Page 488 - Instrumentation Reference Book 3E

The measurement of resistance, capacitance, and inductance 471
balanced bridge are at ground potential and thus tor in both positions. The balance conditions for
the effect of stray impedances at these points is the main bridge and the auxiliary arm are then
eliminated. This is achieved by means of an aux- given by
iliery arm of the bridge consisting of the elem-
ents Yj and Y,. The bridge is first balanced
with the detector between D and B by adjusting
Y3. The detector is moved between B and E and
the auxiliary bridge balanced by adjusting Y5 20.7.4 Transformer ratio bridges
and y6. This ensures that point B is at earth
potential. The two balancing processes are These bridges, which are also called inductively
repeated until the bridge balances with the detec- coupled bridges, largely eliminate the problems

Bridge Circuit Balance conditions Notes
R2
Maxwell Li=-L3
R4 Ratio bridge with inductive and
resistive standards for the
1 R2
Rj=-R3 measurement of the series inductance
R4 and resistance of an unknown
inductor; balance condition is
frequency independent and therefore
purity of source is unimportant; a
parallel form of the bridge can be
used to measure the parallel
components of an unknown
inductance

Maxwell-Wien L1 =R2R3C4
Product bridge employing capacitive
and resistive standards for the
R2R3
R1=- measurement of the series inductance
R4 and resistance of an unknown
01 =wC4R4 inductor; widely used for the
measurement of inductance; if C4 and
R4 are variable bridge measures L1
and R1; if R4 and R2 or R3 are
variable bridge measures 61 and Q1
R2R3C4
Hay L,=-
1 + a2C;?Rj Product bridge employing capacitive
and resistive standards for the
R1= R2R3w2C'R' measurement of the series inductance
(' +w2CjRa) and resistance of an unknown
1 inductor; suitable for the
0, measurement of ax. inductance in
=-
WC4R4
the presence of d.c. bias current;
used for the measurement of
inductances with high 6 and 0
Owen L1= CdR,. R2
Ratio bridge employing capacitive
and resistive standards for the
1 1
G, = -= c, measurement of the series inductance
Rl C4R3 and conductance of an unknown
inductor; used as a high-precision
bridge