link to page 20 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- 0.1µF500Ω ature at the RTD. ADR4214.12kΩ4.37kΩ200Ω For δ << 1, the preceding expression becomes 6 ⎛ ⎞ ⎜ ⎟ 4.12kΩ1/2V ⎛ R2 ⎞ δ OUT100Ω7 V ≅ V ⎜ ⎟ OP2177 O ⎜ ⎟ = REF R1 R1 5 ⎝ R ⎠ ⎜⎜ 1+ + ⎟⎟ ⎝ R R2 ⎠ 100Ω20Ω ⎡⎛ R2 ⎞ ⎛ R1 ⎞ ⎛ R1 ⎞⎤ ⎜ ⎟ ⎜ 1+ ⎟ + ⎜ ⎟ V δ ⎢ ⎥ ⎣⎝ R ⎠ ⎝ R2 ⎠ ⎝ R2 ⎠⎦ REF 5kΩ49.9kΩ100ΩV+ With V RTD REF constant, the output voltage is linearly proportional to δ with a gain factor of 821/2 ⎛ R2 ⎞ ⎡⎛ R1 ⎞ ⎛ R1 ⎞⎤ 1 V 1 REF ⎜ ⎟ ⎜ + ⎟ + OP2177VOUT ⎢ ⎜ ⎟⎥ ⎝ R ⎠ ⎝ R2 ⎠ ⎝ R2 ⎠ 3 ⎣ ⎦ 4 65 -0 15V 27 V– 26 R 0 F Figure 65. Low Power Linearized RTD Circuit 0.1µFADR421V+SINGLE OPERATIONAL AMPLIFIER BRIDGERR72V The low input offset voltage drift of the OP1177 makes it very 6OUTR(1+δ)ROP1177 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