CSV data format

CSV Data Format

bcMeter stores measurement data as CSV files. This page documents the file format and column definitions.

File Format

Property	Value
Delimiter	Semicolon (;)
Encoding	UTF-8
Decimal separator	Dot (.)
Line ending	LF (\n)
First row	Column headers

Filename Convention

• Active session: YY-MM-DD_HHMMSS.csv on ESP32 builds, DD-MM-YY_HHMMSS.csv on Raspberry Pi builds (based on session start time)
• Fallback (no RTC sync): nosync_HHMMSS.csv (based on uptime)

Column Definitions

Core Columns (always present)

Column	Type	Unit	Description
bcmDate	string	DD-MM-YY	Measurement date
bcmTime	string	HH:MM:SS	Measurement time
bcmRef_880nm	float	V	Reference channel voltage (880nm LED through clean filter)
bcmSen_880nm	float	V	Sensor channel voltage (880nm LED through sample spot)
bcmATN_880nm	float	—	Attenuation at 880nm = −100·ln(Sen/Ref), dimensionless. The absorption cross-section σ enters the BC concentration, not ATN.
BCngm3_unfiltered_880nm	float	ng/m³	Real-time BC concentration (unsmoothed)
BCngm3_880nm	float	ng/m³	BC concentration with rolling average applied
relativeLoad	float	%	Filter loading (0 = clean, 100 = saturated)
AAE	float	—	Ångström Absorption Exponent (requires multi-wavelength)
Temperature	float	°C	Internal device temperature
airflow	float	L/min	Measured airflow rate

Multi-Wavelength Columns (in development, not in shipped hardware)

Same structure as 880nm, repeated for each wavelength:

• bcmRef_520nm, bcmSen_520nm, bcmATN_520nm, BCngm3_unfiltered_520nm, BCngm3_520nm
• bcmRef_370nm, bcmSen_370nm, bcmATN_370nm, BCngm3_unfiltered_370nm, BCngm3_370nm

Environmental Columns (optional, sensor-dependent)

Column	Type	Unit	Description
humidity	float	%	Relative humidity (BME280/SHT4x)
hPa	float	hPa	Atmospheric pressure (BME280)
PM2.5	float	µg/m³	Particulate matter <2.5µm (SPS30)
PM10	float	µg/m³	Particulate matter <10µm (SPS30)

GPS Columns (optional, if GPS module connected and has fix)

Column	Type	Unit	Description
lat	float	degrees	Latitude (WGS84)
lon	float	degrees	Longitude (WGS84)
altitude	float	m	GPS altitude above sea level

Metadata Columns

Column	Type	Description
notice	string	System notices or warnings per data point
sampleDuration	float	Actual measurement duration for this sample (seconds)
notes	string	User-added annotations

Example Data

bcmDate;bcmTime;bcmRef_880nm;bcmSen_880nm;bcmATN_880nm;BCngm3_unfiltered_880nm;BCngm3_880nm;relativeLoad;AAE;Temperature;airflow
04-03-26;19:37:09;0.9679;0.9321;3.76;1686;1686;0;0;0;0.4659
04-03-26;19:42:09;0.9745;0.9335;4.3;4028.5;1686;0;0;0;0.3088
04-03-26;19:47:09;0.9752;0.9315;4.59;2371.4;1830.2;0;0;0;0.2832

Import Notes

• Excel: Use "Text Import Wizard" and set delimiter to semicolon. The date format DD-MM-YY may need manual conversion.
• Python/Pandas: pd.read_csv('file.csv', sep=';')
• R: read.csv2('file.csv') (uses semicolon by default)