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6. Operating principle
6.1 General
The new Siemens SITRANS FM100 Flowmeter is designed to measure and
monitor small and medium flows of conductive fluids in piping.
The device works on the magnetic-inductive measuring principle. According to
Faraday's law of induction, a voltage is induced in a conductor moving in a
magnetic field. The electrically conductive measuring medium corresponds to the
moving conductor in the process. The voltage induced by the measuring medium
is proportional to the flow rate and thus a measure of the volume throughput.
Prerequisite is a minimum electrical conductivity of the flowing medium. The
induced voltage is fed to a measuring amplifier via two electrodes, which are in
conductive contact with the medium. The volume flow is calculated via the
defined pipe diameter.
The measurement is independent of the medium and its physical properties such
as density, viscosity and temperature. The device can be configured via the
display. There are two outputs available, which can each be configured as alarm,
frequency, pulse, voltage, and current outputs.
The device also provides a dosing function. The dosing function can be activated
in measuring mode via the four buttons. The dosing function controls simple filling
tasks and also measures flow rate and partial amount.
6.2 Minimum electrical conductivity / Gas bubbles
For the correct function of the instrument, it is necessary that the flow channel is
always completely filled with medium. From a minimum electrical conductivity of
20 μS / cm, the FM100 operates within the specified error limits. The conductivity
of the medium is constantly monitored by the device electronics. If the electronics
detects that the minimum conductivity has fallen below min. value, this is signaled
by displaying the error message 'Empty pipe' and the flow rate reading is set to
'0'. Air bubbles in the flowing medium or media with varying conductivity in the
range of the minimum conductivity can disturb the measuring function and reduce
the measuring accuracy of the FM100. Gases contained in the liquid are also
measured as a flow volume and lead to measurement errors. If necessary, install
appropriate vents in the flow of the unit.
6.3 Deposits
Minor deposits on the measuring tube generally do not affect the measuring
accuracy unless their conductivity deviates significantly from the liquid. For liquids
that have a tendency to deposit, periodically inspect the meter tube and, if
necessary, clean it.
6.4 Measuring electrodes
The FM100 uses electrodes with galvanic tapping. They are in direct contact with
the medium. The standard electrodes are made of stainless steel 1.4404.
7. Mechanical connection
A5E48762204-AB
SITRANS FM100
page 5
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