/*************************************************************************
 * vishay_NTCLE100E3103_to_F
 *
 * Conversion routine: Thermistor reading (volts) to degF
 *                     Uses extended Steinhart and Hart approximation
 * Routine takes 1 argument:
 *   psub->a    - Voltage drop across thermistor (some_PV_name)
 *   psub->val  - returns calculated temperature in degrees Farenheight
 *
 ***************************************************************************/

#include        <vxWorks.h>
#include        <types.h>
#include        <dbDefs.h>
#include        <dbAccess.h>
#include        <dbFldTypes.h>
#include        <errMdef.h>
#include        <recSup.h>
#include        <subRecord.h>

float vishay_NTCLE100E3103_to_F(struct subRecord *psub)
  {
/*constants for extended Steinhart and Hart equation for Vishay NTCLE100E3103*/
  float A = 3.354016E-3;
  float B = 2.569850E-4;
  float C = 2.620131E-6;
  float D = 6.383091E-8;
/*fixed resistor value in voltage divider*/
  float RFIXED = 10000.0;
/*voltage output of voltage reference used as source*/
  float VREF = 10.0;
  float Inv_Temperature,G1,G2,G3,R1,Temperature;
/*voltage drop across thermistor*/
  float VDROP;

  static unsigned char UDF = TRUE;
  if(UDF)
    {
    psub->udf = FALSE;
    UDF = FALSE;
    }

  VDROP = psub->a;
  psub->val = 0.;

/*The constants from Vishay use the ratio R1/RFIXED in the equation. So, we can
simplify the equation R1 = (RFIXED)/((VREF/VDROP)-1) to be...*/
    R1 = 1/((VREF/VDROP)-1);

    G1=log(R1);
    G2=exp(2*log(B1));
    G3=exp(3*log(B1));
    Inv_Temperature=A+(B*G1)+(C*G2)+(D*G3);
    Temperature=(1/Inv_Temperature)-273.15;
/*now we have centigrade*/
    Temperature=(Temperature*1.8)+32;
/*now we have farenheight*/

  psub->val = Temperature;
  return(0);           
  };