18WuD2x

220 dust-ignition-proof motor • dynamic debugging
dust-ignition-proof motor A motor whose housing
completely prevents the entry of dust, virtually
eliminating the danger of fine dust sparking
inside the machine.
dust precipitator An electrostatic device for removing
dust, lint, and other particles from the
air. It consists essentially of a pair of screens or
wires through which the air passes; a potential of
several thousand volts is maintained between
them. The particles acquire a charge, then stick
to the oppositely charged screen.
Dutch metal A copper-zinc alloy.
duty cycle 1. The proportion or percentage of
time during which a device, circuit, or system is
operating or handling power. For example, when
a radiotelegraph transmitter is keyed on and off
to send Morse code, the duty cycle is approximately
50 percent; with frequency-shift keying,
the duty cycle is 100 percent. 2. The conditions
under which an electrochemical cell or battery
is used. In particular, the proportion or percentage
of time during which current is drawn from
the cell or battery for the purpose of operating
an electrical or electronic circuit, device, or
system.
duty cyclometer A direct-reading instrument for
measuring duty cycle.
duty factor 1. The ratio P avg /P pk , where P avg is the
average power in a system and P pk is the peak
power. 2. The product of the duration and the
repetition rate of regularly recurring pulses comprising
a carrier.
duty ratio See DUTY FACTOR, 1.
DVM Abbreviation of DIGITAL VOLTMETER.
DVOM Abbreviation of DIGITAL VOLT-OHM-
MILLIAMMETER.
dwell meter An instrument that shows the period
(or angle) during which contacts remain closed.
dwell switching Switching action in which the
contacts are held closed (or a circuit kept on) for
specified periods, as opposed to MOMENTARY
SWITCHING.
dwell tachometer A combination dwell meter/
tachometer for automobile engine testing and adjustment.
The dwell meter allows observation and
adjustment of the ignition point cam angle; the
tachometer shows the motor speed in revolutions
per minute (rpm).
DX 1. Radiotelegraph abbreviation meaning long
distance or foreign country. 2. A communication
or broadcast station located far away and/or in a
foreign country. 3. Abbreviation of DUPLEX.
DXer An amateur radio operator who prefers to
communicate with stations far away and/or in
foreign countries.
Dy Symbol for DYSPROSIUM.
dyadic operation A binary operation (i.e., one using
two operands).
dyn Abbreviation of DYNE.
dyna- A prefix (combined form) meaning power
(e.g., dynamometer and dynatron).
dynamic acceleration Acceleration whose magnitude
and direction are constantly changing.
dynamic allocation In multiprogramming, a system
in which a monitor program assigns peripherals
and areas of memory to a program.
dynamic analogy A mathematical similarity between
or among various phenomena involving the
motion of particles.
dynamic base current See AC BASE CURRENT.
dynamic base resistance See AC BASE RESIS-
TANCE.
dynamic base voltage See AC BASE VOLTAGE.
dynamic behavior 1. The behavior of a component,
device, or system when signals are applied, as
opposed to static behavior under no-signal conditions.
2. The behavior of a device or system involving
the motion of particles over a period of time.
dynamic braking A technique for stopping a motor
quickly using a resistor (the dynamic braking resistance)
connected across the spinning armature.
The resistor dissipates the energy generated
by the motor, producing a damping action that
results in braking.
dynamic characteristic The performance characteristic
of a device or circuit under alternatingcurrent
(ac) operating conditions, as opposed to
the static characteristic, when only direct current
(dc) flows.
dynamic check 1. A test made under actual operating
conditions of a device or circuit. 2. A test
made with an alternating-current (ac) applied signal,
rather than with direct-current (dc) quantities.
dynamic collector current See AC COLLECTOR
CURRENT.
dynamic collector resistance See AC COLLEC-
TOR RESISTANCE.
dynamic collector voltage See AC COLLECTOR
VOLTAGE.
dynamic contact resistance In relay or switch
contacts, variation in the electrical resistance of
the closed contacts because of variations in contact
pressure.
dynamic convergence In a color picture tube, the
meeting of the three beams at the aperture mask
during scanning.
dynamic current amplification Abbreviation,
DCA. An expression of gain in a bipolar transistor.
Specified as the ratio of the difference in collector
current I C to the difference in base current I B
DCA = dI C /dI B
Geometrically, the dynamic current amplification
at a given bias point is the slope of a line tangent
to the I C -versus-I B curve at that point.
dynamic curve A characteristic curve that accounts
for the presence of resistance in series
with the device to which the curve applies.
dynamic debugging Any debugging operation performed
on a computer system during a normalspeed
program run.