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OP4177_15 Datasheet, PDF (20/24 Pages) Analog Devices – Precision Low Noise, Low Input Bias Current Operational Amplifiers | |||
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OP1177/OP2177/OP4177
+15V
0.1µF
ADR421
4.12kâ¦
4.37kâ¦
500â¦
200â¦
4.12kâ¦
100â¦
100â¦
20â¦
6
1/2
7
OP2177
5
VOUT
100â¦
V+
RTD
5kâ¦
49.9kâ¦
2
8
1/2 1
OP2177
3
4
VOUT
Vâ
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
VO
=
R2
R
â¡
â¢
â¢â¢VREF
â¢â£
ââ
â
â
ââ
δ
âââ¥â¤
ââ¥
R1
R
+
âââ1 +
R1
R2
ââ â
(1 +
δ)
ââ¥
ââ â¥â¦
where δ = ÎR/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
VO
â
âââ
R2
R
ââ â
VREF
ââ
â
âââ 1+
δ
R1 +
R
R1
R2
ââ
â
âââ
=
â¢â£â¡âââ
R2
R
ââ â
âââ1
+
R1
R2
ââ â
+
âââ
R1
R2
ââ ââ¥â¦â¤
VREF
δ
With VREF constant, the output voltage is linearly proportional
to δ with a gain factor of
VREF
âââ
R2
R
ââ â
â¢â£â¡âââ1 +
R1
R2
ââ â + âââ
R1
R2
ââ ââ¥â¦â¤
15V
RF
0.1µF
ADR421
R
R
R(1+δ)
R
V+
2
7
6
OP1177
3
4
Vâ
VOUT
RF
Figure 66. Single Bridge Amplifier
Rev. G | Page 20 of 24
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