Can the SMPS spectrometer measure aerosols at different temperatures and pressures?
Temperature and pressure affect the mean-free-path in air which will affect the electrical mobility of the particles. Charging of the aerosol will also be effected. The effects of pressure and temperature deviating from standard conditions have not been characterized; however, the sample temperature and pressure measured by the SMPS spectrometer are used in electrical mobility and charging calculations
Can the SMPS spectrometer measure particles in a gaseous medium other than air?
The SMPS program has built in gas and charging parameters for air (or nitrogen) but physical properties of other carrier gases such as temperature, pressure, mean free path, and gas viscosity can be manually entered and used for calculations.
Do I need a 10-to-1 flow ratio between the aerosol flow and the sheath air flow?
The SMPS software allows for flow ratios other than 10 to 1. For most applications, the recommended flow ratio is 10 to 1. High flow ratios will give better size resolution but lower the particle count statistics. This may be useful when measuring the exact size of monodisperse aerosols. Lower flow ratios will improve the counting statistics, but decrease the effective size resolution. This is useful for filter testing when measuring downstream of a high-efficiency filter. Flow ratios that differ too much from 10 to 1 may cause turbulence in the DMA and degrade the sizing resolution.
Does the SMPS software collect particle concentration data on both the up and down voltage scans?
The SMPS spectrometer Model 3938 has implemented an instantaneous down scan; therefore only up scan data are used.
How is the charge distribution determined?
The SMPS software uses tables of charge probabilities named Charge***.dat, where *** represents the type of aerosol neutralizer (soft x-ray, or krypton) and the particle polarity (positive or negative) used. The tables contain 162 particle size channels with charge probabilities up to 10 positive charges and were generated based on the work of Alfred Wiedensohler1.References 1. Wiedensohler, A., 1988, "An Approximation of the Bipolar Charge Distribution for Particles in the Submicron Size Range," Journal of Aerosol Science, 19(1): 387–389
How is the SMPS spectrometer calibrated?
Complete SMPS spectrometer systems purchased from TSI are
set up and compared to standard instruments at TSI to verify correct operation.
The CPC, Electrostatic Classifier, and impactor are components of the SMPS spectrometer
system and are calibrated independently.