A new method of DMA operation has been implemented in which the flow rates are continuously changed in conjunction with the applied voltage. By optimizing the flow and voltage ramps, improvements can be made in the DMA's measurable size range, counting statistics, resolution, or a partial combination of each of these. Detailed modeling of this technique suggests that errors on the order of 2 to 5% result from incorrect assumptions concerning the flow profile within the DMA. The experimental system enabled accurate control of flows that were varied by an order of magnitude in as little as 30s. Excellent agreement was obtained between mobility distributions recovered from a voltage ramp, a flow ramp, and a combined voltage and flow ramp. Slight deviations were apparent in the recovered data as the flow scan time was reduced from 60 to 30s. Copyright (C) 2000 Elsevier Science B.V.