Endress+Hauser ria45 - Appendix; Differential Pressure Application Explanations; Calculation of Filling Level

Appendix RIA45
54 Endress+Hauser
14 Appendix
The following tables show all the parameters available in the configuration menu. The
values configured at the factory are marked in bold.
14.1 Further explanations on the differential pressure
application at level measurement
At both universal inputs pressure sensors are connected. With the following calculation
steps the volume in the CV channels is finally calculated:
14.1.1
1
st
Calculation Step: Calculation of the filling level
Both pressure sensors provide the actual pressure at the installation point.From both
pressures (possibly adjusted for an offset; this has to be set in AI1 respectively AI2) a
pressure difference (Δp) is determined. If the pressure difference is divided through the
density of the medium multiplied with the gravitational acceleration the measured height
is gained.
Level h= Δp/(ρ*g)
The following units form the basis of the calculation:
• Density ρ [kg/m³]
• Pressure p: [Pa] or [N/m²]
The gravitational acceleration is defined by a constant:
Gravitational acceleration g=9.81m/s²
NOTICE
Wrong calculation results through use of incorrect engineering units
‣
If the calculation is to be carried through correctly the measured signal (e.g. in mbar)
has to be converted into the according unit Pascal (Pa). This is achieved by a conversion
factor. Conversion factors can be found in the table →  55.
Examples for the conversion:
Water: density ρ=1 000 kg/m
3
Pressure measurement: pressure1 (bottom): Scale 0 to 800 mbar (0 to 80000 Pa);
Present value: 500 mbar (50000 Pa)
Pressure measurement: pressure2 (top): Scale 0 to 800 mbar (0 to 80000 Pa);
Present value: 150 mbar (15000Pa)
When using Pascal:
h =
1
* (50000-15000 Pa) = 3.57 m
1 000 kg/m
3
* 9.81 m/s²
When using mbar:
h =
1
* ((500 - 150 mbar)) * (1.0000 · 10
2
)) = 3.57 m
1 000 kg/m
3
* 9.81 m/s²
h = b * Δp
Calculation of the correction factor b:
b = 1/(ρ*g)
for water: b = 1/(1000*9.81) = 0.00010194
Tables and examples for the conversion of application related units into the defined values
kg/m³ and Pa or N/m²: