18WuD2x

494 on-state resistance • open-frame machine
on-state resistance The resistance of a voltagedependent
resistor that is conducting current.
on-state voltage The voltage drop across a semiconductor
device (such as a diode, rectifier, or
thyristor) when the device is conducting current.
Also see ON-STATE CURRENT.
on the air 1. The state of a radio station that is
transmitting. 2. In broadcasting, the condition in
which the transmitter is operational and the
sound and/or video from the studio is being disseminated.
on time The length of time a switch or switching
device (such as a flip-flop) remains on.
on voltage See ON-STATE VOLTAGE.
OOP Abbreviation of OBJECT-ORIENTED PRO-
GRAMMING.
op 1. Abbreviation of OPERATE. 2. Abbreviation of
operator (see OPERATOR, 1). 3. Abbreviation of
OPERATION. 4. Abbreviation of operational.
opacimeter 1. An instrument for measuring the
extent to which a material blocks light. 2. An instrument,
such as a field-strength meter, used to
measure the effectiveness of an electrical shielding
material in blocking radio waves, X rays, or
other radiation.
opacity The condition of being opaque. This applies
to all forms of radiation. For example, a
material can be opaque to light rays, but be
transparent to radio waves, or it can be transparent
to gamma rays while being opaque to alpha
particles.
op amp See OPERATIONAL AMPLIFIER.
op code Abbreviation of OPERATION CODE.
open-air line See OPEN-WIRE LINE.
open-back cabinet A loudspeaker enclosure in
which the space behind the speaker is open to the
room.
open capacitance The value of a variable capacitor
whose rotor plates have been rotated completely
out of mesh with the stator plates. Compare
CLOSED CAPACITANCE.
open-center display A radar display in which a
ring around the center indicates zero range.
open-chassis construction A method of assembling
electronic equipment by mounting components
and wiring them on an unenclosed chassis,
often without a front panel. Similar to breadboard
construction.
open circuit 1. A discontinuous circuit (i.e., one
that is broken at one or more points and, consequently,
cannot conduct current nor present a
voltage at its extremities). Compare CLOSED
CIRCUIT. 2. Pertaining to no-load conditions, for
example, the open-circuit voltage of a battery.
3. For a bipolar transistor, the operating characteristics
under independent input and output conditions.
open circuit breaker A circuit breaker whose contacts
are open.
open-circuit current Current flowing in the primary
winding of an unloaded transformer.
open-circuited line See OPEN-CIRCUITED
TRANSMISSION LINE.
open-circuited transmission line Abbreviation,
OCTL. An unterminated transmission line in
which the conductors at the far end are not connected
together.
open-circuit impedance For a transmission line
or a four-terminal network, the input or drivingpoint
impedance when the output end of the line
or network is open-circuited.
open-circuit jack A telephone jack that introduces
a break in a circuit until a plug connected to a
closed external circuit is inserted.
open-circuit plug See OPEN PLUG.
open-circuit resistance For a four-terminal network,
the input or driving-point resistance when
the output end of the network is unterminated.
open-circuit signaling A system of signaling in
which no current flows until the signal circuit is
in active operation. In a simple telegraph circuit,
for example, current flows only when the key is
pressed (to form a dot or dash).
open-circuit alarm system A security system in
which all the actuating sensors are normally
open and connected in parallel. When one of the
sensors is actuated, it closes, causing a short circuit
that triggers the alarm.
open-circuit voltage See NO-LOAD VOLTAGE.
open-collector configuration In an integrated circuit,
an output scheme utilizing no internal pullup
resistor. Wired-OR outputs can thus have
opposite states without risk of damage to the device.
open component An open-circuit component (e.g.,
an open diode, coil, resistor, etc.).
open core A magnetic core having a cylindrical
shape. A disadvantage of this core configuration,
in some applications, is that much of the magnetic
flux extends outside the core. Compare
CLOSED CORE.
open-core choke A choke coil wound on an open
core. Also called OPEN-CORE INDUCTOR. Compare
CLOSED-CORE CHOKE.
open-core transformer A transformer wound on
an open core. Compare CLOSED-CORE TRANS-
FORMER.
open-delta connection See VEE-CONNECTION
OF TRANSFORMERS.
open-ended Pertaining to a circuit or device that
can be built upon without modifying its original
configuration.
open-end stub A stub that is neither shortcircuited
nor terminated at its far end.
open-end stub tuning Adjustment of an OPEN-
END STUB, by pruning its length, for optimum
operation at a given frequency.
open-entry contact In a connector, an unprotected,
opening contact of the female type.
open feeder See OPEN-WIRE LINE.
open-frame machine See OPEN GENERATOR and
OPEN MOTOR.