SCD30 - CO2, Temperature and Humidity Sensor
The SCD30 is an CO2, Temperature and Humidity sensor using the I2C-protocol for communication. For setting up the Raspberry Pi for I2C and connecting the sensor please check the example page.
SCD30_Open
SCD30_Open()
Connects to the SCD30 sensor.
SCD30_Close
SCD30_Close()
Closes the connection to the SCD30 sensor
SCD30_Start
SCD30_Start()
SCD30_Start(Pressure)
Pressure: optional parameter to set the ambient air pressure in mBar
Pressure = 0 -> Pressure compensation will be disabled
Pressure = 700..1200 -> ambient air pressure in mBar
Starts continuous measurement with optional ambient air pressure compensation
The CO2 measurement value can be compensated for ambient air pressure by feeding the pressure value in mBar to the sensor. Setting the ambient pressure will overwrite previous and future settings of altitude compensation. Setting the argument to zero will deactivate the ambient pressure compensation.
SCD30_Start() 'Starts measurement with deactivated ambient pressure compensation
SCD30_Start(0) 'Starts measurement with deactivated ambient pressure compensation
SCD30_Start(1010) 'Starts measurement with activated ambient pressure compensation of 1010mBar
SCD30_Stop
SCD30_Stop()
Stops the continuous measurement. This command can be used to save energy. To keep stable and reliable measurement conditions, let the sensor always run.
SCD30_DataAvailable
DataIsAvailable = SCD30_DataAvailable()
DataIsAvailable = 0 or 1
Returns 1, if a measurement is completed and the data can be read, otherwise 0.
while(SCD30_DataAvailable() != 1)
delay(100)
wend
SCD30_ReadData
M = SCD30_ReadData()
M(0) = CO2
M(1) = Temperature
M(2) = Humidity
Reads the data of the last measurement and returns an array with three elements. First element is CO2 in ppm; second elements is temperature in °C; third element is humidity in %RH
Measurement = SCD30_ReadData()
print "CO2: "; Measurement(0)
print "Temperature: "; Measurement(1)
print "Humidity: ";Measurement(2)
SCD30_SetInterval
SCD30_SetInterval(Interval)
Interval = 2…1800
Sets the interval in seconds between the measurements. Interval must be at leat 2s, max. 1800s.
SCD30_SetInterval(2)
SCD30_SetTemperatureOffset
Expert command
SCD30_SetTemperatureOffset(Offset)
Offset >= 0
The on-board humidity and temperature sensor is influenced by thermal self-heating of SCD30 and other electrical components. Design-in alters the thermal properties of SCD30 such that temperature and humidity offsets may occur when operating the sensor in end-customer devices. Also changing the measurement intervall might result in different heat contribution in the sensor. Compensation of those effects is achievable by writing the temperature offset found in continuous operation of the device into the sensor. Temperature offset value is saved in non-volatile memory. The last set value will be used for temperature offset compensation after repowering.
The new temperature offset can be calculated using following equation:
T_Offset,New = (T_SCD30 − T_Reference ) + T_Offset,Old
T_SCD30: actual temperature reading of the sensor
T_Reference: ambient temperature measured with an additional device
T_Offset,Old: The old temperature offset.
Since the CO2 sensor is actively heated, the temperature reading of the sensor is suposed to be higher then the real ambient temperature. Therefore the temperature offset must be a positive value in Kelvin.
Setting up the temperature offset is quite tricky. Maybe it is easier to introduce an offset in your SmallBASIC program.
SCD30_SetTemperatureOffset(2)
SCD30_SetCO2Recalibration
Expert command
SCD30_SetCO2Recalibration(CO2ReferenceValue)
Set Forced Recalibration value (FRC).
Forced recalibration (FRC) is used to compensate for sensor drifts when a reference value of the CO2 concentration in close proximity to the SCD30 is available. For best results the sensor has to be run in a stable environment in continuous mode at a measurement rate of 2s for at least two minutes before applying the calibration command and sending the reference value. Setting a reference CO2 concentration by the here described method will always overwrite the settings from ASC and vice-versa. The reference CO2 concentration has to be within the range 400 ppm ≤ cref(CO2) ≤ 2000 ppm. FRC value is saved in non-volatile memory, the last set FRC value will be used for field-calibration after repowering.
SCD30_SetCO2Recalibration(1000)
SCD30_SetAltitudeRecalibration
Expert command
SCD30_SetAltitudeRecalibration(Altitude)
Altitude >= 0 -> Height over sea level in m
Altitude Compensation.
Measurements of CO2 concentration based on the NDIR principle are influenced by altitude. SCD30 offers to compensate deviations due to altitude by using the following command. Setting altitude is disregarded when an ambient pressure is given
SCD30_SetAltitudeRecalibration(1000)
SCD30_AutomaticSelfCalibration
Expert command
SCD30_AutomaticSelfCalibration([TRUE or FALSE])
(De-)Activate Automatic Self-Calibration (ASC)
Continuous automatic self-calibration can be (de-)activated with the following command. When activated for the first time a period of minimum 7 days is needed so that the algorithm can find its initial parameter set for ASC. The sensor has to be exposed to fresh air for at least 1 hour every day. Also during that period, the sensor may not be disconnected from the power supply, otherwise the procedure to find calibration parameters is aborted and has to be restarted from the beginning. The successfully calculated parameters are stored in non-volatile memory of the SCD30 having the effect that after a restart the previously found parameters for ASC are still present. Note that the most recently found self-calibration parameters will be actively used for self- calibration disregarding the status of this feature. Finding a new parameter set by the here described method will always overwrite the settings from external recalibration and vice-versa. The feature is switched off by default. To work properly SCD30 has to see fresh air on a regular basis. Optimal working conditions are given when the sensor sees fresh air for one hour every day so that ASC can constantly re-calibrate. ASC only works in continuous measurement mode. ASC status is saved in non-volatile memory. When the sensor is powered down while ASC is activated SCD30 will continue with automatic self-calibration after repowering without sending the command.
SCD30_AutomaticSelfCalibration(1) 'Turns on ASC
SCD30_AutomaticSelfCalibration(0) 'Turns off ASC