7ML19985GE04
SITRANS LC500 – OPERATING INSTRUCTIONS
Page 101
Appendix E
Applications Examples
Generic Application Calculations
The capacitance expected in a cylindrical tank with a probe centrally mounted is
estimated using the following formula:
(L in meters) or
(L in feet)
Examples (using dimensions above):
Capacitance in air:
Dimensions in meters:
Dimensions in feet:
Capacitance in oil:
If the same vessel is filled with oil, relative dielectric constant for oil (2) replaces the
relative dielectric constant for air (1), and the resulting calculation is:
(dimensions in meters)
or
(dimensions in feet)
The initial capacitance value at 0% (probe in air) is 12.7 pF, and the capacitance value for
100% (tank filled with oil) is 25.4 pF.
After calibration:
12.7 pF
0%
4 mA or 20 mA
25.4 pF
100%
20 mA or 4 mA
C
24
L
Log D d
--------------------------
pF
=
SITRANS LC500
0.25 m (0.82’)
L = 0.95 m
(3.12’)
D
= 1.0 m
(3.28’)
d = 16 mm
(0.05’)
Where:
C = capacitance value in pF
r
= relative dielectric constant
L
= active measurement length
D = internal tank diameter
d
= electrode diameter
24 = a K constant for dimensions in meters
7.32 = a K constant for dimensions in feet or inches
r
= 1 (air)
r
= 2 (oil)
C
7.32
L
Log D d
--------------------------
pF
=
C
air
air
24
0.95
Log
1 0.016
-----------------------------------
pF
12.7
pF
=
=
C
air
air
7.32
0.82
Log
1 0.06
--------------------------------
pF
12.7
pF
=
=
C
oil
oil
24
0.95
Log
1 0.016
-----------------------------------
pF
25.4
pF
=
=
Coil
oil
7.32
3.12
Log
3.28 0.05
----------------------------------------
pF
25.4
pF
=
=