Datasheet OP1177, OP2177, OP4177 (Analog Devices) - 20

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OP1177/OP2177/OP4177 +15V
where δ = ΔR/R is the fractional deviation of the RTD resistance with respect to the bridge resistance due to the change in temper-
0.1µF 500Ω
ature at the RTD.
ADR421 4.12kΩ 4.37kΩ 200Ω
For δ << 1, the preceding expression becomes
6
⎛ ⎞ ⎜ ⎟
4.12kΩ 1/2 V
⎛ R2 ⎞ δ
OUT 100Ω 7
V ≅ V ⎜ ⎟
OP2177
O ⎜ ⎟ = REF R1 R1
5
⎝ R ⎠ ⎜⎜ 1+ + ⎟⎟ ⎝ R R2 ⎠
100Ω 20Ω
⎡⎛ R2 ⎞ ⎛ R1 ⎞ ⎛ R1 ⎞⎤ ⎜ ⎟ ⎜ 1+ ⎟ + ⎜ ⎟ V δ ⎢ ⎥ ⎣⎝ R ⎠ ⎝ R2 ⎠ ⎝ R2 ⎠⎦ REF
5kΩ 49.9kΩ 100Ω V+
With V
RTD
REF constant, the output voltage is linearly proportional to δ with a gain factor of
8 2 1/2
⎛ R2 ⎞ ⎡⎛ R1 ⎞ ⎛ R1 ⎞⎤
1
V 1 REF ⎜ ⎟ ⎜ + ⎟ +
OP2177 VOUT
⎢ ⎜ ⎟⎥ ⎝ R ⎠ ⎝ R2 ⎠ ⎝ R2 ⎠
3
⎣ ⎦
4
65 -0
15V
27
V–
26
R
0
F
Figure 65. Low Power Linearized RTD Circuit
0.1µF ADR421 V+ SINGLE OPERATIONAL AMPLIFIER BRIDGE R R 7 2 V
The low input offset voltage drift of the OP1177 makes it very
6 OUT R(1+δ) R OP1177
effective for bridge amplifier circuits used in RTD signal condi-
3
tioning. It is often more economical to use a single bridge
4
operational amplifier as opposed to an instrumentation amplifier.
V–
66 -0
RF
In the circuit shown in Figure 66, the output voltage at the 2627 0 operational amplifier is Figure 66. Single Bridge Amplifier ⎡ ⎛ ⎞⎤ ⎢ ⎜ ⎟⎥ = R2 V ⎢ ⎜ δ ⎟ V ⎥ O R ⎢ REF ⎜ R1 ⎛ R1 ⎞ ⎜ + ⎜1+ ⎟ ( 1+ δ) ⎟⎥ ⎢ ⎟⎥ ⎣ ⎝ R ⎝ R2 ⎠ ⎠⎦ Rev. G | Page 20 of 24 Document Outline FEATURES APPLICATIONS PIN CONFIGURATIONS GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS FUNCTIONAL DESCRIPTION TOTAL NOISE-INCLUDING SOURCE RESISTORS GAIN LINEARITY INPUT OVERVOLTAGE PROTECTION OUTPUT PHASE REVERSAL SETTLING TIME OVERLOAD RECOVERY TIME THD + NOISE CAPACITIVE LOAD DRIVE STRAY INPUT CAPACITANCE COMPENSATION REDUCING ELECTROMAGNETIC INTERFERENCE PROPER BOARD LAYOUT DIFFERENCE AMPLIFIERS A HIGH ACCURACY THERMOCOUPLE AMPLIFIER LOW POWER LINEARIZED RTD SINGLE OPERATIONAL AMPLIFIER BRIDGE REALIZATION OF ACTIVE FILTERS BAND-PASS KRC OR SALLEN-KEY FILTER CHANNEL SEPARATION REFERENCES ON NOISE DYNAMICS AND FLICKER NOISE OUTLINE DIMENSIONS ORDERING GUIDE