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4-2 Model 3936 Scanning Mobility Particle Sizer

(SMPS

) Spectrometer

Selecting Flow Rates

To run the Aerosol Instrument Manager

for SMPS™ software, the

ratio of the Sheath Air to Polydisperse Aerosol flow rates on the

Electrostatic Classifier is normally set to 10:1. To achieve the best

resolution, the Sheath flow rate and the Excess flow rate must

equal each other, and also the Polydisperse Aerosol flow rate and

the Monodisperse Aerosol flow rate must also equal each other.

Figure 4-2

Schematic Flow Diagram of the Classifier with Long DMA

With the Model 3080 Classifier, flow control is very easy (see

Figure 4-2 and Figure 4-3). The Sheath and Excess flows are

running in a continuous loop so they have to be equal. The

polydisperse flow is controlled by the CPC drawing aerosol through

the Classifier, so the monodisperse and polydisperse flows have to

be equal. The Sheath flow is controlled by setting the appropriate

value on the front panel of the Classifier. The CPC flow is fixed at

1 L/min, in the case of a 3772, 3010 CPC or 3785 WCPC. For a

3782 WCPC or 3786 UWCPC, the flow is fixed at 0.6 L/min. And

the flow can be toggled between 0.3 L/min or 1.5 L/min in the case

of the 3775, 3776, 3022A or 3025A CPC. Other flows require the

TSI Instruments 3936 User Manual

Questions and Answers: