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我目前正在使用 Adafruit_MAX31855 IC 和 K 型热电偶。出于某种原因,我在串行监视器中得到了这个......

Internal Temp = 32.44
nan // printed from thermocouple.readCelcius()
Internal Temp = 32.44
nan
Internal Temp = 32.44
nan
Internal Temp = 32.44
nan
Internal Temp = 32.38
nan
Internal Temp = 32.38
nan
Internal Temp = 32.38
nan
Internal Temp = 32.38
nan
Internal Temp = 32.31

现在我知道所有的接线都正确,因为我得到了内部温度。除此之外,.readCelcius() 命令有时会返回正确的读数。起初我以为可能是最高温度超出了芯片的能力范围,但即使在 40 摄氏度下运行时,我有时也会得到这个。

#include <SPI.h>
#include "Adafruit_MAX31855.h"

int HeaterPWM = 12;
int LEDPin = 13;
long _startTime;
long _currentTime;

#define MAXDO   3
#define MAXCS   4
#define MAXCLK  5

Adafruit_MAX31855 thermocouple(MAXCLK, MAXCS, MAXDO);


void setup() {
  while (!Serial); // wait for Serial on Leonardo/Zero, etc

  Serial.begin(9600);
  pinMode(HeaterPWM, OUTPUT);
  pinMode(LEDPin, OUTPUT);

  Serial.println("MAX31855 test");
  // wait for MAX chip to stabilize
  delay(500);
}

void loop() {

  _startTime = millis();
  while (_currentTime - _startTime < 3000) // heater on for 3 seconds at a time
  {
    Serial.print("Internal Temp = ");
    Serial.println(thermocouple.readInternal());

    _currentTime = millis();
    analogWrite(HeaterPWM, 150);
    digitalWrite(LEDPin, HIGH);
    double c = sampleCelcius(1);
    Serial.println(c);
    delay(10);
  }

  _startTime = millis();

  while (_currentTime - _startTime < 10000) // heater on for 3 seconds at a time
  {
    Serial.print("Internal Temp = ");
    Serial.println(thermocouple.readInternal());

    _currentTime = millis();
    analogWrite(HeaterPWM, 0);
    digitalWrite(LEDPin, LOW);
    double c = sampleCelcius(1);
    Serial.println(c);
    delay(10);
  }
}

double sampleCelcius(int maxSamples)
{
  double result = NAN;
  for (int i = 0; i < maxSamples; i++)
  {
    result = thermocouple.readCelsius();
    if (!isnan(result)) // exit on first good reading.
      break;
    delay(10);
  }
  return result;
}

我已经检查了我所有的电压和 PWM 输出等。以及对热电偶进行基准测试。当它在室温下工作时,它是正确的。当加热器打开时我得到读数而不是 Nan 时,我似乎得到了非常高的数字,以千计,这显然是不正确的。它应该在65摄氏度左右。

有任何想法吗?

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1 回答 1

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事实证明,Adafruit_MAX31855 IC 不兼容在导电表面上使用,并且“加热”也会向热电偶发送电压,从而导致读数丢失。

于 2017-11-10T15:46:21.047 回答