Laminar Flow Elements (LFE)

Meriam Laminar Flow Elements (LFEs) are excellent for measuring low gas flow rates from 0.2 SCCM up to 2250 SCFM. They are inherently accurate and repeatable and are calibrated traceable to NIST in our ISO 17025 certified Flow Lab. Flow turndown is 20:1 or better and the differential pressure generated is nearly linear to flow. This combination makes an LFE a great choice for gas flow measurement and flow control applications.

Performance
Standard LFE calibration accuracy is ± 0.72% of Reading (not % of Full Scale) traceable to the National Institute of Standards and Technology (NIST). Rigid construction and lack of any moving parts make the LFE calibration stable. Only physical damage or particulate deposition in the element will cause a calibration shift.

Utility
LFEs can be used to measure flow rate for a variety of gases and applications. Standard models are available to measure as little as 0.2 SCCM (5.9 E-06 SCFM) to as much as 2250 SCFM of air flow at standard conditions. Custom models for up to 15,000 SCFM of air are available. Stainless steel or aluminum materials make LFEs compatible with most gases. Flow rate of gas mixtures can also be measured when the percentages of component gases and mixture properties are known.

The LFE Matrix
The LFE matrix can be made from individual SS tubes or windings of SS foil. These tubes are long enough, relative to their inside diameter, to cause laminar flow to occur inside each tube. The result is a near linear relationship between DP and flow rate. The DP generated across the matrix responds very quickly to changes in flow. All DP is permanent pressure loss to the system but LFEs are sized to produce no greater than 8” water column at maximum flowing conditions. Individual tube diameters are very small so flowing gases need to be clean and dry to preserve the calibration. Filtered inlet versions of most LFE models are available to keep the matrix clean and the calibration constant.

Calibration and Accuracy
Meriam LFEs are calibrated with air at atmospheric conditions referenced to 29.92” mercury absolute (760mm Hg. Abs.) and 70ºF (21.1ºC). Each completed element is calibrated and traceable to the National Institute of Standards and Technology. Our Special Calibration Procedure #A-33544 is designed to meet the basic requirements of MIL-STD-45662A, ANSI Z540, 10CFR50 and MIL-Q-9858A.

Meriam LFEs are supplied with a reproducible flow curve in terms of SCFM versus inches of water differential pressure. Correction factors are included to cover an inlet pressure range from 26 to 36” Hg Abs. and an inlet temperature from 50ºF to 150ºF. For special flow applications, contact Meriam with complete flow information. The rated accuracy* of all Meriam LFEs is percentage of actual reading; not the much wider percentage of full scale flow rate tolerance of other devices.