Answer / r_vaya

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

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 ....

Answer / carl_ellis

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

Answer / dhananjayk

Delta P=(h1-h2)

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