CASE STUDIES IN INNOVATION: Measuring the Flowrate of Reactive Ammonia Gas

Nov. 1, 2012

In the October 2012 issue of Flow Control, 11 case studies/application stories featured the winners of our 2012 Innovation Awards program. In the following weeks, each winner will be featured on the FlowStream blog. The following post focuses on Bios International’s ML One Primary Gas Flow Calibrator.

Amy Richardson

Editor’s Note: In the October 2012 issue of Flow Control, 11 case studies/application stories featured the winners of our 2012 Innovation Awards program. In the following weeks, each winner will be featured on the FlowStream blog. The following post focuses on Bios International’s ML One Primary Gas Flow Calibrator.

The new ML One primary gas flow calibrator measures flowrates from 5 to 50,000 sccm with an accuracy of 0.15 percent. The ML One is constructed from materials resistant to attack by corrosive gases allowing measurement of reactive and non-inert gases. The gas flow is measured by timing the displacement of a precision piston fitted in a borosilicate tube. Simultaneous measurement of gas temperature and pressure along with piston displacement result in highly accurate standardized gas flowrate measurements. Unlike thermal or differential-pressure-based flow measurement technologies, the piston displacement technology is independent of gas species, which allows accurate gas flowrate measurements even with reactive gases and gas mixtures consisting of unknown or varying concentrations. In addition, the ML One features:

•   Three measurement tubes in one instrument that auto select for the flowrate being measured;
•   A clear and simple touch screen user interface;
•   A compact all-in-one design that can be moved on a cart for factory floor measurements; and
•   Built-in self-diagnostics.

This is an ideal instrument for calibration laboratories doing gas flow calibration and for manufacturers of thermal-based gas flow controllers and meters. Several mass flow manufacturers are using the ML One to accurately measure and calibrate thermal-based instruments with reactive gases. Until now, reactive gas flow calibrations were performed by measuring the flowrate with an inert gas and then applying a correction factor derived from gas properties to “correct” the gas calibration. Correction factors vary widely from different manufacturers resulting in significant measurement differences. Now with the introduction of the ML One, thermal-based gas flow manufacturers are calibrating with the actual reactive gases resulting in improved gas flow calibrations critical to many manufacturing processes.

One need for accurate measurement of reactive gases came from the semiconductor industry in the fabrication of wide bandgap semiconductors. A semiconductor manufacturer expressed frustration in variations in thermal- based flow measurements correction factors with the reactive gas ammonia (NH3). Ammonia is critical in the fabrication process used in wide bandgap semiconductor manufacture and gas flowrate variations could not be tolerated. The engineers developing the ML One responded by designing the ML One to measure these gases. The ML One is now being used for thermal-based flow controller calibration to accurately and consistently calibrate ammonia flowrates critical to this industry.