Rosemount 5600 Series, Справочное руководство

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Reference Manual
00809-0100-4024, Rev BA
September 2005
Rosemount 5600 Series
2-28
MEASUREMENT IN LARGE PIPES
When using standard cones in larger (8-in. or larger) still pipe installations,
there is a risk for measurement problems. When standard linear shaped
cones are used in pipes, more than one microwave mode is generated and
each mode has a unique propagation speed. This is a radar physics problem
that is common to all radar gauges when linear shaped cones are used.
In larger pipes, the amplitude of echoes generated by the “unwanted” modes
may become rather high, and may result in loss of the surface echo at certain
locations in the pipe. In addition, there may be measurement errors
associated with two closely spaced echoes where the gauge will not lock on a
single target.
The relative amplitude of the unwanted modes in a straight cone is
proportional to the product of the cone angle and the diameter in the cone
opening. Therefore measurement error increases as pipe diameter increases
since the cone angle is the same for all the cones.
Due to this issue, Emerson Process Management does not recommend using
the 5600 Series 8-in. cone antennas for larger pipe measurements. Instead, a
special pipe antenna should be used.
Table 2-6. Recommendations
Pipe Size
3-in. (76 mm) 4-in. (102 mm) 6-in. (152 mm)
Maximum measuring range 65 ft (20 m) 65 ft (20 m) 65 ft (20 m)
Maximum hole size ( ) 0.24 (6 mm) 0.28 (7 mm) 0.39 (10 mm)
Maximum number of holes per meter 2 2 2
Deflection plate required Yes Yes Yes
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