Level Calculation - Honeywell ST700 User Manual

Level Calculation

The transmitter has the ability to put the measured pressure value through a fifth-order
polynomial equation. This calculation allows the transmitter to closely approximate the
level of an irregularly shaped tank or vessel.
Enabling the Level Calculation
When the channel is fluid level, calculation is enabled in AI block.
Parameters used in the Level Calculation
The following parameters are used do the level calculation and these values are derived
from the particular application:
•
LEVEL_COEFF contains an array of floating point values (coefficients) to be used in
the equation.
•
TANK_RANGE contains the upper and lower ranges of the tank measurements (that
is for a full and empty tank) and the engineering units.
LEVEL_COEFF Parameter
The LEVEL_COEFF parameter contains the coefficients used in the polynomial level
equation. These coefficients must be generated for the application. In addition, the result of
the calculation is expressed in percent.
If the AI block's XD_SCALE is not configured with the engineering units in percent value
(and CHANNEL = Fluid level), then a block configuration error is generated in the AI
block and it remains in Out of Service (OOS) mode.
The polynomial can also be used for measuring flow,
Where flow = f (∆p).
TANK_RANGE Parameter
The TANK_RANGE parameter is configured with the upper and lower range values of the
pressure coming from the tank measurement. This must also take into account the head
pressure of any fill fluid in remote seal tubing (wet legs).
Revision 2.0 FOUNDATION Fieldbus ST 700 Pressure Transmitter User's Guide Page 27