18WuD2x

depth of discharge • designation 179
to which discharging has occurred. It is generally
specified as a percentage. For example, if the
DOD of a 10-ampere-hour (10-AH) battery is 80
percent, then 8 AH have been used up, and 2 AH
remain before recharging will be necessary.
depth of heating In dielectric heating, the depth of
heat penetration in the sample when both electrodes
are applied to one of its faces.
depth of modulation The degree to which a carrier
wave is modulated.
depth of penetration The extent to which a skineffect
current penetrates the surface of a conductor.
depth sounder See ACOUSTIC DEPTH FINDER.
de-Q 1. To reduce the Q of a component or tuned
circuit. 2. To inhibit laser action during an
interval when an ion population excess is
pumped up.
derating To reduce an operating parameter (e.g.,
current, voltage, power) as another factor (such
as temperature) increases, to ensure efficient, reliable,
and safe operation.
derating curve A graph that shows the extent to
which a quantity (such as allowable power dissipation)
must be reduced as another quantity
(such as temperature) increases.
derating factor The amount by which a current,
power, or voltage must be decreased to ensure
safe and efficient operation of a circuit or device
in a given environment (temperature, altitude,
humidity, etc.). Also see DERATING and DERAT-
ING CURVE.
derivative
1. A mathematical expression indicating
the rate at which a function changes, with
respect to the independent variable. See
DERIVATIVE FUNCTION. 2. The slope of a line
tangent to a curve at a given point. 3. The output
signal of a DIFFERENTIATOR, relative to the
input signal.
derivative action In a control system, an action
producing a corrective signal proportional to the
dy
dx =
(Positive)
y
dy
dx =
derivative
dy
dx = 0
(Negative)
x
rate of change (derivative) of the controlled
variable.
derivative control A method of automatic control,
actuated according to the number of errors per
second.
derivative function For a mathematical function
f (x), the function f '(x) = df (x)/dx, over the domain
of f. For any specific point x 0 in the domain of f,
the value of f '(x 0 ) is equal to the slope of a line
tangent to f at the point (x 0 , f (x 0 )).
derived center channel The sum or difference of
the left and right channels in a stereophonic system.
Dershem electrometer A variation of the quadrant
electrometer. In the Dershem instrument, the
needle (to which a small mirror is attached) rotates
within slots cut in the quadrant plates and,
therefore, can never accidentally touch the
plates.
descending node For a satellite orbiting the earth
or another planet, any point at which the groundtrack
crosses the equator as it moves from the
northern hemisphere into the southern hemisphere.
This node generally changes for each succeeding
orbit, because the earth or planet rotates
underneath the orbit of the satellite. Compare
ASCENDING NODE.
descending pass For a specific point on the earth’s
surface, the time during which an artificial communications
satellite is accessible when its latitude
is moving southward. The duration of
accessibility depends on the altitude of the satellite
and on how close its groundtrack comes to
the earth-based point. Compare ASCENDING
PASS.
description A data element that is part of a record
and is used to identify it.
desensitization 1. The process of making a circuit
or device less responsive to small values of a
quantity. 2. Also called desensing. In a communications
receiver, an unwanted, often intermittent
reduction in front-end gain, caused by an extremely
strong local signal.
desensitize 1. To reduce the sensitivity of a receiver.
2. To reduce the gain of an amplifier. 3. To
reduce the small-quantity response of an instrument.
desiccant A compound, such as cobalt chloride,
used for the purpose of keeping enclosed items
dry.
design 1. A unique, planned arrangement of electronic
components in a circuit, in accordance
with good engineering practice, to achieve a desired
end result. 2. A unique layout of components
or controls, in accordance with good
engineering practice, esthetics, and (often) ergonomics.
3. Invention. 4. Plan. 5. To produce a
design, as defined in 1, 2, 3, or 4.
designation Within a computer record, coded information
identifying the record so that it can be
handled accordingly.