Arduino MKR Therm Shield Not Measuring Temperatures Below 0 °C

[hpcgrafana]

Here is calibrated LN2 graph:

And code:

cpp

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#include <WiFiNINA.h>
#include <PubSubClient.h>
#include <Arduino.h>
#include <Arduino_MKRTHERM.h>
#include <math.h>  // for pow function

// WiFi seadistused
const char* ssid = "xxxxxxxxxxxxxxxxxxxxxxxxxxx"; // Sisesta oma WiFi SSID
const char* password = "xxxxxxxxxx"; // Sisesta oma WiFi parool

// MQTT serveri andmed
const char* mqtt_server = "xxxxxxxxx";
const char* mqtt_user = "xxxxxxxx";
const char* mqtt_password = "xxxxxxxxxxxx";
const char* mqtt_topic = "thermocouple1/temperature";
const char* clientId = "arduinotherm1";

// Termopaar
THERMClass myTherm; // Muutke 'THERM' näiteks 'myTherm'

// Non Linear Thermocouple Compensation Coefficients
// Used to calculate actual temp from voltage from the MAX31855
const float c0 = 0;
const float c1 = 27.0;   // alandatud
const float c2 = -0.20;   // hoia
const float c3 = 0.75;    // alandatud
const float c4 = 0.40;    // hoia
const float c5 = 0.12;    // alandatud
const float c6 = 0.018;   // hoia
const float c7 = 0.001;    // hoia
const float d0 = 0;
const float d1 = 24.0;   // alandatud
const float d2 = -0.70;    // hoia
const float d3 = 0.045;    // hoia
const float d4 = -0.002;   // hoia
const float d5 = 0.00005;  // hoia
const float d6 = -0.0000005; // hoia
const float d7 = 0;        // hoia
const float MAXc = 41.276;  // µV/°C

WiFiClient wifiClient;
PubSubClient mqttClient(wifiClient);

void setup() {
    Serial.begin(9600);

    // Ühendu WiFi võrguga
    Serial.print("Connecting to ");
    Serial.println(ssid);
    WiFi.begin(ssid, password);

    // Oota, kuni WiFi on ühendatud
    while (WiFi.status() != WL_CONNECTED) {
        delay(1000);
        Serial.print(".");
    }

    Serial.println("\nWiFi connected!");
    Serial.print("IP address: ");
    Serial.println(WiFi.localIP());

    // Seadista MQTT server
    mqttClient.setServer(mqtt_server, 1883);

    // Termopaar
    if (myTherm.begin() == 0) {
        Serial.println("Termopaar ei initsialiseeru!");
        while (1); // Jääb lõksu
    }
    Serial.println("Termopaar initsialiseeritud.");
}

float TCComp(float external, float internal) {
    float TCTemp;
    float Vout = MAXc * (external - internal) / 1000;  // calculate volts from external and internal temperatures in millivolts

    // Apply non-linear temperature compensation
    if (Vout < 0) {
        TCTemp = internal + c0 + (c1 * Vout) + (c2 * pow(Vout, 2)) + (c3 * pow(Vout, 3)) + (c4 * pow(Vout, 4)) + (c5 * pow(Vout, 5)) + (c6 * pow(Vout, 6)) + (c7 * pow(Vout, 7));  // Below Zero
    } else {
        TCTemp = internal + d0 + (d1 * Vout) + (d2 * pow(Vout, 2)) + (d3 * pow(Vout, 3)) + (d4 * pow(Vout, 4)) + (d5 * pow(Vout, 5)) + (d6 * pow(Vout, 6)) + (d7 * pow(Vout, 7));  // Above Zero
    }

    return TCTemp;
}

void loop() {
    // Kontrolli, kas MQTT on ühendatud, ja ühildu
    if (!mqttClient.connected()) {
        reconnect();
    }
    mqttClient.loop();

    float internalTemp = myTherm.readReferenceTemperature();  // seadme ümbritseva temperatuuri lugemine
    float externalTemp = myTherm.readTemperature();           // termopaari temperatuuri lugemine

    // Rakenda kompensatsioon
    float compensatedTemp = TCComp(externalTemp, internalTemp);

    if (isnan(compensatedTemp)) {
        Serial.println("Kompenseeritud temperatuuri lugemine ebaõnnestus!");
    } else {
        Serial.print("Kompenseeritud temperatuur: ");
        Serial.print(compensatedTemp);
        Serial.println(" °C");

        // Teisenda temperatuur stringiks ja saada MQTT serverisse
        char temperatureStr[6];
        snprintf(temperatureStr, sizeof(temperatureStr), "%.2f", compensatedTemp);
        mqttClient.publish(mqtt_topic, temperatureStr);

        Serial.println("Kompenseeritud temperatuur saadetud MQTT serverisse");
    }

    delay(1000); // Oodake 1 sekund enne järgmise lugemise tegemist
}

void reconnect() {
    // Oota, kuni oleme ühenduses
    while (!mqttClient.connected()) {
        Serial.print("Attempting MQTT connection...");
        // Ühenda, kui oleme ühenduses
        if (mqttClient.connect(clientId, mqtt_user, mqtt_password)) {
            Serial.println("connected");
        } else {
            Serial.print("failed, rc=");
            Serial.print(mqttClient.state());
            Serial.println(" try again in 5 seconds");
            delay(5000);
        }
    }
}