adafruit / Adafruit_CircuitPython_SCD30

Helper library for the SCD30 e-CO2 sensor
MIT License
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Refinement to altitude vs ambient_pressure in documentation #16

Open kevinjwalters opened 3 years ago

kevinjwalters commented 3 years ago

The altitude property which links with the device's NVRAM-stored parameter is currently documented as

Specifies the altitude at the measurement location in meters above sea level. Setting this value adjusts the CO2 measurement calculations to account for the air pressure's effect on readings.

I was about to set both but then couldn't work out why it would need altitude if it had QFE pressure. It's worth something along the lines of the note from Section 1.4.8 of the data sheet:

Setting altitude is disregarded when an ambient pressure is given to the sensor

I.e. ambient_pressure if the first choice of parameter to set if the value is available otherwise it can be disabled with 0 and then altitude (height above mean sea level) can be set as the next best adjustment.

May also be worth a note reminding users not to set altitude frequently as it's stored in NVRAM, presumably some type of write-limited EEPROM.

kevinjwalters commented 3 years ago

Since the pressure only goes down to 700mb (hPa) any users/sensors sited above ~ 9000ft amsl and will have to use altitude setting.