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impedance-matching transformer • impulse ratio 357
impedance-matching transformer See IMPED-
ANCE TRANSFORMER.
impedance meter See Z METER.
impedance plethysmograph An electronic device
used to measure changes in the chemical content
of body cells.
impedance poles See POLES OF IMPEDANCE.
impedance ratio The quotient of two impedances
that are related in some situation, such as
impedance match or impedance mismatch. The
impedance ratio of a transformer is equal to the
square of the turns ratio.
impedance transformer 1. A transformer for converting
an impedance to a different value. The
turns ratio is equal to the square root of the
impedance ratio. 2. An emitter follower or source
follower circuit, used primarily to match a high
impedance to a lower impedance. 3. A shortcircuited
transmission-line section used to match
or convert impedances at radio frequencies.
Z p Primary Secondary Z s
T = N pri /N sec
impedance transformer
impedance triangle A triangular vector diagram in
which the impedance vector is the hypotenuse,
and the reactance and resistance vectors are the
perpendicular sides.
−R
+X L
Z
R
X
+R
imperfection A fault in the lattice of a crystal. Also
see CRYSTAL LATTICE.
implementation 1. Putting a system into operation
and evaluating its performance. 2. Doing
all that is necessary to install a device or system.
implosion The inward collapse of an evacuated
chamber, such as the envelope of a cathode-ray
tube. It is the opposite of explosion, an outward
bursting.
impregnant A substance for the IMPREGNATION
of electronic components. Examples: waxes, oils,
liquid plastics, and varnish.
impregnation The process of filling the spaces
within a material or structure with an insulating
compound. Various electronic components, such
as capacitors, inductors, transformers, transistors,
and diodes, are impregnated for protection
and stability.
impressed voltage The voltage applied or presented
to a circuit or device.
impulse 1. A signal of extremely short duration
(e.g., a noise burst). 2. A brief, unidirectional
surge in voltage (usually) or current.
impulse excitation Driving a tank circuit with a
single pulse, then allowing it to oscillate at its
own frequency until another driving pulse arrives.
impulse frequency In a digital telephone, the
number of pulse periods per second, corresponding
to a dialed digit, generated by the pulse
springs.
impulse generator See MARX GENERATOR.
impulse noise Electrical noise from short-duration
pulses, such as those produced by an automotive
ignition system.
impulse ratio The ratio V p /V s , where V p is the
breakdown (or flashover or sparkover) voltage
caused by an impulse, and V s is the corresponding
voltage at the crest of the power-frequency
cycle.
−X c
impedance triangle
impedance vector In a vector diagram, the resultant
(vector) representing the combined reactance
and resistance vectors. Also see IMPEDANCE
TRIANGLE.
impedance zeros See ZEROS OF IMPEDANCE.
imperative macroinstruction A MACROIN-
STRUCTION used to create object (machine language)
program instructions.
imperative statement A source language program
instruction that is converted into object program
(machine language) instructions.