What is gas flow calibration?

Gas flow calibration refers to the calibration of a flow sensing device such as a flow meter or flow controller by comparing its measurement against a flow measurement reference. Typically the device, or unit under test (UUT) is pneumatically connected in series with the flow reference so that they measure the same gas flow, then the indications of the two devices are compared. molbloc/molbox Gas Flow System and flow meter calibration
molbloc/molbox Gas Flow System »

Where is gas flow calibration used?

  • Flow meter/controller manufacturing and service
    Manufacturers of flow meters and mass flow controllers (MFC) have a large volume of calibrations to perform and require a standard that is fast, accurate and can be automated. molbloc/molbox’s accurate real-time flow output is especially important for manual adjustment of mass flow meters and mass flow controllers. Many MFC service centers use molbloc/molbox to perform manual analog MFC calibrations.
  • Process control
    Technicians use molbloc/molbox for calibration, testing and troubleshooting instruments and test systems from manufacturing to research applications. In these applications, the key requirements are often repeatability, speed and portability.
    • Semiconductor/fiber optics/photovoltaic
      These and other processes involving coatings and gas deposition processes are heavily reliant on the performance and stability of mass flow controllers. Calibrating MFCs at the plant-level may save money over outsourcing the service, and having a reliable reference for troubleshooting can save hours of downtime. A molbloc can often be connected directly into a manifold to check MFC performance without uninstalling.
    • Bio-pharmaceutical
      Gas flow rates into bio-reactors and fermenters can be critical, and molbloc/molbox is used to perform traceable MFC calibration in many pharmaceutical plants. Transportability is key for many in-situ calibration applications, and molbloc/molbox can deliver a portable solution for up to hundreds or even thousands of liters per minute with molbloc-S.
    • Petrochemical (R&D)
      Accurate testing of both flow meters and controllers is key in research facilities developing petrochemical processes that can be later scaled up to production quantities. Fluke Calibration can provide or specify simple hardware setups to allow molbloc to test devices running at pressures of 3,000 psi or more.
    • Fuel cell testing
      Testing fuel cell performance requires accurate measurement of hydrogen and other gas flows. molbloc/molbox is a fast and accurate way to calibrate MFCs in small or large fuel cell testing environments.
    • Gas blending
      Dynamic gas blending is an alternative to weighing or other filling methods to more quickly create standard blends of gases. molbloc/molbox can provide traceability of the blending system flow devices, or in critical applications can be used directly in the blending control system.

  • Environmental quality/monitoring
    molbloc/molbox is the first choice for calibration of ambient and toxic gas monitor “calibrators.” These devices control critical concentrations of pollutant gases for calibration of monitors. molblocs are easily connected to the calibrators in the lab or field for traceable calibrations. molbloc/molbox is used by state, local, national and international agencies to support their air quality monitoring instruments, and by instrument vendors who supply them.

    Calibration of FTS flow transfer standards for PM2.5 particulate monitoring systems is also easy using molbloc-S.
  • Medical/breathing systems
    Calibration of flow meters and testing of breathing air systems is a common and highly critical application for molbloc/molbox, both in production or recertification. Aircraft/safety medical.
  • Leak testing
    • Nuclear, gas mask, manufacturing
      molbloc/molbox is used to test flow meters and orifices used for leak testing of various products, from gas masks to medical devices. molbloc/molbox is the choice for flow calibration of leak rate monitors used in nuclear utilities because the molbloc can be operated at the elevated pressure required for running upstream of the devices.

molbox1+ Flow Terminal and flow meter calibration
molbox1+ Flow Terminal »

molbloc-L Laminar Flow Element and flow meter calibration
molbloc-L Laminar Flow Element »

molbloc-S Sonic Nozzle Flow Element and flow meter calibration
molbloc-S Sonic Nozzle Flow Element »

molbox RFM Reference Flow Monitor and flow meter calibration
molbox RFM Reference Flow Monitor »
  • National Measurement Institutes (NMI)
    Both molbloc/molbox and Fluke Calibration’s primary gravimetric flow standard, GFS2102 are used in premier NMI gas flow laboratories around the world. GFS is a true primary mass flow reference and molbloc/molbox provides the utmost precision as a flow transfer standard.

