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Resistance Temperature Detector (RTD) Solutions

Last modified by Microchip on 2024/10/28 14:26

A Resistance Temperature Detector (RTD) is a temperature sensor that contains a resistor that changes resistance value as its temperature changes. It is made from a pure material, such as platinum. This sensor is typically used in precision applications such as laboratory equipment and medical instrumentation. Precision analog and digital circuits are also needed to accurately detect temperature changes using an RTD. For example, medical laboratory ovens, as shown in Figure 11,  require precision closed-loop temperature control systems. An RTD is the preferred sensor for this application for superior repeatable characteristics as the unit temperature cycles from room temperature to the various preset levels.

System Diagram

Figure 11: Laboratory oven

Microchip provides various precision solutions for RTDs, such as an instrumentation amplifier with an integrated self-calibrating (MCP6N11), an autozeroed op amp with extremely low input offset voltage (MCP6V01), and a high-resolution precision analog to digital converter (MCP3551).

As shown in Figure 12, RTD sensors are available with 2-wire, 3-wire, and 4-wire elements. With the 2-wire sensors, both sensor leads are in series with the sensor element. As temperature increases, the lead resistance also changes and the voltage drop across the leads reduces the measurement accuracy.
 

Figure 12: 2-wire 3-wire and 4-wire elements

Figure 12: 2-wire 3-wire and 4-wire elements

Reference Designs

MCP6N11 Wheatstone Bridge Reference Design (ARD00354)

Microchip provides a reference design that uses a Wheatstone Bridge balanced RTD circuit to analyze and compare the performance of the traditional three op-amp instrumentation amplifier with the MCP6V01 family of op amps and the MCP6N11 instrumentation amplifier. This reference design enables users to perform noise analysis and study each circuit's characteristics to identify the preferred solution using a software Graphical User Interface (GUI).

ARD00354

Figure 13: ARD00354

RTD Reference Design (TMPSNSRD-RTD2)

Microchip also provides a reference design that uses a current source to bias the RTD. This solution uses a high-performance delta-sigma Analog-to-Digital Converter (ADC), two external resistors and a reference voltage to measure temperature 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.
 

TMPSNSRD-RTD2

FIgure 14: TMPSNSRD-RTD2

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