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Model 3068B Features
Increased sensitivity—±1 fA (two times better than Model 3068A)
Wide dynamic range with no range settings(±12,500 fA)
Temperature stabilized to significantly reduce drift
Automatic flow control (0.3 to 10 L/min) when used with external vacuum source
Reduced internal particle losses
Modern communications with RS-232 and USB interface
Membrane touch-panel with two-line, LCD alphanumeric display
Digital displays of either current or concentration and flow rate
Fundamental particle concentration measurement when used with a TSI Electrostatic Classifier
Wide particle size range (0.002 to 5.0 μm)

Applications
The Model 3068B provides accurate measurements of total aerosol charge. In addition to fundamental particle charge experiments, when paired with a TSI Electrostatic Classifier, the Aerosol Electrometer is commonly used to calibrate condensation particle counters too.

Operation
Aerosol is drawn into the Model 3068B by anexternal pump. A built-in thermal flowmeter andproportional valve controlled by a microprocessormaintain the user-set volumetric aerosol sample rate,Q. An electrically-isolated, high-efficiency filter
collects the charged particles. Then, a highly sensitiveBelectrometer measures the electrical current, I, drainingfrom the filter.

A front-panel display and membrane switches provide an easy-to-use interface. The two-line display provides a real-time readout of total current and flow.If a classifier is used and the average particle charge is known, the display will also provide an indication of particle concentration, avoiding a manual calculation.The calculation is based on the equation on the opposite page.

User menus allow the flow to be set anywhere between 0.3 and 10 L/min and then controlled automatically.Averaging time can be set on the display from 1 to 60 seconds, and the analog output can be configured for a variety of ranges. In addition, other parameters, including temperature and pressure, may be displayed.