Emerson Rosemount 3308A Reference Manual page 17

Reference Manual
00809-0100-4308, Rev CA
Figure 2-3. Upper Reference Point
NPT
A. Upper Reference Point
B. Probe Length
Zero reference point
The Zero Reference Point is selected by the user and is usually located close to or at the bottom of the
tank. The Zero Reference Point can be set to any position in the tank by adjusting the Tank Height.
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 2-4
accuracy. Values for different probe types and dielectric constants are presented in section
over measuring range" on page
Transmitter Overview
PRELIMINARY
BSPP (G) Flange Tri Clamp
illustrates how the measuring range is related to the Blind Zones and the areas with reduced
114.
Transmitter Overview
A
B
August 2017
"Accuracy
5