MAX31865 PT100 / PT1000 RTD Temperature Detector Module

Achieve laboratory-grade temperature sensing with the MAX31865 PT100/PT1000 RTD Amplifier Module. Designed to digitize resistance measurements from Platinum Resistance Temperature Detectors (RTDs), this module offers 15-bit ADC resolution ( $0.03125^circ ext{C}$ ) with an accuracy up to 0.5°C. Supporting 2-wire, 3-wire, and 4-wire PT100 and PT1000 sensors, it communicates via a standard 4-wire SPI interface. Featuring onboard 3.3V voltage regulation and level shifting, it is fully compatible with $3.3 ext{V}$ and $5 ext{V}$ microcontrollers like Arduino, ESP32, and Raspberry Pi for high-precision industrial thermal logging.

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Tags MAX31865 Module PT100 RTD Amplifier PT1000 Temperature Sensor MAX31865 Arduino SPI RTD Converter High Precision Temperature Sensor 2 Wire 3 Wire 4 Wire RTD Industrial Temperature Module

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Product Details :

The MAX31865 PT100/PT1000 RTD Converter Module is an ultra-precise resistance-to-digital converter optimized for platinum resistance temperature detectors (RTDs). While thermocouples are great for extreme heat and thermistors offer cheap basic sensing, RTDs (like PT100 or PT1000) are the gold standard for high-accuracy precision measurement over wide temperature ranges ( $-200^circ ext{C}$ to $+850^circ ext{C}$ ).

The onboard MAX31865 IC eliminates complex analog op-amp circuits by using a precision reference resistor ( $430 Omega$ for PT100 or $4300 Omega$ for PT1000) and a delta-sigma 15-bit ADC. It directly calculates the resistance ratio and converts it into a digital readout via a 4-wire SPI interface. The module includes solder jumpers to easily configure it for 2-wire, 3-wire, or 4-wire sensor probes. With integrated logic level conversion ( $3.3 ext{V} - 5 ext{V}$ ), it interfaces seamlessly with microcontrollers ranging from 5V Arduino Unos to 3.3V ESP32 and STM32 boards.

Key Features and Benefits

High Precision 15-Bit ADC: Delivers a temperature resolution of 0.03125°C and an overall system accuracy of 0.5°C across the full operating range.
Universal 2, 3, or 4-Wire RTD Compatibility: Easily configured via onboard solder pads to work with 2-wire, 3-wire (lead wire resistance cancellation), or 4-wire precision probes.
Supports PT100 & PT1000 Sensors: Comes stock-configured for PT100 sensors ( $430 Omega$ reference resistor) and can be modified for PT1000 sensors ( $4.3 ext{ k}Omega$ reference resistor).
Onboard $3.3 ext{V}$ Regulator & Level Shifter: Safely interfaces with both $3.3 ext{V}$ logic (ESP32, Raspberry Pi) and $5 ext{V}$ logic (Arduino) without external level translators.
Comprehensive Fault Diagnostics: Detects open RTD elements, short circuits to ground/VCC, and out-of-range over/under-temperature conditions.

Technical Specifications

Feature Component	Specification Details
Core Converter IC	Maxim MAX31865 RTD-to-Digital Converter
Compatible RTD Types	PT100 (Default) or PT1000
ADC Resolution	15-Bit ( $0.03125^circ ext{C}$ step resolution)
Absolute Accuracy	$0.5^circ ext{C}$ ( $0.05%$ of full scale)
Conversion Time	Max $21 ext{ ms}$ per sample
Reference Resistor ( $R_{REF}$ )	$430 Omega$ ( $0.1%$ tolerance) for PT100
Communication Interface	4-Wire SPI (CS, CLK, SDI/MOSI, SDO/MISO)
Operating Input Voltage ( $V_{IN}$ )	$3.0 ext{V} - 5.0 ext{V DC}$
Logic Input Level	$3.3 ext{V}$ and $5 ext{V}$ Compatible
Fault Protection	$pm 45 ext{V}$ Overvoltage protection on RTD inputs

Pinout & Configuration Guide

1. Terminal Block Side (RTD Connection):

FORCE+ / RTD+: Current excitation positive terminal.
FORCE- / RTD-: Current excitation negative terminal.
IN+ / IN-: Differential voltage sensing terminals for 3-wire and 4-wire configurations.

2. Header Pinout (Microcontroller Connection):

VIN: Main Power Input ( $3.3 ext{V} - 5 ext{V DC}$ ).
GND: Power Ground ( $0 ext{V}$ ).
3V3: Regulated $3.3 ext{V}$ output rail from onboard LDO.
SDO / MISO: SPI Serial Data Output to Microcontroller.
SDI / MOSI: SPI Serial Data Input from Microcontroller.
SCLK / CLK: SPI Serial Clock.
CS: SPI Chip Select (Active Low).
RDY (Optional): Data Ready Interrupt pin.

Arduino Quick-Start Code Example

C++
#include <Adafruit_MAX31865.h>

// Use software SPI or hardware SPI (CS, DI, DO, CLK)
Adafruit_MAX31865 thermo = Adafruit_MAX31865(10, 11, 12, 13);

// Set to 430.0 for PT100 or 4300.0 for PT1000
#define RREF      430.0
// Nominal resistance at 0 degrees C (100.0 for PT100, 1000.0 for PT1000)
#define RNOMINAL  100.0

void setup() {
  Serial.begin(9600);
  Serial.println("MAX31865 PT100 RTD Test Initializing...");

  // Initialize for 3-wire RTD configuration (Change to MAX31865_2WIRE or MAX31865_4WIRE as needed)
  thermo.begin(MAX31865_3WIRE); 
}

void loop() {
  uint16_t rtd = thermo.readRTD();
  float ratio = rtd;
  ratio /= 32768;

  Serial.print("Resistance = "); 
  Serial.print(RREF * ratio, 2);
  Serial.println(" Ohms");

  Serial.print("Temperature = ");
  Serial.print(thermo.temperature(RNOMINAL, RREF));
  Serial.println(" °C");

  // Check for faults
  uint8_t fault = thermo.readFault();
  if (fault) {
    Serial.print("Fault 0x"); Serial.println(fault, HEX);
    thermo.clearFault();
  }
  
  delay(1000);
}

Applications

Precision Chemical & Lab Equipment: Maintains accurate process monitoring in bioreactors, distillation columns, and chemical baths.
Food & Beverage Processing: Temperature verification for commercial pasteurization, ovens, and brewing operations.
Medical Equipment: Thermal sensing in incubators, autoclaves, and diagnostic temperature chambers.
HVAC & Industrial Automation: Monitoring heat exchangers, chillers, and environmental test chambers requiring high stability.