A small needle valve can be placed at the output of the
air pump. This feeds a "tee" connector which has a
tube to the bottom of the tank (or the lowest pressure
that one wants to measure). The other side of the
tee goes to the inlet of the pressure sensor. The
valve is adjusted until there is a small stream of
bubbles (hence the name) coming out of the tube on the
...

A small needle valve can be placed at the output of the
air pump. This feeds a "tee" connector which has a
tube to the bottom of the tank (or the lowest pressure
that one wants to measure). The other side of the
tee goes to the inlet of the pressure sensor. The
valve is adjusted until there is a small stream of
bubbles (hence the name) coming out of the tube on the
bottom of the tank with the tank full.

The amount of pressure on the inlet to the pressure sensor
will be proportional to the depth of the fluid in the
tank. Excess pressure from the air supply will come out
the bottom. So, there will be a greater pressure with
the tank full vs. when the tank is empty.

The bubbler does NOT take into account the density of
the fluid, therefore, if you are changing the components
or concentration of the fluid, a variance will be
observed when tank levels remain the same. This usually
isn't much of a problem in many applications.