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MarcSteven
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How do measure the level of a tank which is in vacuum pressure?

How to measure the liquid level but the tank is in vacuum pressure.
using the level transmitter


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EdBurns
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Re: How do measure the level of a tank which is in vacuum pressure?

Two lines are mounted on the tank and connected to a DP gage. One at the top and one at the bottom. The DP gage needs to located near the bottom, and the level at which it is located will be known as 0 level. The pressure of the tank is null due to the fact that both sensing lines are connected to the tank. However, the lower line senses the pressure from the liquid on top of it, while the other line doesn't sense any liquid pressure, due to the fact that it contains a gas. So the pressure that is shown on the gage is analogous to tank level. I hope you got my point.


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moatsem2000
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Re: How do measure the level of a tank which is in vacuum pressure?

From my opnion
if we have closed tank with two output lines A down & B up
we have pressure defferential transmitter with High side & Low side on the manifold
connect the high side to the outbut line A
connect the low side to the upper output B
adjust the calibration to be 4: 20 ma
if the tank empty, the output reading will be 20 ma
if the tank full, the output reading will be 4 ma
on the DCS adjust the values to be like that:
20ma correspond to 0 meter
4ma correspond to 10 meter as example
am I right?


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larry
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Re: How do measure the level of a tank which is in vacuum pressure?

to set the 4 mA output of the transmitter, a pressure equivalent to wet leg pressure must be applied to the low side of the transmitter with the high side vented to atmosphere and the adjustment made. Alternatively a vacuum equivalent to fill fluid pressure can be drawn on the high side and adjustment made.
When the tank contents are at the max level the pressure applied to the high side of the transmitter is Y x s.g of tank fluid (ignoring vapour pressure which is subtracted). The pressure acting on the low side of the transmitter is the h x s.g. of the fluid in the leg/capillary. Therefore, to set the 20 mA output of the transmitter, a pressure equivalent to tank fluid pressure minus wet leg pressure must be applied to the low side of the transmitter with the high side vented to atmosphere and the adjustment made. Alternatively a vacuum equivalent to tank fluid pressure minus wet leg pressure can be drawn on the high side and adjustment made.


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