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Manual 111-082010_Nall Mass Flowmeters Page 11 of 23
5.0 USING THE FLOWMETER
USING THE HASTINGS LINEAR MASS FLOWMETER
5.1 Warm-Up Time:
When the flowmeter is first turned on, the meter will fluctuate somewhat before settling to a stable
indication. The flowmeter indicates the mass flow to +/- 3% of full scale in about 5 minutes, but should be
allowed to warm up for 30 minutes to achieve maximum accuracy.
5.2 Response Time:
The response time to a change in flow is logarithmic and is approximately 7 seconds for a 67% change and
30 seconds for a 90% change. Pneumatic imbalance in the associated plumbing will often cause the response
time to appear longer due to additional time required for flow to stabilize in the system. If a faster response
time is desired, consult the factory.
5.3 Mass Flow Units:
The units of mass flow used with the Models NALL, ENALL, NALL-P, and ENALL-P mass flowmeters are
the “standard cubic centimeter per minute” (SCCM) and/or the “standard litre per minute” (SLPM). An
SCCM is the volume occupied by a given mass of gas at a specified temperature and pressure referred to as
standard conditions (STP). These conditions are defined as 0° C (32°F) and 760 Torr (14.7 psia). A one
litre volume of gas is equivalent to 1000 cm³ of the same gas. Those models incorporating a Laminar Flow
Element (LFE) use “standard cubic foot per minute” (SCFM) units, which are equivalent to a flow of
28,300 SCCM or 28.3 SLPM. To convert to other units of mass flow, multiply the mass flow rate of the gas
by the density of the gas at standard conditions.
Example: What is the equivalent mass flow in grams per minute of 100 SCCM of air?
Solution: The density of air at 0° C and 760mm of Hg is .00129 gm/cm³.
Mass Flow = 100 SCCM X .00129 gm/cm³.
= .129 gm/min.
5.4 Special Factory Calibrations:
All Hastings Mass Flowmeters are calibrated for air unless otherwise specified. Calibrations for a special
range or for a gas other than air are clearly indicated on the front panel readout of standard models, or by
special comments or curves in the manual. Calibrations traceable to the National Institute of Standards &
Technology (NIST), can also be made for an extra charge.
5.5 Gas Conversion Factors:
The Hastings Linear Mass Flowmeter can be used for many different gases as long as the gas is compatible
with materials of construction. No electrical adjustments are necessary when using the gas conversion factors
so the original calibration is undisturbed.
5.5.1 Flowmeters Factory Calibration for Air
A flowmeter originally calibrated for air can measure other gases by using the Hastings Gas Conversion
Factors on Page 35 of this manual. Simply multiply the meter indication by the appropriate gas conversion
factor (K).
Example: What is the actual flow rate of Helium through a flowmeter calibrated for Air if the
meter reading is 50 SCCM?
Solution: From the table on page 35, the gas conversion factor for Helium is 1.382.