The Hydrostatic Load Cell is a simple mechanical mechanism
which functions according to known hydrostatic Laws of Physics.
It consists of a piston, a base, a cylinder and a diaphragm.
A thin film of fluid is sandwiched between the base and the diaphragm.
The piston presses against the diaphragm.
The result is only a small amount of fluid is required (e.g.
less than one pint of fluid used in a 80 foot truck scale). Each
Hydrostatic Load Cell type is designed with an exact "acting
area" - a known value in units of square inches. For example,
when a known weight is applied to a hydrostatic load cell with a
known "acting area", the output in PSI is predictable.
A 50,000 lb. weight applied to an "acting area"
of 50 square inches will have an output of 1,000 PSI.
The secret, of course, is to design the hydrostatic load cell
with a linear relationship between weight applied and pressure output.
For example, if 50,000 lbs. yields 1,000 PSI, then 25,000 lbs.
must yield 500 PSI and 100,000 must yield 2,000 PSI.