18WuD2x

floating probe • fluorescent materials 291
floating probe A test electrode (wire or plate) inserted
in a discharge tube at a desired point to
sample the potential gradient, but which acquires
a misleading negative charge, with respect to the
gas cloud, because electrons (traveling faster
than the positive ions) tend to accumulate on the
probe.
floating zero A control system in which the reference
point is easily moved.
floating zone In a semiconductor ingot undergoing
purification, a molten zone in which impurities
float. The material in the zone is melted by the
radio-frequency (RF) field of an external heating
coil, which is passed along the ingot to move the
molten zone to one end, picking up impurities
along the way and concentrating them at the end
that is later sawed off.
float switch A switch operated by a float, such as
in a sump pump.
flocking 1. Particulate felt used on phonograph
turntables to protect disks from being scratched.
2. To coat with flocking.
flood gun In a storage (image-holding) oscilloscope,
the electron gun that sprays the storage
target with low-velocity electrons and makes the
image visible on the viewing screen. The gun is
mounted next to one pair of deflection plates.
Compare WRITING GUN.
floor stand A support for a microphone, consisting
of a heavy base that rests on the floor, and an adjustable,
vertical boom that allows the microphone
to be set at various heights.
floppy disk A flexible magnetic disk used in
recording, as in computer and data system storage.
It usually refers to a 5.25-inch diskette.
flow 1. The movement of current carriers under
the influence of an electric field. 2. See ANGLE
OF CONDUCTION. 3. A series of interrelated
events in a time sequence.
flow angle See ANGLE OF CONDUCTION.
flowchart 1. A diagram depicting the logic steps in
a digital-computer program. 2. A diagram showing
the flow of material through a sequence of
processes.
flow direction The method of delineating antecedent
and successor events on a flowchart;
usually arrows and flowlines connecting the
events in the way a page is read (top to bottom,
left to right).
flowed-wax disk A form of recording disk, in which
wax is melted onto a plastic or metal base. The
grooves are cut in the wax layer.
flowline A line showing flow direction on a
flowchart.
flowmeter An instrument for measuring liquid
flow rate.
flow relay A relay that is actuated by a predetermined
rate of fluid flow.
fluctuating current See COMPOSITE CURRENT.
fluctuating voltage See COMPOSITE VOLTAGE.
fluid absorption See LIQUID ABSORPTION.
fluid analogy The comparison of electric current
flow to the movement of a simple fluid. Also see
WATER ANALOGY.
fluid capacitor See WATER CAPACITOR.
fluid computer A digital computer that uses fluid
logic elements (i.e., one that contains no electronic
circuits or moving parts).
fluid damping Use of a viscous fluid to damp a mechanical
member’s movement.
fluid-flow alarm An electronic circuit that actuates
an alarm when fluid flowing through pipes or other
channels changes from a predetermined rate.
fluid-flow control A servo system that automatically
maintains or adjusts liquid flow through
pipes or other channels.
fluid-flow gauge See FLUID-FLOW METER.
fluid-flow indicator See FLUID-FLOW METER.
fluid-flow meter An instrument that indicates
fluid flow rate through pipes or other channels.
fluid-flow switch In a fluid-cooled system, a
switch that actuates an alarm when the fluid
slows or stops.
fluidics 1. A form of digital logic in which circuits
operate by means of fluid flow. 2. A branch of
physics concerned with the behavior of fluids;
more commonly called fluid dynamics.
fluid-level control A servo system that automatically
maintains the level of a fluid in a tank.
fluid-level gauge An electronic system that provides
direct readings of the level of a fluid in a tank.
fluid-level indicator See FLUID-LEVEL GAUGE.
fluid logic Logic operations carried out by varying
the flow and pressure of a gas or liquid in a circuit
of channels. Also see FLUID COMPUTER.
fluid ounce (U.S.) Abbreviation, fl. oz. A unit of volume
equal to 2.957 × 10 –5 cubic meters, or
0.02957 liter. A quart is 32 ounces; a gallon is
128 ounces.
fluid-pressure alarm An electronic circuit that actuates
an alarm when fluid pressure rises or falls
beyond set limits.
fluid-pressure control A servo system that automatically
maintains or adjusts fluid pressure in
pipes or other channels.
fluid-pressure gauge See FLUID-PRESSURE ME-
TER.
fluid-pressure indicator See FLUID-PRESSURE
METER.
fluid-pressure meter An instrument that indicates
the pressure of a fluid in a pipe or other channel.
fluid valve See ELECTROMECHANICAL VALVE.
fluorescence The property of some materials to
glow when excited by a stimulus, such as ultraviolet,
X rays, or an electron beam. Compare
PHOSPHORESCENCE.
fluorescent lamp See FLUORESCENT TUBE.
fluorescent materials Materials that glow when
irradiated, but cease to glow when the source of
excitation is removed. An example is the phosphor
coating on the screen of a cathode-ray tube
(CRT).