[High Accuracy]Flow rate accuracy improvements achieved by new measurement method

CRITERION™ achieves improved accuracy and better device to device repeatability in flow measurements, compared to older technology MFCs, by determining mass flow based on pressure measurements rather than the temperature measurements methods historically utilized by previous MFCs. CRITERION™ routes the entire flow of gas to be measured through a specialized compressible laminar flow element. There are no split paths between a thermal sensor and a flow bypass like in a thermal MFC. In the narrow passages of the specialized flow element, the gas is driven to the temperature of the element avoiding uncertainties in measuring gas temperature that have been seen in sonic approaches. The newly developed restrictor technology does not have to satisfy the critical pressure condition, P1/P2 >2, required by competing sonic nozzle approaches. As a result, CRITERION™ can be used in vacuum and non vacuum applications.
The flow element is intentionally designed to operate in the compressible laminar flow regime which gives it a beneficial and stable non-linearity. Simply put, it takes more pressure drop per unit of flow at low flows than it does at higher flows. This non-linear restrictor results in an MFC with a percent of reading error characteristic in contrast to the percent full scale error characteristic seen in linear thermal MFCs, allowing a larger dynamic range of high accuracy flow measurement.
To ensure and maintain accuracy in process gases, Horiba operates two metrology labs (Japan and USA) with refined process gas measurement capabilities. These lab’s measure more than 50,000 data points per process gas on multiple restrictors for each process gas to correlate the relationship between pressures, temperature and flow rate. This data is then entered into a unified database which is used to calculate the optimum correction function that maps CRITERION™’s N2 factory calibration accurately to your process gas application.