18WuD2x

semitone • sequential 619
semitone See HALF STEP.
sender See TRANSMITTER, 1, 3.
sending-end impedance See DRIVING-POINT
IMPEDANCE.
sending set 1. See RADIO TRANSMITTER. 2. An
equipment for transmitting electromagnetic
waves. Also see TRANSMITTER, 1.
sensation level The level of sound that produces a
tingling or noticeable sensation in the ear.
sense 1. To check the condition of a switching device,
such as a gate. 2. See READ.
sense amplifier A device that produces a control
signal when some characteristic of the input signal
changes.
sense determination In a direction finder that
provides an ambiguous indication (two readings
180 degrees apart), the process of deducing, or
the ability of the apparatus to deduce, the true direction
from which the signal is coming.
sense resistor A (usually low-value) resistor used
to sense current in a circuit without introducing
a significant loss. The voltage drop across this resistor
is proportional to the current and can be
applied to a voltmeter, oscilloscope, or other instrument
for measurement or observation.
sensing circuit 1. A circuit that samples a quantity.
2. In a voltage regulator, the circuit that
monitors the output voltage and delivers a control
voltage proportional to the output-voltage error.
sensing window See WINDOW, 2.
sensitive communications Two-way communications
of an emergency or priority nature, or involving
the security of government operations.
sensitive device A device that responds to a signal
of low amplitude.
sensitivity 1. The ability of a circuit or device to
respond to a low-level applied stimulus. 2. For a
receiver, the input-signal (in microvolts or millivolts)
required for a specified output level. 3. For
a galvanometer, microamperes or milliamperes
per scale division. 4. The ohms-per-volt rating of
a voltmeter. Also see VOLTMETER SENSITIVITY.
sensitivity adjustment 1. An input gain control in
an amplifier circuit. 2. The radio-frequency gain
control of a receiver. 3. A control or switch that is
used to select the range or threshold of a piece of
test equipment.
sensitivity control A manual or automatic device
for adjusting the sensitivity of a circuit or device.
sensitometer An instrument used to measure the
sensitivity of certain materials to light.
sensor 1. A device that samples a phenomenon,
and delivers a proportionate current or voltage in
terms of which the intensity of the phenomenon
can be measured, or with which control action
can be initiated. 2. An electronic device that detects
abnormal conditions (e.g., smoke and heat)
and delivers a warning signal to human operators
and/or computers. 3. An electronic device that
detects intrusion to a premises and delivers a
warning signal to human operators and/or computers.
sentry robot In a smart home or business, a robot
that alerts the owner to abnormal conditions. It
can detect fire, burglars, or water in places it
should not be. It might also detect abnormal temperature,
barometric pressure, wind speed, humidity,
or air pollution. A wireless link alerts the
owner via a device similar to a common beeper.
Compare SECURITY ROBOT. Also see SMART
HOME OR BUSINESS.
separately excited generator An alternatingcurrent
generator whose field coils are supplied
with direct current from another generator or from
a battery. Compare SELF-EXCITED GENERATOR.
separately quenched detector A superregenerative
detector (see SUPERREGENERATIVE CIR-
CUIT) in which the quenching voltage is supplied
by a separate low-frequency oscillator. Also see
QUENCHING ACTION and QUENCH OSCILLA-
TOR. Compare SELF-QUENCHED OSCILLATOR.
separation See CHANNEL SEPARATION.
separation energy The energy required to remove
a proton or neutron from the nucleus of an atom.
The separation energy depends on the atomic
number.
separator 1. See FILTER, 1. 2. A perforated or
porous plate of insulating material (usually plastic
or wood) for holding active plates apart in a
storage cell. 3. In computer operations, a character
marking the division between logical data
units. Also called data delimiter.
septate cavity A coaxial cavity containing a SEP-
TUM between the inner and outer conductors.
septate waveguide A waveguide containing one or
more septa (see SEPTUM) to control power transmission.
septum A thin metal vane used as a reflector in a
waveguide or cavity.
sequence 1. A succession of objects, parameters,
or numbers. 2. An ordered set of numbers—each
of which is related to its predecessor by a specific
mathematical function.
sequence checking routine In computer operations,
a routine that verifies the order of items of
data.
sequence control register In a computer memory,
a register whose contents determine the instruction
to be implemented next.
sequence programmer A timing device that can be
preset to start or stop various operations at predetermined
times.
sequencer A device that initiates or terminates
events in a desired sequence.
sequence relay A relay whose several contacts
close in a predetermined order.
sequence timer A timer in which separate delay
circuits are actuated in a predetermined sequence.
sequential In computer operations, a term denoting
operations on data items in which the items