Manual
LFE-LDS
page 4 LFE-LDS_man_e.doc
INTRODUCTION
This manual describes the LFE-LDS slit type Laminar Flow Elements for all kind of different flow
channel shapes which have a full scale flow between 0,05 SL/min to 150 SL/min air. This slit type
LFE can be evaluated with any differential pressure measurement devices to determine the flow of
air and gases. The LFEs are calibrated with air at room temperature between 16 – 26°C. A simple
conversion for other gases can be made with the viscosity relation of air and the operating gas by
using the formula of Hagen-Poiseuille. The LFE-LDS measure the actual volume flow with the dif-
ferential pressure (drop) which is created by friction! The total pressure drop across the LFE is
about 1,5 to 2-times of the measured DP. The flow direction is preferred in unidirectional way, can
be principally also used in bi-directional way. The LFE-LDS are calibrated normally for atmospheric
pressure (1 bar abs.). But they can also be used in the pressure range between 0,1 – 2 bar abs..
Higher static pressures are possible respectively with a reduced DP range.
Suppliable LFE-LDS Laminar Flow Meter
Supplied can be the „LDS-ES“ type made of stainless steel, as well as „LDS-AL“ made of alumin-
ium. The series „ES“ is designed for flow rate full scales between 0,01 l/min to 5 l/min. The series
„AL“ is designed for flow rate full scales between 10 l/min und 150 l/min. The nominal differential
pressure across the LFE -LDS is as a standard for all flow rate full scales 10 mbar. It can be ex-
tended without a bigger problem to 20 mbar on request. Beside of the LFE-LDS standard model
series-we can laso supply on customer request special sizes and intermediate sizes.
Specific safety instructions for secure handling of the LFE-LDS elements
The very small size of the flow channel is quite sensible against pollution. So please ensure that
these LFE are only operated with clean dry air and gases. If the flow channel is closed partially the
characteristics will change and the original calibration may no more be valid anymore. In this case
the LFE-LDS must be cleaned and recalibrated in the factory.
Check Delivery Content
• The LFE-LDS comes along with a manual of operation and a calibration data sheet
• The LFE-LDS were supplied with closing caps on the thread connection. Dismount these and
have a look through the flow channel cross section against a bright light. There should be
none of the flow paths closed.
Installation Requirements
Ensure before mounting: connect the LFE-LDS into a pipe, tube or measurement section only if
there is no dirt or other particles inside to see. If dirt is not to exclude in operation and the section
will not stay clean for ever it is strictly recommended to use an inlet filter with a filter rate of equiva-
lent to 5µm.
The two pressure connection lines for the DP pressure transmitter should have about the same
pipe length and diameter if possible and should be absolutely tight.
The temperature sensor should have a distance of about twice of the used pipe diameter in front of
the LFE-LDS input. If an absolute pressure sensor is used it should be connected at the positive
(+ plus) pressure tap of the DP.
The LFE-LDS can be connected into the line by a thread connection. In any case please verify and
respect the flow direction of the LFE-LDS (see arrow mark). Concerning the mounting direction
there is no limitation. In general the horizontal mounting direction is preferred compared to the ver-
tical direction, because the temperature may increase with 1°C/m height.
To achieve good measurement results one have to pay attention that the free cross section close
to the process connections is reduced as little as possible. This means that the wall thickness of
threads or directly screwed pipes shouldn’t be larger than 2 mm. Is it not possible to hold this rec-
ommendation the LFE-LDS should be calibrated from the manufacturer with the actually used flow
sections. This allows the maximum possible accuracy for your application.
