Teledyne NALL instruction manual Using the Flowmeter

5.0 USING THE FLOWMETER

USING THE HASTINGS LINEAR MASS FLOWMETER

5.1Warm-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.

5.2Response 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.

5.3Mass 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.

5.4Special 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.

5.5Gas 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.

5.5.1Flowmeters 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.

Manual 111-082010_Nall Mass Flowmeters Page 11 of 23