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Precision RTD Instrumentation for Temperature Sensing
Ezana Haile
Precision RTD (Resistive Temperature Detector) instrumentation is key for high performance thermal management applications. This application note shows how to use a high resolution Delta-Sigma Analog-to-Digital converter, and two resistors to measure RTD resistance ratiometrically. A ±0.1°C accuracy and ±0.01°C measurement resolution can be achieved across the RTD temperature range of -200°C to +800°C with a single point calibration. A high resolution Delta-Sigma ADC can serve well for high performance thermal management applications such as industrial or medical instrumentation. Traditionally, RTDs are biased with a constant current source. The voltage drop across the RTD is conditioned using an Instrumentation Amplifier which requires multiple resistors, capacitors and few operation amplifiers and/or a stand-alone instrumentation amplifier. This analog instrumentation technique requires a low noise and stable system to calibrate and accurately measure temperature. It also requires an operator for optimization on the production floor. With the Delta-Sigma ADC solution, the RTD is directly connected to the ADC (Microchip?s MCP3551 family of 22 bit Delta-Sigma ADCs) and a single low tolerance resistor is used to bias the RTD from the ADC reference voltage (Figure 1) and accurately measure temperature ratiometrically. A low drop out linear regulator (LDO) is used to provide a reference voltage.
Precision RTD, RTD Instrumentation, RTD Self-Heat, RTD Linearization, RTD Simulator, MCP3551, Ratiometric
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