Difference between revisions of "Best practices"

Revision as of 20:43, 8 June 2026

Best Practices

Environment

Keep the device away from direct sunlight, radiators, and fireplaces — it is sensitive to temperature and lighting changes.
Position the inlet away from localized emission sources unless intentionally measuring them.
For indoor use, avoid placement near HVAC vents or drafts.

Sampling Configuration

Sample frequency:
- Ambient immission monitoring: 180–600 seconds (3–10 min)
- Direct emissions from wood stoves (µg vs ng range): 10–30 seconds
- Note: increasing frequency may increase noise.

Airflow:
- Adjustable roughly between 25 and 500 mL/min (default 300 mL/min); the usable range narrows as the filter loads. With Auto Flow Control the device sets the rate automatically from the measured BC concentration.
- Higher airflow improves signal strength but loads the filter faster.

Pollution Level	Daily Avg BC	Recommended Airflow
Heavy pollution	>2000 ng/m³	50 mL/min
Typical urban	~500 ng/m³	100–250 mL/min
Low pollution	<500 ng/m³	300–400 mL/min

When Auto Flow Control is enabled, the device adjusts airflow automatically based on measured BC concentration — reducing flow when BC is high (to extend filter life) and increasing flow when BC is low (for better signal).

Signal Quality

Signal-to-noise ratio improves with:

Higher BC loads
Higher air volume per sample
Smaller sample spot diameter

Filtering: Apply median/average filtering (denoise slider) to reduce noise. The rolling average is closer to the "real" value than individual data points.

Calibration: Always calibrate after every filter change for reliable filter status indication and accurate measurement.

Filter Management

At the default airflow in a typical urban environment (~500 ng/m³), a filter lasts approximately 3–5 days.
In heavily polluted areas, a filter may saturate in 6–12 hours.
Filter status is derived from attenuation (ATN): measurements are fully quantitative up to about ATN 75 and degrade at higher loading; the device flags the filter for replacement around ATN 120. (The ATN value is not a simple percentage of light loss.)
The Airflow Reference table in Settings helps estimate filter lifetime for your conditions.

Supported Filter Papers

Filter Paper	Scattering Correction Factor
Pall T60A20	1.0
AE33 Filter	0.75
AE51 Filter	1.0

Other filter papers can be supported by determining their scattering factor. Send a sample to jd@bcmeter.org for calibration.

@@ Line 15: / Line 15: @@
 * '''Airflow:'''
-** Minimum 40 mL/min, maximum 400 mL/min (hardware-dependent).
+** Adjustable roughly between 25 and 500 mL/min (default 300 mL/min); the usable range narrows as the filter loads. With Auto Flow Control the device sets the rate automatically from the measured BC concentration.
 ** Higher airflow improves signal strength but loads the filter faster.
@@ Line 45: / Line 45: @@
 * At the default airflow in a typical urban environment (~500 ng/m³), a filter lasts approximately '''3–5 days'''.
 * In heavily polluted areas, a filter may saturate in '''6–12 hours'''.
-* The filter is considered saturated at approximately '''30% attenuation'''. Beyond this, accuracy degrades — values are flagged in the CSV.
+* Filter status is derived from attenuation (ATN): measurements are fully quantitative up to about ATN 75 and degrade at higher loading; the device flags the filter for replacement around ATN 120. (The ATN value is not a simple percentage of light loss.)
 * The [[Configuration#Measurement Tab|Airflow Reference table]] in Settings helps estimate filter lifetime for your conditions.