New applications in biology, medicine, and manufacturing require reliable measurements of liquid flows smaller than 100 υL/min. NIST addressed this requirement by improving the reliability and ease of use of NISTs Dynamic Gravimetric Micro-Flow Standard. The meter under test is now connected to the weighing beaker by a liquid bridge that reduces variations in parasitic surface tension forces as the level of liquid in the collection beaker rises. We describe other improvements to NISTs standard (e.g. pipette positioning and evaporation reduction) and provide an uncertainty analysis for the present system. The gravimetric standard measures liquid flow between 0.1 υL/min and 100 υL/min with uncertainty ranging from 4.5 % to 0.04 %. Repeated calibrations of five commercially available micro-flow meters (one for nearly 2 years) show that their calibrations are reproducible within 1.5 % for many months.
June 26-28, 2019
micro-flow, flow meter, primary standard, uncertainty