18WuD2x

86 bridge-type meter • British Standard wire gauge
its adjustable arm can be calibrated to read the
frequency directly.
bridge-type impedance meter An impedancemeasuring
circuit in which unknown impedance
Z is connected in series with a calibrated variable
resistor R. An ac voltage is applied to the series
circuit. The separate voltage drops across the resistor
and impedance are measured successively
as the value of R is varied. When the two voltage
drops are identical, Z equals R, and the
impedance can be read from a calibrated dial on
the variable-resistor control.
bridge-type oscillator A resistance-capacitance
(RC) tuned oscillator in which a Wien bridge is
used as the frequency-determining circuit in the
feedback loop.
bridge-type power meter 1. See BOLOMETER
BRIDGE. 2. A four-arm bridge specially designed
to operate at radio frequencies. At null, the
impedance of the unknown is read directly from
the balancing dial or calculated from bridge constants.
This instrument is used to measure the
impedance of circuit components, antennas, and
transmission lines.
bridge-type SWR meter A four-arm bridge that is
specially designed to operate at radio frequencies.
At null, the standing-wave ratio (SWR) is calculated
from the bridge resistance values or read
from a direct-reading scale on the null-indicating
meter.
bridging amplifier An amplifier whose input impedance
is so high that it can be considered infinite
for practical purposes. Thus, the amplifier
can be connected across a load or line without
significantly affecting the operation of the system.
bridging coupler A voltage-dependent resistor that
permits an occasionally used device (such as a bell)
to be connected permanently across a regularly
used device (such as a telephone) without continuously
short-circuiting the latter. Thus, the bridging
coupler ordinarily has very high resistance; but
when the line voltage is momentarily raised, the resistance
lowers and the occasionally used device is
actuated (e.g., the bell rings).
bridging gain The gain of a bridging amplifier expressed
as the ratio (in decibels) of the power developed
in the amplifier load to the power in the
load to which the input terminals of the amplifier
are connected.
bridging loss The loss that results from the shunting
of a speaker, microphone, earphone, or other
transducer by a resistor, capacitor, or inductor.
Generally, the loss is expressed as a power ratio
in decibels.
Briggsian logarithm (Henry Briggs, 1556-1631). A
base-10 logarithm, generally known as a
COMMON LOGARITHM. Compare NAPIERIAN
LOGARITHM.
brightness SI unit, candela per square meter
(cd/m 2 ); cgs unit, lambert (L). The quantity of
light, per unit area, emitted or reflected perpendicular
to a light-emitting surface.
brightness control 1. In a computer monitor, television
receiver, or oscilloscope, a potentiometer
that varies the negative bias voltage on the control
grid of the cathode-ray tube (CRT). The
brightness of the image is inversely proportional
to this negative bias voltage. 2. The control of the
brightness of an illuminated area.
brilliance See BRIGHTNESS.
brilliance control 1. The BRIGHTNESS CONTROL
in a television receiver or computer monitor. 2.
The brightness control in a cathode-ray oscilloscope.
3. A control for adjusting the level of the
tweeter output in a speaker system.
British Standard wire gauge Abbreviation, NBS
SWG. A classification of wire sizes sometimes
used in England, Australia, and New Zealand.
The higher the number, the thinner the wire. The
designator does not take into account any coatings
on the wire, such as enamel, rubber, or plastic
insulation. In the United States, the American
wire gauge is more often used. See AMERICAN
WIRE GAUGE.
British Standard Wire Gauge (NBS SWG) Diameters
NBS SWG Millimeters Inches
1 7.62 0.300
2 7.01 0.276
3 6.40 0.252
4 5.89 0.232
5 5.38 0.212
6 4.88 0.192
7 4.47 0.176
8 4.06 0.160
9 3.66 0.144
10 3.25 0.128
11 2.95 0.116
12 2.64 0.104
13 2.34 0.092
14 2.03 0.080
15 1.83 0.072
16 1.63 0.064
17 1.42 0.056
18 1.22 0.048
19 1.02 0.040
20 0.91 0.036
21 0.81 0.032
22 0.71 0.028
23 0.61 0.024
24 0.56 0.022
25 0.51 0.020
26 0.46 0.018
27 0.42 0.0164
28 0.38 0.0148
29 0.345 0.0136
30 0.315 0.0124
31 0.295 0.0116
32 0.274 0.0108