The 40 mV of positive feedback via R8 to reference U1 increases PRT excitation current with increasing temperature and thus linearizes the temperature reading, making the thermometer accurate to ±0.1 °C

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Other Materials from the Main Document

• Article «The power of practical positive feedback to perfect PRTDs»
• Figure 1. PRTD circuit shamelessly copies Nick C's idea for making an ordinary DMM into a precision digital thermometer
• Figure 2. The Callendar-Van Dusen polynomial used here to predict that for any given temperature, an excitation current increment exists that will give an accurate readout, e.g., 0.5% for 33 °C, 1% for 67 °C, and 1.5% for 100 °C
• Figure 3. The 40 mV of positive feedback via R8 to reference U1 increases PRT excitation current with increasing temperature and thus linearizes the temperature reading, making the thermometer accurate to ±0.1 °C
• Figure 4. Residual error with Figure 3's positive feedback