SBVS020C September 2000 – February 2020 REF200
Figure 12 and Figure 13 shows the schematic of the RTD amplifier for minimum and maximum output conditions. This circuit was designed for a –50°C to 150°C RTD temperature range. At –50°C the RTD resistance is 80.3 Ω and the voltage across it is 8.03 mV (VRTD = (100 μA) (80.3 Ω), see Figure 2). Notice that R3 develops a voltage drop that opposes the RTD drop. The drop across R3 is used to shift amplifiers input differential voltage to a minimum level. The output is the differential input multiplied by the gain (Vout = 698 ∙ 160 μV = 0.111 V). At 150°C, the RTD resistance is 148 Ω and the voltage across it is 14. 8 mV (VRTD = (100 μA × 148 Ω ). This produces a differential input of 6.93 mV and an output voltage of 4.84 V (VOUT = 698 ∙ 6.93 mV = 4.84 V , see Figure 13). For more detailed design procedures and results, refer to the reference guide, RTD to Voltage Reference Design Using Instrumentation Amplifier and Current Reference (TIDU969).