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34-ST-03-57
Page 11
Application Data
Liquid Level: Closed Tank
Determine the minimum and
maximum pressure differentials to
be measured (Figure 17).
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 = 4mA
maximum level = 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 9 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 17—Closed tank liquid level measurement distances