After installing the library we can open an example sketch. Just go to File > Examples > BlueDot SGP40 SHT40 and open the sketch SGP40_SHT40_Test.

At the start of the sketch, you can make a few changes to your SHT40 setup, but you can upload and run your sketch without changes as well. 

The default setup for the SHT40 is to run all measurements with high precision. Changing the measurement precision affects the measurement duration, noise level, and energy consumption of your sensor. If power consumption is not an issue for your application, just run the sensor with high precision.

   //Here we can configure the SHT40 Temperature and Humidity Sensor 
   //First we set the measurement precision
   //There are three precision levels: High, Medium and Low
   //The precision levels direclty affect the measurement duration, noise level and energy consumption
   //On doubt, just leave it on default (High precision)
   sht4.setPrecision(SHT4X_HIGH_PRECISION);

   switch (sht4.getPrecision()) {
     case SHT4X_HIGH_PRECISION: 
       Serial.println(F("SHT40 set to High precision"));
       break;
     case SHT4X_MED_PRECISION: 
       Serial.println(F("SHT40 set to Medium precision"));
       break;
     case SHT4X_LOW_PRECISION: 
       Serial.println(F("SHT40 set to Low precision"));
       break;

The second setup allows you to activate the internal hotplate from the SHT40 sensor, as well as to adjust the temperature level and heating duration.

But why would you need to activate the hotplate in the first place? The SHT40 is a polymer-based capacitive sensor, which operates best between 5°C to 60°C and 20% and 80% relative humidity. When the sensor is permanently operating in an environment with very high relative humidity, for example close to 90%, the measured value may slowly increase due to an offset.

You can correct this offset by activating the hotplate and shortly increasing the temperature from the SHT40. By periodically activating the hotplate you can eliminate any long-term offsets caused by high humidity. For more information, please consult the Sensirions application note on the subject.

  // The SHT40 has a built-in heater, which can be used for self-decontamination.
  // The heater can be used for periodic creep compensation in prolongued high humidity exposure.
  // For normal operation, leave the heater turned off.

  sht4.setHeater(SHT4X_NO_HEATER);

  
  switch (sht4.getHeater()) {
     case SHT4X_NO_HEATER: 
       Serial.println(F("SHT40 Heater turned OFF"));
       break;
     case SHT4X_HIGH_HEATER_1S: 
       Serial.println(F("SHT40 Heater: High heat for 1 second"));
       break;
     case SHT4X_HIGH_HEATER_100MS: 
       Serial.println(F("SHT40 Heater: High heat for 0.1 second"));
       break;
     case SHT4X_MED_HEATER_1S: 
       Serial.println(F("SHT40 Heater: Medium heat for 1 second"));
       break;
     case SHT4X_MED_HEATER_100MS: 
       Serial.println(F("SHT40 Heater: Medium heat for 0.1 second"));
       break;
     case SHT4X_LOW_HEATER_1S: 
       Serial.println(F("SHT40 Heater: Low heat for 1 second"));
       break;
     case SHT4X_LOW_HEATER_100MS: 
       Serial.println(F("SHT40 Heater: Low heat for 0.1 second"));
       break;
  }

After starting the sketch, you will notice that the VOC Index will still be at zero. This is normal and only lasts for a few moments.