Introduction
A simple pressure gauge can be used for level measurement if its scale is properly calibrated for the actual level, inside the tank or vessel
We are considering open tank
Case1
Consider for instance the tank is 1000mm height & is filled with water of specific gravity 1.00 as shown in fig below
Now we will install the pressure gauge on the bottom of the tank .here the tank is 1000mm so we can select the gauge range as 0 to 1000mmwc .in this case if we fill 50% of tank with water the gauge will show 500mmwc which is direct reading of level which is equal to 500mmWC=50% level. For 100% level in the tank the gauge will show 1000mmWC
So like that we can measure 25%.50%,75% and so on
For example if 35% of the tank is filled with water the gauge reading will be ((35/100)*1000)=350mmWC
Case 2
Consider the same situation above but the liquid in the tank is different. Other than water consider crude oil whose specific gravity is .800
Then the gauge should be range 0 to (height of tank *specific gravity of liquid inside the tank ) here 1000*.800=800mmWC,thus the range of the gauge should be 0 to 800mmWC for 1000mm height tank installed at the bottom of the tank
Here also for 40% level in the tank the gauge will show a reading of (40/100) of span ie
((40/100)*800)=320 mmWC reading in the pressure gauge
