Fig. 207. KEMPE'S DISCHARGE KEY.
Key, Kempe's Discharge.
A key giving a charging, discharging and insulating connection, for
static condenser work. Referring to the cut l is a lever or spring with
upper discharging contact s, and lower charging contact s'. In use it is
pressed down by the insulating handle or finger piece C, until caught by
the hook attached to the key I. This hook is lower down than that on the
key D, and holds it in contact with the charging contact piece S'. On
pressing the key I, marked or designated "Insulate," it springs up,
breaks contact at S', and catching against the hook on D, which key is
designated "Discharge," remains insulated from both contacts; next on
pressing D it is released and springs up and closes the discharge
contact S. It is a form of charge and discharge key. (See Key, Charge
and Discharge.)
Key, Magneto-electric.
A telegraph key whose movements operate what is virtually a small
magneto-generator, so as to produce currents of alternating direction,
one impulse for each motion of the key. It is employed for telegraphing
without a line battery, a polarized relay being used. In one very simple
form a key is mounted on a base with a permanent magnet and connected to
the armature, so that when the key is pressed downwards it draws the
armature away from the poles of the magnet. If the magnet or its
armature is wound with insulated wire this action of the key will cause
instantaneous currents to go through a circuit connected to the magnet
or armature coils.
Fig. 208. SIEMENS' MAGNETO-ELECTRIC KEY.
In Siemens & Halske's key an H armature E is pivoted between the poles N
S, of a powerful compound horseshoe magnet, G G. It is wound with fine
wire and a key handle H is provided for working it. In its normal
position the handle is drawn upward, and the end S S of the armature
core is in contact with the south pole S of the permanent magnet, and
the end D D with the north pole. This establishes the polarity of the
armature. On depressing the key the contacts are broken and in their
place the end D D comes in contact with the south pole and the end S S
with the north pole. This suddenly reverses the polarity of the armature
and sends a momentary current through the armature coil which is in
circuit with the line. The cut only shows the principle of the key,
whose construction is quite complicated.