Laminar Flow Elements

Precision Instruments for Pressure, Flow, Temperature, and Level

Meriam 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.

Applications

LFEs are applicable in most clean and non-condensing gas flow applications. They excel in critical gas flow measurement applications and make excellent calibration standards because of their inherent accuracy, stable calibration, excellent response time and repeatability. LFEs are used to calibrate turbine meters, variable area meters, flow regulators, mass flow meters, and thermal anemometers to name a few. Gas flow measurement for demanding flow control is a common application. Other applications include leak detection and quantifi cation, design and testing of discrete parts, automotive engine and emissions testing, and window and door leak testing.

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 & Accuracy

Meriam LFEs are calibrated with air at atmospheric conditions referenced to 29.92" mercury absolute (760mm Hg. Abs.) and 70? F. (21.1? C). Each completed element is calibrated and traceable to the National Institute of Standards and Technology in our ISO 17025 certified flow lab. Meriam LFEs are supplied with a reproducible flow curve in terms of SCFM versus inches of water diff erential pressure. Correction factors are included to cover an inlet pressure range from 26 to 36" Hg Abs. and an inlet temperature from 50? F to 150? F. For special flow applications, we request that you 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.

*Accuracy Levels Available:

† ± 0.86% Reading for full scale flow of 1000 SCFM or higher
†† ± 0.70% Reading for full scale flow of 1000 SCFM or higher

Special calibration procedure service is available from our ISO 17025 certified flow lab for customers governed by aggressive quality programs requiring periodic recalibration. The Special Calibration Procedure #A- 33544 is designed to meet the basic requirements of MIL-STD-45662A, ANSI Z540, 10CFR50 and MIL-Q-9858A.

LFS-3 FLOPAC Flow Measurement System

The Meriam FLOPAC Flow Measurement System is designed to allow users to accurately measure gas flow rate through Meriam LFEs using state-of-the-art electronic instruments, electronics and software. Real-time data measured by the instrumentation is transmitted via RS-485 to a personal computer. The SOFTFLOW software enables the PC to automatically calculate flow rate and compensate for changes in line pressure, temperature, and relative humidity. System accuracy is ?1.0% at full scale of LFE, ?1.3% at 5:1 turndown, and ?2.0% at 10:1 turndown. The user can select the units for flow rate, temperature, and pressure using the system software. Confifigurations for multiple flow elements can be saved and recalled for later use. Results of flow tests can be saved for post processing or archiving purposes.

LFS-1 Flow Measurement System

The LFS-1 Flow Measurement System for Meriam LFEs takes advantage of the wide fl ow turndown and the percent of Reading precision of the LFE, as well as Meriam?s calibration expertise, to provide a superior gas fl ow measurement solution. The integral fl ow computer makes real time corrections for changes in diff erential pressure, static pressure, temperature and relative humidity to provide the most accurate results possible. Calibration coefficients for up to five (5) LFEs can be stored in memory and called up for later use with a push of a button. For control or data transmission purposes, the LFS-1 Flow Measurement System has both analog and digital outputs. 4?20 mA and 0?10 volts analog output options are ideal for control and recording functions. RS- 232 and RS-485 digital communications are standard.

Special application requirements can often be accommodated by the LFS. For example, simultaneous flow measurement of two LFEs can be made and the summation of the two fl ows calculated and displayed. Or, for testing over a wide range for flow, the LFS can be set up to automatically switch from one LFE to an LFE of a different flow capacity as flow rate increases to a predetermined set point.

Meriam?s LFS-1 provides standard system accuracy of ? 1.0% of Reading over a 10:1 flow turndown and ? 1.1% over 20:1 turndown. Calibration of the LFE and LFS-1 as a system makes this possible. Meriam can offer LFS accuracy as low as 0.60% of Reading over a 10:1 flow turndown by using better calibration standards. All LFS packages include complete instrumentation, system calibration and NIST traceable documentation. LFEs and systems cover gas flow ranges from 0.2 SCCM to 15,000 SCFM.

To provide the accurate answers you need in the shortest amount of time...

Please Provide us With the Following Ordering Data:

1. Model number
2. Flowing gas data;
3. 1. Flow rate in desired units
   2. Base conditions
   3. 1. Pressure
      2. Temperature
   4. Flowing conditions
   5. 1. Pressure
      2. Temperature
      3. Viscosity at flowing temperature
   6. Differential at maximum flow.
   7. Specific gravity, if other than air
   8. Flowing gas, if other than air
4. Readout instrument
5. Description of installation configuration
6. Line size
7. Line Material
8. Accuracy required

For more part/model information, please refer to page 5 of the datasheet