|
 One
of the oldest and most common methods of measuring liquid level
is to measure the pressure exerted by a column (or head) of liquid
in the vessel on the sensor. The sensor converts Hydrostatic Level
Pressure into current signals proportional to the liquid level.
A semiconductor transducer containing oil and a metal or ceramic
sealing diaphragm is employed to achieve accuracy and durability.
In order to compensate for atmospheric pressure the cable contains
a hollow “breathing” tube. The Hydrostatic Level Pressure
being exerted depends on the height of the liquid column as well
as its specific gravity.
Hydrostatic Level
Pressure Advantages:
- Can
be externally mounted or retrofitted
- Can
be isolated from process using block valves
- User
familiarity
- Can
be calibrated from a pressure standard
- Reasonable
instrument cost
Hydrostatic Level
Pressure Disadvantages:
- Subject
to errors due to changes in liquid density
- Bottom
mounted
- Valving
and piping increase cost of installation
- Multiple
fugitive emission points
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