PT100是指温度为0时电阻值为100的高精度温度传感器， 它的电阻变化很小，因此需要做一个外接增益板才能读取数据，max31865就是集成了增益的芯片，将数据直接转化为SPI信号传输到板子上，本次采用了esp32进行读取数据

        本次采用的是三线PT100，其接法如下图片是官方的，如果你是两蓝一红的线，就按照这个图片反着接就好了，两颗蓝线接RTD+,红线接RTD-.然后记得按照图片上的把触点焊起来。

        然后关键的来了，如果你没有刮掉24连接，上电测量会发现PT100的比正常值电阻少一半！！没上电测量为112，上电测量发现只有60多了，这是因为24之间有连接地，然后还有一个并联电阻就会出现电阻变小的情况。具体如下图原理图及其PCB

原理图是我参照官方的画的没画触点，直接接三线的，PCB是管方的，通过PCB将以下位置用小刀刮断

将蓝色标记处刮断，具体如下这样才能正常使用

esp32代码如下

/*************************************************** 
  This is a library for the Adafruit PT100/P1000 RTD Sensor w/MAX31865

  Designed specifically to work with the Adafruit RTD Sensor
  ----> https://www.adafruit.com/products/3328

  This sensor uses SPI to communicate, 4 pins are required to  
  interface
  Adafruit invests time and resources providing this open source code, 
  please support Adafruit and open-source hardware by purchasing 
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.  
  BSD license, all text above must be included in any redistribution
 ****************************************************/

#include <Adafruit_MAX31865.h>

// Use software SPI: CS, DI, DO, CLK
Adafruit_MAX31865 max = Adafruit_MAX31865(15, 23, 19, 18);
// use hardware SPI, just pass in the CS pin
//Adafruit_MAX31865 max = Adafruit_MAX31865(10);

// The value of the Rref resistor. Use 430.0!
#define RREF 430.0


void setup() {
  Serial.begin(115200);
  Serial.println("Adafruit MAX31865 PT100 Sensor Test!");

  max.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
}


void loop() {
  uint16_t rtd = max.readRTD();

  Serial.print("RTD value: "); Serial.println(rtd);
  float ratio = rtd;
  ratio /= 32768;
  Serial.print("Ratio = "); Serial.println(ratio,8);
  Serial.print("Resistance = "); Serial.println(RREF*ratio,8);
  Serial.print("Temperature = "); Serial.println(max.temperature(100, RREF));

  // Check and print any faults
  uint8_t fault = max.readFault();
  if (fault) {
    Serial.print("Fault 0x"); Serial.println(fault, HEX);
    if (fault & MAX31865_FAULT_HIGHTHRESH) {
      Serial.println("RTD High Threshold"); 
    }
    if (fault & MAX31865_FAULT_LOWTHRESH) {
      Serial.println("RTD Low Threshold"); 
    }
    if (fault & MAX31865_FAULT_REFINLOW) {
      Serial.println("REFIN- > 0.85 x Bias"); 
    }
    if (fault & MAX31865_FAULT_REFINHIGH) {
      Serial.println("REFIN- < 0.85 x Bias - FORCE- open"); 
    }
    if (fault & MAX31865_FAULT_RTDINLOW) {
      Serial.println("RTDIN- < 0.85 x Bias - FORCE- open"); 
    }
    if (fault & MAX31865_FAULT_OVUV) {
      Serial.println("Under/Over voltage"); 
    }
    max.clearFault();
  }
  Serial.println();
  delay(1000);
}

我接的CS是15 ，MOSI是23，MISO接19,SCLK接18,最后就可以成功读取了，库的话再这个github地址GitHub - adafruit/Adafruit_MAX31865: Arduino Library for Adafruit MAX31865 RTD Sensor