8AA-1A1A-006 Datasheet, PDF (6/20 Pages) Magnetrol International, Inc. – Kotron® RF Sensing Probes

CAPACITANCE
GAIN GRAPHS
PICOFARAD
(PF)
The following pages contain capacitance
gain graphs which can be used to deter-
mine the proper probe/electronics choice
for any given application. To use the
graphs, follow the steps below.
1. Determine the dielectric of the
process medium being measured.
If the dielectric is unknown, use a
dielectric of 2 for non-conductive
media such as hydrocarbons or dry
media, and a dielectric value of 80
for water based, conductive liquids
(dielectric values are along the X axis).
2. Choose a probe. Because more than
one probe will usually work, consider
the other application parameters such
as temperature, pressure, material com-
patibility, etc.
3. Find the graph which covers the
chosen probe. Choose the curve on the
graph which most closely relates to
your particular application.
4. Using the chosen curve, determine the
amount of pF/inch or pF/centimeter
your application will develop (values
are on Y axis).
5. Multiply the pF/inch value by the trans-
mitter span needed in the application.
6. Compare total capacitance generated
by the probe against the needed zero
and span of the Kotron electronics to
be used.
pF per
inch cm
20 8.0
18 7.2
16 6.4
14 5.6
12 4.8
10 4.0
8 3.2
6 2.4
4 1.6
2 0.8
00
Stillwell
Tank diameter
inches (cm)
4 (10)
12 (30)
24 (60)
48 (120)
96 (240)
1
2
3
4
5
6
7
8
9 10
Dielectric value of media
Example:
Parameters: a. Dielectric = 2.0
b. Probe = Part No. 8AB-AA2B-072 (with stillwell)
c. pF/inch = 2.00
d. Electronics = Kotron Two-Wire Transmitter
e. Required application span = 72 in.
f. Electronics span = 50 pF min. to 4000 pF
maximum (See chart below)
2.00 pF/inch × 72 in = 144 pF
The total capacitance is enough to meet the 50 pF minimum
span of the electronics.
These charts are meant as an application aid; actual values may differ
slightly. Always provide a 10% margin of error to ensure satisfactory
performance.
These curves represent the probe located in the center of the vessel.
If the probe is near one wall of a large vessel, multiply the distance
from the vessel wall by 2 (to develop a diameter), choose the closest
curve in the chart to your application, and then multiply the resultant
pF value × 78%. This will account for the probe not being totally sur-
rounded by the ground reference.
RANGE OF CAPACITANCE ADJUSTMENT
Level
Kotron Electronics
Model 80-8032
Model 810
Point
Model 811
Narrow
Models 80/81
Wide High Range
Wide Low Range
Models 822/832/842
Model 82CE
Continuous
Model 804
Model 801
Model 805
Zero set point
0 to 350 pF
0 to 500 pF
0 to 1000 pF
0 to 3000 pF
0 to 3000 pF
0 to 3000 pF
0 to 50,000 pF
0 to 1000 pF
0 to 50,000 pF
0 to 50,000 pF
0 to 10,000 pF
Span/Differential
0.5 pF, fixed
0.5 pF, fixed
0.5 pF to 700 pF
0.5 pF, fixed
4 to 1500 pF
2 to 1500 pF
0.5 to 50,000 pF
50 to 4000 pF
5 to 50,000 pF, 0.5 pF (setpoint min.)
5 to 50,000 pF, 0.5 pF (setpoint min.)
5 pF to 10,000 pF
6