rtd_basic.c

来自「8051试验程序 基础教材」· C语言 代码 · 共 87 行

/*
Author      : MicroConverter Apps

Date     : April 2004

Hardware : ADuC845, ADuC847

Description : Performs conversions on an external RTD connected as shown in the diagram below, and
           returns the result via the UART to a PC. Use Hyperterminal to view the results.

           This progrqam will also work on an ADuC848 except account must be taken of the fact that
           the ADuC848 ADC is only 16-bits. Therefore the calculations will have to be edited as will
           the output code.


     ADuC845/7: RTD sensors
RTD CONNECTIVITY & CALCULATION
                    |-------|
          o---------| RTD#1 |-------o-------- Ain1
          |         |-------|       |
          |                         o-------- IEXC1(Ain7).....200uA
          |
          0-------------------------o-------- Ain2
          \                         |
          /                         o-------- Refin+
          \5k56 RTD load
          /
          |
          o---------------------------------- Refin-
          |
         AGND
 RTD equation = Trtd = (Rrtd-100ohm)/0.3851ohm/'C
    therefore at 0ohm Trtd = (-100)/0.3851 = -259.67'C
 Voltage across 5k6 resistor = 200uA x 5k56 = 1.112V
    Using 80mV unipolar range we get (1.112V x 80mV)/2.5v = 35.56mV
 therefore with 35.56V across RTD Trtd =
             Trtd = [(35.56mV/200uA) - 100]/0.3851  = +202.03'C
 Total temperature span = -259.67'C -> +202.03'C = 461.70
 The offset is the 0ohm figure of -259.67'C

ADuC845/847 Eval board S4 switch settings: RTD Ain1, RTD Ain2, RTD REFIN+, RTD REFIN- should be ON.
All other switches should be OFF.
*/


#include<ioADuC845.h>         //To use ADuC847 simply change this include file to <ADuC847.h>
#include<stdio.h>

long ADC=0;                            // raw ADC conversion result
float RTD=0;                  // final result

void serial_init()
{
   T3CON = 0x83;                  //configure timer 3...
   T3FD  = 0x12;                  //...for 9600 baud
   SCON  = 0x52;
}


void main (void)
{
   serial_init();                //Configure serial port for 9600 Baud
   ADC0CON1 = 0x22;              // Full Buff, unipolar, 0->80mV
   SF       = 0x45;              // ADC rate = 20Hz
   ADCMODE  = 0x24;        // Ofs Cal
   ADCMODE  = 0x25;        // Gain cal

   ADC0CON1 = 0x22;           //Full Buff, unipolar, 80mV
   ICON     = 0x01;           //Enable RTD#1 current source (IEXC1 on pin 11/Ain7)


   for(;;)              //Do forever
   {
      //RTD measurement and temperature calculation
      ADC0CON2 = 0x4A;             // Refin+/-, Ain1->Ain2
      ADCMODE  = 0x22;            // Single conv, primary ADC....Conv on RTD on Ain1
      while(! ADCSTAT_bit.RDY0){
      }             // Wait for RDY0 Flag
      ADC = ADC0H*0x10000+ADC0M*0x100+ADC0L;// raw ADC data
      RTD = 461.7*ADC/16777215.0-259.67;   // gain & offset
      //Based on [Trtd = (Rrtd - 100ohms)/0.3851ohms/'C] sensor
      ADCSTAT_bit.RDY0     = 0;               // clear ready bit...
      printf("%+.2fC\n\r", RTD);

   }
}