18WuD2x

142 constant-current supply • contactor noise
constant-current supply See CONSTANT-
CURRENT SOURCE.
constant-current transformer A transformer supplied
from a constant-voltage source that automatically
delivers a constant current to a varying
secondary load.
constant-k filter Also called a Zobel filter. A filter
section in which Z 1 Z 2 equals k 2 at all frequencies,
where Z 1 is the impedance of the series element
and Z 2 is the impedance of the shunt element.
constant-power dissipation line A line connecting
points on a family of current-voltage characteristic
curves, the points corresponding to the
maximum power that can safely be dissipated by
the device to which the curves apply.
constant-resistance network A circuit of resistors
that, when terminated in a resistance load, presents
a constant resistance to a driving source
under various conditions of operation.
constant-speed motor 1. Also called a shunt motor.
A motor whose speed varies little, or not at all,
with variations in the armature current. 2. A motor
that runs at an unvarying speed through the
action of associated automatic electronic control
circuitry.
constant voltage A voltage that does not change
as the load resistance varies. Compare CON-
STANT CURRENT.
constant-voltage, constant-current supply A
combination current-regulated and voltageregulated
power supply; delivers constant current
to low load resistances and constant voltage
to high load resistances.
constant-voltage drive Driving power obtained
from a CONSTANT-VOLTAGE SOURCE.
constant-voltage source A power supply whose
output voltage remains steady during variations
in load current. Also called constant-voltage supply
and voltage-regulated supply.
constant-voltage transformer A special transformer
used to reduce variations in power-line
voltage. A capacitor in the device causes a winding
to resonate at the line frequency (e.g., 60 Hz). This
tends to maintain a more constant current than
would be the case in an ordinary transformer.
construct A source (user’s) computer program
statement that, when implemented, produces a
predetermined effect.
consumer reliability risk 1. The chance a consumer
takes when buying a component or piece
of equipment that has not been subjected to
quality-assurance/quality-control (QA/QC) testing.
2. An expression of the failure rate for a consumer
item.
contact 1. A conducting body (such as a button,
disk, or blade) that serves to close an electric circuit
when pressed against another conductor.
Example: switch contact and spring contact. 2.
The state of being touched together, as when two
conductors are brought into contact to close a
circuit.
contact arc The arc that initially occurs when
current-carrying contacts are separated.
contact area 1. The face of an electrical contact.
2. The common area shared by two conductors in
mutual contact.
contact bounce The springing apart or vibration of
contacts upon making or breaking.
contact chatter The abnormal vibration of mating
contacts, caused by contact bounce or by an extraneous
alternating current.
contact-closure input The input circuit of a device,
such as a control-system amplifier, that is
actuated by the closing of switching contacts.
Compare CONTACT-OPEN INPUT.
contact combination The set of contacts on a
switch or electronic relay.
contact detector A rectifier or demodulator, composed
of two dissimilar materials in contact with
each other. Semiconductor diodes are of this general
type. Some contact-detector action can be
obtained with two dissimilar fine wires (such as
copper and iron) by touching their tips lightly together.
contact EMF Short for contact electromotive force;
also called contact potential. A low direct-current
(dc) voltage that is sometimes generated by the
contact of two dissimilar materials.
contact follow The tendency of relay contacts to
follow the actuating signals.
contact force 1. The force with which relay contacts
close with a given amount of coil current. 2.
The force with which a pair of relay contacts are
held together when current flows through the
coil. 3. In a mercury-wetted relay, the force exerted
by the mercury on the contacts as the relay
closes.
contact gap The distance between contacts when
they are open.
contact load 1. The power dissipated by a load
that is connected to a power supply through a
closed set of contacts. 2. The current passing
through a set of closed contacts.
contact microphone A microphone placed in direct
contact with a vibrating surface for pickup.
Actuated by the vibration of a solid, rather than
by the movement of air molecules.
contact miss 1. The improper alignment of contacts
in a switch or relay. 2. The condition of relay
contacts not lining up properly.
contact modulator An electromechanical CHOP-
PER.
contact-open input The input circuit of a device,
such as a control-system amplifier, that is actuated
by the opening of switching contacts. Compare
CONTACT-CLOSURE INPUT.
contactor A switch used for frequent opening or
closing of a circuit. An example is a relay contactor
used for keying a transmitter.
contactor noise 1. Electrical noise that is the
product of make-and-break contact action or
fluctuations in conduction when the contacts are