MCP3551 Delta-Sigma-ADC Ungenau

PTCoolDown++;

    // PT100 Test:

    if(PTCoolDown >= 100)

    {    

      if(!SEN_PT100_MessungLaeuft)

      {

        // Wenn alle Teilmessungen erledigt, neue Messreihe starten:

        // PT100 Messung anregen:

        mcp3551_StosseMessungAn();

        SEN_PT100_MessungLaeuft = 1;      

      }

      else if(BerechnePT100Temperatur(&SEN_DeciTemperatur))

      {      

        if(tmin > SEN_DeciTemperatur)

          tmin = SEN_DeciTemperatur;

        if(tmax < SEN_DeciTemperatur)

          tmax = SEN_DeciTemperatur;

        SEN_PT100_MessungLaeuft = 0;      

        PTCoolDown = 0;

      }

    }

uint8_t stelle;

    if((SEN_DeciTemperatur % 10) < 0)

      stelle = (SEN_DeciTemperatur % 10) * -1;

    else

      stelle = (SEN_DeciTemperatur % 10); 

    sprintf(Str, "PT100: %d.%d C", (SEN_DeciTemperatur / 10), stelle);      

    Ft_Gpu_CoCmd_Text(Ft_DispWidth/2 + 150, 30, 27,OPT_RIGHTX|OPT_CENTERY,Str);  

    if((tmin % 10) < 0)

      stelle = (tmin % 10) * -1;

    else

      stelle = (tmin % 10); 

    sprintf(Str, "min: %d.%d C", (tmin / 10), stelle);      

    Ft_Gpu_CoCmd_Text(Ft_DispWidth/2 + 150, 55, 27,OPT_RIGHTX|OPT_CENTERY,Str);  

    if((tmax % 10) < 0)

      stelle = (tmax % 10) * -1;

    else

      stelle = (tmax % 10); 

    sprintf(Str, "max: %d.%d C", (tmax / 10), stelle);      

    Ft_Gpu_CoCmd_Text(Ft_DispWidth/2 + 150, 80, 27,OPT_RIGHTX|OPT_CENTERY,Str);  

_delay_ms(1);

void mcp3551_init()

{

  _delay_ms(10);

  // Init:

   ConfigureCSPin();

  // Toggle CS one time to init MCP355x

  SelectMCP();

  _delay_ms(80);

  SPID.DATA = 0;

  while(!(SPID.STATUS & 0x80)); 

  SPID.DATA = 0;

  while(!(SPID.STATUS & 0x80)); 

  SPID.DATA = 0;

  while(!(SPID.STATUS & 0x80)); 

  DeselectMCP();

  _delay_ms(10);

}

void mcp3551_StosseMessungAn()

{  

  int32_t tmp;

  SelectMCP();  

  _delay_us(15);  

  // Wenn RDY auf Low, Messung abholen:

  if(IsMCPReady())

  {

    tmp = mcp3551_getData();

    _delay_us(15);

    mcp3551_StosseMessungAn();    

  }  

  DeselectMCP();  

  _delay_us(15);

}

int32_t mcp3551_getData()

{  

  // CS low

  SelectMCP();

  _delay_us(15);

  if(IsMCPReady())

  {

    // Wenn Messung fertig:  

    uint32_t LSByte=0;

    uint32_t MSByte=0;

    uint32_t HSByte=0;

    uint8_t is_neg = 0;  

    SPID.DATA = 0;

    while(!(SPID.STATUS & 0x80)); 

    HSByte=(uint32_t)SPID.DATA;

    SPID.DATA = 0;

    while(!(SPID.STATUS & 0x80)); 

    MSByte=(uint32_t)SPID.DATA;

    SPID.DATA = 0;

    while(!(SPID.STATUS & 0x80)); 

    LSByte=(uint32_t)SPID.DATA;    

    // CS high

    DeselectMCP();

    _delay_us(15);

    uint32_t data = LSByte;

    data |= (MSByte<<8);

    if(HSByte & 32)

      is_neg = 1;

    HSByte &= 0b00111111;    // Clear OV and DR

    data |= (HSByte<<16);

    // Check if sign bit is set

    if(is_neg)

    {    

      // Measure is negative

      int32_t ret = 0xFFE00000;

      ret |= data;

      return ret;

    }

    else

    {

      // Measure is positive

      return (int32_t)data;

    }    

  }

  // CS high

  DeselectMCP();

  _delay_us(15);

  return 0;

}

// Berechnung der PT100 Temperatur:

uint8_t BerechnePT100Temperatur(int16_t *Temperatur)

{

  int32_t Spannung;

  float Widerstand, delta;

  float Berechnung;

  float A = (float)3.9083 / pow(10,3);

  float B = (float)-5.775 / pow(10,7);

  float R0 = (float)100;

  Spannung = mcp3551_getData();

  if(Spannung <= (int32_t)0)

    return 0;    

  // Spannung über den Refferenzwiderstand:

   delta = (float)2097152 - (float)Spannung;

  // Widerstand berechnen:

  Widerstand = ((float)6800 / delta) * (float)Spannung;

  Widerstand *= 2;

  // Wenn Temperatur tiefer als -100 °

  if(Widerstand < 60)

    return 0;

  // Temperatur Polynomial berechnen:

   Berechnung = (sqrt(pow((R0*A),2)-(float)4*B*R0*(R0 - (float)Widerstand))-(A*R0)) / ((float)2*B*R0);

   *Temperatur = (int16_t)(Berechnung*(float)10);

  return 1;

}