Primary Gas Flow Calibrators

Selecting a gas flow meter can be complex task with several key parameters and attributes to consider. With several options in the marketplace, it can become a monumental task comparing features and benefits with your process and regulatory needs. With our decades of experience and several thousand units in the field, these are the main 3 items that we find most helpful to customers when looking for a gas flow meter.

1. Flow Range

From a purely technical standpoint, flow is the measurement of a quantity of fluid (liquid or gas) that moves past a point per unit time.  You are essentially measuring how much “fluid” moves through the system over time.  Regardless of the process, knowing how much material you will flow is necessary from the initial design of your flow system to quality control.  In the case of flow controllers and meters, they require calibration by equipment that can match their flow range.  The DryCal product line now includes products that span flow ranges as low as 0.5sccm, up to 1500slm.

2. Accuracy

Having a documented, defensible calibration is critical for any organization.  The question that comes up is: “what accuracy do you need?”.  As much as everyone can agree on the advantages of primary standards over transfer standards, level of accuracy is not as clear cut.  In some industries 4:1 is the norm, some have less stringent requirements, some more so.  Amongst the Defender, FlexCal, and Metrology Series lines of DryCal products, Mesa Labs can provide you with the right product for your needs; offering superior measurement uncertainties as tight as 0.15%.

3. Gas species

So, you are measuring gas flow through your system.  You may ask yourself, what happens to my system if I decide to flow a different species of gas?  Will anything in my system change?  In many cases that answer is yes, things will change.  Many types of gas metering and gas controlling hardware are impacted by the species of gas flowing through them.  As these devices typically use indirect methods to identify flow such as thermal change or differential pressure.  These methods rely on the particular behaviors of a specific gas.  The DryCal primary flow standards are not plagued with these issues.  As the technology used is direct measurement of a volume per time, the data is unaffected by gas species.  That means you can calibrate all your different equipment that flow different gases with the same DryCal.  Mesa Labs offers different series of calibrator to accommodate a variety of flow ranges and different applications.

Keeping these items in mind will make your selection of the appropriate gas flow meter for your specifications much more successful. Identifying the important parameters ahead of time will ensure that you are making an appropriate investment. Let Mesa assist with your decision making process, contact us for specialized consultation today.

The volumetric flow rate  (V) is the measure of a volume of fluid (gas) passing a point in a system per a unit of time.  The volumetric flow rate can be calculated as the cross sectional area (A) for flow and the average flow velocity (v).  Stated mathematically as:

V=Av

In terms of a round cylinder the flow rate is:

V=Pr2v   if we substitute v=d/t

V=Pr2d/t   V= (area) x (distance)/(time)

This is the basic equation used in calculating the volumetric flow rate for all DryCal units.

Note: Some of the units used for volumetric flow include L/m, ccm, m3h, cfm, and cfh.

The standardized flow rate  (Vs) is the volumetric flow rate corrected for both pressure and temperature. When using the standardized flow rate, the reference pressure and temperature are usually fixed at standard conditions.  These conditions are usually defined as 1 atm (760 mmHg) for pressure and 273°K (0°C) for temperature.  These corrections are based on the ideal gas law. The relationship of standardized flow rate  (Vs) to the volumetric flow rate  (V) is:

Vs=V*(P1/760)*(273/T1)

Where:  Vs = the standardized flow rate at 760 mmHg and 0°C (273°K)

V = the volumetric flow rate

T1 = the absolute temperature of V (K)

P1 = the atmospheric pressure of V (mmHg)

Note: Sometime the reference temperature may be something other than 0°C.

Note: Some of the units used for standardized flow include sL/m, sccm, sfm, and scfh.

Most of the time it is based on the device you are testing (DUT).  The DUT may either be outputting volumetric or standardized flow.  Basic pumps are volumetric.  Mass flow controllers (MFC’s) are standardized.  Do not confuse the two, as the difference can be quite substantial.  It should also be noted that certain MFC’s are not standardized to 0°C, but to 21.1°C (70°F).  This too will make a difference in the standardized flow measurement.

Note: This is handled by a setting on all standardized DryCal units.