2. System Description
2.1 Fields of application
With the Promag 30 measuring system it is possible to obtain precise magneto-
inductive measurements of flow at low cost. All liquid media with a minimum
conductivity of 5 µS/cm can be measured, e.g.:
• acids, alkalis, pastes, pulps
• drinking water, waste water, sewage sludge
• milk, beer, wine, mineral water, yoghurt, molasses
2.2 Principle of measurement
In accordance with Faraday’s law of induction, a voltage is induced in a conductor
that is moved through a magnetic field. In the magneto-inductive principle of
measurement the flowing medium represents the moving conductor. The induced
voltage is proportional to the flow velocity and is fed to the measuring amplifier by a
pair of electrodes. Across the cross-section of the pipe the flow volume is calculated.
The DC magnetic field is generated by a switched direct current of alternating
polarity. Together with the patented “Integrated Autozero Circuit” this assures a stable
zero point and makes the measurement independent of the medium and insensitive to
entrained solid particles. In our works every unit is calibrated on modern calibrating
facilities, referable to international standards. There is no need for it to be adapted to
suit changing media.
U
e
=B ⋅ L ⋅ v
Q=v ⋅ A
U
e
= induced voltage
B = magnetic induction
L = distance between electrodes
v = flow velocity
Q = volume flow
A = pipe cross-section
ba008y01
Fig. 1
Promag 30 2. System Description
Endress+Hauser 7
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