max31865

Overview

The max31865 node reads temperature from PT100 or PT1000 RTD (Resistance Temperature Detector) sensors using the Maxim MAX31865 RTD-to-digital converter. Supporting 2-, 3-, and 4-wire RTD configurations, it provides exceptional accuracy and stability for precision temperature measurement in laboratory, industrial process, and scientific applications.

Properties

RTD Wire Configurations

Output

{
  "temperature": 23.45,
  "resistance": 109.12,
  "rtdType": "PT100",
  "wires": 3,
  "unit": "celsius",
  "fault": null,
  "timestamp": 1640000000000
}

Wiring

  PT100 RTD (3-wire)     MAX31865
  ─────────────────     ────────
   Wire 1 (Red)    →   RTD+
   Wire 2 (Red)    →   RTD-
   Wire 3 (White)  →   F+

  Board Jumpers (3-wire mode):
  - Solder jumper on "2/3" position
  - Cut trace on "4" position

  Enable SPI:
  sudo raspi-config
  # Interface Options → SPI → Enable

Example: Laboratory Temperature Logger

High-precision temperature logging with statistical analysis for laboratory environments.

// Function node: Precision temperature statistics
var temp = msg.temperature;
var resistance = msg.resistance;

var stats = flow.get('tempStats') || {
    readings: [],
    windowSize: 60 // Keep last 60 readings
};

stats.readings.push(temp);
if (stats.readings.length > stats.windowSize) {
    stats.readings.shift();
}

// Calculate statistics
var n = stats.readings.length;
var sum = stats.readings.reduce((a, b) => a + b, 0);
var mean = sum / n;

var variance = stats.readings.reduce((acc, val) => {
    return acc + Math.pow(val - mean, 2);
}, 0) / n;

var stdDev = Math.sqrt(variance);
var min = Math.min(...stats.readings);
var max = Math.max(...stats.readings);

flow.set('tempStats', stats);

msg.payload = {
    temperature: temp.toFixed(3),
    resistance: resistance.toFixed(2),
    mean: mean.toFixed(3),
    stdDev: stdDev.toFixed(4),
    min: min.toFixed(3),
    max: max.toFixed(3),
    range: (max - min).toFixed(3),
    samples: n,
    stable: stdDev < 0.05
};

return msg;

Example: Industrial Process Monitor

Monitor process temperatures with alarm bands and trend detection.

// Function node: Process alarm handler
var temp = msg.temperature;
var fault = msg.fault;

// Check for sensor faults first
if (fault !== null) {
    msg.payload = {
        alarm: "SENSOR_FAULT",
        severity: "critical",
        message: "RTD sensor fault: " + fault,
        timestamp: msg.timestamp
    };
    msg.topic = "alarms/critical";
    return msg;
}

// Process alarm bands
var setpoint = 85.0;   // Target process temperature
var warnHigh = 90.0;
var warnLow = 80.0;
var alarmHigh = 95.0;
var alarmLow = 75.0;

var alarm = "NORMAL";
var severity = "info";

if (temp >= alarmHigh || temp <= alarmLow) {
    alarm = "ALARM";
    severity = "critical";
} else if (temp >= warnHigh || temp <= warnLow) {
    alarm = "WARNING";
    severity = "warning";
}

msg.payload = {
    temperature: temp.toFixed(2),
    setpoint: setpoint,
    deviation: (temp - setpoint).toFixed(2),
    alarm: alarm,
    severity: severity,
    inSpec: (temp >= warnLow && temp <= warnHigh)
};

msg.topic = "process/temperature";
return msg;

Common Use Cases