MAX31865 help - loss of resolution

I change this, and installed in arduino. I am trying using PID, without LCD. the output is:

RTD Sensor Trtd = 18.50 deg C
RTD Sensor Trtd = 18.47 deg C
RTD Sensor Trtd = 18.50 deg C

/*    Arduino Uno   -->  SEN-30201
*    CS: pin 4     -->  CS
*    MOSI: pin 11  -->  SDI (must not be changed for hardware SPI)
*    MISO: pin 12  -->  SDO (must not be changed for hardware SPI)
*    SCK: pin 13   -->  SCLK (must not be changed for hardware SPI)
*    GND           -->  GND
*    5V            -->  Vin (supply with same voltage as Arduino I/O, 5V)
***************************************************************************/

// the sensor communicates using SPI, so include the hardware SPI library:
#include <SPI.h>
// include Playing With Fusion MAX31865 libraries
#include <PlayingWithFusion_MAX31865.h>              // core library
#include <PlayingWithFusion_MAX31865_STRUCT.h>       // struct library

#include <PID_v1.h>

#define RelayPin 6

//Define Variables we'll be connecting to
double Setpoint, Input, Output;

//Specify the links and initial tuning parameters
PID myPID(&Input, &Output, &Setpoint,2,5,1, DIRECT);

int WindowSize = 5000;
unsigned long windowStartTime;


//Sensor addresses:
const byte CONFIG_REG_W = 0x80; // Config register write addr
const byte CONFIG_VALUE = 0xC3; // Config register value (Vbias+Auto+FaultClear+50Hz, see pg 12 of datasheet)
const byte ADC_WORD_MSB = 0x01; // Addr of first byte of data (start reading at RTD MSB)
const byte ADC_FAULT_REG = 0x07; // Addr of the fault reg

// CS pin used for the connection with the sensor
// other connections are controlled by the SPI library)
const int CS_PIN = 4;

PWFusion_MAX31865_RTD rtd_ch0(CS_PIN);


void setup() {
  Serial.begin(9600);

  // setup for the the SPI library:
  SPI.begin();                        // begin SPI
  SPI.setDataMode(SPI_MODE3);         // MAX31865 is a Mode 3 device
  
  // initalize the chip select pin
  pinMode(CS_PIN, OUTPUT);
  rtd_ch0.MAX31865_config();
  
    // give the sensor time to set up
  delay(100);
  
  windowStartTime = millis();
  
  //initialize the variables we're linked to
  Setpoint = 40;

  //tell the PID to range between 0 and the full window size
  myPID.SetOutputLimits(0, WindowSize);

  //turn the PID on
  myPID.SetMode(AUTOMATIC);
}


void loop() 
{
  temp_sensor();
  
  myPID.Compute();

  /************************************************
   * turn the output pin on/off based on pid output
   ************************************************/
  if(millis() - windowStartTime>WindowSize)
  { //time to shift the Relay Window
    windowStartTime += WindowSize;
  }
  if(Output < millis() - windowStartTime) digitalWrite(RelayPin,HIGH);
  else digitalWrite(RelayPin,LOW);
  
}

void temp_sensor()
{
  static struct var_max31865 RTD_CH0;
  double tmp;
  
  RTD_CH0.RTD_type = 1;                         // un-comment for PT100 RTD
  
  struct var_max31865 *rtd_ptr;
  rtd_ptr = &RTD_CH0;
  
  rtd_ch0.MAX31865_full_read(rtd_ptr);          // Update MAX31855 readings 
  
  // Print information to serial port
  Serial.print("RTD Sensor ");              // Print RTD0 header
  
  if(0 == RTD_CH0.status)                       // no fault, print info to serial port
  {
    // calculate RTD temperature (simple calc, +/- 2 deg C from -100C to 100C)
    // more accurate curve can be used outside that range
    tmp = ((double)RTD_CH0.rtd_res_raw / 32) - 256;
    Input = tmp;
    delay(500);
    Serial.print("Trtd = ");                    // print RTD temperature heading
    Serial.print(tmp);
    Serial.println(" deg C");                   // print RTD temperature heading

  }  // end of no-fault handling
  else 
  {
    Serial.print("RTD Fault, register: ");
    Serial.print(RTD_CH0.status);
    Serial.print(" - ");
    if(0x80 & RTD_CH0.status)
    {
      Serial.println("RTD High Threshold Met");  // RTD high threshold fault
    }
    else if(0x40 & RTD_CH0.status)
    {
      Serial.println("RTD Low Threshold Met");   // RTD low threshold fault
    }
    else if(0x20 & RTD_CH0.status)
    {
      Serial.println("REFin- > 0.85 x Vbias");   // REFin- > 0.85 x Vbias
    }
    else if(0x10 & RTD_CH0.status)
    {
      Serial.println("FORCE- open");             // REFin- < 0.85 x Vbias, FORCE- open
    }
    else if(0x08 & RTD_CH0.status)
    {
      Serial.println("FORCE- open");             // RTDin- < 0.85 x Vbias, FORCE- open
    }
    else if(0x04 & RTD_CH0.status)
    {
      Serial.println("Over/Under voltage fault");  // overvoltage/undervoltage fault
    }
    else
    {
      Serial.println("Unknown fault, check connection"); // print RTD temperature heading
    }
  }  // end of fault handling
}