Standard Gas Flow Meter Calibration – A Guarantee of Accuracy

The accuracy of the mass flow controller (MFC) is important to ensure the performance, quality, and efficiency of a flow meter.

If an instrument is not calibrated, its performance can decline as a result of sensor drift from the factory calibration. Such a drift can be caused by various things such as aging of electronics, physical change in the sensor, and dirt buildup, among others.

Many users validate or recalibrate the MFC or the flow meter annually to ensure that the accuracy of MFC reading is maintained. In some industries, government regulations such as FDA, MACT or EPA mandates, or corporate policy require the assurance of flow meter’s accuracy.

Although there are numerous ways to calibrate MFCs, the ideal method to ensure accuracy is a primary standard calibration.

Primary Standard = Precision Calibration

World-class levels of traceability and accuracy can only be obtained through primary standard gas flow calibration systems. The following aspects have to be considered in mass flow meter primary standard calibration:

1. Unlike laminar flow elements and other transfer or secondary standards that are calibrated against another instrument, primary standards are characterized by the basic quantities of distance and time. In addition, all national laboratories can verify primary standards.
2. The calibration standard must be NIST traceable standard accuracy, better than 1% of full scale
3. The NIST “rule of four” is followed by the most accurate primary standards. This means the accuracy of the gas flow primary standards must be four times that of the device under test. All calibration houses and factory calibrations must make this “rule of four” a basic requirement.
4. Flow meter calibration is both an art and a science. Expertise in flow meter calibration or flow meter manufacturing must be sought. The best flow meter calibration can be obtained in a manufacturing factory rather than a third party calibration house, as a factory would possess working knowledge of the meter and flow calibration core competency.
5. Facilities (Figure 1) should have ISA 17025 & NAVLAP compliance and/or ISO 9001 certification

Figure 1. Calibration facility

Sierra’s SmartTrak Mass Flow

Sierra is among the few manufacturers that perform a thorough 10-point calibration across the full mass flow range. The company strictly follows the NIST “rule of four” and adheres to employing primary standards.

Sierra’s SmartTrak mass flow controller is a great example of this. The controller’s NIST-traceable standard accuracy is better than 1% of full scale. The company offers even better accuracy, up to half a percent of full scale, upon request.

This information has been sourced, reviewed and adapted from materials provided by Sierra Instruments.

For more information on this source, please visit Sierra Instruments.