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34-ST-03-64
Page 15
Application Data*
Liquid Level: Closed Tank
Determine the minimum and
maximum pressure differentials to
be measured (Figure 18).
P
Min
= (SG
p
x a) – (SG
f
x d)
= LRV when HP at bottom
of tank
= –URV when LP at
bottom of tank
P
Max
= (SG
p
x b) – (SG
f
x d)
= URV when HP at bottom
of tank
= –LRV when LP at bottom
of tank
Where:
Minimum level at 4 mA
Maximum level at 20 mA
a = distance between bottom
tap and minimum level
b = distance between bottom
tap and maximum level
d = distance between taps
SG
f
= Specific Gravity of capillary
fill fluid (see page 11 for
values)
SG
p
= Specific Gravity of
process fluid
b
a
LP
HP
24253
Max
Level
Min
Level
Transmitter above datum
LP
HP
b
a
Max
Level
Min
Level
Transmitter at datum
LP
HP
b
a
Max
Level
Min
Level
Transmitter below datum
Figure 18—Closed tank liquid level measurement distances.
* Contact STC-Phoenix concerning
applications for model STR13D.