Datasheet

OP1177/OP2177/OP4177
Rev. G | Page 20 of 24
0
2627-065
200Ω
500Ω
4.37kΩ
100Ω
100Ω 20Ω
4.12kΩ
4.12kΩ
5kΩ
49.9kΩ
ADR421
+15
V
0.1µ
F
V+
100Ω
RTD
1/2
OP2177
7
6
5
1/2
OP2177
1
8
2
3
4
V–
V
OU
T
V
OUT
where δ = ∆R/R is the fractional deviation of the RTD resistance
with respect to the bridge resistance due to the change in temper-
ature at the RTD.
For δ << 1, the preceding expression becomes
δ
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
+
⎟
⎠
⎞
⎜
⎝
⎛
+
⎟
⎠
⎞
⎜
⎝
⎛
=
⎟
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎜
⎝
⎛
++
δ
⎟
⎠
⎞
⎜
⎝
⎛
≅
REF
REF
O
V
R2
R1
R2
R1
R
R2
R2
R1
R
R1
V
R
R2
V
1
1
With V
REF
constant, the output voltage is linearly proportional
to δ with a gain factor of
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
+
⎟
⎠
⎞
⎜
⎝
⎛
+
⎟
⎠
⎞
⎜
⎝
⎛
R2
R1
R2
R1
R
R2
V
REF
1
02627-066
R
R
R
R(1+δ)
ADR421
15V
0.1µ
F
OP1177
6
7
4
2
3
V+
V–
R
F
R
F
V
OUT
Figure 65. Low Power Linearized RTD Circuit
SINGLE OPERATIONAL AMPLIFIER BRIDGE
The low input offset voltage drift of the OP1177 makes it very
effective for bridge amplifier circuits used in RTD signal condi-
tioning. It is often more economical to use a single bridge
operational amplifier as opposed to an instrumentation amplifier.
In the circuit shown in Figure 66, the output voltage at the
operational amplifier is
Figure 66. Single Bridge Amplifier
()
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎣
⎡
⎟
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎜
⎝
⎛
δ+
⎟
⎠
⎞
⎜
⎝
⎛
++
δ
=
1 1
R2
R1
R
R1
V
R
R2
V
REF
O