Sierra SL-800 instruction manual Calibration of Mass Flow Meters MFMs

GasAdjustable

SupplyRegulator

MFC

DryCal

Cal=Trak

Figure 11 Setup for Calibrating MFCs

7.7Calibration of Mass Flow Meters (MFMs)

Mass flow meters can be calibrated with the setup of Figure 12, which is similar to that shown for LFE transfer standards. Again, the flow must not be affected significantly by the Cal=Trak’s cyclic pressure increase. This can be achieved by use of a sonic nozzle as the stable flow source, or by feeding a fixed restrictor with a precisely regulated pressure of more than 200 kPa. (At 200 kPa [30 PSI], the dynamic flow decrease caused by the piston’s weight will be about 0.05%.) Alternately, a stable mass flow controller may be used to maintain specific flows into the MFM under test. In this scenario, the MFC will function as a pressure stabilizer and precision flow regulator with the Cal=Trak defining the accuracy of the device under test. Contact Sierra Instruments for special Smart-Trak flow controllers designed for this application.

If the MFM under test must be calibrated at pressure (i.e. because it is always used under pressure) then a fine resolution valve (needle valve) and a gauge should be installed between the MFM and the Cal=Trak. Adjust the valve until the pressure gauge reads the correct pressure for the MFM under test.

GasFixed Adjustable Sonic

Supply Regulator Regulator Nozzle

Flow Meter

Stable Pressure	OR Porous Plug
> 200 kPa
	OR MFC

Figure 12 Setup for Calibrating Mass Flow Meters

Cal=TraDryCalk

7.8Calibration of Rotameters (Variable Area Flow Meters)

Variable-area meters can become unstable when connected in series with a volume. Cavity resonance may even occur. They are best calibrated using the setup of Figure 13. The flow stream is alternately applied to the Cal=Trak and to the device under test. A sonic nozzle or a large “swamping” pressure restriction is used to render the differences in the two devices’ insertion pressures insignificant with respect to the required accuracy.

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