GFS Gravimetric Flow Standard  and flow meter calibration
GFS Primary Gravimetric Flow Standard »

Additional reference materials

Four steps to more effective gas flow calibration »
Mass flow vs volume flow in gas flow measurement »

Mass flow vs. volume flow

A frequent topic of discussion and confusion surrounding gas flow measurement is that of mass flow and volume flow. Flow meters and flow units used for flow measurements are inherently used to measure and express either the amount of volume of gas, or the amount of mass (or number or moles or molecules) passing through the device. When performing a gas flow calibration it is nearly always beneficial to use a mass flow reference measurement, because the mass flow rate stays constant throughout a flow system in steady state. Since gas is compressible, the volume flow rate varies at different locations in a flow system due to changes in density caused by changing temperature and pressure. molblocs are mass flow standards, which allow reliable comparisons to other flow devices. The molbox terminal is also able to calculate and express the flow rate in terms of volume flow at another point in the system to allow testing of volume-based devices.

Primary flow standard vs. transfer standard
Fluke Calibration offers both primary gas flow standards and secondary standards (or transfer standards) that deliver the utmost in measurement performance. Customers are sometimes faced with the question of whether they are best served by using a primary or secondary standard. Our advice is that customers should use a standard that provides the required measurement uncertainty and reliability and also compliments the needs of the calibration lab. Fluke Calibration’s GFS2102 dynamic gravimetric mass flow system is a primary mass flow standard offering the lowest possible measurement uncertainty. But for the vast majority of customers, it is more effective to use a molbloc/molbox flow calibration system. molblocs are calibrated by comparison to a calibration chain based on primary gravimetric flow measurements and produce highly repeatable and precise performance as a flow calibrator. Meanwhile, molbloc/molbox offers far greater speed, convenience and portability and is more cost effective than GFS.

molbloc/molbox has been selected by laboratories to replace many piston prover and bell prover systems in mass flow calibration and rotameter calibration applications. Piston provers and bell provers are widely considered primary standards, but it is important to note that they are primary volume flow measurement devices. Most often, they use a direct volume flow measurement along with pressure and temperature measurements and gas property data to calculate a mass flow rate that is used for calibrations.

An important characteristic of secondary flow standards is that they must undergo a rigorous flow comparison during each recalibration. Primary standards are not calibrated by comparison to another flow measurement standard, but are instead calibrated by only testing their measurement components individually (time, distance, mass, pressure, or temperature for example). Without regular proficiency testing and intercomparisons to a suitable flow reference, the user does not have assurance of the primary standard’s flow measurement performance. Most importantly, laboratories must select a flow calibrator that offers the best measurement reliability, and operational features.

Related reference materials

Mass flow vs volume flow in gas flow calibration

Video: molbox: Gas Flow Calibration system

Fluke Calibration is a leading manufacturer of high performance pressure and gas flow standards including calibration process software. We offer A2LA-accredited pressure and gas flow calibration services, as well as metrology training courses. Visit our products in detail using the Quick Links at right or the descriptions below.
Quick Links
Gas Flow Standards »
Gas Flow Accessories »
GFS Primary Gravimetric Flow Standard »
Flow Calibration Software »
  • Gas Flow Standards »

    Fluke Calibration offers molbloc/molbox gas flow calibration systems to calibrate flow meters and controllers over a very wide range of flows. The systems are fast, precise and transportable and can be fully automated using COMPASS for Flow software. molblocs, which are the heart of the measurement system, are mechanically stable, gravimetrically calibrated laminar flow and sonic nozzle elements.

    Gas Flow Standards
  • Gas Flow Accessories »

    Fluke Calibration offers several gas flow calibration accessories to provide clean, stable gas flow and make the required electrical and pneumatic connections. MFC Switchbox supports MFC set and measure and can use an additional switchbox for connecting up to five MFCs simultaneously. molstics™ provide an engineered setup solution to mount molblocs, regulate pressure and connect a device to be tested.
    Gas Flow Accessories
  • GFS Primary Gravimetric Flow Standard »

    The GFS dynamic gravimetric mass flow calibration system allows users to maintain the accuracy and traceability of molblocs or other high precision devices using the same primary reference used by Fluke Calibration. GFS is a true mass flow reference suitable for use in premier measurement institutes who require the lowest measurement uncertainty.
    GFS Primary Gravimetric Flow Standard
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