Key, Charge and Discharge.
A key for use in observing the discharge of a condenser immediately
after removing the battery. In one typical form it has two contacts, one
below and one above, and being a spring in itself is pressed up against
the upper one. Connections are so made that when in its upper position
it brings the two coatings of the condenser in circuit with the
galvanometer. When depressed it does the same for a battery. In use it
is depressed and suddenly released when the galvanometer receives the
full charge, before there has been time for leakage. This is one method
of connection illustrating its principle.
In the cut L is the spring-key proper. S2, is the upper contact screw
against which the spring normally presses. In this position the
galvanometer G is in circuit with the opposite coatings of the condenser
C. On depressing the contact S2, is broken and S1, is made. This brings
the battery B in circuit with the condenser coatings. On releasing the
key it springs up and the galvanometer receives the effect of the charge
of the condenser as derived from the battery.
Key, Double Contact.
A key arranged to close two distinct circuits, holding the first closed
until the second is completed. It is used for Wheatstone bridge work.
Key, Double Tapper.
A telegraph key giving contacts alternately for currents in opposite
directions, used in needle telegraphy.
Key, Increment.
A key for use in duplex and quadruplex telegraphy. Its action is to
increase the line current, not merely to suddenly turn current into it.