Principle of operation, DP-Flow Measurement
The Eletta Flow Monitor’s function is based on the proven and dependable di-
ferential pressure principal, using interchangeable sharp-edge orifice plates
for different measuring ranges. This is perhaps the oldest and most widely
used principle for flow metering, mainly because of its simplicity, its relative-
ly low cost and high volume of research data available for predicting the Flow
Monitors behavior. In the Pipe Section, a fixed area flow restriction (the orifi-
ce plate) causes a pressure drop, which varies with the flow rate. This pressu-
re drop has a high and a low pressure, which is lead through two channels
from each side of the orifice plate, to the Control Unit. By measure the pres-
sure drop allows flow rate measurement by means of a mathematical formula.
A short form of the calculation can be described as Q=√ ∆ρ.
In most Eletta Flow Monitors, the differential pressure is sensed and measured
mechanically via a rubber diaphragm and linked to an outside of the process
liquid/gas, mechanism. This mechanism transforms the movement into a Flow
rate value shown on the dial. All the Eletta Flow Monitors are tested and ap-
proved according to the European CE-mark regulations. (Pls. contact your
Distributor or Eletta Sweden for copy of certificate or go to www.eletta.com).
Change of Flow Range
The Eletta Flow Monitor features an orifice mechanism that does not require
recalibration after replacement and can easily be rebuild in the field to
change the flow range to another from the flow rate ordered. This is valid for
all Pipe Sections except the GSS/FSS-models where you have to order a
completely new Pipe Section, as the flow selector is an integrated part of the
orifice plate. The orifice plate inside the pipe section is the only part in the li-
quid/gas that has to be changed. You can order and change any flow range that
suits your specific application, as long as the new flow rate falls within the to-
tal possible span for the actual Flow Monitor (see section 6.1 page 29).
In each case of rebuilding the flow Monitor in the field, we kindly ask you to
consult Eletta or your local Distributor for advise of the right orifice plate be-
fore ordering.
First empty the piping system so it is un-pressurized and has no flow!
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