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1.4
Operating principles
The meterhead consists of a metering pipe and two magnetic coils. When a current is applied
to the coils a magnetic field is produced at right angles to the metering pipe.
With a conductive liquid flowing through the metering pipe an electrical voltage is induced
and measured by two electrodes mounted in the metering pipe. This voltage is proportional to
the average velocity of flow and therefore to the volume flowing.
The PD 340 Flow Transmitter utilizes a square measurement chamber. The shape of the
measurement chamber significantly reduces the influence of viscosity, type of liquid, and flow
profiles (see details in the next section, Reducing the influence of varying flow profiles).
Practical tests with the PD 340 confirm that it is not necessary to recalibrate the meter when
changing product, such as from water to milk. This would normally be necessary when using
magnetic flowmeters that have traditional round measuring chambers.
Current
genera-
tion
Figure 2: Operating principles
•
Ue = K x B x V x D
•
Ue = voltage across electrodes
•
K = system constant
•
B = magnetic field
•
V = average velocity
•
D = distance between electrodes
The micro-processor in the transmitter controls the current generator, keeping the magnetic
field constant. The voltage across the electrodes is amplified and converted to a digital value
from which the micro-processor calculates the liquid flow.
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V
D
Flow Transmitter, PD 340
Ue
B
551 098 01
Manual
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