Produced in the 1960’s, mass flow devices are essential components in systems that create specialty gas standards necessary to calibrate a wide range of gas analysis instrumentation.
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Mass flow devices create a signal that corresponds to the mass flow of a gas. At their foundation, mass flow devices are independent to fluctuations in temperature and pressure because the heat of a gas is distinct to its particular type. The signal that they produce is highly stable and precise.
The Accuracy of Flow Controllers
The accuracy of a flow controller is typically represented as a percent of full-scale flow (%FS) that indicates the maximum accuracy achieved by a flow controller when operated at its rated full-scale flow rate.
The accuracy of the flow controller is represented as a percent of set-point that can be significantly reduced when the flow controller is operated at lower flow rates.
For example, a 1000 cc/min flow controller with +/- 1% FS accuracy and operating at a set-point of 1000 cc/minute can be determined to be accurate to +/- 1% of the set-point.
However, if this same flow controller is operated at a set-point of 100 cc/min, the accuracy is then represented as a percent of set-point that is reduced to +/- 10% of the set-point.
Choosing a Flow Controller for Accuracy
Qualifying and selecting a mass flow controller for a dynamic gas blender just as the MFC is the heart of a high accuracy gas blender, the flow sensor is using mass flow controller based dynamic gas blenders to produce accurate calibration gas standards electronic mass flow controllers and mass flow meters ensure that vapor gas flow measurement and control is accurate producing gas standards.
By Tom Bramford second quarter 2007 specialty gas report 27 the heart of a mass flow controller. The most common and traditional technique for measuring and controlling mass flow is with a thermal mass flow controller.
As noted earlier, this type of device measures the temperature shift (or differential) that occurs in a small tube as heat transfers to and from the gas.
Recommended Flow Controllers
The Environics flow controllers are calibrated to an accuracy of +/- 1% of the set-point, rather than the full scale to ensure that the accuracy remains the same, regardless of the operating point of the flow controller.
To achieve this accuracy, an 11-point calibration of each flow controller in the instrument is performed.
The following graph shows a comparison of the percent set-point error of an Environics instrument using calibrated flow controllers to that of a standard uncalibrated flow controller.
This information has been sourced, reviewed and adapted from materials provided by Environics, Inc.
For more information on this source, please visit Environics, Inc.