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Manual
00809-0500-4881
For complete descriptions of supported input options, refer to the Options
Bitstring parameter.
8.10.6
Application information
The arithmetic function block can be used to calculate tank level changes based
on greatly changing temperature conditions in devices that depend on the
physical properties of the fluid.
For example, a differential pressure cell's analog input can be scaled initially to
provide a 4-20 mA signal for 0 -100% of level indication. As the temperature of the
system rises, the density of the fluid decreases. For a system that requires
accurate level indication at widely ranging temperature, changing density proves
inconvenient.
The arithmetic function block allows for the automatic compensation of this
change by incorporating gain and bias adjustments to the temperature signal. It
then applies both the compensated temperature signal and the level signal to a
characteristic system equation. The result is a level that is a true indication of fluid
in the vessel.
Different fluids over the same temperature range have different effects on level
due to their thermal expansion coefficients. Vessel geometry also plays a major
role. As the height of the vessel increases, the effect of thermal expansion
becomes more apparent.
level signal.
Figure 8-26: Relative Temperature Effects on Level
A. Elevated temperature level
B. Indicated level calibrated at ambient temperature
C. Level percent
D. Milliamp signal
Rosemount OCX8800C
Figure 8-26
shows the relative temperature effects on a
F
Fieldbus
™
OUNDATION
December 2022
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