MAX31865 Temperature Transducer Module from PT100-PT1000 Sensors to SPI Arduino

MAX31865 Description

The MAX31865 is used for precision temperature sensing, nothing beats a Platinum RTD. Resistance temperature converters (RTDs) contain a resistor that changes its resistance value as its temperature changes, basically a kind of thermistor. In this sensor, the resistor is actually a small strip of platinum with a resistance of 100 ohms at 0°C, hence the name PT100. Compared to most NTC/PTC thermistors, the RTD type is much more stable and accurate (but also more expensive) PT100s have been used for many years to measure temperature in laboratory and industrial processes and have earned a reputation for accuracy (better than thermocouples), repeatability and stability.

Can be used with PT1000 sensor only if you replace the reference resistor.

Precision

However, to achieve that accuracy you must use an amplifier designed to read this low resistance. Such an amplifier can automatically adjust and compensate for the resistance of the connecting wires. If you are looking for a great RTD converter, today is your lucky day as we have an awesome MAX31865 offset RTD sense amplifier for use with any 100, 2 or 3 wire PT4!

Cod

I've tested various MAXIM thermocouple amplifiers and they're all great – but the thermocouples don't have the best accuracy or stability. The MAX31865 handles all your RTD needs and can even compensate 3- or 4-wire RTDs for better accuracy. Connect to it with any microcontroller via the SPI bus and read the resistance ratio from the internal ADC. I put a 430Ω 0,1% resistor as a reference resistance. We have sample code that will calculate the temperature based on the resistance for you. Below is an example of a function that will get the temperature value:

// Use SPI software: CS, DI-mosi, DO-miso, CLK
Adafruit_MAX31865 ttemp1 = Adafruit_MAX31865(temp_Pin);//, 51, 50, 52
// The value of the Rref resistor. Use 430.0 for PT100 and 4300.0 for PT1000
#define RREF 430.0
// The 'nominal' 0-degrees-C resistance of the sensor
// 100.0 for PT100, 1000.0 for PT1000
#define RNOMINAL 100.0
float TakeTemp(Adafruit_MAX31865 sensor) {
float ratio = sensor.temperature(RNOMINAL, RREF);
uint8_t fault = sensor.readFault();
if (fault) {
Serial.print(F(“Fault 0x”)); Serial.println(fault, HEX);
if (fault & MAX31865_FAULT_HIGHTHRESH) Serial.println(F(“RTD High Threshold”));
if (fault & MAX31865_FAULT_LOWTHRESH) Serial.println(F(“RTD Low Threshold”));
if (fault & MAX31865_FAULT_REFINLOW) Serial.println(F(“REFIN- > 0.85 x Bias”));
if (fault & MAX31865_FAULT_REFINHIGH) Serial.println(F(“REFIN- < 0.85 x Bias – FORCE- open”));
if (fault & MAX31865_FAULT_RTDINLOW) Serial.println(F(“RTDIN- < 0.85 x Bias – FORCE- open”));
if (fault & MAX31865_FAULT_OVUV) Serial.println(F(“Under/Over voltage”));
sensor.clearFault();
}
return ratio;
}

You will find the complete code in the MAX31865 library on GitHub

supply voltage

The module is 5V compatible, contains a 3,3V regulator and level shifter for signals, so you can use it with any Arduino or other 5V microcontroller.

Each shipment will contain an assembled RTD amplifier board. It also comes with two 2-pin terminal blocks (to connect to the RTD sensor) and pin header (to connect the SPI bus). A PT100 thermistor is required which is not included!. There will be some soldering to do to secure the terminals, but it's an easy task with any letcon.

Useful Links

Detailed tutorial for beginners

Tutorial for using this module.

Specifications for the MAX31865