Guy's need your support,I want to measure closed tank level which is under vacuum -630mmHg using DP Transmitter, tank fluid density 1.38, Tank height is 7ft
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In such case vaccume will apply in both lags equally .
Now hight is 7 ft and density 1.38
7 ft is equal to 84 inches
So ,
84 X 1.38 = 115.92 inches of H2O became our span.
1 inches of H2O = 1.87 mmHg
Thus,
115.92 inches H2O = 216mmHg
tank is closed thats why ,
LRV = - 216 mmHg
URV = 0 mmHg
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Answer / sr
mothods of measurements don't change with change in line pressures ... the methods r same for both +ve and -ve pressure .... in vacuum u just have to take care that vacuum shud not break ....
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A differential pressure transmitter is required to correct for vacuum pressure. The DP's low side is installed high up, tapped into the vacuum and the DP's high side tapped in near the bottom.
The DP transmitter's minimum range (LRV) is zero
The DP transmitter's maximum range (URV) is:
maximum level height (inches or mm) * specific gravity
Liquid level = measured pressure in water column units (inches or mm) / specific gravity
Many digital indicators just scale the 4-20mA to the desired level range; so a calculation involving specific gravity isn't needed.
For example:
4.0 mA = 0.0 inches level
20.0 mA = 84.0 inches level
Carl Ellis
Measure First
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