21Analog Applications Journal4Q 2011 www.ti.com/aaj High-Performance Analog ProductsTexas Instruments IncorporatedGeneral Interest?Bruce Trump? ? (TI) ? (RTD) ? ?(Pt) ? ? ? 800C ? ? 1?Pt100? 0C ? 100 ?Callendar-Van Dusen ? ? RTD ?R0 ? 0C ? 100 ?Pt100?A = 3.9083 103B = 5.775 107T 0C ?C = 0? T 0C ?C = 4.23225 1012? 0.39%/C ?Pt100 RTD ? ? 100C ?RTD ? ? 0.38% ? 1? ? ?RTD? RTD ? ? ? ? ? 2 ? ? ?0C ?Pt100 ? ? ? ? RTD ? RTD ? ? ? RTD ?400350300250200150100500 1000100200300400500600700800Temperature (C)Resistance ( )?100at 0C?Curvature due to second-order nonlinearityFigure 1. Resistance of Pt100 RTD versus temperature? 1 Pt100 RTD ?RTD TemperatureRTD VoltageRTDVOUTARTD voltage is gradually boosted with increasing excitation currentRTD resistance with second-order nonlinearity (exaggerated)Figure 2. RTD voltage versus temperature? 2 RTD ? ? 2 ? ? RTD ? ? ? ? ?RTD? ? ? S ? ? ? ? ? 3? ? RTD? ? ? 3 ? 100C ? +800C ? 900C? ? 3.7% RTD ? 0.11%? 1/33? ?200C ? 150 ? 1/150? ? ? 4 ? RTD ? ?R1 ? VREF?R5 ? ?A1? R2?R3?R4? ? ?TI?OPA188*? ? ? ? ? TI OPA277 ? ? ? ?RTD?RTD ?VREF?R1?R5 ? VOUT ? ?Texas Instruments IncorporatedGeneral Interest22Analog Applications JournalHigh-Performance Analog Products www.ti.com/aaj 4Q 20114.03.53.02.52.01.51.00.50.00.5 1000100200300400500600700800Temperature (C)Error (%)Corrected output with nonlinearity peaks at and scaleNonlinearity of RTD for 900 C spanZero error at midscale and endpointsFigure 3. Percentage of RTD error versus temperature0C to 200CPt100 100 ?R1 4.99 k?R4 1 k?R5 106.18 k?R3 60.44 k?R2 49.13 k?A1 OPA188V 0 V at 0C 5 V at 200COUTV 5 VREF+Figure 4. Typical RTD configuration with error compensation? 3 RTD? 4 ? RTD ?RTDRTDRTDRTD RTDREFOUT RTDRTDRTDRTDRR5RR1 RR5RR1VVVRR5RR1R1R5RR5RR1? ? ? ? ? ? R5 ? ? RTD ? ? ? R5 ? ?R5 ? ? Excel ?http:/www.ti.com/ lit/zip/SLYT442? WinZip ? ?WinZip? RTD_Linearization_ v7.xls? ? ? ? ? ?SPICE? ? WinZip ? TINA-TI SPICE ? ? RTD ? ?RTD? ?SPICE RTD ? ? 2? 5 ? RTD ? ? 500C ? 2%? RTD ? ? 500C ? ? 8%? RTD ? ? Pt1000 ?Pt5000 ? RTD ? RTD ? ? RTD ? ? 6?1614121086420 0100200300400500600700800Temperature Measurement Span (C)Percent ()?Uncorrected RTD errorRequired change in excitation currentFigure 5. Correlation of excitation current to RTD error0C to 200CREFPt100 100 ?R1 4.99 k?R5 106.18 k?R6 4.99 k?R7 99.9 ?A1 INA826V 5 VREFR8 801 ?RGRG+Equal resistance creates common-mode voltageResistance creates common-mode voltageV 0 V at 0C 5 V at 200COUTFigure 6. Amplifier with three-wire RTD connection? 5 RTD ? 6 ? RTD ?23Analog Applications Journal4Q 2011 www.ti.com/aaj High-Performance Analog Products? RTD ? ? ? ? R5 ? ? ?Texas Instruments IncorporatedGeneral Interest? ? ? ?TI ? RTD ? ? 1? ?4 ? 20Ma ?XTR106 ?PGA309? ? ? ? ?1?http:/ en.wikipedia.org/wiki/Resistance_thermometer2?SPICE?Pt100 RTD? Tho