Eventually, automated, batch verified, basement blending and loop distribution systems came into use. These systems reduced batch to batch variation but, still relied upon peristaltic pumps for dispense volume control.
Particle generation from tubing and high chemical cost drove a need for a change at sub-micron (90 Nanometer) geometries. Various flow control schemes were evaluated including paddle wheel, turbine and differential pressure based systems ultimately settling on ultrasonic based flow controllers as the preferred technology.
However, as feature sizes continue to shrink, the chemistries required to achieve smaller feature sizes becomes more and more exotic. Mixtures including peroxides and hydroxides naturally out-gas which produce bubbles in the dispensed flow streams, and in some cases results in a two-phase flow regime. At comparatively low volumetric void fractions bubble concentrations (less than 10%) can adversely affect measurement accuracy of DP, Paddle Wheel, Turbine or Ultrasonic flow measurement technologies to the extent that many of these flow measurement technologies cease to operate satisfactorily.
Malema has developed a mass based, flow controller for slurry and clear chemical dispense applications. Based on Coriolis mass flow rate measurement, the Malema Coriolis Mass Flow Controller (CMFC) is essentially bubble tolerant.
Flow meter / flow controller manufacturers used an assortment of software techniques to filter the effects of these entrained bubbles with limited results. Since Coriolis measures mass directly, bubbles have very little effect on measured or dispensed volumes.
A brief history of the Coriolis Effect, how it is applied to direct mass flow rate measurements will be presented and discussed including a description of Malema’s family of CMFCs and associated performance data.