How does the Precision
Turbine Flowmeter generate a signal?
What is the signal?
Electrical output is most often generated using the principle of
reluctance. A pickup coil, wrapped around a permanent magnet, is installed on the exterior
of the flow tube or the meter body immediately adjacent to the perimeter of the rotor. The
magnet is the source of the magnetic flux field that cuts through the coil. Each blade of
the PTF rotor passing in close proximity to the pickup coil causes a deflection in the
existing magnetic field. This change in the reluctance of the magnetic circuit generates a
voltage pulse within the pickup coil.
Electrical output is also generated using the principle of inductance. A
pickup coil is installed on the exterior of the flow tube immediately adjacent to the
perimeter of the PTF rotor. The magnetic source of the flux field in this type of output
is either the rotor itself or small magnets installed in the rotor. In the case of the
rotor, the material of construction would be 17-4SS or some other magnetic material. The
results are identical to that of the reluctance principal.
Many applications where flow is very low require a special type of coil
assembly commonly referred to as Modulated Carrier. This type of coil produces no magnetic
drag on the rotor, resulting in the ability to measure very small flows where velocity is
minimal. Instead of a sine wave output, this coil assembly produces a carrier wave.
Otherwise the performance of the meter is essentially the same as the reluctance coil
design.
