What is a Resistive Temperature Detector (RTD)?
RTDs (Resistive Temperature Detectors) are extremely accurate temperature sensors. They have consistent repeatable performance and low drift error (-200 °C to +850 °C). RTDs provide the designer with an absolute result that is fairly linear over temperature. The RTD’s linear relationship between resistance and temperature simplifies the implementation of signal conditioning circuitry. For high precision applications, these sensors require a linearization look-up table in the microcontroller due to sensor nonlinearities.
Resistive Temperature Measurement Circuits
Circuit A can be easily modified for a desired temperature-to-frequency range. It uses the MCP6541 comparator and can be implemented with either precision, low-drift components or a calibration step to achieve high accuracy. Circuit B utilizes pull-up and pull-down resistors to excite the RTD, employing the TC913A Auto Zero op amp to amplify the small voltage changes that correspond to temperature.