Emerson 3308A Rosemount 3308 Series, Справочное руководство

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5
Reference Manual
00809-0100-4308, Rev BA
Section 2: Transmitter Overview
December 2014
Transmitter Overview
Tank height
The Tank Height is the distance from the Upper Reference Point to the Zero Reference Point. The
transmitter measures the distance to the product surface and subtracts this value from the Tank
Height to determine the level.
Probe length
The probe length is the distance between the Upper Reference Point and the end of the probe. If
a weight is used at the end of the probe it shall be included.
Blind zones
The measuring range depends on probe type, dielectric constant of the product and installation
environment, and is limited by the Blind Zones at the very top and bottom of the probe. In the
Blind Zones, the accuracy exceeds ±1.18 in. (30 mm), and measurements may not be possible.
Measurements close to the Blind Zones will have reduced accuracy.
Figure 2-3 illustrates how the measuring range is related to the Blind Zones and the areas with
reduced accuracy. Values for different probe types and dielectric constants are presented in
section
“Accuracy over measuring range” on page 108 .
Figure 2-3. Blind Zones
Note
Measurements may not be possible in the Blind Zones, and measurements close to the Blind
Zones will have reduced accuracy. Therefore, the alarm points should be configured outside
these zones.
Maximum Measuring Range
Upper Blind Zone
Reduced Accuracy
Reduced Accuracy
Lower Blind Zone