18WuD2x

736 voltaic series • volume-limiting amplifier
voltaic series See ELECTROMOTIVE SERIES.
voltameter An electrolytic cell for determining the
value of an unknown current, or of an unknown
quantity of electricity, from the weight of metal
deposited out of an electrolyte onto the cathode
by the passage of current over an accurately
timed interval.
volt-ammeter A combination meter for measuring
electrical voltages and currents.
volt-ampere Symbol, VA. Unit, watt. The simple
product of voltage and current in volts and amperes,
yielding the true power in a direct-current
circuit and the apparent power in an alternatingcurrent
circuit. Also see APPARENT POWER and
TRUE POWER.
volt-ampere-hour meter See VAR-HOUR METER.
volt-ampere meter See VAR METER.
volt-amperes reactive Abbreviation, VAR. The
product of volts and amperes for a purely reactive
circuit. This product does not produce the true
power because the power factor is neglected; it
produces only the apparent power. A true reactance
absorbs power during one half-cycle of alternating
current, and returns it to the generator
during the next half-cycle.
Volta’s law See VOLTA’S PRINCIPLE.
Volta’s pile See VOLTAIC PILE.
Volta’s principle Two dissimilar metals brought
into contact (even in air) will generate a difference
of potential whose value is characteristic of the
metals. Also see ELECTROMOTIVE SERIES.
volt box A precision, potentiometer-type voltage
divider used in the calibration of meters and
other instruments. The device is usually provided
with a set of terminal posts for selecting various
ratios of output voltage to input voltage.
volt-electron See ELECTRONVOLT.
voltmeter A usually direct-reading instrument
used to measure voltage. Also see ELECTRONIC
VOLTMETER, FET VOLTMETER, TRANSISTOR
VOLTMETER, and VACUUM-TUBE VOLTMETER.
voltmeter-ammeter See VOLT-AMMETER.
voltmeter amplifier A wideband, flat-frequencyresponse,
low-distortion preamplifier used to
boost the sensitivity of an alternating-current
voltmeter.
voltmeter-millivoltmeter A voltmeter that provides
several low ranges, as well as several high
ones. A familiar example is an alternatingcurrent
voltmeter, which has various full-scale
ranges from about 1 millivolt to about 1000 volts.
voltmeter multiplier A resistor connected in series
with a current meter (usually a milliammeter
or microammeter) to convert it into a voltmeter.
voltmeter sensitivity Unit, ohm per volt. For a
voltmeter, the total resistance of the instrument
(multiplier resistance plus the resistance of the
meter movement) divided by the full-scale deflection
of the meter. Thus, a 0-to-10 direct-current
voltmeter with an input resistance of 100 kilohms
has a sensitivity of 10,000 ohms per volt.
volt-milliammeter A combination meter for measuring
volts and milliamperes.
volt-ohm-ammeter A multimeter for measuring
voltage, resistance, and current (in amperes).
volt-ohmmeter A combination meter for measuring
voltage and resistance.
volt-ohm-milliammeter Abbreviation VOM. A
multimeter for measuring voltage, resistance,
and current (in milliamperes and microamperes).
voltsensor See VOLTAGE DETECTOR.
volts per meter Abbreviation, V/m or Vpm. The
unit of electric field strength.
volume 1. Intensity of sound. Also called LOUD-
NESS. 2. A circumscribed portion of space, either
imaginary or actually occupied, and described by
three dimensions (e.g., sphere, ellipsoid, cube,
pyramid, etc.). 3. In a computer system, a unit of
magnetic storage medium (e.g., a diskette).
volume compression The automatic reduction of
the gain of an audio amplifier. The process differs
from clipping (which “slices off” the tops of waves)
in that compression (ideally) reduces the amplitude
while preserving the waveform. Compare
VOLUME EXPANSION.
volume compressor A circuit or device (such as an
automatic-gain-control amplifier) for achieving volume
compression. Compare VOLUME EXPANDER.
volume conductivity The reciprocal of VOLUME
RESISTIVITY.
volume control A variable resistor (usually a potentiometer)
or a network of resistors (such as a
pad) for adjusting the gain, and, consequently,
the output-signal loudness, of an amplifier.
volume equivalent In wire telephony, speech
loudness throughout the system, expressed in
terms of the trunk loss in a reference system and
adjusted for equal loudness.
volume expander A circuit or device for automatically
boosting the volume of an audio-frequency
signal. Also see EXPANDER. Compare VOLUME
COMPRESSOR.
volume expansion The technique of automatically
increasing the gain, and consequently the
output-signal volume, of an audio amplifier. Also
see VOLUME EXPANDER. Compare VOLUME
COMPRESSION.
volume indicator A fast-acting alternatingcurrent
meter used to monitor the volume level in
an audio channel in which the signal level is
fluctuating. The scale is graduated in VOLUME
UNITS. Also called VU meter.
volume lifetime In a homogeneous semiconductor,
the interval between minority-carrier generation
and recombination.
volume limiter A circuit or device that automatically
holds the volume level of an audio channel
to a predetermined maximum. Also see VOLUME
COMPRESSION and VOLUME COMPRESSOR.
volume-limiting amplifier An amplifier that functions
as a volume limiter through the action of
volume-limiting subcircuits.