corrected value code

Projects Programming
1

I'm trying to set up two Max31865 boards and one of the boards is reading 8 deg different from the other. so I'm trying the implement the corecctedvalue code

CorrectedValue = (((RawValue – RawLow) * ReferenceRange) / RawRange) + ReferenceLow

I'm not sure how to implement it or what value to use for the Rawvalue in the code? I came up with this-
CorrectedValue = (((RawValue – -1.52) * 99.99) / 72) + 0.01 anyone able to help? Thank you,

void loop() {
  uint16_t rtd1 = thermo.readRTD();

  Serial.print("RTD value: "); Serial.println(rtd1);
  float ratio = rtd1;
  ratio /= 32768;
  
  Serial.print("Ratio = "); Serial.println(ratio, 8);
  Serial.print("Resistance = "); Serial.println(RREF * ratio, 8);
  Serial.print("Temperature = "); Serial.println(thermo.temperature(RNOMINAL, RREF) * 9 / 5 + 32);
 
  lcd.setCursor(0, 0);
  //lcd.print("Temperature = ");
  lcd.print("Deg.F= ");
  lcd.print(thermo.temperature(RNOMINAL, RREF) * 9 / 5 + 32);
2

8 degrees is a terrible error with precision RTDs. Why not fix the real problem?

If you wish to go that route, post the required details.

3

ok so must be something with the board? got any suggestions on what to look for?

4

Do you have a problem with posting the details of the sensors, the wiring and code, as described in the How to use this forum post?

5

You may want to give this a read:

What library and breakout board are you using?

Ron

6

here's the code I'm using. They are Max31865 boards. I've tried the code using a single board and the temp reading is the same so its definitely something with the board.

#include <Adafruit_MAX31865.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <SPI.h>
// Define LCD pinout
const int  en = 2, rw = 1, rs = 0, d4 = 4, d5 = 5, d6 = 6, d7 = 7, bl = 3;

// Define I2C Address - change if reqiuired
const int i2c_addr = 0x27;

// DHT-22
//#define DHTPIN 7       // DHT-22 Output Pin connection
//#define DHTTYPE DHT11   // DHT Type is DHT 22 (AM2302)

// Define LCD display connections
LiquidCrystal_I2C lcd(i2c_addr, 16, 2);


// SPI.h: CS, DI, DO, CLK
Adafruit_MAX31865 thermo = Adafruit_MAX31865(10, 11, 12, 13);
Adafruit_MAX31865 thermo1 = Adafruit_MAX31865(9, 11, 12, 13);
// use hardware SPI, just pass in the CS pin
//Adafruit_MAX31865 thermo_1 = Adafruit_MAX31865(10);
//Adafruit_MAX31865 thermo_2 = Adafruit_MAX31865(9);

// 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

void setup() {
  Serial.begin(115200);
  Serial.println("Adafruit MAX31865 PT100 Sensor Test!");
  lcd.init();
  // Set display type as 16 char, 2 rows
  lcd.begin(16, 2);
  lcd.backlight();

  thermo.begin(MAX31865_2WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo1.begin(MAX31865_2WIRE);
}


void loop() {
  uint16_t rtd1 = thermo.readRTD();

  Serial.print("RTD value: "); Serial.println(rtd1);
  float ratio = rtd1;
  ratio /= 32768;
  
  Serial.print("Ratio = "); Serial.println(ratio, 8);
  Serial.print("Resistance = "); Serial.println(RREF * ratio, 8);
  Serial.print("Temperature = "); Serial.println(thermo.temperature(RNOMINAL, RREF) * 9 / 5 + 32);
 
  lcd.setCursor(0, 0);
  //lcd.print("Temperature = ");
  lcd.print("Deg.F= ");
  lcd.print(thermo.temperature(RNOMINAL, RREF) * 9 / 5 + 32);
  
  uint16_t rtd2 = thermo1.readRTD();

  Serial.print("RTD value: "); Serial.println(rtd2);
  float ratio2 = rtd2;
  ratio2 /= 32768;
  Serial.print("Ratio2 = "); Serial.println(ratio2, 8);
  Serial.print("Resistance = "); Serial.println(RREF * ratio2, 8);
  Serial.print("Temperature = "); Serial.println(thermo1.temperature(RNOMINAL, RREF) * 9 / 5 + 32);
  lcd.setCursor(0, 3);
  //lcd.print("Temperature = ");
  lcd.print("Deg.F= ");
  lcd.print(thermo1.temperature(RNOMINAL, RREF) * 9 / 5 + 32);
 
  delay(1000);

boardcrp.jpg
boardcrp.jpg1881×1945 1020 KB

7

Or the sensors. You forgot to post links to them, and a wiring diagram.

The photo doesn't tell us anything.