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AN1154

Title	Title Precision RTD Instrumentation for Temperature Sensing
Name	Name AN1154
Date	Date 06/24/2015
Description	Description 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.

Development Tools

Title		Part Number	Title
TMPSNSRD-RTD2 RTD REFERENCE DESIGN BOARD		TMPSNSRD-RTD2	RTD REFERENCE DESIGN BOARD
MCP42XXEV MCP42XX EVALUATION BOARD		MCP42XXEV	MCP42XX EVALUATION BOARD

Silicon Products

Title	Product	Title
MCP3553 22-Bit, 60SPS, Single Channel ADC	MCP3553	22-Bit, 60SPS, Single Channel ADC
MCP3551 22-Bit, 14SPS, Single Channel ADC	MCP3551	22-Bit, 14SPS, Single Channel ADC
AT91M55800A ARM7-based Microcontroller	AT91M55800A	ARM7-based Microcontroller
AT91M40800 ARM7-based microcontroller	AT91M40800	ARM7-based microcontroller
AT91M42800A ARM7-based Microcontroller	AT91M42800A	ARM7-based Microcontroller
MCP6V28 620 µA, 2 MHz Auto-Zeroed Op Amps	MCP6V28	620 µA, 2 MHz Auto-Zeroed Op Amps
MCP6V26 620 µA, 2 MHz Auto-Zeroed Op Amps	MCP6V26	620 µA, 2 MHz Auto-Zeroed Op Amps
MCP6V27 620 µA, 2 MHz Auto-Zeroed Op Amps	MCP6V27	620 µA, 2 MHz Auto-Zeroed Op Amps