5
Issue/Rev. 0.6 (2/06)
Magnetic Pickups
Flow in the turbine flowmeter is sensed by a non-wetted sensor called a variable reluctance magnetic pickup. The
magnetic pickup is an assembly consisting of a permanent magnet and a coil bobbin on which several hundred turns of
wire are wound (Figure 6). This combination produces a magnetic field at the top of the pickup. The pickup is placed in
close proximity to the rotor blades, but is separated from it and the process fluid by the wall of the flowmeter housing. As
the rotor turns, the blades disrupt the magnetic field of the pikcup and generate a sine wave voltage signal across the
terminals of the magnetic pickup coil. Each time a rotor blade passes through the magnetic field, one alternating current
(AC) cycle is generated (Figure 7). The number of pulses produced by a turbine flowmeter per gallon of water is known
as the “K-Factor”.
Figure 6
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