18WuD2x

592 rejection notch • reluctance motor
rejection notch A sharp dip in the transmission
characteristic of a crystal filter. It provides rejection-filter
action at the notch frequency. Also see
CRYSTAL RESONATOR and REJECTION FILTER.
rejectivity The degree to which a selective circuit
rejects an unwanted signal. Compare TRANSMIT-
TIVITY.
rejuvenation See REACTIVATION.
rel Symbol, R. The cgs unit of reluctance, equivalent
to gilberts per maxwell.
relative accuracy In a measuring instrument, the
error determined as a percentage of the actual
value; the difference between the actual and measured
values, divided by the actual value, then
multiplied by 100.
relative address In the address part of a computer
program instruction, a number specifying a location
relative to a BASE ADDRESS. When the base
address is added to the relative address, it yields
the ABSOLUTE ADDRESS.
relative error The ratio of the absolute error to the
exact value of a quantity.
relative gain The current, voltage, or power gain,
measured, with respect to a reference standard.
relative humidity Abbreviation, rh. The ratio, as a
percentage, of the amount of moisture in the air
to the amount the air could contain at a given
temperature. Compare ABSOLUTE HUMIDITY.
relative luminosity Luminosity measured with respect
to a reference level.
relative permeability The ratio of the permeability
of a given material to the permeability of another
material (or of the same material under different
conditions).
relative power Power level specified with respect
to another (often reference) power level.
relative uncertainty The uncertainty of a measurement
divided by the measured value. The
maximum value that this quotient can have is 1.
Also see UNCERTAINTY IN MEASUREMENT.
relative visibility Response of the human eye to
light. This is relative because the eye does not see
equally well throughout the visible spectrum. The
peak response of the human eye is around 5.4 ×
10 14 Hz; this represents yellow-green light. Photoelectric
devices have peak responses that can differ
considerably from this value.
relativity theory See EINSTEIN’S THEORY.
relaxation A delayed change in circuit conditions,
as a result of change in the input.
relaxation inverter An inverter circuit in which
the direct-to-alternating-current conversion device
is a RELAXATION OSCILLATOR.
relaxation oscillator An oscillator whose operation
results from the buildup of a charge in a capacitor,
followed by sudden discharge of the capacitor,
the sequence being repeated periodically. In one
circuit, a capacitor is connected in series with a
resistor and a direct-current power supply, and a
neon bulb is connected in parallel with the capacitor.
The output is a sawtooth wave.
relaxation time 1. The time required for an exponentially
decreasing variable to fall to 1/e (approximately
36.8 percent) of its initial value,
where e is the natural-logarithm base (approximately
2.71828). 2. For a gas, the time required
for it to return to its original state after having
been disturbed.
relay 1. A signal-actuated switching device. In
most instances, a relatively weak current or voltage
is used to make the relay switch a higher current
or voltage. A relay can be electromechanical
or fully electronic (no moving parts). See, for example,
ELECTROMECHANICAL RELAY and
ELECTRONIC RELAY. 2. A repeater station. 3. In
communications, to receive a message and retransmit
it en route from a source to a destination.
relay amplifier See RELAY DRIVER.
relay booster See RELAY DRIVER.
relay driver A direct-current amplifier (usually one
stage) used to actuate an electromechanical relay
in response to a low-powered signal.
relay flip-flop See BISTABLE RELAY.
relay logic Abbreviation, RL. In computer and
industrial-control operations, a logic system using
electromechanical relays as flip-flops (see
BISTABLE RELAY).
relay transmitter See AUTOMATIC REPEATER
STATION.
release time 1. The interval between the instant
power is removed from a relay and the instant
the armature is released sufficiently to operate
the contacts. 2. The time between one control input
becoming inactive and another becoming active.
3. The time required for reception to
resume in a transceiver, once transmission has
stopped. 4. An expression for the rapidity with
which an automatic gain control reverts to maximum
sensitivity following the reception of a
strong signal.
reliability 1. The dependability of operation of a
device or circuit under specified conditions.
2. The proportion of units that still work after a
set of units has been in use for a specified length
of time.
reliability engineering The branch of engineering
devoted to the theory and application of reliability;
based on fundamental engineering and advanced
statistical concepts.
reluctance Symbol, R. SI unit, A/Wb; cgs unit, rel.
In a magnetic circuit, the opposition to the establishment
of a magnetic field; it is analogous to resistance
in electric circuits.
reluctance motor An electric motor having a
squirrel-cage rotor with some of its teeth ground
down, and a shaded-pole or split-phase type of
stator that supplies a rotating magnetic field.
When starting, this motor comes up to speed like
an induction motor, but the protruding teeth of
the rotor then follow the field in the manner of the
poles of a hysteresis motor.