Laminar flowmeter is a flowmeter with linear relationship between the volumetric air flow rate and its differential pressure. The differential pressure in rated flow rate is quite low so it doesn’t affect the characteristics for any test parts. Also the combination of LFEs and LFC300 does produce no square root errors under the pulsation flow like orifices or round nozzles because of its linear pressure drop characteristics.
Products
Line up
LFE series laminar flowmeters
B seriesTotal 11 models from 10 to 500 Litre/sec. 

LM seriesTotal 9 models from 27 to 1,000 Litre/min. 

LMS seriesTotal 5 models from 1 to 15 Litre/min. CCM seriesTotal 5 models from 1 to 15 Litre/min. 
Laminar flow calculator model LFC300

Surge tube ST300

Options
with air filter and duct 
with upstream/downstream ductswith flexible duct 
Features
Low pressure drop and high accuracy in flow rate
 Approx 0.8kPa in pressure drop with rated flow
 Accuracy in +/1%FS within the rated flow
 Accuracy in +/1.5%FS over 150% rated flow
Excellent response time
By assuming pay attention to occur no columnar vibration in the pressure leads with fast response pressure transducer then the
95% amplitude ratio response time can be derived with the pulsating frequency in 150Hz.
Accurate flow measurement can be made under pulsating flow
The average of the pressure drop fluctuation corresponds to the average of air flow rate since the relationship between volumetric air flow rate and pressure drop is linear.
Laminar flowmetersAverage of pressure pulsation=Average of air flow rate

Restriction type flowmeters like orifices or nozzlesaverage of pressure pulsation≠average of air flow rate 
Applications
Optimal flowmeter for engine intake air measurement
 Less errors under pulsating flow
 Except the low engine speed or single cylinder engines air flow can be measured without surge tank
 Doesn’t affect the engine performance with its low pressure dropCan be covered the whole engine conditions with its wide dynamic flow range
Keep the accuracy good combined with surge tube
The rubber tube volume (approx. 3 litres) in the metal cylinder will change correspond to the pressure so the pulsating flow reduce downstream of the surge tube.
Accurate flow measurement for gas conveyancing system
Sokken will recommend configuring the several LFEs, line selector valves and LFC300 below to measure the wide dynamic flow range
accurately. In order to connect the best LFE then an appropriate LFE will be chosen by presetting the flow rate in LFC300.
The other applications
 As a calibration tool for various flowmeters
 Evaluate and develop the flow characteristics regarding engines
 Flow measurement for blowers or air compressors
Specifications
Rated flow rate  Refer to the table in "How to express the model number?" 
Pressure drop  Approx. less than 0.8kPa at the rated flow 
Linearity of the pressure drop for flow rate  within +/1%FS in rated flow and +/1.5%FS in over 150% rated flow rate 
Accuracy for the laminar coefficient  within +/1%FS 
Allowable line pressure  less than 30kPa 
Response time  approx. 150Hz (Refer the graph in features) 
Allowable temperature range  5 to 50C (without water condensation) 
Note:
An additional differential pressure gauge and a temperature sensor are required to measure the volumetric flow rate.
An additional differential pressure gauge, a temperature sensor and an absolute pressure gauge are required to measure mass flow rate.
Sokken recommend using a laminar flow calculator LFC300 which equips a differential pressure gauge, a temperature sensor and an absolute pressure gauge.
How to express model number?
Model number selection guide
LFE100BFD Model:B series, Rated flow rate:100L/sec, An inlet air filter and a duct for downstream as options
External view and detailed dimensions
CCM and LMS series laminar flowmeters
Note: The fittings for pressure taps are the common for whole flowmeters
LM series laminar flowmeters
B series laminar flowmeters
Note: Please refer to the downloaded brochure on this site regarding the detailed dimensions for ducts, air filter and flexible duct etc.
Surge tube ST300
The nominal connection size for the flexible duct, cuff and wire band is “65”.
FAQ
Which part is the flow rate calculated according to the instruction manual?
It is the volumetric air flow rate at the inlet conditions (pressure and temperature) of flowmeter if calculating the Q_{real}. It is also the volumetric air flow rate in standard conditions (converting the inlet conditions to 20C, 101.3kPa) if calculating Q_{normal}.
Where is the best position to measure the temperature and the line pressure?
Near the inlet of flowmeter is the best position for temperature measurement, and recommend the fast response sensor. The line pressure is measured by branching the upstream pressure tap.
What is the lower or upper flow limit for flowmeter?
The lower flow limit is 1/15FS with the high class differential pressure gauge and is 1/10FS with the middle class differential pressure gauge.
The upper flow limit is nearly 1.5 times of the maximum flow.
When the optimum timing for overhaul?
Normally recommend once every year.
Priciple
If the flow is laminar flow, the pressure drop across a capillary caused by the viscosity of fluid is proportional to its volumetric flow rate. This is called Hagen Poiseulle’s law. The laminar flow elements for Sokken’s LFE series flowmeters are configured by bundling multiple trapezoidal cross section flow paths. The fluid flows inside the paths as laminar flow.
Volumetric flow rate : Q ∝ K × P_{x}
The volumetric flow rate as Q_{t} at the inlet of flowmeter in temperature t is expressed as following equation.
Q_{t} = K_{20} × (μ_{20}／μ_{t}）×P_{x}
where
K_{20 }: Laminar coefficient in standard conditions (P0=101.3kPa, RH=65%)
μ_{20} : The viscosity of air in 20C
μ_{t} : The viscosity of air in tC
Px : The differential pressure for laminar flowmeter
The viscosity of air is a function of air temperature so measuring the air temperature is required.
To calculate the standard volumetric flow rate or mass flow rate from the above flow rate Q_{t}, it is also required to measure the absolute pressure at the inlet of laminar flowmeter.
Calibration
Traceability
The traceability is generally expressed as “Traceable to national standard” and it indicates that an instrument can arrive to the national standard with the chain of calibrations. It also guarantees the link of measuring instruments.
The instruments for Sokken’s calibration work use any of the traceable instrument listed below;
 An instrument with “Calibration certificate with IRACMRA symbol”: International traceable instrument
 An instrument with “Calibration certificate according to the technical standard of the calibration agency”: General traceable instrument
 An instrument with “Calibration certificate according to own technical standard”: Sokken’s standard instrument
How to calibrate a laminar flowmeter?
The calibration is performed by connecting the same flowmeter models (target LFEX and standard LFEstd) in series and comparing
each pressure drop by flowing clean air.
Plotting the flow rate Q calculated from Pstd and the pressure drop for LFEX, and determine the laminar coefficient of K_{20} by using least squares method. By using the K_{20}, the relationship between the pressure drop and the flow rate has +/1%FS linearity within the rated flow rate.
Also plotting K_{20} and Px for each point, determine the coefficient A and B for K_{20} as the function of pressure drop in Px. These coefficients are the correction factor for the effect of inlet open ends and are suitable for the precise flow measurement.
The calculated laminar coefficient K_{20} and the coefficient A, B is described in the attached data sheet. If using K_{20} then the flow rate can be simply obtained.
If using the K_{20} calculated from the coefficient A and B then more accurate flow rate can be obtained.