simplest form of a
condenser is illustrated in Fig. 28, in which two conducting surfaces
are separated by an insulating material. The larger the surfaces, the
closer they are together; and the higher the specific inductive
capacity of the insulator, the greater the capacity of the device. An
insulator used in this relation to two conducting surfaces is called
the _dielectric_.
[Illustration: Fig. 28. Simple Condenser]
[Illustration: Fig. 29. Condenser Symbols]
Two conventional signs are used to illustrate condensers, the upper
one of Fig. 29 growing out of the original condenser of two metal
plates, the lower one suggesting the thought of interleaved conductors
of tin foil, as for many years was the practice in condenser
construction.
With relation to this property, a telephone line is just as truly a
condenser as is any other arrangement of conductors and insulators.
Assume such a line to be open at the distant end and its wires to be
well insulated from each other and the earth. Telegraphy through such
a line by ordinary means would be impossible. All that the battery or
other source could do would be to cause current to flow into the line
for an infinitesimal time, raising the wires to its potential, after
which no current would flow. But, by virtue of electrostatic capacity,
the condition is much as shown in Fig. 30. The condensers which that
figure shows bridged across the line from wire to wire are intended
merely to fix in the mind that there is a path for the transfer of
electrical energy from wire to wire.
[Illustration: Fig. 30. Line with Shunt Capacity]
A simple test will enable two of the results of a short-circuiting
capacity to be appreciated. Conceive a very short line of two wires to
connect two local battery telephones. Such a line possesses
negligible resistance, inductance, and shunt capacity. Its insulation
is practically infinite. Let condensers be bridged across the line,
one by one, while conversation goes on. The listening observer will
notice that the sounds reaching his ear steadily grow less loud as the
capacity across the line increases. The speaking observer will notice
that the sounds he hears through the receiver in series with the line
steadily grow louder as the capacity across the line increases. Fig.
31 illustrates the test.
The speakers observation in this test shows that increasing the
capacity across the line increased the amount of current entering it.
The hearers observation in this test shows that increasing the
capacity across the line decreased the amount of energy turned into
sound at his receiver.
[Illustration: Fig. 31. Test of Line with Varying Shunt Capacity]
The unit of electrostatic capacity is the _farad_. As this unit is
inconveniently large, for practical applications the unit
_microfarad_–millionth of a farad–is employed. If quantities are
known in microfarads and are to be used in calculations in which the
values of the capacity require to be farads, care should be taken to
introduce the proper corrective factor.
The electrostatic capacity between the conductors of a telephone line
depends upon their surface area, their length, their position, and the
nature of the materials separating them from each other and from other
things. For instance, in an open wire line of two wires, the
electrostatic capacity depends upon the diameter of the wires, upon
the length of the line, upon their distance apart, upon their distance
above the earth, and upon the specific inductive capacity of the air.
Permalink
04.04.08
Posted in Uncategorized at 12:51 am by admin
The circuit of Fig. 193 is somewhat simplified from that in actual
practice, and it should be remembered that the hook switch, which is
not shown in this figure, controls in the usual way the continuity of
the receiver and the transmitter circuits as well as of the generator
circuits, the generator being attached to the line as in an ordinary
telephone.
Broken-Line System. The broken-line method of accomplishing
selective signaling and locking-out on telephone party lines is due to
Homer Roberts and his associates.
[Illustration: Fig. 194. Roberts Latching Relay]
To understand just how the principles illustrated in Figs. 186 and 187
are put into effect, it will be necessary to understand the latching
relay shown diagrammatically in its two possible positions in Fig. 194,
and in perspective in Fig. 195. Referring to Fig. 194, the left-hand
cut of which shows the line relay in its normal position, it is seen
that the framework of the device resembles that of an ordinary
polarized ringer. Under the influence of current in one direction
flowing through the left-hand coil, the armature of this device
depresses the hard rubber stud _4_, and the springs _1_, _2_, and _3_
are forced downwardly until the spring _2_ has passed under the latch
carried on the spring _5_. When the operating current through the coil
_6_ ceases, the pressure of the armature on the spring _1_ is relieved,
allowing this spring to resume its normal position and spring _3_ to
engage with spring _2_. The spring _2_ cannot rise, since it is held by
the latch _5_, and the condition shown in the right-hand cut of Fig.
194 exists. It will be seen that the spring _2_ has in this operation
carried out just the same function as the switch lever performed as
described in connection with Figs. 186 and 187. An analysis of this
action will show that the normal contact between the springs _1_ and
_2_, which contact controls the circuit through the relay coil and the
bell, is not broken until the coil _6_ is de-energized, which means
that the magnet is effective until it has accomplished its work. It is
impossible, therefore, for this relay to cut itself out of circuit
before it has caused the spring _2_ to engage under the latch _5_. If
current of the proper direction were sent through the coil _7_ of the
relay, the opposite end of the armature would be pulled down and the
hard rubber stud at the left-hand end of the armature would bear
against the bent portion of the spring _5_ in such manner as to cause
the latch of this spring to release the spring _2_ and thus allow the
relay to assume its normal, or unlatched, position.
Permalink
04.01.08
Posted in Uncategorized at 6:39 am by admin
I knew Wii Madden allowed for juking, passing, etc with the Wii remote, but this new video is the first one that really shows how sports games will be revolutionized. Includes interviews/demonstrations with the developers & producers.
read more | digg story
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Posted in Uncategorized at 6:39 am by admin
The government of Dubai installed a rather large speed bump on a street that locals had developed a habit of traveling on at very high speeds. Only one minor problem, the government didn’t tell anyone it had installed the speed bump.
read more | digg story
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Posted in Uncategorized at 6:39 am by admin
Having his eyes removed as a child he has developed his other senses to totally makeup for his lack of sight. He can even play foosball and video games…and win.
read more | digg story
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Posted in Uncategorized at 6:38 am by admin
These guys have developed a new form of high-tech graffiti and they can simply ’spray’ an entire appartment building or skyscraper with it just like that. Watch em do it in this vid, crazy shit.
read more | digg story
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Posted in Uncategorized at 6:38 am by admin
Is this the End? F1 Bans Engine Development for 10 Years
read more | digg story
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Posted in Uncategorized at 6:37 am by admin
This guy developed a camera that mounts onto the cockpit of a remote control plane and transmits to a headset worn by the flyer. Makes flying awesome!
read more | digg story
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Posted in Uncategorized at 6:37 am by admin
ISPs have been throttling BitTorrent traffic for years now, but only recently this turned into a political issue. The BitTorrent client Azureus has now developed a plugin through which you can help distinguishing the good from the bad ISPs, data they will use to strengthen their argument in the ongoing Comcast debate.
read more | digg story
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