OP1177ARMZ-R7 datasheet(20/24 Pages) AD

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OP1177/OP2177/OP4177

Data Sheet

Rev. I | Page 20 of 24

200Ω

500Ω

4.37kΩ

100Ω

20Ω

4.12kΩ

5kΩ

49.9kΩ

ADR421

+15V

0.1µF

V+

100Ω

RTD

1/2

OP2177

1/2

OP2177

V–

VOUT

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

 







































 







REF

where δ = ΔR/R is the fractional deviation of the RTD

resistance with respect to the bridge resistance due to the change

in temperature at the RTD.

For δ << 1, the preceding expression becomes



































 

















































REF

With VREF constant, the output voltage is linearly proportional

to δ with a gain factor of

































 













REF

R(1+δ)

ADR421

15V

0.1µF

OP1177

V+

V–

VOUT

Figure 66. Single Bridge Amplifier

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