MAX31865 RTD-to-Digital Converter Module

The MAX31865 is a highly accurate, easy-to-use resistance-to-digital converter optimized for use with Platinum Resistance Temperature Detectors (RTDs), such as the PT100 or PT1000. This module handles the complex task of compensating for lead wire resistance and converting the small resistance changes of an RTD into a high-resolution digital temperature reading.

Key Technical Specifications

• RTD Compatibility: Supports 2-wire, 3-wire, and 4-wire PT100 and PT1000 RTDs.

• Resolution: 15-bit ADC resolution (nominal temperature resolution of 0.03125°C).

• Accuracy: Total accuracy over all operating conditions is 0.5°C (0.05% of full scale).

• Conversion Time: Fast 21ms (max) conversion time.

• Communication Interface: standard SPI (Serial Peripheral Interface).

• Input Protection: Fault detection for overvoltage, undervoltage, and RTD short/open circuits.

• Operating Voltage: Typically 3.3V to 5V (onboard voltage regulator included on most breakout boards).

Features & Advantages

• Integrated Solutions: Replaces complex analog circuitry with a single chip that handles excitation current and precise voltage measurement.

• Lead Wire Compensation: Specifically designed to cancel out the resistance of long lead wires in 3-wire and 4-wire configurations, ensuring high accuracy even when the sensor is far from the controller.

• Versatile Design: Easy to configure for different RTD types by adjusting the onboard reference resistor ($R_{REF}$).

• Robust Fault Management: Automatically detects if the sensor is disconnected or if the wiring has shorted, protecting your industrial equipment.

Typical Wiring Configuration

The module features solder jumpers or terminals to toggle between different wiring modes:

1. 2-Wire: Simplest connection; however, it does not compensate for wire resistance.

2. 3-Wire: The industrial standard; balances cost and accuracy by using a third wire to cancel lead resistance.

3. 4-Wire: The most precise method; uses separate pairs for current excitation and voltage sensing to eliminate lead wire errors entirely.

Applications

• Industrial Process Control: Ideal for ovens, kilns, and environmental chambers.

• Medical Equipment: High-precision temperature monitoring for lab samples.

• Automotive: Monitoring oil or coolant temperatures with high reliability.

• HVAC Systems: Precision sensing in large-scale climate control units.

Package Includes2

• 1 x MAX31865 RTD Amplifier Module

• 2 x 2-Pin Terminal Block (for sensor connection)

• 1 x 6-Pin Male Header (for SPI interface)