The Electrical experimenter
The Electrical experimenter
The Electrical experimenter
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
m36 THE ELECTRICAL EXPERIMENTER May, 1917<br />
CeN5TRUQTeR<br />
An <strong>Electrical</strong> Paradox or Selective Lamp Controller<br />
average person is always in-<br />
THEterested in a puzzle. When that<br />
])uzzle is electrical, it is certain<br />
to appeal to the amateur <strong>experimenter</strong>.<br />
Can any of you think<br />
of an arrangement by means of which a<br />
single pole, single throw, knife switch may<br />
be made to operate three different lamps<br />
individually, during three successive inter-<br />
vals that the circuit is closed? For example,<br />
if the switch is closed once, light No.<br />
1 will light and remain lit until the switch<br />
is opened again. It will then go out. If<br />
the switch is again closed, light Xo. 2<br />
OXLY will light and remain lit until the<br />
circuit is again opened. Similarly with light<br />
No. 3.<br />
To secure the result described, an arrangement<br />
is employed somewhat similar<br />
to that used on the automatic block signaling<br />
systems of single-track electric railroads,<br />
and elsewhere. .\ commutator is<br />
made to move from one contact segment to<br />
another every time an electro-magnet<br />
draws its armature down (or up).<br />
Referring to Figs. 1 and 3, when the circuit<br />
is closed, the magnets attract the armature,<br />
pulling it down. <strong>The</strong> hook C<br />
catches over a tooth of the ratchet wheel<br />
R. By notin.g the direction of pitch of the<br />
teeth, it will be seen that the movement of<br />
the hook will not cause the ratchet to move.<br />
<strong>The</strong> ratchet is rigidly attached to a shaft<br />
B. on which a gear wheel K is also firmly<br />
fastened (Fig. IV This cog meshes with<br />
1 smaller one, J, which is tight on shaft A.<br />
BY ALBERT H. BEILER<br />
A vv'ooden cylinder, G, is fi.xt on A, which<br />
has brass segments fastened along its perifery<br />
as shown at E. It will be Seen that E<br />
touches one of the brass strips I. This<br />
closes a circuit and lights a lamp. If some<br />
means could now be employed to move the<br />
wooden cylinder Y} o{ a. revolution, another<br />
segment seen slightly under the middle<br />
brass strip would touch the strip, while the<br />
Perspective View of Selective Lamp Control ler Built from a Telegraph Sounder, a Few<br />
Gear Wheels and Other Odd Parts. At the Left Is Shown the Brushes and Commutator<br />
Unit with Gear Attachment fo r Rotating the Segment Drum.<br />
first segment would have moved away from<br />
the end strip. Another third of a revolution<br />
would cause the foremost segment to<br />
touch the foremost I and close another cir-<br />
cuit, while the other two circuits would remain<br />
open. When the switch is closed,<br />
the cylinder with the brass segments, called<br />
the commutator, will not move, but the hook<br />
will engage a tooth of the ratchet. Simultaneously<br />
a lamp will light.<br />
When the switch is now opened,<br />
the lamp will go out and the<br />
same instant the retractile<br />
spring T will pull the armature<br />
up again, since the magnets<br />
have lost their power of attraction.<br />
Hook C will pull the<br />
ratchet up a distance equal to<br />
its (the hook's) travel. This<br />
distance is such that the ratchet<br />
will have completed l/12th of a<br />
revolution when the armature<br />
shaft F strikes its stop screw<br />
N. It must here be stated that the ratchet<br />
has 12 teeth, gear K, 48 teeth, while<br />
gear J has 12 teeth ; the ratio between<br />
the two latter being 4 to 1. When the<br />
ratchet makes l/12th of a turn, K will also<br />
turn l/12th of a revolution. Thus the<br />
third of a revolution movement, which is<br />
necessary to bring each segment under its<br />
respective contact, is accomplished.<br />
It is possible that the reader who has followed<br />
this explanation carefully w-ill ask<br />
why the movement of the ratchet should be<br />
accomplished by the retractile spring T<br />
when the magnet exerts a greater force.<br />
In other words, why should not the segments<br />
change on the down stroke of the<br />
armature instead oi on the up stroke-' <strong>The</strong><br />
answer is this : Suppose the commutator<br />
turned if a circuit was closed<br />
when it was opened, then, for<br />
instead of<br />
an instant<br />
the lamp would light which had just previously<br />
been lit. It is true that almost immediately<br />
it would go out and tlie required<br />
lamp would light but tlie result would very<br />
obviously be unsatisfactory. <strong>The</strong> time taken<br />
for the cylinder to commutate would be the<br />
time required for the magnets to pull the armature<br />
down. As this does not occur instantaneously,<br />
the above described result<br />
would occur. .Another objection to having<br />
the commutator rotate on the down stroke<br />
of the armature is that a segment and a<br />
brass strip, each carrying current, would be<br />
separated from each other by the movement<br />
of the commutator and create a spark<br />
v.'hich would soon pit the segments and<br />
brass contacts and thus interfere with the<br />
satisfactory operation of the device. With<br />
the device arranged as just described the<br />
commutator moves an instant .\FTER the<br />
circuit has been opened, thus preventing any<br />
arc from forming.<br />
<strong>The</strong> wiring diagram is shown in Figure<br />
8. B B B are the strips I of Figure 1.<br />
C represents the commutator segments. M<br />
is the electro-magnet. R is the rheostat,<br />
made of salt water with carbon electrodes,<br />
or sulfuric acid, and carbon or lead electrodes.<br />
Two 100 watt lamps in jjarallel may<br />
be connected<br />
stead of the<br />
in series<br />
rheostat.<br />
with the magnet in-<br />
<strong>The</strong> magnets must<br />
receive from IJj to 2 amperes, since they<br />
have quite a pull to make. <strong>The</strong> smaller<br />
circles B show where the wires from the<br />
device are connected to the binding posts<br />
seen in Fig. 1.<br />
.\nyone sufficiently interested may tnake<br />
one of these contrivances by following the<br />
diagrams and instructions which follow.<br />
Photo of Selective Lamp Switch or Controller as Built<br />
by the Author, Together with Three Lamps to Be Controlled<br />
and Main Circuit Switch.<br />
Secure an old telegrapli sounder of the<br />
sort that is generally sold to amateurs for<br />
practising telegraphy. Unscrew the parts<br />
from the base and mount the frame, mag-