Mobility Analyzers

Mobility analyzer
The principle of the mobility analyzer

The mobility analysis in NAIS corresponds exactly to the parallel electrical aerosol measurement principle. The capacitances between the collecting sections and sections of central electrodes for the NAIS are presented in Table 1. The table also shows the voltages of the respective sections.

Note that the collecting sections 9, 13 and 17 have some capacitance with two adjacent central sections. These sections may show higher noise levels compared to neigbouring sections when the central electrode voltages have not stabilized yet after power-on or when the instrument is vibrating.

The electrical capacitance (in pF) between collecting sections and the four central sections of the NAIS mobility analyzer.

Collecting
section
Central section (UA)
9V 25V 220V 800V
03.03000
12.53000
22.43000
32.50000
42.91000
53.86000
65.59000
78.25000
88.71000
94.004.5200
1008.6900
1108.7400
1209.8500
1305.855.20
140010.60
150011.10
160013.50
170011.78.0
1800019.0
1900025.3
2000025.4
2100025.5

Under NTP conditions the NAIS uses a sheath flow rate of 60\,l/min and a sample flow of 27 l/min per analyzer (30 l/min per analyzer on some older instruments).

The NAIS automatically adjusts its sample and sheath airflow speeds so that the particle sizing and volume sample flow remain constant regardless of air pressure. This allows the instrument to be used in varying conditions e.g. for airborne measurements \citep{smirme2010as3p}.